CN101826301B - Light-emitting diode driving circuit and its driving method and display device - Google Patents

Abstract

The invention relates to a light emitting diode driving circuit, a driving method thereof and a display device. The control end of the first transistor is controlled by a first signal to determine whether the first transistor is conducted or not; the second transistor is coupled between the power supply potential and the light emitting diode, and the control end of the second transistor receives the data signal transmitted by the first transistor when the first transistor is conducted; the control end of the third transistor is controlled by the second signal to determine whether to transmit the power supply potential to the first end of the capacitor, and the second end of the capacitor is coupled to the control end of the second transistor; the one-way conducting element is coupled between the first end of the capacitor and the reference signal. Furthermore, the reference signal makes the one-way conducting element non-conducting due to reverse bias in a certain period of time.

Description

Light-emitting diode driving circuit and its driving method and display device

technical field

The invention relates to the field of display technology, and in particular to a light emitting diode driving circuit, a driving method thereof and a display device.

Background technique

The pixel of a light emitting diode (Light Emitting Diode, LED) display device generally uses a transistor and a storage capacitor to store charges to control the brightness of the light emitting diode; where the light emitting diode is a current-driven element, which varies according to the magnitude of the current flowing through it. Produces varying degrees of shine. Please refer to FIG. 1 , which is a schematic diagram of a single pixel circuit of a conventional LED display device. The pixel circuit 10 is a single light-emitting module, which includes a LED driving circuit 12 and an OLED 16; the LED driving circuit 12 is used to control the brightness performance of the OLED 16, and has a two-transistor-capacitor (2T1C) structure. Specifically, the LED driving circuit 12 includes a transistor M1, a transistor M2, and a capacitor C1; the drain of the transistor M1 receives the data signal Vdata due to an electrical coupling relationship, and the gate of the transistor M1 is controlled by the control signal SCAN to determine whether to use The data signal Vdata is transmitted to the source of the transistor M1; the gate of the transistor M2 is electrically coupled to the source of the transistor M1, the source of the transistor M2 is electrically coupled to the power supply potential OVDD, and the drain of the transistor M2 is electrically coupled to the To the anode of the organic light emitting diode 16 , the cathode of the organic light emitting diode 16 is electrically coupled to another power supply potential OVSS; both ends of the capacitor C1 are connected between the gate and the source of the transistor M2 .

However, since the OVDD power lines of the pixel circuits of the light emitting diode display device are connected together, when the organic light emitting diode 16 emits light, the OVDD power line will have a current flow. However, since the OVDD power supply line has metal impedance, a power supply voltage drop (that is, IR Drop) will occur, so that the power supply potential OVDD of each pixel circuit will be different. Since the luminance of the organic light-emitting diode 16 is proportional to the magnitude of the current flowing through it, and because the power supply potential OVDD of each pixel circuit is different, the current difference between the pixel circuits will be caused, and the resulting luminance will be different. , thus causing uneven panel display. In addition, due to the influence of the manufacturing process, the threshold voltages of the transistors of each pixel circuit are not completely the same, so that even if the same data signal is given, the currents generated by different pixel circuits are still different, which will also lead to uneven panel display.

Contents of the invention

The object of the present invention is to provide a light emitting diode driving circuit to improve the problem of uneven panel display in the prior art.

Another object of the present invention is to provide a method for driving a light-emitting diode, so as to improve the problem of uneven panel display in the prior art.

Another object of the present invention is to provide a display device to solve the problem of uneven panel display in the prior art.

A light-emitting diode driving circuit provided by an embodiment of the present invention is suitable for driving a light-emitting diode. Wherein, there are multiple transistors in the LED driving circuit, and each transistor includes a control terminal, a first channel terminal and a second channel terminal. Specifically, the LED driving circuit includes a first transistor, a second transistor, a third transistor, a unidirectional conduction element and a capacitor. Wherein, the control terminal of the first transistor is controlled by the first signal to determine the electrical conduction state between the first channel terminal and the second channel terminal of the first transistor, and the first channel terminal of the first transistor is electrically coupled The control terminal of the second transistor is electrically coupled to the second channel terminal of the first transistor, the first channel terminal of the second transistor is electrically coupled to a preset potential, and the second channel terminal of the second transistor is electrically coupled to the preset potential. The access end is electrically coupled to the light emitting diode; the control end of the third transistor is controlled by the second signal to determine the electrical conduction state between the first access end and the second access end of the third transistor, and the third transistor The first channel end is electrically coupled to the above-mentioned preset potential; one end of the unidirectional conduction element is electrically coupled to the second channel end of the third transistor, and the other end receives the reference signal due to the electrical coupling relationship; the capacitor circuit Sexually coupled between the second pass terminal of the third transistor and the control terminal of the second transistor. Furthermore, the reference signal will make the unidirectional conduction element non-conductive due to the reverse bias in a certain period of time.

