CN103117040B - Image element circuit, display device and display drive method - Google Patents

Abstract

The present application discloses a pixel circuit, a display device, and a display driving method. The first threshold voltage information of the second transistor and the second threshold voltage information of the light-emitting element are extracted by means of current bias, and used together with the grayscale information of the pixel as The reference voltage of the first capacitor, so that in the light-emitting stage, the driving current passing through the light-emitting element has nothing to do with the above-mentioned first threshold voltage information and second threshold voltage information, and accurately compensates the threshold voltage drift of TFT devices and OLEDs or various parts of the display panel. The non-uniformity of the threshold voltage of the TFT device stores the grayscale information to the first capacitor through voltage programming, which realizes fast data input, and the simple circuit structure increases the aperture ratio of the pixel and the yield of the display device, reducing the production cost.

Description

Pixel circuit, display device and display driving method

technical field

The present application relates to the technical field of display devices, in particular to a pixel circuit, a display device and a display driving method.

Background technique

Organic Light-Emitting Diode (OLED) display has been widely studied in recent years due to its advantages of high brightness, high luminous efficiency, wide viewing angle and low power consumption, and has been rapidly applied to a new generation of displays. OLED display can be driven in two ways: passive matrix drive (PassiveMatrixOLED, PMOLED) and active matrix drive (ActiveMatrixOLED, AMOLED). Although the cost of passive matrix driving is low, it cannot realize high-resolution display due to crosstalk phenomenon, and the passive matrix driving current is large, which reduces the service life of OLED. In contrast, the active matrix driving method sets a different number of transistors on each pixel as a current source, which avoids crosstalk, requires less driving current, and lower power consumption, which increases the life of the OLED and can achieve High resolution display.

The pixel circuit of a traditional AMOLED is a simple two Thin Film Transistor (TFT) structure. As shown in FIG. The switching transistor 13 samples the data signal from the data line DATA11 in response to the control signal from the scan control line SCAN12. The capacitor 16 stores the sampled data signal voltage after the switching transistor 13 is turned off. The driving transistor 14 supplies an output current according to the input voltage held by the capacitor 16 during a given light emitting period. The light emitting element OLED15 emits light whose brightness is commensurate with the data signal by the output current from the driving transistor 14 . According to the voltage-current formula of the transistor, the current flowing through the driving transistor 14 can be expressed as:

I _DS =1/2μ _n C _ox W/L(V _G -V _OLED -V _TH ) ² ……（1）

Among them, I _DS is the drain current flowing from the drain to the source of the driving transistor 14, μ _n is the effective mobility of the TFT device, C _ox is the gate capacitance per unit area of the TFT device, W and L are the effective channel of the TFT device respectively channel width and channel length, V _G is the gate voltage of the TFT device, V _OLED is the bias voltage on the OLED15, V _TH is the threshold voltage of the TFT device, and V _OLED is related to the threshold voltage of the OLED15.

Although this kind of circuit has a simple structure, it cannot compensate the drift of the threshold voltage V _TH of the driving transistor 14, the drift of the threshold voltage of the OLED 15, or the non-uniformity of the threshold voltage V _TH of the TFT devices at various parts of the panel caused by the TFT devices made of polysilicon material. When the threshold voltage V _TH of the driving transistor 14 and the threshold voltage of the OLED 15 drift or the values of V _TH on the panel are inconsistent, the driving current I _DS will change according to the formula (1), and different pixels on the panel will be affected by the bias voltage The different drift conditions are also different, which will cause the unevenness of the panel display.

Therefore, for now, in order to solve the problems caused by the V _TH drift of TFT devices, regardless of whether the AMOLED pixel circuit adopts polysilicon (poly-Si) technology, amorphous silicon (a-Si) technology or oxide semiconductor technology technology, it is necessary to provide a threshold voltage V _TH compensation mechanism when forming a pixel circuit. At present, there are many pixel circuits that provide compensation, and these circuits can be roughly divided into two categories: voltage-driven pixel circuits and current-driven pixel circuits. The current-driven pixel circuit mainly uses a current mirror or a current source to copy the data current as a driving current in a certain proportion to light up the light-emitting element. Since the OLED is a current-mode device, the drift of the threshold voltage and the difference in mobility can be compensated precisely by using a current-driven circuit. However, in practical applications, due to the parasitic capacitance effect on the data line, it takes a long time to establish the data current. This problem is more prominent in the case of low current, which seriously affects the driving speed of the circuit. Compared with the current-driven pixel circuit, the voltage-driven pixel circuit has a faster charging and discharging speed, which can meet the needs of large-area and high-resolution display. However, many voltage-driven pixel circuits require a complex circuit structure and introduce multiple scanning lines when compensating for the drift of the threshold voltage _VTH , which reduces the aperture ratio of the pixel and requires higher external gate driver ICs. And increased line costs.

Considering the above factors, one can accurately compensate the threshold voltage drift of TFT devices or OLEDs or the non-uniformity of threshold voltages of TFT devices around the display panel like a current-type circuit, and can achieve fast data input like a voltage-type drive circuit. Moreover, the circuit structure is simple, and the use of a pixel driving circuit with a small number of components will have obvious advantages.

Contents of the invention

The present application provides a pixel circuit, a display device and a display driving method, which can accurately compensate the threshold voltage drift of TFT devices and OLEDs or the non-uniformity of the threshold voltages of TFT devices in various parts of the display panel, and realize fast data input, and the circuit structure The invention is simple, increases the aperture ratio of the pixel and the yield of the display device, and reduces the production cost.

According to the first aspect of the present application, the present application provides a pixel circuit, comprising:

light emitting element;

a second transistor, the third electrode of which is used to be connected to a bias current line, and the fourth electrode is connected to the light emitting element, and is used to provide a driving current for the light emitting element;

A first capacitor, the first end of which is connected to the second control electrode of the second transistor, and the second end is connected to a data line for providing pixel grayscale information, and is used for providing a reference voltage for the second transistor;

A first transistor, the first electrode of which is used to be connected to the bias current line, the second electrode is connected to the second control electrode, and the first control electrode is used to be connected to a scan line for providing a scan signal, for use in Turning on under the control of the scanning signal, so that the second transistor is turned on so that the reference voltage provided by the first capacitor includes the first threshold voltage information of the second transistor, the second threshold voltage information and grayscale information of the light-emitting element .

According to the second aspect of the present application, the present application provides a pixel circuit, comprising:

light emitting element;

a second transistor, the third electrode of which is used to be connected to a bias current line, and the fourth electrode is connected to the light emitting element, and is used to provide a driving current for the light emitting element;

a first capacitor, the first end of which is connected to the second control electrode of the second transistor, and the second end is connected to a common node, for providing a reference voltage for the second transistor;

A first transistor, the first electrode of which is used to be connected to the bias current line, the second electrode is connected to the second control electrode, and the first control electrode is used to be connected to a scan line for providing a scan signal, for use in Turning on under the control of the scanning signal, so that the second transistor is turned on so that the reference voltage provided by the first capacitor includes the first threshold voltage information of the second transistor, the second threshold voltage information and grayscale information of the light-emitting element .

