TWI796723B - Display device - Google Patents

Abstract

A display device, comprising a plurality of pixel circuits arranged in array. Each of the pixel circuit comprises a light emitting diode, a driving circuit and a reset switch. The driving circuit is coupled to the light emitting diode, for driving the light emitting diode to emit. A first end of the reset switch is coupled to a node between the light emitting diode and the driving circuit. When the light emitting diode is being driven to emit, a voltage difference between a second end and a first end of the reset switch is within a predetermined voltage range.

Description

display device

The present invention relates to a device, and in particular to a display device.

In the existing light-emitting diode display devices, the flickering problem will greatly affect the user's viewing experience. Therefore, the flickering problem is one of the main problems to be solved in this field.

The invention provides a display device for improving the problem of screen flickering.

A display device of the present invention includes a plurality of pixel circuits arranged in an array. Each pixel circuit includes a light emitting diode, a driving circuit and a reset switch. The driving circuit is coupled to the light-emitting diode, and the driving circuit is used to drive the light-emitting diode to emit light. The first end of the reset switch is coupled to a node between the light emitting diode and the driving circuit. When the light emitting diode is driven by the driving circuit to emit light, the voltage difference between the second terminal and the first terminal of the reset switch is within a preset voltage range.

Based on the above, the reset switch in the display device of the present invention can be in the light-emitting diode When the body is driven, the voltage difference is kept within the preset voltage range, so the problem of screen flickering is effectively improved.

1: Display device

10, 30: Pixel circuit

11, 31: drive circuit

12, 32: reset switch

13, 33: light emitting diode

B1, B2: Bias point

C1: capacitance

EM, EMn, EMn+1, EMn+2: laser signal

L1, L2: curve

M1~M8: Transistor

N1: node

SA, SAn, SAn+1, SAn+2: Precharge signal

SB, SBn, SBn+1, SBn+2: scan signal

SFn, SFn+1, SFn+2, SFn+3, SFn+4: time interval

SR: reset control signal

Vd: data signal

VR: reset voltage

VDD, Vref1, Vref2, VSS: reference voltage

FIG. 1 is a schematic diagram of a display device according to an embodiment of the present invention.

FIG. 2 is a schematic block diagram of the pixel circuit in FIG. 1 .

FIG. 3 is a schematic diagram of a pixel circuit according to an embodiment of the invention.

FIG. 4 is a graph showing the relationship between the voltage difference and the current between the control terminal and the first terminal of the reset switch according to an embodiment of the present invention.

FIG. 5 is an operation waveform diagram of a display device according to an embodiment of the present invention.

FIG. 1 is a schematic diagram of a display device 1 according to an embodiment of the present invention. The display device 1 includes a plurality of pixel circuits 10 arranged in an array. Generally speaking, the pixel circuit 10 in the display device 1 can be controlled by the laser signal to display according to the data signal. More specifically, the pixel circuit 10 in the display device 1 can improve the problem of screen flicker when displaying a screen, thereby improving display quality and user experience.

FIG. 2 is a schematic block diagram of the pixel circuit 10 in FIG. 1 . The pixel circuit 10 includes a driving circuit 11 , a reset switch 12 and a light emitting diode (LED) 13 . The driving circuit 11 can be connected in series with the light-emitting diode 13 to provide driving Flow current to the light-emitting diode 13 to drive the light-emitting diode 13 to emit light. An anode of the light-emitting diode 13 is coupled to the driving circuit 11 , and a cathode of the light-emitting diode 13 receives a reference voltage VSS (for example, -3.3 volts). A first terminal of the reset switch 12 is coupled to a node N1 between the driving circuit 11 and the LED 13 , and a second terminal of the reset switch 12 receives the reset voltage VR.

In detail, the reset switch 12 can be controlled to turn on the first end and the second end of the reset switch 12 in the reset time interval before the LED 13 is driven by the driving circuit 11 to emit light. to provide the reset voltage VR to the node N1 between the LED 13 and the driving circuit 11 . Therefore, the reset switch 12 can increase the driving current provided by the driving circuit 11 to the light-emitting diode 13. By resetting the light-emitting diode 13 with a high current, the pixel circuit 10 as a whole is in low gray scale or black gray scale. The drive current is too low when driving, and the problem of writing time is too long to effectively improve.

