CN104183220A - Pixel circuit - Google Patents

Abstract

The invention discloses a pixel circuit. The pixel circuit comprises a driving unit, a switch unit, an energy storage unit connected between the control end of the driving unit and the output end of the driving unit, and an organic light emitting diode connected with the output end of the driving unit, wherein the switch unit comprises a second switch element, a third switch element, a fourth switch element and a fifth switch element, the control end and output end of the second switch element are both connected with the control end of the driving unit, the output end of the third switch element is connected with the input end of the second switch element, the control end and input end of the third switch element are connected with a second row of scanning signals and data voltage respectively, the control end and input end of the fourth switch element are connected with a first row of scanning signals and reference voltage respectively, the output end of the fourth switch element is connected with the control end of the second switch element, the input end and output end of the fifth switch element are connected with the control end and output end of the driving unit respectively, and the control end of the fifth switch element is connected with the first row of scanning signals. The pixel circuit has the advantages of being simple in structure and easy to obtain.

Description

A kind of image element circuit

Technical field

The present invention relates to display driver technology, especially relate to a kind of image element circuit.

Background technology

Chinese patent application CN201110376530.2 proposes a kind of image element circuit.Wherein, Fig. 1～Fig. 3 of the application is Fig. 1～Fig. 3 of CN201110376530.2, for describing circuit structure and the principle of work of existing image element circuit.

Shown in Fig. 1, described image element circuit comprises driver element 10, switch element 20, energy-storage units 30 and Organic Light Emitting Diode OLED 40.Shown in Fig. 2, in an embodiment of existing image element circuit, driver element 10 is polysilicon transistors T1, switch element 20 comprises amorphous silicon transistor T2, energy-storage units 30 is for being connected to the capacitor C s between grid and the source electrode of polysilicon transistors T1, wherein, the drain electrode that the source electrode of polysilicon transistors T1 is connected with supply voltage VDD, drain electrode is connected with OLED OLED, grid is connected amorphous silicon transistor T2.In this embodiment, polysilicon transistors T1, as driving transistors, its role is to provide the current signal that drives Organic Light Emitting Diode OLED work; Amorphous silicon transistor T2 is as switching transistor, and line scan signals is applied to the grid of amorphous silicon transistor T2, to control the circulation of the data voltage (DATA) on the source electrode that is applied to amorphous silicon transistor T2; By capacitor C, s stores data voltage with voltage form, and capacitor C s controls and keeps the stable of data voltage, and then keeps screen body brightness preservation in a frame time constant.

In a scanning frame, in the process that line scan signals is high level, polysilicon transistors T1 remains on state of saturation, so flow through the electric current I of Organic Light Emitting Diode OLED _oLEDas formula (1)

$I_{\mathrm{OLED}}=\frac{1}{2}{\mathrm{\μ}}_X{C}_{\mathrm{ox}}\frac{W}{L}(U_{\mathrm{SG}}-U_{\mathrm{TH}})---\left(1\right)$

Wherein, μ _xfor the carrier mobility of polysilicon transistors T1, C _oxfor the gate oxide unit-area capacitance of polysilicon transistors T1, for the width (W) of TFT display screen and the ratio of length (L), U _sGfor the voltage difference between source electrode and the grid of driving polysilicon transistors T1, U _tHfor driving the threshold voltage of polysilicon transistors T1.

As can be seen here, flow through the electric current of Organic Light Emitting Diode OLED and threshold voltage U as the polysilicon transistors T1 of driver element _tHthere is relation closely, if the threshold voltage U of each pixel _tHdifferent, the electric current that flows through Organic Light Emitting Diode OLED will change, and threshold voltage, carrier mobility and the resistance in series of each polysilicon transistors T1 inconsistent in each image element circuit in TFT display screen, thereby cause the demonstration of whole TFT display screen inhomogeneous, the output characteristics that is TFT display screen has very large dispersiveness, has luminous (demonstration) inhomogeneous defect.

Summary of the invention

For overcoming the inhomogeneous technological deficiency of demonstration of existing TFT display screen, the present invention proposes the simple image element circuit of a kind of circuit structure, uses this image element circuit can make the demonstration of TFT display screen have consistance.

