CN106448554A - OLED (organic light-emitting diode) driving circuit and OLED display panel - Google Patents
OLED (organic light-emitting diode) driving circuit and OLED display panel Download PDFInfo
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- CN106448554A CN106448554A CN201611079525.4A CN201611079525A CN106448554A CN 106448554 A CN106448554 A CN 106448554A CN 201611079525 A CN201611079525 A CN 201611079525A CN 106448554 A CN106448554 A CN 106448554A
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- G—PHYSICS
- G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
- G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
- G09G3/00—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes
- G09G3/20—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters
- G09G3/22—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources
- G09G3/30—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels
- G09G3/32—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED]
- G09G3/3208—Control arrangements or circuits, of interest only in connection with visual indicators other than cathode-ray tubes for presentation of an assembly of a number of characters, e.g. a page, by composing the assembly by combination of individual elements arranged in a matrix no fixed position being assigned to or needed to be assigned to the individual characters or partial characters using controlled light sources using electroluminescent panels semiconductive, e.g. using light-emitting diodes [LED] organic, e.g. using organic light-emitting diodes [OLED]
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- Control Of Indicators Other Than Cathode Ray Tubes (AREA)
- Electroluminescent Light Sources (AREA)
Abstract
The invention provides an OLED (organic light-emitting diode) driving circuit and an OLED display panel. The OLED driving circuit comprises a switching thin film transistor, a driving thin film transistor, a storage capacitor and a compensation circuit, wherein each of the switching thin film transistor and the driving thin film transistor comprises a grid electrode, a first end and a second end; the first end of the switching thin film transistor receives a data signal; the grid electrode of the switching thin film transistor receives an n-th stage scanning signal (SCAN[n]); the second end of the switching thin film transistor is electrically connected with the second end of the driving thin film transistor; the grid electrode of the driving thin film transistor is electrically connected to a voltage source through the storage capacitor; the second end of the driving thin film transistor is electrically to a positive electrode of the OLED through part of components in the compensation circuit; a negative electrode of the OLED loads low electrical level; the compensation circuit is used for compensating the change, caused by drifting of threshold voltage of the driving thin film transistor, of the driving current of the OLED; and the compensation circuit is also used for stabilizing the electric potential of the grid electrode of the driving thin film transistor.
Description
Technical Field
The invention relates to the field of display, in particular to an OLED (organic light emitting diode) driving circuit and an OLED display panel.
Background
Organic Light-Emitting Diode (OLED) display panels are popular because they are Light, thin, energy-saving, wide in viewing angle, wide in color gamut, high in contrast, and the like. The basic driving circuit of OLED is shown in FIG. 1, FIG. 1 isSchematic diagram of OLED driving circuit in the prior art. The driving circuit is used for driving the OLED, and includes a switching thin film transistor (Switch TFT) T1, a driving thin film transistor (Driver TFT) T2, and a storage capacitor Cst, which is also referred to as a 2T1C structure. The gate electrode of the switching thin film transistor T1 receives SCAN information SCAN, the drain electrode of the switching thin film transistor T1 receives Data signal Data, and the source electrode of the switching thin film transistor T1 is electrically connected to the gate electrode of the driving thin film transistor T2. The source electrode of the switching thin film transistor T1 and the drain electrode of the switching thin film transistor T1 are turned on or off under the control of the SCAN signal SCAN. When the source electrode of the switching thin film transistor T1 and the drain electrode of the switching thin film transistor T1 are turned on under the control of the SCAN signal SCAN, the Data signal Data is transmitted to the gate electrode of the driving thin film transistor T2. The source of the driving thin film transistor T2 is electrically connected to a high potential VDD, and the drain of the driving thin film transistor T2 is electrically connected to the anode of the OLED. The anode of the OLED is electrically connected to a low potential VSS. Both ends of the storage capacitor Cst are electrically connected to the gate electrode of the driving thin film transistor T2 and the drain electrode of the driving thin film transistor T2, respectively. The driving current generated by the driving circuit to drive the OLED is: i isOLED＝k(Vgs-Vth)2. Wherein, IOLEDThe driving current for driving the OLED is also the current flowing through the OLED; k is a current amplification factor of the driving thin film transistor T2, and is determined by characteristics of the driving thin film transistor T2 itself; vgsIs the voltage between the gate and the source of the driving thin film transistor T2; vthIs the threshold voltage of the driving thin film transistor T2. It can be seen that the current flowing through the OLED and the threshold voltage V of the driving TFT T2thIt is related. Due to the threshold voltage V of the driving thin film transistor T2thEasily drifts, resulting in a drive current I driving the OLEDOLEDVarying a drive current I for driving the OLEDOLEDThe variation may cause the luminance of the OLED to vary, thereby affecting the image quality of the OLED display panel.