In an embodiment of the present invention, the above-mentioned unidirectional conduction element is a diode.

In an embodiment of the present invention, the above-mentioned unidirectional conduction element is a fourth transistor, and the control terminal and the first channel terminal of the fourth transistor receive the reference signal due to the electrical coupling relationship at the same time, and the second transistor of the fourth transistor The access end is electrically coupled to the second access end of the third transistor.

A light emitting diode driving method proposed in an embodiment of the present invention is applicable to the above light emitting diode driving circuit. Specifically, the LED driving method includes steps: (1) In the first period, adjust the first signal, the second signal and the reference signal to turn on the first transistor and the unidirectional conduction element, and make the third transistor unable to turn on and (2) in a second period following the first period, adjusting the first signal, the second signal and the reference signal to turn on the third transistor, and make the first transistor and the unidirectional conduction element unable to conduct. Wherein, in the second period, the unidirectional conduction element cannot conduct due to the reverse bias voltage.

In an embodiment of the present invention, the above-mentioned first signal and the second signal are out of phase, and the reference signal is in phase with the second signal.

A display device provided by an embodiment of the present invention includes a power supply device and a light emitting source. Wherein, the power supply device is used to provide power; the light source is electrically coupled to the power supply device to receive power. Specifically, the light emitting source includes at least one light emitting module, and the light emitting module includes a light emitting diode and a driving circuit for the light emitting diode. Wherein, there are multiple transistors in the LED driving circuit, and each transistor includes a control terminal, a first channel terminal and a second channel terminal. More specifically, the LED drive circuit includes a first transistor, a second transistor, a third transistor, a unidirectional conduction element, and a capacitor; the control terminal of the first transistor is controlled by a first signal to determine the first pass terminal of the first transistor In an electrically conductive state with the second access end, the first access end of the first transistor receives the data signal due to the electrical coupling relationship; the control end of the second transistor is electrically coupled to the second end of the first transistor. The access end, the first access end of the second transistor is electrically coupled to the preset potential provided by the power supply device, the second access end of the second transistor is electrically coupled to the light-emitting diode; the control end of the third transistor is controlled by the first The control of the two signals determines the electrical conduction state between the first access end and the second access end of the third transistor, and the first access end of the third transistor is electrically coupled to the above-mentioned preset potential; unidirectional conduction One end of the element is electrically coupled to the second channel end of the third transistor, and the other end receives the reference signal due to the electrical coupling relationship; the capacitor is electrically coupled to the second channel end of the third transistor and the control of the second transistor between the ends. Furthermore, the reference signal will make the unidirectional conduction element non-conductive due to the reverse bias in a certain period of time.

In an embodiment of the present invention, the unidirectional conduction element of the above-mentioned display device is a diode.

In an embodiment of the present invention, the unidirectional conduction element of the above-mentioned display device is a fourth transistor, the control terminal of the fourth transistor and the first channel terminal simultaneously receive the reference signal due to the electrical coupling relationship, and the fourth transistor The second access end is electrically coupled to the second access end of the third transistor.

The embodiment of the present invention designs the structural configuration of the light emitting diode driving circuit, so that the light emitting diode driving circuit includes a plurality of transistors and unidirectional conduction elements such as transistors connected in a diode manner, through the specific connection mode and connection between each transistor. On the premise that the difference between the control method and the manufacturing process of adjacent transistors is small and negligible, the current flowing through the light-emitting diode is basically independent of the critical voltage of the transistor and the preset potential during the light-emitting stage of the light-emitting diode, so the manufacturing process factors can be suppressed The influence of the power supply voltage drop on the current can be better compensated, and the problem of uneven display of the panel in the prior art can be effectively improved.

In order to make the above and other objects, features and advantages of the present invention more comprehensible, preferred embodiments will be described in detail below together with the accompanying drawings.

Description of drawings

FIG. 1 is a schematic diagram of a single pixel circuit of a conventional LED display device.