Generally speaking, when the driving circuit 11 drives the light emitting diode 13 to display low gray scale or black gray scale brightness, the current provided by the driving circuit 11 to the light emitting diode 13 is relatively small. Therefore, when the pixel circuit 10 displays low grayscale or black grayscale brightness, it is more obviously affected by the leakage current of the reset switch 12 . And by keeping the voltage difference between the second terminal and the first terminal of the reset switch 12 within the preset voltage range, the leakage current of the reset switch 12 can be controlled within the preset current range, so the pixel circuit 10 is The flicker problem when displaying low or black grayscales can also be effectively improved.

In some embodiments, the preset voltage range can be, for example, the voltage difference between the second terminal of the reset switch 12 and the first terminal is less than 10 volts, and the preset current range can be, for example, the second terminal of the reset switch 12 and the first terminal. The leakage current between the first terminals is less than 5 x 10 ^-8 amperes. In some embodiments, the preset voltage range can be, for example, the voltage difference between the second terminal of the reset switch 12 and the first terminal is less than 0 volts, and the preset current range can be, for example, the voltage difference between the second terminal of the reset switch 12 and the first terminal. The leakage current between the first terminals is less than or equal to 2 x 10 ^-14 amperes. In some embodiments, the preset voltage range can be, for example, that the voltage difference between the second terminal of the reset switch 12 and the first terminal is less than -1.7 volts, and the preset current range can be, for example, the second terminal of the reset switch 12 The leakage current between the first terminal and the first terminal is less than 10 ^-14 ampere. In some embodiments, the preset voltage range can be, for example, that the voltage difference between the second terminal of the reset switch 12 and the first terminal is less than 5 volts, and the preset current range can be, for example, the second terminal of the reset switch 12 and the first terminal. Leakage current between one end is less than 10 ^-12 amperes.

FIG. 3 is a schematic diagram of a pixel circuit 30 according to an embodiment of the invention. In some embodiments, the pixel circuit 30 can be applied in the display device 1 of FIG. 1 for displaying. The pixel circuit 30 includes a driving circuit 31 , a reset switch 32 and a light emitting diode 33 . The driving circuit 31 is connected in series with the LED 33 , and the reset switch 32 is coupled to a node N1 between the driving circuit 31 and the LED 33 .

In detail, the driving circuit 31 may include transistors M1 - M7 . In the illustrative example of Fig. 3, the transistors M1~M7 are P-type Metal-Oxide-Semiconductor Field-Effect Transistors (PMOSFET), but of course, any of the transistors M1~M7 It can also be implemented in an alternative manner of an N-type Metal-Oxide-Semiconductor Field-Effect Transistor (NMOSFET). The first terminal of the transistor M1 receives the reference voltage VDD, and the control terminal of the transistor M1 can receive the control of the data signal Vd. Transistor The first terminal of M2 is coupled to the second terminal of the transistor M1, the second terminal of the transistor M2 is coupled to the first terminal of the LED 33, and the control terminal of the transistor M2 receives the laser signal EM. Therefore, the transistors M1 , M2 and the light emitting diode 33 can form a series connection and be connected between the reference voltages VDD and VSS. The transistor M1 can generate a driving current according to the data signal Vd, and the transistor M2 can determine whether to provide the driving current to the light-emitting diode 33 to emit light according to the control of the laser signal EM.

Further, in the driving circuit 31 , the first terminal of the transistor M3 receives the reference voltage Vref1 , and the control terminal of the transistor receives the laser signal EM. The first terminal of the transistor M4 is coupled to the second terminal of the transistor M3, and the second terminal of the transistor M4 receives the data signal Vd. The first terminal of the capacitor C1 is coupled to the second terminal of the transistor M3 and the first terminal of the transistor M4, and the second terminal of the capacitor is coupled to the control terminal of the transistor M1. The first terminal of the transistor M5 is coupled to the two terminals of the capacitor and the control terminal of the transistor M1. The first terminal of the transistor M6 is coupled to the second terminal of the transistor M5, and the second terminal of the transistor M6 is coupled to the second terminal of the transistor M1 and the first terminal of the transistor M2. The first terminal of the transistor M7 is coupled to the second terminal of the transistor M5 and the first terminal of the transistor M6, and the second terminal of the transistor M7 receives the reference voltage Vref2. Moreover, the control terminal of the transistor M7 receives the pre-charge signal SA, and the control terminals of the transistor M4 , the transistor M5 and the transistor M6 receive the scanning signal SB.