Disclosure of Invention
The invention provides an OLED driving circuit, which is used for generating a driving current to drive an OLED, and comprises a switch thin film transistor, a driving thin film transistor, a storage capacitor and a compensation circuit, wherein the switch thin film transistor and the driving thin film transistor respectively comprise a grid electrode, a first end and a second end, the first end of the switch thin film transistor receives a data signal, the grid electrode of the switch thin film transistor receives an nth-level scanning signal (SCAN [ n ]), the second end of the switch thin film transistor is electrically connected with the second end of the driving thin film transistor, the grid electrode of the driving thin film transistor is electrically connected to a voltage source through the storage capacitor, the second end of the driving thin film transistor is electrically connected to the anode of the OLED through partial elements in the compensation circuit, and the cathode of the OLED is loaded with a low level, the compensation circuit is used for compensating the change of the drive current of the OLED caused by the shift of the threshold voltage of the drive thin film transistor, and the compensation circuit is also used for stabilizing the potential of the grid electrode of the drive thin film transistor; wherein the first end is a source electrode, and the second end is a drain electrode; or the first end is a drain electrode, and the second end is a source electrode.
Wherein the compensation circuit comprises: the first thin film transistor, the second thin film transistor, the third thin film transistor and the fourth thin film transistor comprise a grid electrode, a first end and a second end;
a gate of the first thin film transistor receives an (n-1) th SCAN signal (SCAN [ n-1]), a first terminal of the first thin film transistor is electrically connected to the gate of the driving thin film transistor, and a second terminal of the first thin film transistor receives a low level (Vint), wherein the nth SCAN signal (SCAN [ n ]) is delayed by T/M compared with the (n-1) th SCAN signal (SCAN [ n-1]), where M is a positive integer and T is a period of a SCAN signal;
a gate of the second thin film transistor receives an enable signal (Em), a first end of the second thin film transistor is electrically connected with the anode of the OLED, and a second end of the second thin film transistor is electrically connected with a second end of the driving thin film transistor;
a gate of the third thin film transistor receives an nth-level SCAN signal (SCAN [ n ]), a first end of the third thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the third thin film transistor is electrically connected to the gate of the driving thin film transistor;
a gate of the fourth thin film transistor receives the enable signal (Em), a first end of the fourth thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the fourth thin film transistor is electrically connected to the voltage source;
in the lighting phase: the electric potential of the grid electrode of the driving thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the driving thin film transistor, the enable signal (Em) is a first level, the (n-1) th-level scanning signal (SCAN [ n-1]) and the n-th-level scanning signal (SCAN [ n ]) are both second levels, the second thin film transistor and the fourth thin film transistor are switched on, the first thin film transistor, the third thin film transistor and the switch thin film transistor are all switched off, a path from the voltage source to the cathode of the OLED is switched on, and the grid electrode voltage of the driving thin film transistor controls the size of the driving current for driving the OLED.
Wherein, in the reset stage of the grid voltage of the driving thin film transistor: the enable signal (Em) is at a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is at a first level, the nth SCAN signal (SCAN [ n ]) is at a second level, the first thin film transistor is turned on, and the second thin film transistor, the third thin film transistor, the fourth thin film transistor, and the switching thin film transistor are all turned off;
in the data writing and threshold voltage compensation stages: the enable signal (Em) is a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is a second level, the nth SCAN signal (SCAN [ n ]) is a first level, the third thin film transistor and the switch thin film transistor are turned on, the first thin film transistor, the second thin film transistor and the fourth thin film transistor are all turned off, and at the moment, the electric potential of the grid electrode of the drive thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the drive thin film transistor, wherein the grid electrode voltage resetting stage of the drive thin film transistor, the data writing and threshold voltage compensation stage, and the light emitting stage are three stages which are sequentially continuous.
Wherein the compensation circuit further includes a fifth thin film transistor including a gate electrode, a first terminal and a second terminal, the gate electrode of the fifth thin film transistor receiving the (n-1) th SCAN signal (SCAN [ n-1]), the first terminal of the fifth thin film transistor receiving the low level (Vint), the second terminal of the fifth thin film transistor being electrically connected to the anode of the OLED.