According to a third aspect of the present application, the present application provides a display device, comprising:

A display panel, including a plurality of pixel circuits as described in the first type above;

a gate drive circuit, configured to provide a scan signal to the pixel circuit through the scan line;

A data driving circuit, used to provide gray scale information to the pixel circuit through the data line, the data driving circuit also includes a bias current source, a voltage source and a controllable switch, and the bias current source and the voltage source respectively pass the bias The setting current line provides bias current and power supply voltage to the pixel circuit;

The timing control circuit is used to control the controllable switch to switch to the state where the bias current source and the bias current line are connected in the data input stage, and to switch to the state of the voltage in the light-emitting stage within the scanning signal scanning time of one frame. The state in which the source and bias current lines are connected.

According to a fourth aspect of the present application, the present application provides a display device, including:

A display panel, including a plurality of pixel circuits as in the second type above;

a gate drive circuit, configured to provide a scan signal to the pixel circuit through the scan line;

A data driving circuit, configured to extract the first threshold voltage information and the second threshold voltage information from the bias current line, the data driving circuit includes a bias current source, a data voltage source, a voltage source and a controllable switch , the bias current source, the data voltage source, and the voltage source respectively provide a bias current, a driving voltage including the first threshold voltage information, the second threshold voltage information, and the gray scale information to the pixel circuit through the bias current line, voltage;

The timing control circuit is used to control the controllable switch to switch to the state where the bias current source and the bias current line are connected in the threshold value extraction mode during the scan signal scan time of one frame; In the frame time, control the controllable switch to switch to the state where the data voltage source and the bias current line are connected in the data input stage of the light-emitting mode, and switch to the state where the voltage source and the bias current line are connected in the light-emitting stage of the light-emitting mode. connected state.

According to the fifth aspect of the present application, the present application provides a display driving method, the method is based on the above-mentioned first display device, and the method includes: dividing the scanning signal into a data input phase and a light emitting phase by scanning one frame time ; In the data input phase, provide the second transistor with a reference voltage including the first threshold voltage information, the second threshold voltage information of the light-emitting element and the grayscale information through a current bias mode; in the light-emitting phase , providing a power supply voltage to the second transistor, so that the second transistor provides a driving current for the light-emitting element that is not related to the first threshold voltage information and the second threshold voltage information.

According to the sixth aspect of the present application, the present application provides a display driving method, the method is based on the above-mentioned second display device, and the method includes: in the threshold extraction mode in which the scanning signal scans one frame time, passing a current The bias mode extracts the first threshold voltage information and the second threshold voltage information from the bias current line; divides the scanning signal scanning another frame time into a data input phase and a light emitting phase, and during the data input In the stage of voltage programming, a reference voltage including the first threshold voltage information, second threshold voltage information and grayscale information is provided to the second transistor by means of voltage programming; in the light emitting stage, a power supply voltage is provided to the second transistor , so that the second transistor provides a driving current for the light-emitting element that is independent of the first threshold voltage information and the second threshold voltage information.

The beneficial effect of this application is:

By providing a pixel circuit, a display device and a display driving method, the first threshold voltage information of the second transistor and the second threshold voltage information of the light-emitting element are extracted through a current bias method, and together with the grayscale information of the pixel are used as the first The reference voltage of the capacitor, so that in the light-emitting stage, the driving current through the light-emitting element has nothing to do with the above-mentioned first threshold voltage information and second threshold voltage information, and accurately compensates the threshold voltage drift of TFT devices and OLEDs or TFT devices around the display panel The non-uniformity of the threshold voltage stores the grayscale information in the first capacitor through voltage programming, which realizes fast data input, and the simple circuit structure increases the aperture ratio of the pixel and the yield of the display device, reducing the production rate. cost.

Description of drawings

FIG. 1 is a prior art non-compensated two TFT pixel circuit;

FIG. 2 is a structural diagram of a display device according to Embodiment 1 of the present application;

FIG. 3 is a structural diagram of a data driving circuit 53 according to Embodiment 1 of the present application;

FIG. 4 is a structural diagram of a pixel circuit 56 according to Embodiment 1 of the present application;

FIG. 5 is a signal timing diagram during the display driving process of the display device according to Embodiment 1 of the present application;

FIG. 6 is a structural diagram of a pixel circuit 56 according to Embodiment 2 of the present application;

FIG. 7 is a signal timing diagram during the display driving process of the display device according to Embodiment 2 of the present application;

FIG. 8 is a structural diagram of a data driving circuit 53 in Embodiment 3 of the present application;

FIG. 9 is a structural diagram of a pixel circuit 56 according to Embodiment 3 of the present application;

FIG. 10 is a signal timing diagram during the display driving process of the display device according to Embodiment 3 of the present application;

FIG. 11 is a structural diagram of a pixel circuit 56 according to Embodiment 4 of the present application;

FIG. 12 is a schematic diagram of adding a pre-charging power supply 46 to a display device according to another embodiment of the present application.

detailed description

The present invention will be further described in detail below through specific embodiments in conjunction with the accompanying drawings.

First some terminology is explained. The transistor may be a transistor of any structure, such as a field effect transistor (FieldEffectTransistor, FET) or a bipolar transistor (BipolarJunctionTransistor, BJT). When the transistor is a BJT, its control electrode refers to the base B of the BJT, and the first and second electrodes refer to the collector C and emitter E of the BJT respectively; when the transistor is a FET, its control electrode refers to the gate G of the FET , The first and second electrodes (that is, the current conduction electrodes) refer to the drain D and source S of the FET, respectively. The transistor in the display device is usually a TFT device. At this time, the control electrode of the transistor is the gate G of the TFT device, and the first and second electrodes refer to the drain D and the source S of the TFT device respectively. When the transistor is used as a switching element, The drain D and the source S can be interchanged, that is, the first and second electrodes can also refer to the source S and the drain D of the TFT device respectively. The third and fourth electrodes mentioned later are also similar.

Embodiment one:

Please refer to FIG. 2 . FIG. 2 shows the structure of the display device according to the first embodiment of the present application, which mainly includes a display panel, a gate driving circuit 52 and a data driving circuit 53 . The display panel includes several pixel arrays 51 . Wherein, the pixel array 51 is composed of N rows and M columns of pixel circuits 56 arranged in a matrix, that is, the pixel array 51 has N rows and M columns, where N and M are both positive integers. Generally, the pixel circuits 56 in the same row in the pixel array 51 are connected to the same scan line 57 , and the pixel circuits 56 in the same column in the pixel array 51 are connected to the same data line 55 and bias current line 54 . The gate driving circuit 52 is used to provide scanning signals to the pixel circuits 56 through the scanning lines 57 . The data driving circuit 53 is used to provide grayscale information to the pixel circuit through the data line 55, that is, to transmit the grayscale information to the corresponding pixel unit through the data line 55 to realize the image grayscale, and to provide the pixel circuit 56 with a bias current source 47 , the voltage source 45 and the controllable switch 411 , the bias current source 47 provides a bias current, and the voltage source 45 provides a power supply voltage for the final display of the pixel circuit 56 .

