TWI467537B - Driving circuit for pixels of an active matrix organic lighting-emitting diode display - Google Patents

Description

Driving circuit of pixel of active organic light emitting diode display

The present invention relates to a driving circuit for a pixel of an active organic light emitting diode display, and more particularly to an active organic light emitting diode for changing the layout of pixels to increase current driving capability and thereby achieving power saving. The drive circuit of the pixels of the display.

Please refer to FIG. 1A. FIG. 1A is a schematic diagram of a conventional pixel unit 100 of an Active Matrix Organic Lighting-Emitting Diode (AMOLED). When the thin-film transistor (TFT) 102 in the pixel unit 100 receives the control signal VG outputted by the scan line 104 as the high potential VDDG, the thin film transistor 102 is turned on and the data line 106 turns on the pixel according to the data voltage VD. The storage capacitor CS in the cell 100 is charged and discharged to a corresponding gray scale voltage Vgray. At this time, the gate potential of the thin film transistor 102 is the potential VDDG of the control signal VG. Then, when the thin film transistor 102 is turned off according to the control signal VG, the thin film transistor 108 can generate a driving current I _OLED to drive an organic light emitting diode 110 according to the gray scale voltage Vgray. Further, as shown in FIG. 1A, Cgd is a parasitic capacitance of the thin film transistor 102. Referring to FIG. 1B, FIG. 1B is a schematic diagram showing the variation of the gray scale voltage Vgray of the storage capacitor CS due to the leakage of the parasitic capacitance Cgd of the thin film transistor 102 when the thin film transistor 102 is turned off according to the control signal VG. As shown in FIG. 1B, when the thin film transistor 102 is turned off according to the control signal VG outputted by the scan line 104 (the gate potential of the thin film transistor 102 is low potential VEEG), the gray scale voltage Vgray of the storage capacitor CS is due to The voltage variation ΔV is generated by the influence of the parasitic capacitance Cgd leakage of the thin film transistor 102, wherein the voltage variation ΔV is determined by the equation (1), and the driving current I _OLED is determined by the equation (2):

I _OLED =K(V _108GS -V _108TH ) ² =K((V _108G -V _108S )-V _108TH ) ² (2)

In the formula (1), Vgh is a high voltage received by the gate terminal of the thin film transistor 108 and Vgl is a low voltage received by the gate terminal of the thin film transistor 108. In the formula (2), V _108GS is the gate-source voltage of the thin film transistor 108, V _108G is the gate voltage of the thin film transistor 108 (equal to Vgray-ΔV), and V _108S is the source of the thin film transistor 108. The pole voltage and V _108TH are the threshold voltages of the thin film transistor 108. Therefore, it can be known from the equation (2) that the smaller the voltage variation amount ΔV is, the better the current driving capability of the thin film transistor 108 will be, thereby achieving power saving.

As can be seen from the equation (1), increasing the capacitance value of the storage capacitor CS or increasing the parasitic capacitance Cgd of the thin film transistor 102 can reduce the voltage variation amount ΔV. However, increasing the capacitance value of the storage capacitor CS means increasing the area of the storage capacitor CS, resulting in a decrease in the aperture ratio.

An embodiment of the invention provides a driving circuit for a pixel of an active organic light emitting diode display. The driving circuit includes a first switch, a storage capacitor and a second switch. The first open relationship is formed between a data line, a scan line, a first electrode and an organic light emitting diode. The first switch has a first end coupled to the data line and a second end. The storage capacitor is coupled to the data line, the scan line, the first electrode and the organic light emitting diode, and the first end of the storage capacitor is coupled Connected to the third end of the first switch; the second open relationship is formed between the data line, the scan line, the first electrode and the organic light emitting diode, and the second switch has a first end, The second electrode is coupled to the first end of the storage capacitor, and the third end is coupled to the organic light emitting diode; wherein the second end of the second switch is Extending to the rear of the first electrode and below the organic light emitting diode.

The invention provides a driving circuit for a pixel of an active organic light emitting diode display. The driving circuit uses a layout manner of changing a second end (ie, a gate electrode) of a second switch to increase a first capacitor and a second capacitor, thereby causing a gray scale voltage stored by a storage capacitor. A voltage change amount decreases when the first switch is turned on and off. Therefore, compared with the prior art (the voltage variation is large), the present invention can not only increase the brightness uniformity of a panel, but also increase the current driving capability of the driving circuit, thereby achieving the purpose of saving power.

