CN203366706U - Pixel drive circuit and display device - Google Patents

Abstract

The utility model relates to the technical field of organic light emitting display, especially to a pixel drive circuit and a display device. The pixel drive circuit comprises an electroluminescent component, a driving transistor, a switch unit, a charging unit, a compensation unit, an isolating unit and a memory cell. According to the pixel drive circuit provided by the embodiment of the utility model, a storage capacitor is firstly charged by the charging unit; then, by the method of firstly charging and then discharging, voltage in the storage capacitor rapidly matches drive current and threshold voltage Vth is rapidly compensated such that drive current provided by the driving transistor is not influenced by the threshold voltage Vth. Thus, consistency of the drive current is raised, uniformity of display brightness is improved, and user experience is promoted.

Description

Pixel-driving circuit and display device

Technical field

The utility model relates to the organic light emitting display technical field, particularly a kind of pixel-driving circuit and display device.

Background technology

Compare traditional liquid crystal panel, AMOLED(Active Matrix/Organic Light Emitting Diode, active matrix organic light-emitting diode) display panel has the characteristics such as reaction velocity is faster, contrast is higher, visual angle is wider, therefore, AMOLED has obtained the increasingly extensive concern of display technique developer.

The active matrix organic light-emitting diode display panel can luminously be by driving Thin Film Transistor (TFT) (Thin Film Transistor, TFT) electric current produced when state of saturation drives, because while inputting identical gray scale voltage, different critical voltages can produce different electric currents, causes the inconsistency of drive current.Low temperature polycrystalline silicon technology (Low Temperature Poly-silicon, LTPS) processing procedure upper threshold voltage V _ththe non-constant of homogeneity, threshold voltage V simultaneously _thalso have drift, therefore, traditional 2T1C circuit brightness uniformity is very poor.

Fig. 1 is 2 TFT transistors of available technology adopting, 1 voltage driven type pixel-driving circuit structure (2T1C) that electric capacity forms.Wherein the first transistor M1 arrives the voltage transmission on data line the grid of driving transistors DTFT, driving transistors DTFT is converted into corresponding electric current supply Organic Light Emitting Diode by this data voltage, when normal operation, driving transistors DTFT should, in saturation region, provide stable drive current within the sweep time of a line.Drive current (flowing through the circuit of Organic Light Emitting Diode OLED) can be expressed as:

$I_{\mathrm{OLED}}=\frac{1}{2}{\mathrm{\μ}}_n\·C_{\mathrm{OX}}\·\frac{W}{L}\·{(V_{\mathrm{data}}-V_{\mathrm{oled}}-V_{\mathrm{th}})}^2$

μ wherein _nfor carrier mobility, C _oXfor gate oxide electric capacity, W/L is the transistor breadth length ratio, V _datafor data voltage, V _oledfor the operating voltage of OLED, for all pixel cells are shared, V _ththreshold voltage for driving transistors DTFT.From above formula, if the V between the different pixels unit _thdifference, cause drive current there are differences; If the threshold voltage V of driving transistors _thdrift about in time, may cause first after-current difference, cause ghost, reduced display effect, affect the user and experience.

The utility model content

(1) technical matters that will solve

The technical problems to be solved in the utility model is for the deficiencies in the prior art, to provide a kind of pixel-driving circuit and driving method thereof, by the threshold voltage V of compensation for drive transistor _th, the drive current that driving transistors is provided is not subject to threshold voltage V _thimpact, to improve the consistance of drive current, improve the homogeneity of brightness.

(2) technical scheme

A kind of pixel-driving circuit, comprise electroluminescent cell, driving transistors, switch element, charhing unit, compensating unit, partition unit and storage unit;

Described switch element writes for the data voltage of controlling data line, the first end of described switch element is connected with described data line, and the second end of described switch element is connected with the first end of described charhing unit, the first end of compensating unit, the first end of storage unit and the grid of driving transistors respectively;

Described charhing unit is described storage unit charging for controlling driving power, and the second end of described charhing unit is connected with the first end of described driving power and electroluminescent cell respectively;

Described partition unit is for being electrically connected between the source electrode that cuts off described electroluminescent cell and driving transistors, the first end of described partition unit is connected with described electroluminescent cell the second end, and the second end of described partition unit is connected with the source electrode of described driving transistors;

Described compensating unit is for the threshold voltage to the pre-stored described driving transistors of described storage unit, and the second end of described compensating unit is connected with the source electrode of described driving transistors;

The second end ground connection of the drain electrode of described driving transistors and storage unit.