The present invention adopts following technical scheme to realize: a kind of image element circuit, comprise driver element, switch element, be connected to the energy-storage units between control end and the output terminal of driver element and be connected the Organic Light Emitting Diode OLED of driver element output terminal, switch element specifically comprises that second switch elements T 2 is to the 5th on-off element T5;

The control end of second switch elements T 2 is all connected with the control end of driver element with output terminal;

The output terminal of the 3rd on-off element T3 is connected with the input end of second switch elements T 2, and the control end of the 3rd on-off element T3 and input end connect respectively the second line scan signals and data voltage;

The control end of the 4th on-off element T4 and input end connect respectively the first row sweep signal and reference voltage, and the output terminal of the 4th on-off element T4 is connected with the control end of second switch elements T 2;

The input end of the 5th on-off element T5 is connected with output terminal with the control end of driver element respectively with output terminal, the control termination the first row sweep signal of the 5th on-off element T5.

Wherein, second switch elements T 2 is amorphous silicon transistor, and control end, input end and the output terminal of second switch elements T 2 is respectively grid, source electrode and the drain electrode of amorphous silicon transistor.

Wherein, the 3rd on-off element T3, the 4th on-off element T4 and the 5th on-off element T5 are polysilicon transistors, and control end, input end and the output terminal of the 3rd on-off element T3, the 4th on-off element T4 and the 5th on-off element T5 are grid, source electrode and the drain electrode of polysilicon transistors.

Wherein, driver element is polysilicon transistors T1, between its grid and source electrode, be connected the capacitor C s as energy-storage units, and the grid of polysilicon transistors T1 connects supply voltage, draining is connected with the anode of OLED OLED, and the plus earth of Organic Light Emitting Diode OLED.

Compared with prior art, the present invention has following beneficial effect:

The present invention, by improving the circuit structure of switch element in image element circuit, makes to flow through the electric current I of Organic Light Emitting Diode OLED _oLEDthreshold voltage U with the polysilicon transistors T1 as driver element _tHirrelevant, thus the threshold voltage U of each polysilicon transistors T1 in each image element circuit can be evaded in prior art _tH, carrier mobility and resistance in series inconsistent and cause the inhomogeneous defect of demonstration of whole TFT display screen.The present invention have circuit structure simple, realize and be easy to advantage, use this image element circuit can make the demonstration of TFT display screen there is consistance, there is implementation prospect widely.

Brief description of the drawings

Fig. 1 is the circuit module schematic diagram of existing image element circuit;

Fig. 2 is the circuit diagram of an embodiment of existing image element circuit;

Fig. 3 is the circuit diagram of driving circuit in one embodiment of the invention;

Fig. 4 is the circuit timing diagram of Fig. 3.

Embodiment

The image element circuit that the present invention proposes, is also prior art as shown in Figure 1, and this image element circuit comprises driver element, switch element, energy-storage units and Organic Light Emitting Diode OLED.

Specifically, as shown in Figure 3, polysilicon transistors T1 is driver element, and capacitor C s is energy-storage units, forms switch element by amorphous silicon transistor T2, polysilicon transistors T3, polysilicon transistors T4 and polysilicon transistors T5.Therefore,, compared with the prior art shown in Fig. 2, the present invention has changed the circuit structure of switch element.

Wherein, as the polysilicon transistors T1 of driver element, between its grid and source electrode, be connected the capacitor C s as energy-storage units, and the grid of polysilicon transistors T1 connects supply voltage VDD, draining is connected with the anode of OLED OLED, and the plus earth of Organic Light Emitting Diode OLED.

Wherein, switch element specifically comprises: the amorphous silicon transistor T2 that grid is connected with drain electrode, and the drain electrode of this amorphous silicon transistor T2 connects the grid of polysilicon transistors T1; Drain electrode connects the polysilicon transistors T3 of amorphous silicon transistor T2 source electrode, and the grid of this polysilicon transistors T3 connects the second line scan signals S2, source electrode meets data voltage DATA; Drain electrode connects the polysilicon transistors T4 of amorphous silicon transistor T2 grid, and the grid of this polysilicon transistors T4 connects the first row sweep signal S1, source electrode connects reference voltage U _rEF; Grid connects the polysilicon transistors T5 of the first row sweep signal S1, and the source electrode of this polysilicon transistors T5 is connected with grid and the drain electrode of polysilicon transistors T1 respectively with drain electrode.