Wherein the first thin film transistor, the second thin film transistor, the third thin film transistor, the fourth thin film transistor, the fifth thin film transistor, the switching thin film transistor, and the driving thin film transistor are all PTFTs, the first level is a low level, and the second level is a high level;
or the first thin film transistor, the second thin film transistor, the third thin film transistor, the fourth thin film transistor, the fifth thin film transistor, the switch thin film transistor, and the driving thin film transistor are all NTFTs, the first level is a high level, and the second level is a low level.
The invention also provides an OLED display panel, which includes an OLED driving circuit and an OLED, wherein the OLED driving circuit is configured to generate a driving current to drive the OLED, the OLED driving circuit includes a switching thin film transistor, a driving thin film transistor, a storage capacitor, and a compensation circuit, the switching thin film transistor and the driving thin film transistor each include a gate, a first terminal, and a second terminal, the first terminal of the switching thin film transistor receives a data signal, the gate of the switching thin film transistor receives an nth SCAN signal (SCAN [ n ]), the second terminal of the switching thin film transistor is electrically connected to the second terminal of the driving thin film transistor, the gate of the driving thin film transistor is electrically connected to a voltage source through the storage capacitor, and the second terminal of the driving thin film transistor is electrically connected to the anode of the OLED through a part of elements in the compensation circuit, the negative pole of the OLED is loaded with a low level, the compensation circuit is used for compensating the change of the driving current of the OLED caused by the drift of the threshold voltage of the driving thin film transistor, and the compensation circuit is also used for stabilizing the potential of the grid electrode of the driving thin film transistor; wherein the first end is a source electrode, and the second end is a drain electrode; or the first end is a drain electrode, and the second end is a source electrode.
Wherein the compensation circuit comprises: the first thin film transistor, the second thin film transistor, the third thin film transistor and the fourth thin film transistor comprise a grid electrode, a first end and a second end;
a gate of the first thin film transistor receives an (n-1) th SCAN signal (SCAN [ n-1]), a first terminal of the first thin film transistor is electrically connected to the gate of the driving thin film transistor, and a second terminal of the first thin film transistor receives a low level (Vint), wherein the nth SCAN signal (SCAN [ n ]) is delayed by T/M compared with the (n-1) th SCAN signal (SCAN [ n-1]), where M is a positive integer and T is a period of a SCAN signal;
a gate of the second thin film transistor receives an enable signal (Em), a first end of the second thin film transistor is electrically connected with the anode of the OLED, and a second end of the second thin film transistor is electrically connected with a second end of the driving thin film transistor;
a gate of the third thin film transistor receives an nth-level SCAN signal (SCAN [ n ]), a first end of the third thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the third thin film transistor is electrically connected to the gate of the driving thin film transistor;
a gate of the fourth thin film transistor receives the enable signal (Em), a first end of the fourth thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the fourth thin film transistor is electrically connected to the voltage source;
in the lighting phase: the electric potential of the grid electrode of the driving thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the driving thin film transistor, the enable signal (Em) is a first level, the (n-1) th-level scanning signal (SCAN [ n-1]) and the nth-level scanning signal (SCAN [ n ]) are both second levels, the second thin film transistor and the fourth thin film transistor are conducted, the first thin film transistor, the third thin film transistor and the switch thin film transistor are all cut off, and the passage from the voltage source to the cathode of the OLED is conducted.
Wherein, in the reset stage of the grid voltage of the driving thin film transistor: the enable signal (Em) is at a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is at a first level, the nth SCAN signal (SCAN [ n ]) is at a second level, the first thin film transistor is turned on, and the second thin film transistor, the third thin film transistor, the fourth thin film transistor, and the switching thin film transistor are all turned off;
in the data writing and threshold voltage compensation stages: the enable signal (Em) is a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is a second level, the nth SCAN signal (SCAN [ n ]) is a first level, the third thin film transistor and the switch thin film transistor are turned on, the first thin film transistor, the second thin film transistor and the fourth thin film transistor are all turned off, and at the moment, the electric potential of the grid electrode of the drive thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the drive thin film transistor, wherein the grid electrode voltage resetting stage of the drive thin film transistor, the data writing and threshold voltage compensation stage, and the light emitting stage are three stages which are sequentially continuous.
Wherein the compensation circuit further includes a fifth thin film transistor including a gate electrode, a first terminal and a second terminal, the gate electrode of the fifth thin film transistor receiving the (n-1) th SCAN signal (SCAN [ n-1]), the first terminal of the fifth thin film transistor receiving the low level (Vint), the second terminal of the fifth thin film transistor being electrically connected to the anode of the OLED.