It should be noted that although the pixel array 51 is arranged in the form of an N×M matrix, for the sake of simplification of illustration, the pixel array 51 shown in FIG. 2 is only arranged in the form of a 2×2 matrix. The layout in the form of ×5 matrix can be selected according to the actual situation.

Please refer to FIG. 3 , the data driving circuit 53 mainly includes a digital-to-analog converter 49 , an output buffer 48 , a voltage source 45 , a bias current source 47 and a controllable switch 411 . Wherein, the digital-to-analog converter 49 receives the digital signal representing grayscale information and the control signal from the bus 410, and under the control of the control signal, converts the digital signal into an analog signal and outputs it to the data line 55 through the output buffer 48. The current source 47 is used to provide bias current, the controllable switch 411 is controlled by a timing control circuit, the voltage source 45 and the bias current source 47 are coupled to the bias current line 54 through the controllable switch 411 . It should be noted that, in this embodiment, the timing control circuit is included in the bus 410. Therefore, the bus 410 needs to provide grayscale information on the one hand, and on the other hand, also needs to provide timing control signals to control the controllable switch 411 and the digital-to-analog conversion. device etc.

Please refer to FIG. 4, the pixel circuit 56 mainly includes: an organic light emitting diode 29 as a light emitting element, a first capacitor 27, a second capacitor 26, a first transistor 24 with a first control electrode, a first electrode and a second electrode , and the second transistor 25 provided with a second control electrode, a third electrode and a fourth electrode. For convenience, a storage node 28 (ie, the first end of the first capacitor 27 ) is set here. The first control electrode is coupled to the scan line 57, the first electrode is coupled to the bias current line 54, and the bias current line 54 can be switched between the bias current source 47 and the voltage source 45 due to the action of the controllable switch 411; The control electrode is coupled to the second electrode, the third electrode is coupled to the bias current line 54, the fourth electrode is coupled to the anode of the organic light emitting diode 29, and the bias current provided by the bias current source 47 can trigger the first transistor 24 and the second transistor 24. The transistor 25 stores the first threshold voltage information of the second transistor 25 and the second threshold voltage information of the organic light emitting diode 29 to the first capacitor 27, so as to provide a reference voltage for the second transistor 25; the first terminal of the first capacitor 27 is coupled to The second electrode, the second end is coupled to the data line 55, the data line 55 can provide grayscale information or reference potential, the third end of the second capacitor 26 is coupled to the scan line 57, and the fourth end is coupled to the second electrode; organic light emitting The cathode of diode 29 is coupled to ground.

During specific implementation, the bias current line 54 is coupled to a 10 μA bias current source 47 to provide a 10 μA bias current to the pixel circuit 56 coupled thereto. The scanning line 57 can be coupled to a certain row driving circuit of the gate driving circuit 52 to provide a selection or non-selection signal for a certain or a row of pixel circuits 56. For example, if the scanning line 57 is charged to 15V, the coupled The pixel circuit 56 is in the following data input selection phase, if the scan line 57 is charged to -5V, the coupled pixel circuit 56 will be in the following data input non-selection phase. Of course, the above numerical values are examples, and other numerical values may be selected in actual application and are not limited thereto.

Please refer to FIG. 5 . FIG. 5 is a signal timing diagram of the pixel circuit 56 shown in FIG. 4 , wherein SCAN[1] is the scanning signal of the first row of pixels, and so on. A display driving process of the pixel circuit 56 shown in FIG. 4 , that is, a display driving method according to Embodiment 1 of the present application, will be described in detail below in conjunction with FIG. 5 .

As shown in FIG. 5 , the whole scan signal scanning time of one frame is divided into a data input phase and a light emitting phase. In the data input phase, the pixel circuits 56 of each row are further divided into a data input selection phase and a data input non-selection phase. When the level of the scan line 57 coupled with the pixel circuit 56 is high, the pixel circuit 56 is in the data input selection stage; when the level of the scan line 57 coupled with the pixel circuit 56 is low, the pixel circuit 56 is in the data input selection stage; Enter the non-selection stage.

During the data input selection phase, since the bus 410 controls the controllable switch 411, the bias current line 54 is coupled to the bias current source 47 and provides a constant bias current. When the scanning line 57 coupled with the pixel circuit 56 becomes high level, the first transistor 24 is in the conduction state, so that the pixel circuit 56 is in the data input selection phase. At this time, the bias current on the bias current line 54 charges the first capacitor 27 through the first transistor 24 , that is, charges the storage node 28 , so the potential of the storage node 28 will gradually increase. Since the second control electrode of the second transistor 25 is coupled to the storage node 28 , the second transistor 25 will gradually change from the off state to the on state due to the increase in the potential of the storage node 28 . After the second transistor 25 is turned on, the bias current on the bias current line 54 will partially flow through the third electrode and the fourth electrode of the second transistor 25, and the magnitude of the current flowing through the second transistor 25 is:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; DS</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; ox</span>}}\frac{\mathrm{<span\; class="notranslate">\; W</span>}}{\mathrm{<span\; class="notranslate">\; L</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; store</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Wherein, μ _n , C _ox , W, L and V _TH2 are the effective mobility, the gate capacitance per unit area, the channel width, the channel length and the first threshold voltage of the second transistor 25 respectively. V _store and V _OLED are the voltage of the storage node 28 and the voltage of the OLED 29 respectively. From formula (2), it can be seen that the current flowing through the second transistor 25 increases as the potential of the storage node 28 increases. Finally, when I _DS2 is equal to the bias current I _BIAS , the bias current I _BIAS is fully established in the pixel circuit 56, and at this time the potential V _store of the storage node 28 can be deduced from the formula (2):

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; store</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; BIAS</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; ox</span>}}\mathrm{<span\; class="notranslate">\; W</span>}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Here, I _BIAS is the bias current, and V _OLED can be regarded as the bias voltage of the OLED 29 , which is related to the second threshold voltage of the OLED 29 . It can be found from (3) that the potential of the storage node 28 at this time includes the first threshold voltage information of the second transistor 25 and the second threshold voltage information of the organic light emitting diode 29 .

In the data input selection phase, the data line 55 will synchronously provide a data voltage representing gray scale information, and the voltage value thereof is set to V _data here. The data voltage V _data and the storage voltage V _store of the storage node 28 are respectively stored at both ends of the first capacitor 27 , and the voltage difference on the first capacitor 27 is: V _data −V _store .