In conjunction with the sequential circuit shown in Fig. 4, the principle of work of the image element circuit that the present invention proposes is as follows:

1, in the t1 time period, in the time arriving in a frame scan interval, the first row sweep signal S1 becomes low level, the second line scan signals S2 keeps high level, polysilicon transistors T4 and polysilicon transistors T5 become conducting, amorphous silicon transistor T2 remains unchanged, polysilicon transistors T3 remain off state, the grid of polysilicon transistors T1 and drain voltage conducting, and equal reference voltage U _rEF, now the anode of Organic Light Emitting Diode OLED also equals reference voltage U _rEF.When so this image element circuit arrives at a frame scan interval, initialization the grid voltage of polysilicon transistors T1, also initialization the anode of OLED, increased serviceable life of OLED.

2, in the t2 time period, the first row sweep signal S1 becomes high level, the second line scan signals S2 becomes low level, transistor T 4 and transistor T 5 end, transistor T 3 conductings, data voltage DATA is transferred to the source electrode of transistor T 2 by transistor T 3, be initialized to reference voltage U before the grid due to transistor T 1 _rEF(being low-voltage), so in the time that data voltage DATA arrives, the grid of transistor T 1 starts charging, slowly raises, and finally brings up to DATA-U _tH(U _tHfor driving the threshold voltage of polysilicon transistors T1) time stop charging.

(3, in the t3 time period, the first row sweep signal S1 and the second line scan signals S2 become high level, transistor T 3, transistor T 4 and transistor T 5 all end, the grid voltage of transistor T 1 is remained on (DATA-∣ U by capacitor C s _tH∣), the source voltage of transistor T 1 equals supply voltage VDD.Now, according to the formula of mentioning in background technology (1), flow through the electric current I of Organic Light Emitting Diode OLED _oLEDshown in following formula (2):

$I_{\mathrm{OLED}}=\frac{1}{2}{\mathrm{\μ}}_X{C}_{\mathrm{ox}}\frac{W}{L}{(\mathrm{VDD}-\mathrm{DATA})}^2---\left(2\right)$

Wherein, μ _xfor the carrier mobility of polysilicon transistors T1, C _oxfor the gate oxide unit-area capacitance of polysilicon transistors T1, for the width (W) of TFT display screen and the ratio of length (L).

As can be seen here, flow through the electric current I of Organic Light Emitting Diode OLED _oLEDthreshold voltage U with the polysilicon transistors T1 as driver element _tHirrelevant, thus the threshold voltage U of each polysilicon transistors T1 in each image element circuit can be evaded in prior art _tH, carrier mobility and resistance in series inconsistent and cause the inhomogeneous defect of demonstration of whole TFT display screen.

The foregoing is only preferred embodiment of the present invention, not in order to limit the present invention, all any amendments of doing within the spirit and principles in the present invention, be equal to and replace and improvement etc., within all should being included in protection scope of the present invention.

Claims (4)

1. an image element circuit, comprise driver element, switch element, be connected to the energy-storage units between control end and the output terminal of driver element and be connected the Organic Light Emitting Diode OLED of driver element output terminal, it is characterized in that: switch element specifically comprises that second switch elements T 2 is to the 5th on-off element T5;

The control end of second switch elements T 2 is all connected with the control end of driver element with output terminal;

The output terminal of the 3rd on-off element T3 is connected with the input end of second switch elements T 2, and the control end of the 3rd on-off element T3 and input end connect respectively the second line scan signals and data voltage;

The control end of the 4th on-off element T4 and input end connect respectively the first row sweep signal and reference voltage, and the output terminal of the 4th on-off element T4 is connected with the control end of second switch elements T 2;

The input end of the 5th on-off element T5 is connected with output terminal with the control end of driver element respectively with output terminal, the control termination the first row sweep signal of the 5th on-off element T5.

2. a kind of image element circuit according to claim 1, is characterized in that: second switch elements T 2 is amorphous silicon transistor, and control end, input end and the output terminal of second switch elements T 2 is respectively grid, source electrode and the drain electrode of amorphous silicon transistor.

3. a kind of image element circuit according to claim 1, it is characterized in that: the 3rd on-off element T3, the 4th on-off element T4 and the 5th on-off element T5 are polysilicon transistors, control end, input end and the output terminal of the 3rd on-off element T3, the 4th on-off element T4 and the 5th on-off element T5 are grid, source electrode and the drain electrode of polysilicon transistors.

4. according to a kind of image element circuit described in claim 1 or 2 or 3, it is characterized in that: driver element is polysilicon transistors T1, between its grid and source electrode, be connected the capacitor C s as energy-storage units, and the grid of polysilicon transistors T1 connects supply voltage, draining is connected with the anode of OLED OLED, and the plus earth of Organic Light Emitting Diode OLED.