Wherein the first thin film transistor, the second thin film transistor, the third thin film transistor, the fourth thin film transistor, the fifth thin film transistor, the switching thin film transistor, and the driving thin film transistor are all PTFTs, the first level is a low level, and the second level is a high level;
or the first thin film transistor, the second thin film transistor, the third thin film transistor, the fourth thin film transistor, the fifth thin film transistor, the switch thin film transistor, and the driving thin film transistor are all NTFTs, the first level is a high level, and the second level is a low level.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
Fig. 1 is a schematic diagram of an OLED driving circuit in the prior art.
Fig. 2 is a schematic diagram of an OLED driving circuit according to a first preferred embodiment of the invention.
Fig. 3 is a timing diagram of signals of the OLED driving circuit shown in fig. 2.
Fig. 4 is a schematic diagram of an OLED driving circuit according to a second preferred embodiment of the invention.
Fig. 5 is a timing diagram of respective signals of the OLED driving circuit shown in fig. 4.
Fig. 6 is a schematic view of an OLED display panel according to a preferred embodiment of the invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 2 and 3 together, fig. 2 is a schematic diagram of an OLED driving circuit according to a first preferred embodiment of the invention; fig. 3 is a timing diagram of signals of the OLED driving circuit shown in fig. 2. The OLED driving circuit 100 is used for generating a driving current to drive an Organic Light-Emitting Diode (OLED). The OLED driving circuit 100 includes a switching thin film transistor M5, a driving thin film transistor MD, a storage capacitor Cst, and a compensation circuit 110. The switching thin film transistor M5 and the driving thin film transistor MD each include a gate, a first terminal and a second terminal. In this embodiment, the first terminal is a source and the second terminal is a drain. In other embodiments, the first terminal is a drain and the second terminal is a source. A first terminal of the switching thin film transistor M5 receives the Data signal Data, a gate of the switching thin film transistor M5 receives the nth SCAN signal SCAN [ n ], and a second terminal of the switching thin film transistor M5 is electrically connected to a second terminal of the driving thin film transistor MD. The gate of the driving thin film transistor MD is electrically connected to a voltage source VDD through the storage capacitor Cst, the second terminal of the driving thin film transistor MD is electrically connected to the anode of the OLED through a part of the elements 110 in the compensation circuit, and the cathode of the OLED is loaded with a low level. The compensation circuit 110 is used to compensate for a change in the driving current of the OLED due to a drift in the threshold voltage of the driving thin film transistor MD, and the compensation circuit 110 is also used to stabilize the potential of the gate electrode of the driving thin film transistor MD.
Compared with the prior art, the OLED driving circuit 100 of the present invention includes the compensation circuit 110, the compensation circuit 110 is configured to compensate for a change in a driving current for driving the OLED due to a drift of a threshold voltage of the driving thin film transistor MD, and the compensation circuit 110 further stabilizes a potential of a gate of the driving thin film transistor MD, so as to stabilize the driving current for driving the OLED generated by the driving circuit 100, and the stabilization of the OLED driving current does not affect a light emitting brightness of the OLED, thereby improving an image quality of an OLED display panel to which the OLED driving circuit is applied.
The compensation circuit 110 includes: a first thin film transistor M1, a second thin film transistor M2, a third thin film transistor M3, and a fourth thin film transistor M4. The first thin film transistor M1, the second thin film transistor M2, the third thin film transistor M3, and the fourth thin film transistor M4 each include a gate, a first terminal, and a second terminal.
The gate of the first thin film transistor M1 receives the (n-1) th SCAN signal SCAN [ n-1], the first terminal of the first thin film transistor M1 is electrically connected to the gate of the driving thin film transistor MD, and the second terminal of the first thin film transistor M1 receives the low level Vint. Wherein the nth stage SCAN signal SCAN [ n ] is delayed by T/M compared to the (n-1) th stage SCAN signal SCAN [ n-1], where M is a positive integer and T is a period of a SCAN signal.
The gate of the second thin film transistor M2 receives the enable signal Em, the first terminal of the second thin film transistor M2 is electrically connected to the anode of the OLED, and the second terminal of the second thin film transistor M2 is electrically connected to the second terminal of the driving thin film transistor MD.
The gate of the third tft M3 receives the nth SCAN signal SCAN [ n ], the first terminal of the third tft M3 is electrically connected to the first terminal of the driving tft MD, and the second terminal of the third tft M3 is electrically connected to the gate of the driving tft MD.