Preferably,

Described electroluminescent cell is Organic Light Emitting Diode, and described storage unit is memory capacitance, and described switch element is the first transistor, and described charhing unit is the 3rd transistor, and described compensating unit is transistor seconds, and described partition unit is the 4th transistor;

The grid of described the first transistor connects the first sweep trace, the source electrode connection data line of described the first transistor, the drain electrode of described the first transistor is connected with the grid of source electrode, the 3rd transistorized drain electrode and the driving transistors of the first end of memory capacitance, transistor seconds respectively;

Described the 3rd transistorized grid connects described the second sweep trace, and described the 3rd transistorized source electrode is connected with the first end of driving power and Organic Light Emitting Diode respectively;

The described the 4th transistorized grid connection control signal line, described the 4th transistorized source electrode connects the second end of described Organic Light Emitting Diode, and described the 4th transistorized drain electrode is connected with the source electrode of described driving transistors and the drain electrode of transistor seconds respectively;

The grid of described transistor seconds connects described the first sweep trace.

Preferably, all crystals Guan Jun has identical channel type.

Preferably, described transistor is N channel-type thin film transistor (TFT); The anode that the first end of described Organic Light Emitting Diode is described Organic Light Emitting Diode, and the anode of described Organic Light Emitting Diode is connected with the high level output end of driving power, the negative electrode that the second end of described Organic Light Emitting Diode is described Organic Light Emitting Diode.Preferably, described transistor is equal P channel-type thin film transistor (TFT); The negative electrode that the first end of described Organic Light Emitting Diode is described Organic Light Emitting Diode, and the anode of described Organic Light Emitting Diode is connected with the low level output end of driving power, the anode that the second end of described Organic Light Emitting Diode is described Organic Light Emitting Diode.The utility model also provides a kind of driving method that drives above-mentioned any one pixel-driving circuit:

A kind of pixel-driving circuit driving method comprises step:

S1. apply control signal conducting the 3rd transistor at the second sweep trace, at the first sweep trace and control signal wire, apply control signal control the first transistor, transistor seconds and the cut-off of the 4th transistor; Driving power charges to memory capacitance;

S2. apply control signal at the first sweep trace and control the first transistor and transistor seconds conducting, apply control signal at the second sweep trace and control the 3rd transistor cut-off; Threshold voltage and the data voltage on data line of driving transistors write described memory capacitance;

S3. apply control signal conducting the 4th transistor at control signal wire, at the first sweep trace, apply control signal cut-off the first transistor and transistor seconds; The voltage that utilization is stored in described memory capacitance drives described Organic Light Emitting Diode luminous.

The utility model also provides a kind of display device that comprises above-mentioned any one pixel-driving circuit.

(3) beneficial effect

The pixel-driving circuit that the utility model embodiment provides, at first charge to memory capacitance by charhing unit, then utilizes the method first charge and discharge afterwards, the quick and drive current of voltage in memory capacitance is complementary and to threshold voltage V _thcompensate fast, the drive current that driving transistors is provided is not subject to threshold voltage V _thimpact, improved the consistance of drive current, improved the homogeneity of display brightness, promoted user's experience.

The accompanying drawing explanation

Fig. 1 is 2T1C pixel-driving circuit structural representation of the prior art;

Fig. 2 is the structural representation of pixel-driving circuit in the utility model embodiment mono-;

Fig. 3 is a kind of specific implementation schematic diagram of pixel-driving circuit in Fig. 2;

Fig. 4 is the driving sequential chart of pixel-driving circuit shown in Fig. 3;

Fig. 5 is the equivalent circuit structure schematic diagram of pixel-driving circuit shown in Fig. 3 in the S1 stage;

Fig. 6 is the equivalent circuit structure schematic diagram of pixel-driving circuit shown in Fig. 3 in the S2 stage;

Fig. 7 is the equivalent circuit structure schematic diagram of pixel-driving circuit shown in Fig. 3 in the S3 stage.