In this way, the driving circuit 31 can provide the reference voltage Vref2 to the node between the transistors M5 and M6 according to the control of the precharge signal SA. The driving circuit 31 provides the reference voltage Vref2 to the control terminal and the second terminal of the transistor M1 according to the control of the scanning signal SB to compensate the threshold voltage of the transistor M1. therefore, The transistor M1 can generate a driving current at the control terminal according to the control of the data signal Vd, and the transistor M2 can determine whether to provide the driving current to the light emitting diode 33 according to the control of the laser signal EM at the control terminal.

The reset switch 32 can be, for example, a metal-oxide-semiconductor field-effect transistor. In FIG. Alternative implementations of N-type metal oxide half field effect transistors. The first end (for example, the source) of the transistor M8 is coupled to the second end of the transistor M2 and the anode of the light-emitting diode 33, and the second end (for example, the drain) of the transistor M8 receives the reset voltage VR, A control terminal (for example, a gate) of the transistor M8 receives the reset control signal SR. Specifically, the reset switch 32 can be turned on between the first terminal and the second terminal of the reset switch according to the reset control signal SR in the reset time interval before the LED 31 is driven to emit light by the driving circuit 31 connection to supply the reset voltage VR to the node N1 between the LED 33 and the driving circuit 31 . Moreover, when the light-emitting diode 33 is driven by the driving circuit 31 to emit light, the voltage difference between the second end and the first end of the reset switch 32 can be within a preset voltage range, thereby controlling the flow through the reset switch 32. The leakage current of the first terminal and the second terminal can be smaller than a preset current range. Accordingly, the pixel circuit 30 can effectively improve the picture flickering.

FIG. 4 is a diagram showing the relationship between the voltage difference and the current between the control terminal and the first terminal of the reset switch 32 according to an embodiment of the present invention. In FIG. 4 , an implementation manner in which the reset switch 32 is a P-type metal oxide semi-transistor is used for illustration. In detail, the vertical axis of FIG. 4 is the current flowing through both ends of the reset switch 32, the horizontal axis is the voltage difference between the control terminal and the first terminal of the reset switch 32, and the curves L1, L2 in FIG. then reset switch 32 The relationship between current and voltage generated when the second terminal and the first terminal have different voltage differences. For example, the curves L1 and L2 can respectively represent the voltage difference between the second terminal of the reset switch 32 and the first terminal of 8.8 volts and 0.1 volts, as the control terminal of the reset switch 32 and the first terminal The current change of the reset switch 32 is caused by the change of the voltage difference between the terminals.

In some embodiments, when the light emitting diode 33 is driven to emit light by the driving circuit 31, the reset switch 32 has completed the reset operation, so the control terminal of the reset switch 32 can be provided with a high logic level voltage (for example, 5 volts) and cutoff (Cutoff). At the same time, the second terminal of the reset switch 32 may be provided with a low logic level voltage (for example, -5 volts). In this way, the reset switch 32 can operate close to the bias point B1 on the curve L2, and the leakage current flowing through the first terminal and the second terminal of the reset switch can be, for example, 10 ⁻¹⁴ amperes.

In some embodiments, the reset switch may, for example, utilize a diode connected transistor to provide a reset voltage to the anode of the LED. More precisely, the first terminal of the transistor used as a reset switch can be coupled to the anode of the light-emitting diode, and the control terminal and the second terminal of the transistor can be coupled to each other to provide a reset control signal to the electric circuit. Crystal control terminal. In this way, when the reset switch completes the reset operation and the high logic level voltage (for example, 5 volts) is provided to the control terminal of the transistor for disabling, since the control terminal and the second terminal of the transistor are coupled to each other , so a high logic level voltage (for example, 5 volts) will be provided to the second terminal of the transistor at the same time, causing the voltage difference between the second terminal and the first terminal of the transistor to be, for example, 8.8 volts to operate on the curve on L1. Moreover, the voltage difference between the control terminal and the first terminal of the transistor can also be, for example, 8.8 volts, so the reset switch can operate close to the bias point B2. Thus, a reset switch implemented as a diode-coupled transistor has a leakage current of, for example, 10 ⁻⁸ A when disabled.