The gate of the fourth thin film transistor M4 receives the enable signal Em, the first terminal of the fourth thin film transistor M4 is electrically connected to the first terminal of the driving thin film transistor MD, and the second terminal of the fourth thin film transistor M4 is electrically connected to the voltage source VDD.
During the reset phase of the gate voltage of the driving thin film transistor (denoted initial in fig. 3): the enable signal Em is at a second level, the (n-1) th SCAN signal SCAN [ n-1] is at a first level, the nth SCAN signal SCAN [ n ] is at a second level, the first thin film transistor M1 is turned on, and the second thin film transistor M2, the third thin film transistor M3, the fourth thin film transistor M4, and the switching thin film transistor M5 are all turned off. At this time, the low level Vint is transmitted to the gate electrode of the driving thin film transistor MD through the turned-on first thin film transistor M1.
During the data write and threshold voltage compensation phases (denoted by programming in fig. 3): the enable signal Em is at a second level, and the (n-1) th SCAN signal SCAN [ n-1]]At a second level, the nth stage SCAN signal SCAN [ n ]]At the first level, the third thin film transistor M3 and the switching thin film transistor M5 are turned on, the first thin film transistor M1, the second thin film transistor M2 and the fourth thin film transistor M4 are all turned off, and at this time, the gate voltage of the driving thin film transistor MD is the voltage V of the Data signal DatadataAnd an absolute value | V of a threshold voltage of the driving thin film transistor MDthThe sum of | s.
Since the third thin film transistor M3 is turned on, the gate of the driving thin film transistor MD is shorted to the first terminal (source in fig. 3) of the driving thin film transistor MD, and the driving thin film transistor MD is equivalent to a diode. For convenience of description, a point where the gate electrode of the driving thin film transistor MD intersects the storage capacitor Cst and the first end of the first thin film transistor M1 is denoted as a point a. When the driving thin film transistor MD is equivalent to a diode, the Data signal Data charges a point a through the turned-on switching thin film transistor M5 until the point a stores the threshold voltage V of the driving thin film transistor MDthAt this time, the potential at point a is: vA＝Vdata+|VthL. Wherein, VAPotential at point A, VdataVoltage, V, representing Data signal DatathIndicating the threshold voltage of the driving thin film transistor MD.
In the luminescence phase (denoted by emision in fig. 3): the gate potential of the driving thin film transistor MD is an absolute value | V of the voltage Vdata of the Data signal Data and the threshold voltage of the driving thin film transistor MDth| the enable signal Em is a first level, the (n-1) th SCAN signal SCAN [ n-1]]And the nth stage SCAN signal SCAN [ n ]]The second thin film transistor M2 and the fourth thin film transistor M4 are all at a second level, the first thin film transistor M1, the third thin film transistor M3 and the switch thin film transistor M5 are all turned off, the path from the voltage source VDD to the cathode of the OLED is turned on, and the gate voltage of the driving thin film transistor MD controls the magnitude of the driving current for driving the OLED. At this time, the OLED driving circuit 100 drives the OLED to emit light. The driving thin film transistor grid voltage resetting stage, the data writing and threshold voltage compensation stage and the light emitting stage are three stages which are sequentially continuous.
The magnitude of the OLED driving current generated by the OLED driving circuit 100 is: i isOLED＝k[VDD-(Vdata-|Vth|)-|Vth|]2＝k(VDD-Vdata)2. Wherein, IOLEDRepresents the drive current of the OLED; k is a current amplification factor of the driving thin film transistor MD, and is determined by the characteristics of the driving thin film transistor MD itself; vDDIs the voltage of the voltage source VDD; vdataIs the voltage of the Data signal Data. It can be seen that the OLED driving circuit 100 of the present invention generates the OLED driving current IOLEDAnd a threshold voltage V of the driving thin film transistor MDthIs irrelevant. Therefore, compared with the prior art, the OLED driving circuit provided by the invention can generate the OLED driving current which is not accompanied with the threshold voltage V of the driving thin film transistor MDthThe drift of the OLED driving circuit is changed, so that the driving current of the OLED is stabilized, the stability of the driving current of the OLED does not influence the brightness of the OLED, and the image quality of an OLED display panel applied by the OLED driving circuit is improved.