FIG. 2 is a schematic structural diagram of a display device related to an embodiment of the present invention.

FIG. 3 is a timing diagram of various signals related to the LED driving circuit shown in FIG. 2 .

FIGS. 4a and 4b respectively illustrate simulation diagrams of threshold voltage offset compensation effects of the LED driving circuit shown in FIG. 1 and the LED driving circuit shown in FIG. 2 .

5a and 5b respectively illustrate the simulation diagrams of the power supply voltage drop compensation effects of the LED driving circuit shown in FIG. 1 and the LED driving circuit shown in FIG. 2 .

Figure number:

10: Pixel circuit

12: LED drive circuit

16: Organic Light Emitting Diode

Vdata: data signal

SCAN: control signal

OVDD, OVSS: power supply potential

M1, M2: Transistors

C1: capacitance

20: Display device

21: Power supply device

23: Light source

230: Lighting module

232: Organic Light Emitting Diode

234: LED driver circuit

EM: control signal

Vref: reference signal

M3, M4: Transistors

C: Capacitance

A, G: node

V1, V2: the value of the reference signal

T1, T2: time period

Detailed ways

Referring to FIG. 2 , it shows a schematic structural diagram of a display device related to an embodiment of the present invention. As shown in FIG. 2 , the display device 20 includes a power supply device 21 and a light source 23 . Wherein, the power supply device 21 is used to provide power such as power supply potentials OVDD and OVSS; the light emitting source 23 is electrically coupled to the power supply device 21 to receive the power supply potentials OVDD and OVSS. Specifically, the light emitting source 23 includes at least one light emitting module 230 , two of which are shown in this embodiment as an example, but not limiting the present invention.

Each light emitting module 230 includes a light emitting diode such as an organic light emitting diode 232 and a light emitting diode driving circuit 234 . The LED driving circuit 234 includes a plurality of transistors M1 , M2 , M3 , M4 and a capacitor C. As shown in FIG. In this embodiment, the transistors M1, M2, M3, and M4 are all used as switches, and the gate, drain, and source of each transistor M1, M2, M3, and M4 are respectively the control end, the first access end, and the source of the switch. The second access terminal; and the transistors M1, M2, M3, and M4 constitute a switch module for determining whether to allow current to flow through the organic light emitting diode 232; further, the transistor M4 is connected in a diode-connected manner (that is, in this transistor M4 The gate is electrically connected to the source) is disposed in the LED driving circuit 234 as a unidirectional conduction element. In addition, the transistors M1 and M3 are N-type transistors, and the transistors M2 and M4 are P-type transistors, but the invention is not limited thereto.

More specifically, the gate of the transistor M1 is controlled by the control signal SCAN to electrically conduct the drain and the source of the transistor M1, and the drain of the transistor M1 receives the data signal Vdata due to the electrical coupling relationship. The gate of the transistor M2 is electrically coupled to the source of the transistor M1, the source of the transistor M2 is electrically coupled to the power supply potential OVDD provided by the power supply device 21, and the drain of the transistor M2 is electrically coupled to the OLED. 232, and the cathode of the organic light emitting diode 232 is electrically coupled to another power supply potential OVSS provided by the power supply device 21, where OVDD is greater than OVSS. The gate of the transistor M3 is controlled by the control signal EM to determine the electrical conduction state between the drain and the source of the transistor M3, and the drain of the transistor M3 is electrically coupled to the power supply potential OVDD. The drain of the transistor M4 is electrically coupled to the source of the transistor M3, and both the gate and the source of the transistor M4 receive the reference signal Vref due to the electrical coupling. The capacitor C is electrically coupled between the source of the transistor M3 and the gate of the transistor M2. Here, the electrical connection point between the capacitor C and the transistor M3 is marked as node A, and the electrical connection point between the capacitor C and the transistor M2 is marked as for node G.

In addition, it should be noted that the control signals SCAN, EM, data signal Vdata and reference signal Vref received by each light emitting module 230 in FIG. The values of the control signals SCAN, EM, the data signal Vdata and the reference signal Vref must be the same.

The specific operation process of any LED driving circuit 234 will be described in detail below with reference to FIG. 2 and FIG. 3 . FIG.