Referring to FIG. 2A and FIG. 2B , FIG. 2A is a schematic diagram illustrating a driving circuit 200 for a pixel of an active organic light emitting diode display according to an embodiment of the present invention, and FIG. 2B is a diagram illustrating a driving circuit 200 . Schematic of the layout. As shown in FIG. 2A, the driving circuit 200 includes a first switch 202, a storage capacitor CS, a second switch 204, a first capacitor C0 and a second capacitor C1, wherein the first switch 202, the storage capacitor CS and the first The process of the second switch 204 is an amorphous germanium (A-Si) thin film transistor process. As shown in FIG. 2B, the first switch 202 is formed between a data line 206, a scan line 208, a first electrode 210, and an organic light-emitting diode 212. The first switch 202 has a first end. The second end is coupled to the scan line 208 and the third end. In addition, the first electrode 210 is configured to receive a first voltage V1 (high voltage).

As shown in FIG. 2B, the storage capacitor CS is also formed between the data line 206, the scan line 208, the first electrode 210, and the organic light emitting diode 212. The storage capacitor CS has a first end and is transmitted through a gate electrode. 214 (the second end of the second switch 204) is coupled to the third end of the first switch 202, and a second end is formed in front of the first end of the storage capacitor CS for coupling to a ground GND .

As shown in FIG. 2B, the second switch 204 is also formed between the data line 206, the scan line 208, the first electrode 210 and the organic light-emitting diode 212. The second switch 204 has a first end coupled to the second switch 204. The first electrode 210 is coupled to the first end of the storage capacitor 206 and the third end is coupled to the organic light emitting diode 212. In addition, the organic light emitting diode 212 is coupled to the ground GND.

It should be noted that, as shown in FIG. 2B , the second end (gate electrode 214 ) of the second switch 204 extends to the rear of the first electrode 210 and below the organic light emitting diode 212 .

As shown in FIG. 2A, when the first switch 202 is turned on according to the signal of the scan line 208, the storage capacitor CS can be charged and discharged according to the data voltage on the data line 206 to a corresponding gray scale voltage; when the first switch When the signal of the scan line 208 is turned off, the second switch 204 can generate a driving current I _OLED according to the corresponding gray scale voltage stored in the storage capacitor CS to drive the organic light emitting diode 212.

A corresponding gray scale voltage stored in the storage capacitor CS, a voltage change amount ΔV when the first switch 202 is turned on and off is a formula (3), and a driving current I _OLED of the second switch 204 is a formula (4) Decided:

In the formula (3), Vgh is a high voltage received by the second end of the second switch 204 when the first switch 202 is turned on, and Vgl is the second switch 204 when the first switch 202 is turned off. A low voltage received by the two terminals; in equation (4), V _204GS is the gate voltage of the second switch 204, V _204G is the gate voltage of the second switch 204, and V _204S is the second switch. The source voltage of 204 and V _204TH are the threshold voltage of the second switch 204, wherein V _204G is equal to the corresponding gray scale voltage Vgh stored by the storage capacitor CS when the first switch 202 is turned on minus the first switch. The amount of voltage change ΔV when 202 is turned on and off.

As shown in FIGS. 2A and 2B, since the second end (gate electrode 214) of the second switch 204 extends to the rear of the first electrode 210, the capacitance value of the first capacitor C0 (interlayer capacitance) increases; The second end (gate electrode 214) of the second switch 204 also extends to the lower side of the organic light emitting diode 212, so the capacitance value of the second capacitor C1 (lateral capacitance) also increases. In addition, as shown in FIGS. 2A and 2B, since the second end (gate electrode 214) of the second switch 204 extends to the rear of the first electrode 210 and below the organic light-emitting diode 212, The aperture ratio of the organic light-emitting diode 212 is not additionally sacrificed.

Therefore, as shown in the equations (3), (4), and 4, the first capacitor C0 and the second capacitor can be added by changing the layout of the second terminal (gate electrode 214) of the second switch 204. The capacitance value of the capacitor C1 causes the voltage variation amount ΔV to decrease and the drive current I _{OLED to} increase without sacrificing the aperture ratio of the organic light emitting diode 212.

Please refer to FIG. 3 and FIG. 2B . FIG. 3 is a schematic diagram of a driving circuit 300 for a pixel of an active organic light emitting diode display according to another embodiment of the present invention. The driving circuit 300 is different from the driving circuit 200 in that the first end of the second switch 204 is coupled to the organic light emitting diode 212, and the second end is coupled to the gate electrode 214 through the gate electrode 214. The first end of the storage capacitor 206 and the third end are coupled to the first electrode 210. At this time, the first electrode 210 is used to couple to the ground GND. In addition, the remaining operating principles of the driving circuit 300 are the same as those of the driving circuit 200, and are not described herein again.