For convenience of description, a point at which the second terminal of the first thin film transistor M1 receives the low level Vint is denoted as a point B. An intersection of the first terminal (source in fig. 3) of the driving thin film transistor MD and the first terminal of the third thin film transistor M3 is denoted as point C. In the light emitting period, since the third thin film transistor M3 is in the off state, the first terminal of the third thin film transistor M3 is electrically connected to the first terminal of the driving thin film transistor MD, and the second terminal of the third thin film transistor M3 is electrically connected to the gate of the driving thin film transistor MD, the potential at the point C is higher than the potential at the point a, and the leakage current of the third thin film transistor M3 flows from the point C to the point a, so that the potential at the point a is increased. Since the potential at the point a is higher than the potential at the point B, the leakage current of the first thin film transistor M1 flows from the point a to the point B, and the potential at the point a is lowered. It can be seen that, during the light emitting period, the leakage current of the third tft M3 increases the potential at the point a, and the leakage current of the first tft M1 decreases the potential at the point a, so that the potential at the point a is maintained at a stable level, that is, the potential at the gate of the driving tft MD is maintained at a stable level due to the cooperation of the first tft M1 and the third tft M3. Therefore, the driving current generated by the driving circuit 100 for driving the OLED is relatively stable.
In this embodiment, the first Thin Film transistor M1, the second Thin Film transistor M2, the third Thin Film transistor M3, the fourth Thin Film transistor M4, the switching Thin Film transistor M5, and the driving Thin Film transistor MD are all ptft (p Thin Film transistor), the first level is a low level, and the second level is a high level.
In another embodiment, the first Thin Film transistor M1, the second Thin Film transistor M2, the third Thin Film transistor M3, the fourth Thin Film transistor M4, the switching Thin Film transistor M5 and the driving Thin Film transistor MD are all ntft (n Thin Film transistor), the first level is a high level, and the second level is a low level.
Referring to fig. 4 and 5 together, fig. 4 is a schematic diagram of an OLED driving circuit according to a second preferred embodiment of the invention; fig. 5 is a timing diagram of respective signals of the OLED driving circuit shown in fig. 4. The OLED driving circuit shown in fig. 4 is substantially the same as the OLED driving circuit shown in fig. 2, and respective signals in fig. 5 are the same as respective signals in fig. 3. The OLED driving circuit shown in fig. 4 has one more thin film transistor than the OLED driving circuit shown in fig. 2: and a fifth thin film transistor M6. The OLED driving circuit in this embodiment is not described in detail in comparison with the same parts of the OLED circuit in the first embodiment of the present invention. The fifth thin film transistor M6 includes a gate, a first terminal, and a second terminal. A gate of the fifth thin film transistor M6 receives the (n-1) th-stage SCAN signal SCAN [ n-1], a first terminal of the fifth thin film transistor M6 receives the low level Vint, and a second terminal of the fifth thin film transistor M6 is electrically connected to the anode electrode of the OLED. In the reset phase of the gate voltage of the driving thin film transistor (denoted by initial in fig. 5), the fifth thin film transistor M6 can largely shunt the leakage current of the driving thin film transistor MD, thereby solving the problem of a small amount of light emission caused by the fact that the OLED cannot be completely turned off due to the leakage current of the driving thin film transistor in the reset phase of the gate voltage of the driving thin film transistor.
In this embodiment, the first thin film transistor M1, the second thin film transistor M2, the third thin film transistor M3, the fourth thin film transistor M4, the fifth thin film transistor M6, the switching thin film transistor M5, and the driving thin film transistor MD are all PTFTs, the first level is a low level, and the second level is a high level.
In another embodiment, the first thin film transistor M1, the second thin film transistor M2, the third thin film transistor M3, the fourth thin film transistor M4, the fifth thin film transistor M6, the switching thin film transistor M5, and the driving thin film transistor MD are all NTFTs, the first level is a high level, and the second level is a low level.
Fig. 6 shows an OLED display panel 10 according to a preferred embodiment of the present invention, and fig. 6 is a schematic diagram of the OLED display panel according to the preferred embodiment of the present invention. The OLED display panel 10 of the present invention includes the OLED driving circuit 100 described in any of the foregoing embodiments, and will not be described herein again.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.
Claims (10)
1. An OLED driving circuit, wherein the OLED driving circuit is used for generating a driving current to drive an OLED, the OLED driving circuit comprises a switching thin film transistor, a driving thin film transistor, a storage capacitor and a compensation circuit, the switching thin film transistor and the driving thin film transistor each comprise a gate, a first terminal and a second terminal, the first terminal of the switching thin film transistor receives a data signal, the gate of the switching thin film transistor receives an nth SCAN signal (SCAN [ n ]), the second terminal of the switching thin film transistor is electrically connected to the second terminal of the driving thin film transistor, the gate of the driving thin film transistor is electrically connected to a voltage source through the storage capacitor, the second terminal of the driving thin film transistor is electrically connected to the anode of the OLED through a part of elements in the compensation circuit, and the cathode of the OLED is loaded with a low level, the compensation circuit is used for compensating the change of the drive current of the OLED caused by the shift of the threshold voltage of the drive thin film transistor, and the compensation circuit is also used for stabilizing the potential of the grid electrode of the drive thin film transistor; wherein the first end is a source electrode, and the second end is a drain electrode; or the first end is a drain electrode, and the second end is a source electrode.