At this time, the charge amount of the storage node 28 can be expressed as:

Q _A =(V _store -V _data )C1+(V _store -V _H )C2+(V _store -V _OLED -V _TH2 )C _g2 ……（4）

Wherein, V _H is the level value of the scanning signal in the data input selection stage, C _g2 is the gate capacitance of the second transistor, C1 and C2 are the capacitance values of the first capacitor 26 and the second capacitor 27 respectively.

When the data input selection phase ends and the data input non-selection phase begins, the scanning line 57 changes from a high level to a low level. This voltage change not only makes the first transistor 24 change from the on state to the off state, but also passes the second The capacitor 26 is coupled to the storage node 28, so that the potential of the storage node 28 becomes a first negative potential, and the second transistor 25 enters and maintains an off state during the data input non-selection phase.

In the data input non-selection stage, both the first transistor 24 and the second transistor 25 are in the cut-off state, and the bias current line 54 and the data line 55 respectively provide bias current and data voltage representing grayscale information for other pixel circuits 56 . It should be noted that during this process, the level change of the data line 55 may be coupled to the storage node 28 through the first capacitor 27, so that the potential of the storage node 28 will increase. Therefore, in order to ensure that the second transistor 25 is In the non-selection phase, the first negative potential of the storage node 28 needs to be sufficiently low.

In the above data input stage, all pixels enter the data input selection stage and data input non-selection stage row by row, and only one row of pixels is in the data input selection stage at the same time, and in this data input selection stage, the above-mentioned first threshold voltage information, second Two threshold voltage information and gray scale information are stored in the storage node 28 of the pixel as a reference voltage.

After the data input phase, the light phase follows. In the lighting phase, since the bus 410 controls the controllable switch 411, the bias current line 54 is disconnected from the bias current source 47 and coupled to the voltage source 45, which is used to power all the bias current lines. The pixel circuit coupled with 54 provides a constant power supply voltage, so that the second transistor 25 provides a driving current for the OLED 29 . At this time, the data line 55 also provides a reference potential, which is V _ref . The change in the potential on the data line 55 will be coupled to the storage node 28 through the first capacitor 27, so that the potential of the storage node 28 becomes V _HIGH . It should be noted that, during the data input non-selection phase and the light-emitting phase, the storage node 28 is in a floating state, and the amount of charge therein does not change. It can be expressed as:

Q _A =(V _HIGH -V _L )C2+(V _HIGH -V _ref )C1+(V _HIGH -V _OLED -V _TH2 )C _g2 ... (5)

Among them, V _L is the voltage value of the scanning signal in the data input non-selection stage. Substituting formula (4) into formula (5), the expression of VHIGH can be obtained as:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; HIGH</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; store</span>}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; data</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OVERDRIVE</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}$

Wherein, V _OVERDRIVE has nothing to do with the above-mentioned first threshold voltage and second threshold voltage. It can be deduced from formula (6), that in the light-emitting stage, the driving current flowing through the organic light-emitting diode 29 is:

I _OLED =1/2μ _n C _ox W/L(V _HIGH -V _OLED -V _TH2 ) ² =1/2μ _n C _ox W/L(V _OVERDRIVE ) ² ……（7）

From the formula (7), it can be found that in the light-emitting stage, the driving current flowing through the organic light-emitting diode 29 has nothing to do with the first threshold voltage of the second transistor 25 and the second threshold voltage of the organic light-emitting diode 29, that is, it can compensate for the The non-uniformity of the display caused by the variation of the threshold voltage of the two elements, on the other hand, since the above-mentioned drive current _IOLED has nothing to do with the first threshold voltage of the second transistor 25, it can compensate for the TFT device being made of polysilicon material which causes the panel The non-uniformity of the threshold voltage V _TH of the TFT devices in various places ensures the uniformity of the display on the display panel.

On the whole, the work of the display device is divided into a data input phase and a light emitting phase, wherein the data input phase is further divided into a data input selection phase and a data input non-selection phase. The pixel is in the ON state controlled by the scan line 57 during the data input selection phase, the bias current provided by the bias current line 54 coupled to the bias current source 47 flows through the pixel circuit 56, and generates a corresponding reference voltage at the storage node 28 . At this stage, the organic light emitting diode 29 will emit light due to the flow of the bias current. In the non-selection phase of data input, the pixel circuit 56 is turned off due to the negative change of the scanning line 57, and the organic light emitting diode 29 does not emit light. In the light-emitting phase, a high reference potential is provided on the data line 55, and the bias current line 54 is also coupled to the voltage source 45. All pixel circuits 56 on the display panel start to conduct, and the magnitude of the conduction current is the same as that of the data input. The data voltage input in the selection phase is related, that is, the driving current on the OLED 29 is not related to the first threshold voltage of the second transistor 25 and the second threshold voltage of the OLED 29, but related to grayscale information. On average, the overall brightness of the display panel is the average effect of the light emitted by the organic light emitting diode 29 in the data input selection phase and the light emitting phase.

Embodiment two:

Please refer to FIG. 6 , the main difference from Embodiment 1 is that in the display device, the gate drive circuit 52 also provides a control line 64 whose level is opposite to that of the scanning line in the data input stage, and the pixel circuit 56 mainly includes: an organic The light-emitting diode 29 is used as a light-emitting element, the first capacitor 27, the first transistor 24 provided with the first control electrode, the first electrode and the second electrode is used as a switch control module, and the second control electrode, the third electrode and the fourth electrode are provided. The second transistor 25 of the electrode is used as a driving module. For convenience, a storage node 68 (that is, the first terminal of the first capacitor 27 ) is set here. The first control electrode is coupled to the scan line 57, the first electrode is coupled to the bias current line 54, and the bias current line 54 can be switched between the bias current source 47 and the voltage source 45 due to the action of the controllable switch 411; The control electrode is coupled to the second electrode, the third electrode is coupled to the bias current line 54, the fourth electrode is coupled to the anode of the organic light emitting diode 29, and the bias current provided by the bias current source 47 can trigger the first transistor 24 and the second transistor 24. The transistor 25 stores the first threshold voltage information of the second transistor 25 and the second threshold voltage information of the organic light emitting diode 29 to the first capacitor 27, so as to provide a reference voltage for the second transistor 25; the first terminal of the first capacitor 27 is coupled to The second electrode, the second terminal is coupled to the data line 55 , the data line 55 can provide grayscale information or reference potential; the cathode of the organic light emitting diode 29 is coupled to the control line 64 .

Please refer to FIG. 7. FIG. 7 is a signal timing diagram of the pixel circuit 56 shown in FIG. control signals, and so on. A display driving process of the pixel circuit 56 shown in FIG. 6 , that is, a display driving method according to Embodiment 2 of the present application, will be described in detail below in conjunction with FIG. 7 .