In summary, the driving circuit of the pixel of the active organic light emitting diode display provided by the present invention utilizes a layout manner of changing the second end (gate electrode) of the second switch to make the first capacitor and the first When the capacitance is increased, the gray scale voltage stored in the storage capacitor is reduced, and the voltage change amount when the first switch is turned on and off is reduced. Therefore, compared with the prior art (the amount of voltage variation is large), the present invention can not only increase the brightness uniformity of the panel, but also increase the current driving capability of the driving circuit, thereby achieving the purpose of saving power.

The above are only the preferred embodiments of the present invention, and all changes and modifications made to the scope of the present invention should be within the scope of the present invention.

100. . . Traditional pixel unit

102, 108. . . Thin film transistor

104. . . Scanning line

106. . . Data line

110, 212. . . Organic light-emitting diode

200, 300. . . Drive circuit

202. . . First switch

204. . . Second switch

206. . . Data line

208. . . Scanning line

210. . . First electrode

214. . . Gate electrode

CS. . . Storage capacitor

C0. . . First capacitor

C1. . . Second capacitor

Cgd. . . Parasitic capacitance

GND. . . Ground end

I _OLED . . . Drive current

VG. . . Control signal

VDDG. . . High potential

VEEG. . . Low potential

Vgray. . . Gray scale voltage

V1. . . First voltage

ΔV. . . Voltage change

Figure 1A is a schematic diagram of a conventional pixel unit of an active organic light emitting diode display.

FIG. 1B is a schematic diagram showing the variation of the gray scale voltage of the storage capacitor due to the influence of the parasitic capacitance leakage of the thin film transistor when the thin film transistor is turned off according to the control signal.

2A is a schematic diagram illustrating a driving circuit of a pixel of an active organic light emitting diode display according to an embodiment of the present invention.

Fig. 2B is a schematic view showing the layout of the driving circuit.

3 is a schematic view showing a driving circuit of a pixel of an active organic light emitting diode display according to another embodiment of the present invention.

202. . . First switch

204. . . Second switch

206. . . Data line

208. . . Scanning line

210. . . First electrode

212. . . Organic light-emitting diode

214. . . Gate electrode

CS. . . Storage capacitor

C0. . . First capacitor

C1. . . Second capacitor

Claims (6)

A driving circuit for a pixel of an active organic light emitting diode display, comprising: a first switch formed between a data line, a scan line, a first electrode and an organic light emitting diode, the first switch The first end is coupled to the data line, the second end is coupled to the scan line, and a third end; a storage capacitor is formed on the data line, the scan line, the first electrode and The first end of the storage capacitor is coupled to the third end of the first switch; and a second switch is formed on the data line, the scan line, the first electrode, and the Between the organic light-emitting diodes, the second switch has a first end coupled to the first electrode, a second end coupled to the first end of the storage capacitor, and a third end coupled The second end of the second switch extends to the rear of the first electrode and below the organic light emitting diode to increase the second end of the second switch and the first electrode Parasitic capacitance between the second end of the second switch and the organic light emitting diode Parasitic capacitance between, thus reducing the turn-on voltage of the first switch is closed and when the amount of change, to increase the driving current for driving the OLED. The driving circuit of claim 1, wherein the process of the first switch, the storage capacitor and the second switch is an amorphous germanium (A-Si) thin film transistor process. The driving circuit of claim 1, wherein the storage is when the first switch is turned on The storage capacitor is charged and discharged according to the data voltage on the data line to a corresponding gray scale voltage; when the first switch is turned off, the second open relationship is used according to the corresponding gray scale voltage stored by the storage capacitor. The drive current is generated to drive the organic light emitting diode. The driving circuit of claim 3, wherein the corresponding gray scale voltage, the voltage change amount ΔV when the first switch is turned on and off is determined by: Wherein: Vgh is a high voltage received by the second end of the second switch when the first switch is turned on; Vgl is received by the second end of the second switch when the first switch is turned off a low voltage; CS is the storage capacitor; Cgd is the parasitic capacitance of the first switch; and C0 and C1 are the parasitic capacitance between the second end of the second switch and the first electrode, respectively, and the second a parasitic capacitance between the second end of the switch and the organic light emitting diode. The driving circuit of claim 1, wherein the first electrode is configured to receive a first voltage. The driving circuit of claim 1, wherein the first electrode is used to couple to a ground end.