2. The OLED drive circuit of claim 1, wherein the compensation circuit includes: the first thin film transistor, the second thin film transistor, the third thin film transistor and the fourth thin film transistor comprise a grid electrode, a first end and a second end;
a gate of the first thin film transistor receives an (n-1) th SCAN signal (SCAN [ n-1]), a first terminal of the first thin film transistor is electrically connected to the gate of the driving thin film transistor, and a second terminal of the first thin film transistor receives a low level (Vint), wherein the nth SCAN signal (SCAN [ n ]) is delayed by T/M compared with the (n-1) th SCAN signal (SCAN [ n-1]), where M is a positive integer and T is a period of a SCAN signal;
a gate of the second thin film transistor receives an enable signal (Em), a first end of the second thin film transistor is electrically connected with the anode of the OLED, and a second end of the second thin film transistor is electrically connected with a second end of the driving thin film transistor;
a gate of the third thin film transistor receives an nth-level SCAN signal (SCAN [ n ]), a first end of the third thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the third thin film transistor is electrically connected to the gate of the driving thin film transistor;
a gate of the fourth thin film transistor receives the enable signal (Em), a first end of the fourth thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the fourth thin film transistor is electrically connected to the voltage source;
in the lighting phase: the electric potential of the grid electrode of the driving thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the driving thin film transistor, the enable signal (Em) is a first level, the (n-1) th-level scanning signal (SCAN [ n-1]) and the n-th-level scanning signal (SCAN [ n ]) are both second levels, the second thin film transistor and the fourth thin film transistor are switched on, the first thin film transistor, the third thin film transistor and the switch thin film transistor are all switched off, a path from the voltage source to the cathode of the OLED is switched on, and the grid electrode voltage of the driving thin film transistor controls the size of the driving current for driving the OLED.
3. The OLED drive circuit of claim 2, wherein during the drive thin film transistor gate voltage reset phase: the enable signal (Em) is at a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is at a first level, the nth SCAN signal (SCAN [ n ]) is at a second level, the first thin film transistor is turned on, and the second thin film transistor, the third thin film transistor, the fourth thin film transistor, and the switching thin film transistor are all turned off;
in the data writing and threshold voltage compensation stages: the enable signal (Em) is a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is a second level, the nth SCAN signal (SCAN [ n ]) is a first level, the third thin film transistor and the switch thin film transistor are turned on, the first thin film transistor, the second thin film transistor and the fourth thin film transistor are all turned off, and at the moment, the electric potential of the grid electrode of the drive thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the drive thin film transistor, wherein the grid electrode voltage resetting stage of the drive thin film transistor, the data writing and threshold voltage compensation stage, and the light emitting stage are three stages which are sequentially continuous.
4. The OLED driving circuit of claim 3, wherein the compensation circuit further comprises a fifth thin film transistor, the fifth thin film transistor comprising a gate, a first terminal and a second terminal, the gate of the fifth thin film transistor receiving the (n-1) th stage SCAN signal (SCAN [ n-1]), the first terminal of the fifth thin film transistor receiving the low level (Vint), the second terminal of the fifth thin film transistor being electrically connected to the anode of the OLED.
5. The OLED drive circuit of claim 4, wherein the first, second, third, fourth, fifth, switching, and driving thin film transistors are all PTFTs, the first level is low, the second level is high; or,
the first thin film transistor, the second thin film transistor, the third thin film transistor, the fourth thin film transistor, the fifth thin film transistor, the switching thin film transistor, and the driving thin film transistor are all NTFTs, the first level is a high level, and the second level is a low level.