As shown in FIG. 7 , the whole scan signal scanning time of one frame is divided into a data input phase and a light emitting phase. In the data input phase, the pixel circuits 56 of each row are further divided into a data input selection phase and a data input non-selection phase. When the level of the scan line 57 coupled with the pixel circuit 56 is high, the pixel circuit 56 is in the data input selection stage; when the level of the scan line 57 coupled with the pixel circuit 56 is low, the pixel circuit 56 is in the data input selection stage; Enter the non-selection stage.

During the data input selection phase, since the bus 410 controls the controllable switch 411, the bias current line 54 is coupled to the bias current source 47 and provides a constant bias current. When the scanning line 57 coupled with the pixel circuit 56 becomes high level, the first transistor 24 is in the conduction state, so that the pixel circuit 56 is in the data input selection phase. At this time, the control line 64 is at a low level, and the bias current on the bias current line 54 charges the storage node 68 through the first transistor 24, so the potential of the storage node 68 will gradually increase. Since the second control electrode of the second transistor 25 is coupled to the storage node 68 , the second transistor 25 will gradually change from the off state to the on state due to the increase in the potential of the storage node 68 . After the second transistor 25 is turned on, the bias current on the bias current line 54 will partially flow through the third electrode and the fourth electrode of the second transistor 25, and the magnitude of the current flowing through the second transistor 25 can still be determined by the above-mentioned Formula (2) expresses.

From formula (2), it can be seen that the current flowing through the second transistor 25 increases as the potential of the storage node 68 increases. Finally, when I _DS2 is equal to the bias current, the bias current is fully established in the pixel circuit 56 , and the potential V _store of the storage node 68 can be similarly expressed by the above formula (3).

It can be found from (3) that the potential of the storage node 68 at this time includes the first threshold voltage information of the second transistor 25 and the second threshold voltage information of the organic light emitting diode 29 .

It should be noted that during the data input selection stage, the data line 55 will synchronously provide a data voltage representing grayscale information, that is, grayscale information, and its voltage value is set here as V _data . The data voltage V _data and the storage voltage V _store of the storage node 68 are respectively stored at both ends of the first capacitor 27 , and the voltage difference on the first capacitor 27 is: V _data −V _store .

At the end of the data input selection phase and the beginning of the data input non-selection phase, the scanning line 57 changes from high level to low level, so that the first transistor 24 changes from the on state to the off state, and at the same time, the voltage of the control line 64 The level changes from low to high, so that both the second transistor 25 and the organic light emitting diode 29 are also in and remain in the cut-off state.

In the data input non-selection stage, both the first transistor 24 and the second transistor 25 are in the cut-off state, and the bias current line 54 and the data line 55 respectively provide bias current and data voltage representing grayscale information to other pixels. It should be noted that during this process, the level change of the data line 55 may be coupled to the storage node 68 through the first capacitor 27, so that the potential of the storage node 68 will increase. Therefore, the high level of the control line 64 must be sufficient. High to ensure that the second crystal 25 is not turned on during the data input non-selection phase.

In the above-mentioned data input stage, all pixels enter the data input selection stage and data input non-selection stage row by row, and only one row of pixels is in the data input selection stage at the same time, and at this time the above-mentioned first threshold voltage information, second threshold voltage information Information and gradation information are stored in the storage node 68 of the pixel as a reference voltage.

After the data input phase, the light phase follows. In the light-emitting phase, since the bus 410 controls the controllable switch 411, the bias current line 54 is disconnected from the bias current source 47, and coupled to a voltage source 45, which is all connected to the bias current line 54. The coupled pixel circuit provides a constant power supply voltage, so that the second transistor 25 provides a driving current for the OLED 29 . All control lines 64 also go back low. At this time, the data line 55 also provides a reference potential, which is V _ref . The change in potential on the data line 55 will be coupled to the storage node 68 through the first capacitor 27, so that the potential of the storage node 68 becomes:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; HIGH</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; store</span>}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; data</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}$

$<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; BIAS</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; ox</span>}}\mathrm{<span\; class="notranslate">\; W</span>}}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; data</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OVERDRIVE</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}$

C _g2 is the gate capacitance of the second transistor 25 , V _OVERDRIVE is the overdrive voltage of the second transistor 25 , and its value has nothing to do with the first threshold voltage of the second transistor 25 or the second threshold voltage of the OLED 29 .

From formula (8), it can be deduced that in the light-emitting stage, the driving current flowing through the organic light-emitting diode 29 is:

I _OLED =1/2μ _n C _ox W/L(V _HIGH -V _OLED -V _TH2 ) ² =1/2μ _n C _ox W/L(V _OVERDRIVE ) ² ......（9）

From formula (9), it can be found that in the light-emitting phase, the driving current flowing through the organic light-emitting diode 29 has nothing to do with the first threshold voltage of the second transistor 25 and the second threshold voltage of the organic light-emitting diode 29, that is, it can compensate for the The non-uniformity of the display caused by the variation of the threshold voltage of these two elements, on the other hand, because the above-mentioned drive current _IOLED has nothing to do with the first threshold voltage of the second transistor 25, then it can compensate for the TFT device made of polysilicon material. The non-uniformity of the threshold voltage V _TH of the TFT devices in various parts of the panel ensures the uniformity of the display on the display panel.

Compared with the first embodiment, this embodiment further reduces the pixel area and increases the pixel aperture ratio because the second capacitor 26 is omitted.

Embodiment three:

Please refer to FIG. 8 and FIG. 9. The difference from Embodiment 1 is that in the display device, as shown in FIG. 106, a digital-to-analog converter 107 and an output buffer 108, wherein the analog-to-digital converter 104 is coupled to the output end of the bias current source 47 through the input buffer 103, and can be completed by a controllable switch 411 The coupling and disconnection of the bias current line 54 and the functions of the above components are described in the following display driving process. As shown in FIG. 9, the pixel circuit 56 mainly includes: an organic light emitting diode 29 as a light-emitting element, a second capacitor 26, a first capacitor 27, and a first transistor 24 with a first control electrode, a first electrode, and a second electrode. As the switch control module, and the second transistor 25 provided with the second control electrode, the third electrode and the fourth electrode is used as the driving module, for convenience, a storage node 88 (i.e. the first end of the first capacitor 27) is set here ). The first control electrode is coupled to the scan line 57, the first electrode is coupled to the bias current line 54, and the bias current line 54 can be connected between the bias current source 47, the output buffer 108 and the voltage source 45 due to the action of the controllable switch 411. The second control electrode is coupled to the second electrode, the third electrode is coupled to the bias current line 54, the fourth electrode is coupled to the anode of the organic light emitting diode 29, and the bias current provided by the bias current source 47 can trigger the first The transistor 24 and the second transistor 25 store the first threshold voltage information of the second transistor 25 and the second threshold voltage information of the organic light emitting diode 29 to the first capacitor 27 and the external storage 105; the first terminal of the first capacitor 27 is coupled to The second electrode, the second terminal is coupled to the common node 83, the common node 83 is switched between the common node potential and the reference potential, the third terminal of the second capacitor 26 is coupled to the scan line 57, and the fourth terminal is coupled to the second electrode; The cathode of the OLED 29 is coupled to the ground. The common node 83 may be a node shared by one row or all rows of the entire display panel.