Specifically, in the T1 period, the control signal SCAN is adjusted to a high level, the control signal EM and the reference signal Vref are both adjusted to a low level and the value of the reference signal Vref is V1, the transistor M1 is turned on, and the transistor M1 M4 (here, that is, the unidirectional conduction element) is also in the conduction state, and the transistor M3 is in the cut-off state; at this time, the potential at node A is (V1+Vth4), and the potential at node G is Vdata, where Vth4 is Threshold voltage of transistor M4.

In the T2 period, the control signal SCAN is adjusted to a low level, the control signal EM and the reference signal Vref are both adjusted to a high level and the value of the reference signal Vref is V2 (here, V2 is greater than V1), and the transistor M3 is at In the on state, the transistor M1 is in the off state, and the transistor M4 cannot be turned on due to the reverse bias; at this time, the potential at node A is OVDD, and the potential at node G is [Vdata+OVDD-(V1+Vth4)] , the transistor M2 is turned on, and the current flowing through the organic light emitting diode 232 Ids=k(Vsg-Vth) ² =k[(V1-Vdata)+(Vth4-Vth)] ² , where k is a constant, and Vth is the value of the transistor M2 critical voltage. Here, for the transistor M2 and the transistor M4 in the same light-emitting module 230 , it can be considered that Vth4=Vth based on the premise that the manufacturing process difference between adjacent transistors is negligible, so Ids=k(V1-Vdata) ² . It can be seen that the current Ids flowing through the organic light emitting diode 232 in the light-emitting stage has nothing to do with the threshold voltage of the transistor and the power supply voltage OVDD, and the influence of manufacturing process factors and power supply voltage drop on the current can be eliminated to achieve the effect of compensation, and then can be achieved. The problem of uneven display in the prior art is effectively improved.

In addition, it can be found from FIG. 3 that during the operation of the LED driving circuit 234 , the control signal SCAN and the control signal EM are out of phase, and the reference signal Vref is in phase with the control signal EM.

FIGS. 4a and 4b respectively illustrate simulation diagrams of threshold voltage offset compensation effects of the LED driving circuit 12 shown in FIG. 1 and the LED driving circuit 234 shown in FIG. 2 . 4a and 4b both show the Ids vs. Vdata characteristic curves in three situations where the threshold voltage of the transistor M2 is Vth, the negative drift is to (Vth-0.3), and the positive drift is to (Vth+0.3). It can be found from FIGS. 4a and 4b that the LED driving circuit 234 of the embodiment of the present invention has a better threshold voltage offset compensation effect.

FIGS. 5a and 5b respectively illustrate simulation diagrams of the power supply voltage drop compensation effects of the LED driving circuit 12 shown in FIG. 1 and the LED driving circuit 234 shown in FIG. 2 . 5a and 5b both show the characteristic curves of Idsvs.Vdata under three situations where the power supply potential is OVDD, OVDD changes by 5%, and OVDD changes by 10%. It can be found from FIGS. 5a and 5b that the LED driving circuit 234 of the embodiment of the present invention has a better power supply voltage drop compensation effect.

To sum up, the embodiments of the present invention design the structural configuration of the LED driving circuit, so that the LED driving circuit includes a plurality of transistors and unidirectional conduction elements such as transistors connected in a diode manner, and through the On the premise that the specific connection mode and control mode of the LED and the manufacturing process difference based on adjacent transistors are negligible, the current flowing through the LED is basically independent of the critical voltage of the transistor and the power supply potential during the light-emitting phase of the LED, so it can be The influence of manufacturing process factors and power supply voltage drop on the current is suppressed to achieve a better compensation effect, which can effectively improve the problem of uneven panel display in the prior art.

In addition, anyone skilled in the art can also make appropriate changes to the LED driving circuit and driving method proposed in the above embodiments of the present invention, for example, changing the transistor M4 in the LED driving circuit 234 into a diode, and the anode of the diode is electrically coupled to Node A, and the cathode of the diode receives the reference signal Vref due to the electrical coupling relationship; appropriately change the type of transistor (P-type or N-type); and/or exchange the electrical connection relationship between the source and drain of each transistor etc.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, this The scope of protection of the invention should be defined by the scope of the claims.