Therefore, by providing a low logic level voltage to the second terminal of the reset switch 32 when the reset switch 32 is disabled, when the reset switch 32 is disabled, there is a gap between the second terminal and the first terminal of the reset switch 32 The voltage difference can be controlled within a preset voltage range (for example, less than 10 volts), thereby controlling the leakage current between the first terminal and the second terminal of the reset switch 32 within a preset current range (for example, less than 5× ^10-8 amps). Therefore, the pixel circuit 30 can effectively improve the picture flickering.

In some embodiments, the low logic level voltage can be, for example, a low voltage value or a negative voltage value, so that the voltage difference between the second terminal and the first terminal of the reset switch 32 can be controlled to be less than or close to a preset value of 8.8 volts. Voltage range, and then the leakage current between the first terminal and the second terminal of the reset switch 32 is controlled within a preset current range of less than 10 ⁻⁸ amperes. In some embodiments, the predetermined voltage range may be, for example, less than 5 volts, and the predetermined current range may be, for example, a leakage current of less than 10 ⁻¹² amperes. The preset voltage range can also be, for example, less than 0 volts, and the preset current range can be, for example, a leakage current of less than 2×10 ⁻¹⁴ amperes. Alternatively, the preset voltage range may be, for example, less than −1.7 volts, and the preset current range may be, for example, a leakage current of less than 10 ⁻¹⁴ amperes.

Although in FIG. 4 the characteristics of the reset switch 32 implemented by the reset switch 32 using a P-type metal oxide semi-transistor are described, it should be understood that the reset switch 32 implemented by an N-type metal oxide semi-transistor The setting switch 32 will also have a similar distribution characteristic. Therefore, when the reset switch 32 is implemented by an N-type metal-oxide-semiconductor transistor, the pixel circuit 30 is also The leakage current of the reset switch 32 can be reduced by reducing the voltage difference between the second terminal and the first terminal when the reset switch 32 is disabled, thereby improving the flickering problem of the display device.

FIG. 5 is an operation waveform diagram of a display device 1 according to an embodiment of the present invention. In detail, the operation waveform diagram shown in FIG. 5 can be provided to the display device 1 shown in FIG. 1 , and the display device 1 shown in FIG. 1 can be provided with the pixel circuit shown in FIG. 3 , for example. 30. Therefore, please refer to FIGS. 1 , 3 , and 5 together to understand the description of the operation of the display device 1 in the following paragraphs.

Roughly speaking, the display device 1 in FIG. 1 can have a plurality of pixel circuits 10 arranged in an array, and the display device 1 can be driven in a single column or multiple columns as a level to sequentially control the pixel circuits of each level. 10 Scan the data signal and display it.

In one embodiment, the pixel circuit 10 in the display device 1 can be replaced by the pixel circuit 30 shown in FIG. 3 , and the display device 1 can be driven by a single column as a level. Therefore, for the pixel circuit 30 of the nth level in the display device 1 , the pixel circuit 30 can receive the control of the pre-charging signal SAn, the scanning signal SBn and the laser signal EMn. For the n+1th level pixel circuit 30 in the display device 1 , the pixel circuit 30 can be controlled by the pre-charging signal SAn+1, the scanning signal SBn+1 and the laser signal EMn+1, and so on. In addition, in this embodiment, the pixel circuit 30 of the nth stage can also receive the precharge signal SAn+1 of the n+1st stage as the reset control signal SR of the nth stage, and the nth stage of the picture The pixel circuit 30 can also receive the n+2th level laser signal EMn+2 as the nth level reset voltage VR.

Specifically, in the time interval SFn, when the precharge signal SAn changes from high to When the logic level voltage is switched to a low logic level voltage, the reference voltage Vref2 is provided between the second terminal of the transistor M5 and the first terminal of the transistor M6 through the transistor M7.

Next, when the scan signal SBn is switched from a high logic level voltage to a low logic level voltage, and the precharge signal SAn is still kept at a low logic level voltage, the data signal Vd is provided to the first capacitor C1 through the transistor M4. The reference voltage Vref2 can be provided to the second terminal of the capacitor C1 through the transistor M5, and the reference voltage Vref2 can be provided to the second terminal of the transistor M1 through the transistor M6.