In FIG. 8 , the external memory 105 and the adder 106 can be separately arranged outside the data driving circuit 53 to form shared functional elements.

Please refer to FIG. 10 . FIG. 10 shows a signal timing diagram of the pixel circuit 56 shown in FIG. 9 , wherein SCAN[1] is the scanning signal of the first row of pixels, and so on. A display driving process of the pixel circuit 56 shown in FIG. 9 , that is, a display driving method according to Embodiment 3 of the present application, will be described in detail below with reference to FIGS. 8 and 10 .

Figure 8 and Figure 10 show a driving method using external compensation. This driving method mainly extracts the threshold voltage information of the driving module and light-emitting elements that need compensation and stores them in the external storage in the form of digital signals. , when the grayscale information is input, the stored threshold voltage information and grayscale information are superimposed together to realize the compensation function of the threshold voltage. It can be seen from Fig. 10 that the entire driving process of external compensation can be performed in two modes: one is the threshold value extraction mode, and the other is the normal light emitting mode. The threshold extraction mode can be executed once when the display device is turned on and off, and the rest of the time is in the light-emitting mode; or after being executed once when the display device is turned on and off, every frame or several frames in the next light-emitting mode Extract the threshold voltage information of pixels in a certain row to refresh their threshold voltage information in external storage in real time.

In the threshold extraction mode, the working process of the pixel circuit 56 is divided into a threshold extraction selection phase and a threshold extraction non-selection phase. When the level of the scan line 57 coupled with the pixel circuit 56 is high, the pixel circuit 56 is in the threshold extraction selection stage; when the level of the scan line 57 coupled with the pixel circuit 56 is low, the pixel circuit 56 is in the threshold value Extract the non-selection phase.

During the threshold extraction selection phase, since the bus 401 controls the controllable switch 411, the bias current line 54 is coupled to the bias current source 47 and provides a constant bias current. When the scanning line 57 coupled with the pixel circuit 56 becomes high level, the first transistor 24 is in the conduction state, so that the pixel circuit 56 is in the threshold extraction selection stage. At this time, the bias current on the bias current line 54 charges the first capacitor 27 through the first transistor 24 , so the potential of the storage node 88 will gradually increase. Since the second control electrode of the second transistor 25 is coupled to the storage node 88 , the second transistor 25 will gradually change from the off state to the on state due to the increase in the potential of the storage node 88 . After the second transistor 25 is turned on, the bias current on the bias current line 54 will partially flow through the third electrode and the fourth electrode of the second transistor 25, and the magnitude of the current flowing through the second transistor 25 can be obtained by the above formula (2) Representation. It can be seen from formula (2) that the current flowing through the second transistor 25 increases as the potential of the storage node 88 increases. Finally, when I _DS2 is equal to the bias current, the bias current is fully established in the pixel circuit 56. At this time, the potential V _store of the storage node 88 can be expressed by the above formula (3), and the potential V _store includes the above-mentioned first Threshold voltage information and second threshold voltage information.

It can be found from (3) that the potential of the storage node 88 at this time includes the first threshold voltage information of the second transistor 25 and the second threshold voltage information of the organic light emitting diode 29 . Since the voltage on the storage node 88 is the same as the voltage on the bias current line 54, the analog-to-digital converter 104 coupled to the bias current line 54 will sample the voltage information V _store on the bias current line 54 and convert it to It is converted into a digital signal and input to the external storage 105 .

When the threshold value extraction selection phase ends and the threshold value extraction non-selection phase begins, the level of the scanning line 57 changes from high level to low level. This voltage change not only makes the first transistor 24 change from the on state to the off state, but also couples to the storage node 88 through the second capacitor 26, so that the potential of the storage node 88 becomes the first negative potential, and the second transistor 25 is in the data input state. The non-selection phase enters and remains cut-off.

In the non-selection phase of threshold value extraction, both the first transistor 24 and the second transistor 25 are in an off state, and the bias current line 54 provides bias current for other pixel circuits 56 . In the threshold extraction mode, all pixels enter the threshold extraction selection stage and the threshold extraction non-selection stage row by row, and store the first threshold voltage information and the second threshold voltage information on the storage node 88 into the memory chip 105 .

The driving process in the lighting mode is divided into a data input phase and a lighting phase. In the data input phase, because the bus 410 controls the controllable switch 411, the bias current line 54 is disconnected from the bias current source 47, and is coupled to the digital-to-analog converter 107 through the output buffer 108 for outputting a drive voltage, and its driving voltage value is V _drive . Since the adder 106 superimposes the grayscale information from the bus 410 and the storage voltage in the external storage 105 in advance, the driving voltage V _drive will include the voltage information V _store in the threshold value extraction mode and the data voltage representing the grayscale information V _data . When the scanning line 57 coupled with the pixel circuit 56 becomes high level, the first transistor 24 is in the conduction state, so that the pixel circuit 56 is in the data input selection phase. At this moment, the driving voltage V _drive on the bias current line 54 is input into the storage node 88 through the first transistor 24 .

At this time, the charge amount of the storage node 88 can be expressed as:

Q _A =(V _drive -V ₀ )C1+(V _drive -V _H )C2+(V _drive -V _OLED -V _th2 )C _g2 …(10)

Among them, V _H is the level value of the scan signal in the data input selection phase, V ₀ is the voltage value of the common node in the data input phase, C _g2 is the gate capacitance of the second transistor, C1 and C2 are the first capacitor 26 and the second transistor respectively. The capacitance value of the capacitor 27.

When the data input selection phase ends and the data input non-selection phase begins, the scanning line 57 changes from a high level to a low level. This voltage change not only makes the first transistor 24 change from the on state to the off state, but also passes the second The capacitor 26 is coupled to the storage node 88, so that the potential of the storage node 88 becomes a second negative potential, and the second transistor 25 enters and maintains a cut-off state during the data input non-selection phase.

In the data input non-selection stage, both the first transistor 24 and the second transistor 25 are in an off state, and the bias current line 54 provides driving voltage for other pixels.

In the above-mentioned data input stage, all pixels enter the data input selection stage and the data input non-selection stage row by row, and use the first threshold voltage information of the second transistor 25, the second threshold voltage information and grayscale information of the organic light emitting diode 29 as The reference voltage is stored in the storage node 88 of each pixel. During the data input phase, the common node 83 is always kept at a constant potential V ₀ .