6. An OLED display panel, comprising an OLED driving circuit and an OLED, wherein the OLED driving circuit is used for generating a driving current to drive the OLED, the OLED driving circuit comprises a switching thin film transistor, a driving thin film transistor, a storage capacitor and a compensation circuit, the switching thin film transistor and the driving thin film transistor each comprise a gate, a first terminal and a second terminal, the first terminal of the switching thin film transistor receives a data signal, the gate of the switching thin film transistor receives an nth SCAN signal (SCAN [ n ]), the second terminal of the switching thin film transistor is electrically connected to the second terminal of the driving thin film transistor, the gate of the driving thin film transistor is electrically connected to a voltage source through the storage capacitor, and the second terminal of the driving thin film transistor is electrically connected to the anode of the OLED through some components in the compensation circuit, the negative pole of the OLED is loaded with a low level, the compensation circuit is used for compensating the change of the driving current of the OLED caused by the drift of the threshold voltage of the driving thin film transistor, and the compensation circuit is also used for stabilizing the potential of the grid electrode of the driving thin film transistor; wherein the first end is a source electrode, and the second end is a drain electrode; or the first end is a drain electrode, and the second end is a source electrode.
7. The OLED display panel of claim 6, wherein the compensation circuit comprises: the first thin film transistor, the second thin film transistor, the third thin film transistor and the fourth thin film transistor comprise a grid electrode, a first end and a second end;
a gate of the first thin film transistor receives an (n-1) th SCAN signal (SCAN [ n-1]), a first terminal of the first thin film transistor is electrically connected to the gate of the driving thin film transistor, and a second terminal of the first thin film transistor receives a low level (Vint), wherein the nth SCAN signal (SCAN [ n ]) is delayed by T/M compared with the (n-1) th SCAN signal (SCAN [ n-1]), where M is a positive integer and T is a period of a SCAN signal;
a gate of the second thin film transistor receives an enable signal (Em), a first end of the second thin film transistor is electrically connected with the anode of the OLED, and a second end of the second thin film transistor is electrically connected with a second end of the driving thin film transistor;
a gate of the third thin film transistor receives an nth-level SCAN signal (SCAN [ n ]), a first end of the third thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the third thin film transistor is electrically connected to the gate of the driving thin film transistor;
a gate of the fourth thin film transistor receives the enable signal (Em), a first end of the fourth thin film transistor is electrically connected to a first end of the driving thin film transistor, and a second end of the fourth thin film transistor is electrically connected to the voltage source;
in the lighting phase: the electric potential of the grid electrode of the driving thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the driving thin film transistor, the enable signal (Em) is a first level, the (n-1) th-level scanning signal (SCAN [ n-1]) and the nth-level scanning signal (SCAN [ n ]) are both second levels, the second thin film transistor and the fourth thin film transistor are conducted, the first thin film transistor, the third thin film transistor and the switch thin film transistor are all cut off, and the passage from the voltage source to the cathode of the OLED is conducted.
8. The OLED display panel of claim 7, wherein during the drive thin film transistor gate voltage reset phase: the enable signal (Em) is at a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is at a first level, the nth SCAN signal (SCAN [ n ]) is at a second level, the first thin film transistor is turned on, and the second thin film transistor, the third thin film transistor, the fourth thin film transistor, and the switching thin film transistor are all turned off;
in the data writing and threshold voltage compensation stages: the enable signal (Em) is a second level, the (n-1) th SCAN signal (SCAN [ n-1]) is a second level, the nth SCAN signal (SCAN [ n ]) is a first level, the third thin film transistor and the switch thin film transistor are turned on, the first thin film transistor, the second thin film transistor and the fourth thin film transistor are all turned off, and at the moment, the electric potential of the grid electrode of the drive thin film transistor is the sum of the voltage of the data signal and the absolute value of the threshold voltage of the drive thin film transistor, wherein the grid electrode voltage resetting stage of the drive thin film transistor, the data writing and threshold voltage compensation stage, and the light emitting stage are three stages which are sequentially continuous.
9. The OLED display panel of claim 8, wherein the compensation circuit further includes a fifth thin film transistor, the fifth thin film transistor including a gate electrode, a first terminal and a second terminal, the gate electrode of the fifth thin film transistor receiving the (n-1) th-order SCAN signal (SCAN [ n-1]), the first terminal of the fifth thin film transistor receiving the low level (Vint), the second terminal of the fifth thin film transistor being electrically connected to the anode of the OLED.
10. The OLED display panel of claim 9, wherein the first thin film transistor, the second thin film transistor, the third thin film transistor, the fourth thin film transistor, the fifth thin film transistor, the switching thin film transistor, and the driving thin film transistor are all PTFTs, the first level is a low level, and the second level is a high level;
or,
the first thin film transistor, the second thin film transistor, the third thin film transistor, the fourth thin film transistor, the fifth thin film transistor, the switching thin film transistor, and the driving thin film transistor are all NTFTs, the first level is a high level, and the second level is a low level.
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