Embodiment

Below in conjunction with drawings and Examples, embodiment of the present utility model is described further.Following examples are only for the utility model is described, but are not used for limiting scope of the present utility model.

Embodiment mono-

As shown in Figure 2, a kind of pixel-driving circuit provided by the utility model, mainly comprise electroluminescent cell, driving transistors DTFT, switch element, charhing unit, compensating unit, partition unit and storage unit; Switch element writes for the data voltage of controlling data line, and its first end is connected with data line, and the second end is connected with the first end of charhing unit, compensating unit, storage unit and the grid of driving transistors DTFT respectively; Charhing unit is memory capacitance C charging for controlling driving power, and its second end is connected with the first end of driving power and electroluminescent cell respectively; Cut off unit for being electrically connected between the source electrode that cuts off electroluminescent cell and driving transistors DTFT, its first end is connected with electroluminescent cell the second end, and the second end is connected with the source electrode of driving transistors DTFT; Compensating unit is for the threshold voltage to the pre-stored driving transistors DTFT of storage unit, and its second end is connected with the source electrode of driving transistors DTFT; The second end ground connection of the drain electrode of driving transistors DTFT and memory capacitance C.At first by charhing unit, storage unit is charged, then utilize the method first charge and discharge afterwards, the quick and drive current of voltage in storage unit is complementary and to threshold voltage V _thcompensate fast, make the drive current that driving transistors DTFT provides not be subject to threshold voltage V _thimpact, improved the consistance of drive current, improved the homogeneity of brightness, promoted user's experience.

A kind of implementation of above-mentioned pixel-driving circuit is provided in the present embodiment, as shown in Figure 3, comprise driving transistors DTFT and memory capacitance C, electroluminescent cell is Organic Light Emitting Diode OLED, switch element is the first transistor T1, and charhing unit is the 3rd transistor T 3, and compensating unit is transistor seconds T2, cutting off unit is the 4th transistor T 4, also comprises driving power and earth terminal; The first sweep trace SCAN1 provides control signal VSCAN1 to come conducting or cut-off the first transistor T1 and transistor seconds T2, the second sweep trace SCAN2 provides control signal VSCAN2 to carry out conducting or ends the 3rd transistor T 3, control signal wire EM provides control signal VEM to carry out conducting or ends the 4th transistor T 4, data line DATA is by the first transistor T1 to data writing voltage signal Vdata in pixel, and driving power can output HIGH voltage VDD or low-voltage VSS.

Wherein, the grid of the first transistor T1 connects the first sweep trace SCAN1, source electrode connection data line DATA, drain electrode is connected with the first end of memory capacitance C, the source electrode of transistor seconds T2, the drain electrode of the 3rd transistor T 3 and the grid of driving transistors DTFT respectively, under the control of the control signal provided at the first sweep trace SCAN1, the first transistor T1 provides the data voltage signal Vdata of data line DATA and keeps this voltage by memory capacitance C to memory capacitance C; The grid of the 3rd transistor T 3 connects the second sweep trace SCAN2, and source electrode is connected with the first end of driving power and Organic Light Emitting Diode OLED respectively, and driving power is memory capacitance C charging by the 3rd transistor T 3; The grid connection control signal line of the 4th transistor T 4, source electrode is connected with the second end of OLED OLED, and drain electrode is connected with the source electrode of driving transistors DTFT and the drain electrode of transistor seconds T2 respectively; The grid of transistor seconds T2 connects the first sweep trace; The second end ground connection of the drain electrode of driving transistors DTFT and memory capacitance C; Under the control of the control signal provided at the first sweep trace, transistor seconds T2 conducting, the grid of driving transistors DTFT and source electrode conducting, forming a diode connects, guarantee that driving transistors DTFT is in region of saturation current, cause memory capacitance C electric discharge, until make to enter the grid of driving transistors DTFT and the voltage of source electrode is all the data voltage of data line, now, memory capacitance C voltage is