After the data input phase, the light phase follows. In the lighting phase, since the bus 410 controls the controllable switch 411, the bias current line 54 is disconnected from the output buffer 108 and coupled to the voltage source 45, which is the source of all voltage sources coupled to the bias current line 54. The pixel circuit provides a constant supply voltage. At this time, the potential of the common node 83 also changes from the original constant potential V ₀ to the reference potential, and the voltage value of the reference potential is V _ref . The change of the potential on the common node 83 will be coupled to the storage node 88 through the first capacitor 27, so that the potential of the storage node 88 becomes V _HIGH . One point to be noted is that during the data input non-selection phase and the light-emitting phase, the storage node 88 is in a floating state, and the amount of charge therein does not change. It can be expressed as:

Q _A =(V _HIGH -V _L )C2+(V _HIGH -V _ref )C1+(V _HIGH -V _OLED -V _TH2 )C _g2 ... (11)

Among them, V _L is the voltage value of the scanning signal in the data input non-selection stage. Substituting formula (10) into formula (11), the expression of V _HIGH can be obtained as:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; HIGH</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; dirve</span>}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; data</span>}}<span\; class="notranslate">\; +</span>\frac{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; ref</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; h</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; g</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; store</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 12</span>}<span\; class="notranslate">\; )</span>$

$<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OVERDRIVE</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}}$

Wherein, V _OVERDRIVE is the overdrive voltage of the second transistor 25 , and its value has nothing to do with the first threshold voltage of the second transistor 25 or the second threshold voltage of the OLED 29 .

From formula (12), it can be deduced that in the light-emitting stage, the current flowing through the organic light-emitting diode 29 is:

I _OLED =1/2μ _n C _ox W/L(V _HIGH -V _OLED -V _TH2 ) ² =1/2μ _n C _ox W/L(V _OVERDRIVE ) ² ……（13）

From formula (13), it can be found that in the light-emitting phase, the current I _OLED flowing through the organic light-emitting diode 29 has nothing to do with the first threshold voltage of the second transistor 25 and the second threshold voltage of the organic light-emitting diode 29 , that is, it can compensate The non-uniformity of display caused by the threshold voltage variation of these two elements, on the other hand, because the above-mentioned driving current _IOLED has nothing to do with the first threshold voltage of the second transistor 25, then it can compensate for the TFT device being made of polysilicon material. As a result, the threshold voltage V _TH of the TFT devices in various parts of the panel is non-uniform, which ensures the uniformity of the display on the display panel.

The advantage of the third embodiment is that, compared with the first and second embodiments, by adopting the external compensation method, the threshold value extraction mode only needs to be executed once when starting up, and the display device can work in the light-emitting mode at other times; and In the data writing process (that is, the data input phase in the light-emitting mode), no bias current is required, and the driving voltage is directly used to load the above-mentioned first threshold voltage information, second threshold voltage information and grayscale information on the storage node 88 , using the voltage programming method can greatly reduce the data writing time, thereby increasing the proportion of the light-emitting time in the frame. The pixel circuit can be used in a display device with higher resolution or larger area. In addition, the use of external compensation can simplify the pixel structure and reduce the number of control lines.

Embodiment four:

Please refer to FIG. 11 , the main difference from the third embodiment is that in the display device, the gate drive circuit 52 also provides a control line 64 with the level opposite to that of the scanning line, and the second capacitor 26 is removed from the pixel circuit 56, similar to In combination of embodiment two and embodiment three. The pixel circuit, display device and display driving method will not be repeated here.

It should be noted:

1. In other embodiments of the display device, the voltage on the storage node is the same as the voltage on the bias current line 54 during the above data input selection phase, which is much lower than the voltage provided by the voltage source 45 . Therefore, when a new frame comes, the potential on the bias current line 54 needs to be pulled down quickly to establish the above-mentioned bias current. In order to speed up this process, a pre-charge power supply 46 can be set for each column, and the bias current Source 47 , voltage source 45 , precharge power source 46 are coupled to bias current line 54 through controllable switch 411 . As shown in FIG. 12, the voltage _Vpre of this pre-charging power supply 46 is:

${\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; pre</span>}}<span\; class="notranslate">\; =</span>\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; BIAS</span>}}\mathrm{<span\; class="notranslate">\; L</span>}}{{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; ox</span>}}\mathrm{<span\; class="notranslate">\; W</span>}}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; OLED</span>}\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; TH</span>}\mathrm{<span\; class="notranslate">\; 20</span>}}<span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; .</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 14</span>}<span\; class="notranslate">\; )</span>$

Here, V _TH20 and V _OLED0 are the initial threshold of the second transistor and the initial bias potential of the OLED, respectively. The precharge power supply 46 only needs to be connected to the bias current line 54 for a short time at the beginning of the frame to discharge the excess charge on the bias current line 54 .

2. The above-mentioned data driving circuit can be integrated on the display panel, or integrated into a peripheral IC chip, and then bonded to the display panel.

3. Although the pixel circuit 56 uses organic light emitting diodes as light emitting elements, in other embodiments, other light emitting diodes may also be used as light emitting elements.

4. In Embodiment 1 and Embodiment 3, the second capacitor 26 can be realized by increasing the overlapping area of the control electrode of the first transistor and the second electrode, or a separate capacitor element can be made.

5. In each embodiment of the present application, the transistor may be formed of an oxide thin film transistor, or may be formed of a polysilicon or an amorphous silicon thin film transistor.

6. In other embodiments, the timing control circuit may not be integrated into the bus, but the grayscale information is mainly provided by the bus, and the timing control circuit independently controls the controllable switch.

Each embodiment of the present application adopts two TFT devices to build a pixel circuit, and the circuit structure is simple, which can not only compensate the threshold voltage drift of the TFT device, but also compensate the threshold voltage drift of the OLED device 7 to ensure the uniformity of display. In addition, in the prior art, when the threshold voltage of the TFT device becomes negative, the traditional voltage-type threshold compensation circuit can no longer provide compensation. It has a very good compensation effect, so it has a more superior effect, which is extremely beneficial in a display device that uses a depletion transistor as a driving tube.

The above content is a further detailed description of the present application in conjunction with specific implementation modes, and it cannot be deemed that the specific implementation of the present application is limited to these descriptions. For those of ordinary skill in the technical field to which the present application belongs, some simple deduction or replacement can also be made without departing from the concept of the present application.