Claims (8)

1. LED driving circuit; It is characterized in that; Described LED driving circuit is suitable for driving a light emitting diode; A plurality of transistors are arranged in the described LED driving circuit, and each described transistor comprises control end, first path terminal and alternate path end respectively, and described LED driving circuit comprises:

One the first transistor; The control that the described control end of described the first transistor receives one first signal is with described first path terminal that determines described the first transistor and the state that electrically conducts between the described alternate path end, and described first path terminal of described the first transistor receives a data-signal because of the electric property coupling relation;

One transistor seconds; The described control end of described transistor seconds is electrically coupled to the described alternate path end of described the first transistor; Described first path terminal of described transistor seconds is electrically coupled to a preset potential, and the described alternate path end of described transistor seconds is electrically coupled to described light emitting diode;

One the 3rd transistor; The described the 3rd transistorized described control end receives the control of a secondary signal to determine the state that electrically conducts between the described the 3rd transistorized described first path terminal and the described alternate path end, and the described the 3rd transistorized described first path terminal is electrically coupled to described preset potential;

One unidirectional breakover element, an end are electrically coupled to the described the 3rd transistorized described alternate path end, and the other end receives a reference signal because of the electric property coupling relation; And

One electric capacity is electrically coupled between the described control end of the described the 3rd transistorized described alternate path end and described transistor seconds,

Wherein, described reference signal can make the not conducting because of reverse biased of described unidirectional breakover element in a certain period.

2. LED driving circuit as claimed in claim 1 is characterized in that, wherein said unidirectional breakover element is a diode.

3. LED driving circuit as claimed in claim 1; It is characterized in that; Wherein said unidirectional breakover element is one the 4th transistor; The described the 4th transistorized described control end and described first path terminal receive described reference signal because of the electric property coupling relation simultaneously, and the described the 4th transistorized described alternate path end is electrically coupled to the described the 3rd transistorized described alternate path end.

4. a LED driving method is characterized in that, described method is applicable to that in the LED driving circuit as claimed in claim 1, described LED driving method comprises:

In one first period, adjust described first signal, described secondary signal and described reference signal with described the first transistor of conducting and described unidirectional breakover element, and make described the 3rd transistor can't conducting; And

In one second period after described first period, adjust described first signal, described secondary signal and described reference signal, and make described the first transistor and the described unidirectional breakover element can't conducting with described the 3rd transistor of conducting,

Wherein, in described second period, described unidirectional breakover element is because reverse biased and can't conducting.

5. LED driving method as claimed in claim 4 is characterized in that, wherein said first signal and described secondary signal anti-phase, and described reference signal and described secondary signal homophase.

6. a display device is characterized in that, described display device comprises:

One power supply device is in order to provide electric power; And

One light emitting source is electrically coupled to described power supply device to accept electric power, and described light emitting source comprises at least one light emitting module, and described light emitting module comprises:

One light emitting diode; And

One LED driving circuit has a plurality of transistors in the described LED driving circuit, each described transistor comprises control end, first path terminal and alternate path end respectively, and described LED driving circuit comprises:

One the first transistor; The control that the described control end of described the first transistor receives one first signal is with described first path terminal that determines described the first transistor and the state that electrically conducts between the described alternate path end, and described first path terminal of described the first transistor receives a data-signal because of the electric property coupling relation;

One transistor seconds; The described control end of described transistor seconds is electrically coupled to the described alternate path end of described the first transistor; Described first path terminal of described transistor seconds is electrically coupled to a preset potential that is provided by described power supply device, and the described alternate path end of described transistor seconds is electrically coupled to described light emitting diode;

One the 3rd transistor; The described the 3rd transistorized described control end receives the control of a secondary signal to determine the state that electrically conducts between the described the 3rd transistorized described first path terminal and the described alternate path end, and the described the 3rd transistorized described first path terminal is electrically coupled to described preset potential;

One unidirectional breakover element, an end are electrically coupled to the described the 3rd transistorized described alternate path end, and the other end receives a reference signal because of the electric property coupling relation; And

One electric capacity is electrically coupled between the described control end of the described the 3rd transistorized described alternate path end and described transistor seconds,

Wherein, described reference signal can make the not conducting because of reverse biased of described unidirectional breakover element in a certain period.

7. display device as claimed in claim 6 is characterized in that, wherein said unidirectional breakover element is a diode.

8. display device as claimed in claim 6; It is characterized in that; Wherein said unidirectional breakover element is one the 4th transistor; The described the 4th transistorized described control end and described first path terminal receive described reference signal because of the electric property coupling relation simultaneously, and the described the 4th transistorized described alternate path end is electrically coupled to the described the 3rd transistorized described alternate path end.

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