Next, when the precharge signal SAn is switched from a low logic level voltage to a high logic level voltage, and the scanning signal SBn is still kept at a low logic level voltage, the control terminal and the second terminal of the transistor M1 can form a diode coupling. connected, and the transistor M1 can be turned on by the voltage of the control terminal, so that the reference voltage VDD can charge the control terminal of the transistor M1 through the transistor M1 until the voltage difference between the control terminal and the first terminal of the transistor M1 is equal to transistor threshold voltage. Accordingly, the pixel circuit 30 can compensate for the threshold voltage of the transistor M1 stored between the control terminal and the first terminal of the transistor, so as to eliminate the chromatic aberration caused by the characteristic deviation of the transistor M1.

Next, in the time interval SFn+1, when the scan signal SBn switches from a low logic level voltage to a high logic level voltage, and the precharge signal SAn+1 switches from a high logic level voltage to a low logic level voltage, the drawing The pixel circuit 30 is operable in the reset time interval P1. Since the precharge signal SAn+1 is used as the reset control signal SR of the nth level pixel circuit, and the laser signal EMn+2 is used as the reset voltage VR of the nth level, so in the reset time interval , the transistor M8 of the pixel circuit 30 can be turned on by the reset control signal SR, so that the laser signal of the low logic level voltage EMn+2 is supplied to node N1 , thereby resetting the anode of LED 33 .

Finally, when the laser signal EMn switches from a high logic level voltage to a low logic level voltage, the transistor M2 of the pixel circuit 30 can be enabled, and the driving current generated by the transistor M1 according to the data signal Vd can be provided to The light emitting diode 33 is used for driving.

In detail, when the laser signal EM is enabled, in the time interval P2, the laser signal EMn+2 with a high logic level voltage (for example, 5 volts) is provided as the reset voltage VR to the first pin of the reset switch 32 . Two ends. In addition, in the time interval P3 , the laser signal EMn+2 with a low logic level voltage (for example, −5 volts) is provided to the second terminal of the reset switch 32 as the reset voltage VR. Therefore, during most of the time when the laser signal EM is enabled, the voltage difference between the second terminal and the first terminal of the reset switch 32 can be relatively small and maintained within a predetermined voltage range.

More precisely, when displaying high gray scale brightness, the second end of the reset switch 32 can receive the low logic level voltage (for example -5 volts) of the laser signal EMn+2, and the second end of the reset switch 32 One end can receive the reference voltage VSS (for example, -3.3 volts) due to the conduction of the light emitting diode 33, so the voltage difference between the second end and the first end of the reset switch 32 can be maintained at, for example, -1.7 Volt. When displaying low grayscale brightness, the second end of the reset switch 32 can receive the low logic level voltage (for example -5 volts) of the laser signal EMn+2, and the first end of the reset switch 32 can emit light The diode 33 is not conducting and receives, for example, the laser signal EMn+2 (for example, -5 volts) provided during the reset time interval P1, so the reset switch 32 between the second end and the first end The voltage difference can be maintained at, for example, close to 0 volts.

Therefore, in the above embodiment, the display device 1 can use the pre-charge signal SA of other levels as the reset control signal SR, and use the laser signal EM of other levels as the reset voltage VR, the display device 1 can be Without adding additional power supply circuits and pins, hardware costs are saved and flicker problems are improved at the same time.

Of course, those skilled in the art can change or modify the above-mentioned implementation according to different design requirements. For example, in the display device 1, the scan signal SB of the next stage (that is, the n+1th stage) can be used as the reset control signal SR of the pixel circuit 30 of the nth stage, and it is not limited to the latter stage (that is, The pre-charge signal SA of stage n+1). Alternatively, the display device 1 can also use other levels of laser signal EM as the reset voltage VR of the nth level pixel circuit 30 , not limited to the laser signal EM of the rear two poles (that is, the n+2th level). More precisely, as long as the electrical signal or the laser signal EM is at a low logic voltage level in the reset time interval P1, it can be used as the reset voltage VR of the n-th pixel circuit 30 . Alternatively, the display device 1 can also use an independent voltage source (for example, a DC voltage source providing -3.3V, -5V, etc.) as the reset voltage VR of the pixel circuit 30 .