Claims (13)

1. A pixel circuit, characterized in that, comprising: light emitting element; The second transistor, the third electrode of which is used to be connected to a bias current line, the fourth electrode is connected to the light-emitting element, and is used to provide a driving current for the light-emitting element; the bias current line is used to provide a bias current, to extract the first threshold voltage information of the second transistor and the second threshold voltage information of the light emitting element; A first capacitor, the first end of which is connected to the second control electrode of the second transistor, and the second end is connected to a data line for providing pixel grayscale information, and is used for providing a reference voltage for the second transistor; A first transistor, the first electrode of which is used to be connected to the bias current line, the second electrode is connected to the second control electrode, and the first control electrode is used to be connected to a scan line for providing a scan signal, for use in Turning on under the control of the scanning signal, so that the second transistor is turned on so that the reference voltage provided by the first capacitor includes the first threshold voltage information of the second transistor, the second threshold voltage information and grayscale information of the light-emitting element . 2. The pixel circuit according to claim 1, wherein the cathode of the light-emitting element is coupled to a ground line, and the pixel circuit further comprises a second capacitor, the second capacitor is coupled between the scan line and the second between the control poles. 3 . The pixel circuit according to claim 1 , wherein the cathode of the light-emitting element is coupled to a control line for obtaining a control signal from the control line with a level opposite to that of the scanning signal. 4 . 4. A pixel circuit, characterized in that, comprising: light emitting element; The second transistor, the third electrode of which is used to be connected to a bias current line, the fourth electrode is connected to the light-emitting element, and is used to provide a driving current for the light-emitting element; the bias current line is used to provide a bias current, to extract the first threshold voltage information of the second transistor and the second threshold voltage information of the light emitting element; A first capacitor whose first end is connected to the second control electrode of the second transistor, and whose second end is connected to a common node for providing a reference voltage for the second transistor; the common node is one row or the entire Nodes shared by all rows of the display panel; A first transistor, the first electrode of which is used to be connected to the bias current line, the second electrode is connected to the second control electrode, and the first control electrode is used to be connected to a scan line for providing a scan signal, for use in Turning on under the control of the scanning signal, so that the second transistor is turned on, and coupling the driving voltage provided by the bias current line, which includes the first threshold voltage information, the second threshold voltage information and the grayscale information to the second control electrode of the second transistor, so that the reference voltage provided by the first capacitor includes the first threshold voltage information of the second transistor, the second threshold voltage information and grayscale information of the light-emitting element. 5. The pixel circuit according to claim 4, wherein the cathode of the light-emitting element is coupled to a ground line, and the pixel circuit further comprises a second capacitor, the second capacitor is coupled between the scan line and the second between the control poles. 6 . The pixel circuit according to claim 4 , wherein the cathode of the light-emitting element is coupled to a control line for obtaining a control signal from the control line with a level opposite to that of the scanning signal. 7. The pixel circuit according to claim 2 or 5, wherein the second capacitance is realized by increasing the overlapping area of the first control electrode and the second electrode. 8. A display device, characterized in that it comprises: A display panel, comprising several pixel circuits according to any one of claims 1-3; a gate drive circuit, configured to provide a scan signal to the pixel circuit through the scan line; A data driving circuit, used to provide gray scale information to the pixel circuit through the data line, the data driving circuit also includes a bias current source, a voltage source and a controllable switch, and the bias current source and the voltage source respectively pass the bias The setting current line provides bias current and power supply voltage to the pixel circuit; The timing control circuit is used to control the controllable switch to switch to the state where the bias current source and the bias current line are connected in the data input stage, and to switch to the state of the voltage in the light-emitting stage within the scanning signal scanning time of one frame. The state in which the source and bias current lines are connected. 9. A display device, characterized in that it comprises: A display panel comprising several pixel circuits according to any one of claims 4-6; a gate drive circuit, configured to provide a scan signal to the pixel circuit through the scan line; A data driving circuit, configured to extract the first threshold voltage information and the second threshold voltage information from the bias current line, the data driving circuit includes a bias current source, a data voltage source, a voltage source and a controllable switch , the bias current source, the data voltage source, and the voltage source respectively provide a bias current, a driving voltage including the first threshold voltage information, the second threshold voltage information, and the gray scale information to the pixel circuit through the bias current line, voltage; The timing control circuit is used to control the controllable switch to switch to the state where the bias current source and the bias current line are connected in the threshold value extraction mode during the scan signal scan time of one frame; In the frame time, control the controllable switch to switch to the state where the data voltage source and the bias current line are connected in the data input stage of the light-emitting mode, and switch to the state where the voltage source and the bias current line are connected in the light-emitting stage of the light-emitting mode. connected state. 10. The display device according to claim 9, wherein the data voltage source further comprises an analog-to-digital converter, an external storage, an adder, and a digital-to-analog converter connected in sequence, wherein: When the controllable switch is switched to the state where the bias current source and the bias current line are connected in the threshold extraction mode, the analog-to-digital converter extracts the first threshold voltage information and the second threshold voltage information from the bias current line voltage information, and store the first threshold voltage information and the second threshold voltage information in an external storage; When the controllable switch is switched to the state where the data voltage source and the bias current line are connected in the data input stage of the light emitting mode, the adder is used to combine the grayscale information provided by the bus with the first information provided by the external storage. The threshold voltage information and the second threshold voltage information are superimposed and a digital signal is output; the digital-to-analog converter is used to convert the digital signal into a drive voltage in the form of an analog signal and output it to the bias current line, When the controllable switch is switched to a state where the voltage source and the bias current line are connected in the light-emitting phase of the light-emitting mode, the controllable switch is driven by the voltage source to provide a driving current for the light-emitting element. 11. A display driving method, characterized in that the method is based on the display device according to claim 8, the method comprising: dividing the scanning signal into a data input phase and a light emitting phase for scanning one frame time; In the data input stage, the reference voltage including the first threshold voltage information, the second threshold voltage information of the light-emitting element and the grayscale information is provided to the second transistor by means of current bias; The second transistor provides a power supply voltage, so that the second transistor provides a driving current for the light-emitting element that is not related to the first threshold voltage information and the second threshold voltage information. 12. A display driving method, characterized in that the method is based on the display device according to claim 9, and the method comprises: in the threshold extraction mode in which the scanning signal scans for one frame time, biasing by current The method extracts the first threshold voltage information and the second threshold voltage information from the bias current line; divides the scanning signal scanning another frame time into a data input phase and a light emitting phase, and in the data input phase, Provide the second transistor with a reference voltage including the first threshold voltage information, the second threshold voltage information and the gray scale information by means of voltage programming; in the light-emitting phase, provide a power supply voltage to the second transistor, so that The second transistor provides a driving current for the light-emitting element that is not related to the first threshold voltage information and the second threshold voltage information. 13. The display driving method according to claim 12, wherein when the display device according to claim 10 is used as the display device, the method comprises: In the threshold extraction mode in which the scanning signal scans for one frame time, the analog-to-digital converter extracts the first threshold voltage information and the second threshold voltage information from the bias current line and stores them in an external storage; In the lighting mode in which the scanning signal scans another frame time, in the data input stage, the adder combines the grayscale information provided by the bus with the first threshold voltage information and the second threshold voltage information in the external storage After being superimposed to form a digital signal, the digital signal is converted into a driving voltage in the form of an analog signal through the digital-to-analog converter and output to the bias current line, and the driving voltage is used as the second transistor, including the first A reference voltage for threshold voltage information, second threshold voltage information, and grayscale information; in the light-emitting phase, supply a power supply voltage to the second transistor, so that the second transistor provides the light-emitting element with the same threshold voltage as the first threshold The driving current is irrelevant to the voltage information and the second threshold voltage information.