$V_c=\sqrt{\frac{{2V}_{\mathrm{data}}}{K}}+V_{\mathrm{th}},$

K is with technique and drives the relevant constant of design, V _datafor the voltage of data line input, can find out that the threshold voltage of driving transistors DTFT, by the pre-stored memory capacitance C of arriving, has reached the purpose of compensating threshold voltage.In the present embodiment, the other advantage of pixel-driving circuit is exactly that to adopt the transistor of single channel type complete be the N channel transistor, thereby preparation technology's complexity and production cost have been reduced, and adopt the upper luminous mode of Organic Light Emitting Diode OLED, comparing lower illumination mode has higher pixel aperture ratio, certainly, those skilled in the art are easy to draw that it is the pixel-driving circuit of P channel transistor entirely that pixel-driving circuit provided by the utility model can make into easily, with the syndeton difference of N channel-type thin-film transistor circuit, mainly be, when transistor is N channel-type thin film transistor (TFT), the anode that the first end of described Organic Light Emitting Diode is described Organic Light Emitting Diode, and the anode of described Organic Light Emitting Diode is connected with the high level output end of driving power, the negative electrode that the second end of described Organic Light Emitting Diode is described Organic Light Emitting Diode, the anode of Organic Light Emitting Diode OLED is connected with the high level output end of driving power, negative electrode is connected with the source electrode of the 4th transistor T 4, when transistor is equal P channel-type thin film transistor (TFT), the negative electrode that the first end of described Organic Light Emitting Diode is described Organic Light Emitting Diode, and the anode of described Organic Light Emitting Diode is connected with the low level output end of driving power, the anode that the second end of described Organic Light Emitting Diode is described Organic Light Emitting Diode, the negative electrode of light emitting diode OLED is connected with the low level output end of driving power, anode is connected with the source electrode of the 4th transistor T 4.Certainly, pixel-driving circuit provided by the utility model can change CMOS(Complementary Metal Oxide Semiconductor, complementary metal oxide semiconductor (CMOS) easily into) circuit etc.; The pixel-driving circuit provided in the present embodiment is provided, does not repeat them here.

The utility model also provides a kind of driving method that drives above-mentioned image element circuit, and it mainly comprises precharge sequential section S1, compensation sequential section S2 and drives display timing generator section S3; The driving method that is applied to pixel-driving circuit shown in Fig. 3 of below take describes as example, the all crystals pipe is N channel-type thin film transistor (TFT), it drives the sequential schematic diagram as shown in Figure 4, in this sequential chart, illustrated the variation of control signal VEM of data voltage Vdata, control signal wire EM of control signal VSCAN2, data line DATA of control signal VSCAN1, the second sweep trace SCAN2 of the first sweep trace SCAN1 in a frame work schedule.Below in conjunction with Fig. 5-Fig. 7, respectively above-mentioned each sequential section is specifically described:

Precharge sequential section S1:

This sequential section equivalent circuit diagram as shown in Figure 5; In this sequential section, apply control signal conducting the 3rd transistor T 3 of high level at the second sweep trace, apply low level control signal cut-off the first transistor T1, transistor seconds T2 and the 4th transistor T 4 at the first sweep trace and control signal wire; Driving power charges to memory capacitance C;

Compensation sequential section S2:

This sequential section equivalent circuit diagram as shown in Figure 6; In this sequential section, apply control signal conducting the first transistor T1 and the transistor seconds T2 of high level at the first sweep trace, apply low level control signal cut-off the 3rd transistor T 3 at the second sweep trace, make grid and the source shorted of driving transistors DTFT enter state of saturation, cause memory capacitance C electric discharge, until make to flow into grid and the source voltage of driving transistors DTFT, be all the data voltage of data line, now, memory capacitance C voltage is

$V_c=\sqrt{\frac{{2V}_{\mathrm{data}}}{K}}+V_{\mathrm{th}},$

K is the constant relevant with the driving design with technique, and threshold voltage and the data voltage on data line of driving transistors DTFT are written into memory capacitance C;

Drive display timing generator section S3:

This sequential section equivalent circuit diagram as shown in Figure 7; In this sequential section, apply the control signal conducting transistor seconds T2 of high level at control signal wire, apply low level control signal cut-off the first transistor T1 and transistor seconds T2 at the first sweep trace; Because the voltage VDD of driving power is greater than Vgs=VG-Vth, wherein, the grid potential of the gate source voltage that Vgs is driving transistors DTFT, VG driving transistors DTFT, driving transistors DTFT enters state of saturation, and the electric current that now flows through driving transistors DTFT and Organic Light Emitting Diode OLED is:

$I_{\mathrm{oled}}=\frac{1}{2}K{(V_{\mathrm{gs}}-V_{\mathrm{th}})}^2=\frac{1}{2}K{(V_c-V_{\mathrm{th}})}^2=\frac{1}{2}K{(\sqrt{\frac{{2V}_{\mathrm{data}}}{K}}+V_{\mathrm{th}}-V_{\mathrm{th}})}^2=V_{\mathrm{data}}$

Can see, it doesn't matter for the threshold voltage of drive current Ioled and driving transistors DTFT, the drift of driving transistors DTFT threshold voltage, can be to drain current, be the drive current Ioled of image element circuit, exert an influence, make Organic Light Emitting Diode OLED show stable, improve the homogeneity of display brightness, promoted greatly display quality.

Embodiment bis-

A kind of display device is provided in the present embodiment, has comprised above-mentioned image element circuit.Particularly, this display device comprises a plurality of pixel unit array, the arbitrary image element circuit in the corresponding above-described embodiment of each pixel cell.Because this image element circuit has compensated the threshold voltage shift of driving transistors, make Organic Light Emitting Diode OLED show stable, improved the homogeneity of display brightness, promoted greatly display quality.

Above embodiment is only for illustrating the utility model; and be not limitation of the utility model; the those of ordinary skill in relevant technologies field; in the situation that do not break away from spirit and scope of the present utility model; can also make a variety of changes and modification, therefore all technical schemes that are equal to also belong to protection category of the present utility model.

Claims (6)

1. A pixel driving circuit, characterized in that it comprises an electroluminescence element, a driving transistor, a switching unit, a charging unit, a compensation unit, a blocking unit and a storage unit; The switch unit is used to control the data voltage writing of the data line, the first end of the switch unit is connected to the data line, the second end of the switch unit is respectively connected to the first end of the charging unit, the compensation The first end of the unit, the first end of the storage unit and the gate of the drive transistor are connected; The charging unit is used to control the driving power to charge the storage unit, and the second end of the charging unit is respectively connected to the driving power and the first end of the electroluminescent element; The isolation unit is used to isolate the electrical connection between the electroluminescent element and the source of the drive transistor, the first end of the isolation unit is connected to the second end of the electroluminescent element, and the isolation unit The second terminal is connected to the source of the driving transistor; The compensation unit is used to store the threshold voltage of the driving transistor in advance in the storage unit, and the second end of the compensation unit is connected to the source of the driving transistor; The drain of the driving transistor and the second terminal of the storage unit are grounded. 2. The pixel driving circuit according to claim 1, wherein the electroluminescent element is an organic light emitting diode, the storage unit is a storage capacitor, the switching unit is a first transistor, and the charging unit is a third transistor, the compensation unit is a second transistor, and the isolation unit is a fourth transistor; The gate of the first transistor is connected to the first scan line, the source of the first transistor is connected to the data line, and the drain of the first transistor is respectively connected to the first end of the storage capacitor, the source of the second transistor, The drain of the third transistor is connected to the gate of the driving transistor; The gate of the third transistor is connected to the second scanning line, and the source of the third transistor is respectively connected to the driving power supply and the first terminal of the organic light emitting diode; The gate of the fourth transistor is connected to the control signal line, the source of the fourth transistor is connected to the second terminal of the organic light emitting diode, and the drain of the fourth transistor is respectively connected to the source of the driving transistor and the the drain connection of the second transistor; The gate of the second transistor is connected to the first scan line. 3. The pixel driving circuit according to claim 2, wherein all transistors have the same channel type. 4. The pixel drive circuit according to claim 3, wherein the transistors are all N-channel thin film transistors; the first end of the organic light emitting diode is the anode of the organic light emitting diode, and the organic light emitting diode The anode of the organic light emitting diode is connected to the high level output end of the driving power supply, and the second end of the organic light emitting diode is the cathode of the organic light emitting diode. 5. The pixel driving circuit according to claim 3, wherein the transistor is a P-channel thin film transistor; the first end of the organic light emitting diode is the cathode of the organic light emitting diode, and the organic light emitting diode The anode of the organic light emitting diode is connected to the low level output end of the driving power supply, and the second end of the organic light emitting diode is the anode of the organic light emitting diode. 6. A display device, comprising the pixel driving circuit according to any one of claims 1-5.

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