To sum up, the display device and the pixel circuit of the present invention can effectively improve the leakage current of the reset switch when the LED is driven. Therefore, when the display device or the pixel circuit displays brightness of low grayscale or black grayscale, the problem of flickering can be effectively improved, thereby improving user viewing experience and product satisfaction.

10: Pixel circuit 11: Drive circuit 12: Reset switch 13: light emitting diode N1: node VR: reset voltage VSS: reference voltage

Claims (7)

A display device, comprising: a plurality of pixel circuits arranged in an array, wherein each pixel circuit includes: a light emitting diode; a driving circuit coupled to the light emitting diode, the driving circuit is used to drive the the light emitting diode emits light; and a reset switch, the first terminal of the reset switch is coupled to the node between the light emitting diode and the driving circuit, when the light emitting diode is driven by the driving circuit to emit light , the voltage difference between the second terminal and the first terminal of the reset switch is within a preset voltage range, wherein in a reset time interval before the light emitting diode is driven to emit light by the driving circuit, the reset switch The reset switch turns on the connection between the first terminal and the second terminal of the reset switch according to a reset control signal, so as to provide a reset voltage to the node between the light emitting diode and the driving circuit, wherein The reset switch includes a first transistor, the first terminal of the first transistor is coupled to the light-emitting diode, the second terminal of the first transistor receives the reset voltage, and the control of the first transistor The terminal receives the reset control signal, wherein when the light-emitting diode is driven to emit light by the driving circuit, the reset control signal is at a high logic level voltage to disable the first transistor, and the reset voltage is a Low logic level voltage. The display device according to claim 1, wherein when the light emitting diode is driven to emit light by the driving circuit, the leakage current flowing through the first terminal and the second terminal of the reset switch is less than a predetermined current range. The display device according to claim 2, wherein when the light-emitting diode is driven to emit light by the driving circuit, the preset voltage range is that the voltage difference between the second terminal and the first terminal of the reset switch is less than 10 Volt, the preset current range is that the leakage current flowing through the first terminal and the second terminal of the reset switch is less than 5×10 ⁻⁸ amperes. The display device as claimed in item 1, wherein the anode of the light emitting diode (anode) is coupled to the driving circuit, and the first end of the reset switch is coupled between the anode of the light emitting diode and the driving circuit nodes in between. The display device as described in claim 1, wherein the driving circuit includes: a second transistor, the first terminal of the second transistor receives a first reference voltage, and the control terminal of the second transistor receives a data signal and a third transistor, the first end of the third transistor is coupled to the second end of the second transistor, the second end of the third transistor is coupled to the first end of the light emitting diode, The control end of the third transistor receives a laser signal, and the second end of the light emitting diode receives a second reference voltage. The display device as described in claim 5, wherein the drive circuit further includes: a fourth transistor, the first terminal of the fourth transistor receives a third reference voltage, and the control terminal of the fourth transistor receives the laser signal; A fifth transistor, the first end of the fifth transistor is coupled to the second end of the fourth transistor, the second end of the fifth transistor receives the data signal; a capacitor, the first end of the capacitor Coupling the second terminal of the fourth transistor and the first terminal of the fifth transistor, the second terminal of the capacitor is coupled to the control terminal of the second transistor; a sixth transistor, the sixth transistor The first terminal of the capacitor is coupled to the two terminals of the capacitor; a seventh transistor, the first terminal of the seventh transistor is coupled to the second terminal of the sixth transistor, and the second terminal of the seventh transistor is coupled to connected to the second terminal of the second transistor and the first terminal of the third transistor; and an eighth transistor, the first terminal of the eighth transistor is coupled to the second terminal of the sixth transistor and the The first terminal of the seventh transistor, the second terminal of the eighth transistor receives a fourth reference voltage, wherein the control terminal of the eighth transistor receives a pre-charge signal, the control terminal of the fifth transistor, the The control end of the sixth transistor and the control end of the seventh transistor receive a scan signal. The display device as described in claim 1, wherein in a first pixel circuit of the nth stage among the pixel circuits, the control terminal of the reset switch receives an n+1th stage precharge signal as the reset Control signal, the second end of the reset switch receives an n+2th level laser signal as the reset voltage.

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