TWI711027B - Pixel compensation circuit and display device - Google Patents

Abstract

A pixel compensation circuit and a display device are provided. The pixel compensation circuit includes a light-emitting element and a driving circuit. The driving circuit is coupled to the light-emitting component for providing a forward current to drive the light-emitting component to work in a linear rising region, wherein the light-emitting element compensates a present forward current of the light-emitting element according to a present temperature of the light-emitting element so that an external quantum efficiency of the light-emitting element is N times to M times a predetermined external quantum efficiency. The display device includes a plurality of pixel compensation circuits, wherein each of pixel compensation circuits has a light-emitting element and a driving circuit, the driving circuit for driving light-emitting element to work in a linear rising region. The light-emitting element compensates a present forward current of the light-emitting element according to a present temperature of the light-emitting element so that an external quantum efficiency of the light-emitting element is N times to M times the predetermined external quantum efficiency.

Description

Pixel compensation circuit and display device

The present invention relates to a pixel compensation circuit and a display device, and particularly to a pixel compensation circuit and a display device with self-temperature compensation and threshold voltage compensation.

With the popularization of flat-panel displays, various types of flat-panel displays have come out one after another. Whether it is Mini LED, Micro LED or Organic Light Emitting Diode (OLED), it can be used as the pixel of the display device, and it is very suitable for large size or high resolution. Degree panel. Since the light-emitting diode is a current-driven element, the brightness of the light-emitting diode is determined by the magnitude of the forward current. Generally, a thin film transistor (TFT) is used to adjust the size of the driving current to control the brightness of the light-emitting diode, and to control the brightness of the display.

However, thin film transistors may cause a variation in the threshold voltage due to differences in manufacturing processes or long-term operation, which may cause uneven brightness in the display device. Furthermore, the current external quantum efficiency (External Quantum Efficiency) of light-emitting diodes is designed at the highest point to obtain the highest luminous brightness. Therefore, when the temperature changes, such as when the temperature rises, the forward voltage of the light-emitting diode will decrease due to the increase in temperature, and the forward current will increase due to the decrease in the forward voltage, but the external quantum efficiency will be due to The temperature rises and the temperature drops drastically, so that the display device may cause unevenness in overall brightness due to uneven temperature distribution.

Therefore, how to provide a method that can compensate for the variation of the threshold voltage deviation of the driving transistor, and at the same time compensate for the variation of the external quantum efficiency of the light-emitting diode due to the rise in temperature, so as to prevent the display device from being affected by the above factors The phenomenon that causes the overall brightness of the display panel on the display device to be uneven will be the focus of this case and the focus of the solution.

In view of this, an embodiment of the present invention provides a pixel compensation circuit, which includes a light-emitting element and a driving circuit. The driving circuit is coupled to the light-emitting element to provide forward current to drive the light-emitting element to work in the linear rising region. The light-emitting element compensates for the current forward current of the light-emitting element according to the current temperature of the light-emitting element, so as to make the external quantum efficiency of the light-emitting element It is between N times and M times the preset external quantum efficiency.

In an embodiment of the present invention, the current forward current of the light-emitting element is positively correlated with the current temperature, the preset external quantum efficiency corresponds to the preset forward current and the preset temperature, and the external quantum efficiency corresponds to the current forward current and the current temperature. temperature.

In an embodiment of the present invention, the light-emitting element has an anode terminal and a cathode terminal, and the anode terminal of the light-emitting element is used to receive the power supply voltage.

In an embodiment of the present invention, the driving circuit includes a driving transistor, and has a control terminal, a first terminal, and a second terminal. The first terminal of the driving transistor is coupled to the cathode terminal of the light-emitting element, the second terminal of the driving transistor is used to receive a reference voltage, and the driving transistor is used to generate a smooth sequence according to the potential difference between the control terminal and the first terminal. To current.

In an embodiment of the present invention, the pixel compensation circuit further includes a control circuit, which is coupled to the drive circuit, wherein the control circuit includes: a pulse width modulation circuit and a pulse amplitude modulation circuit. Change circuit. The pulse width modulation circuit is coupled to the control terminal of the driving transistor, and is used for controlling the on-time of the driving transistor according to the pulse width data. The pulse amplitude modulation circuit is coupled to the control terminal of the driving transistor, and is used to control the voltage amplitude applied to the control terminal of the driving transistor according to the pulse amplitude data.

In another embodiment of the present invention, a pixel compensation circuit includes: a light-emitting element and a driving transistor. The light-emitting element has an anode end and a cathode end, and the anode end of the light-emitting element is used for receiving the power supply voltage. The driving transistor has a control terminal, a first terminal, and a second terminal. The first terminal of the driving transistor is coupled to the cathode terminal of the light-emitting element, and the driving transistor is used to determine the potential difference between the control terminal and the first terminal. Drive the light-emitting element to work in a linear rising region, where the current forward current of the light-emitting element is positively correlated with the current temperature, so that the external quantum efficiency of the light-emitting element is between N and M times the preset external quantum efficiency, where M is greater than N , M and N are positive real numbers.

In another embodiment of the present invention, the current forward current of the light emitting element is positively correlated with the current temperature, the preset external quantum efficiency corresponds to the preset forward current and the preset temperature, and the external quantum efficiency corresponds to the current forward current and Current Temperature.

In another embodiment of the present invention, the pixel compensation circuit further includes: a data input circuit, a first scan control circuit, a second scan control circuit, a first light emission control circuit, a second light emission control circuit, and a capacitor. The data input circuit is coupled to the first end of the driving transistor, and is used for providing pixel data to the first end of the driving transistor according to the first scan control signal. The first scan control circuit is coupled between the second terminal of the driving transistor and the control terminal, and is used for coupling the first terminal of the driving transistor to the control terminal of the driving transistor according to the first scan control signal. The second scan control circuit is coupled to the first scan control circuit and the control terminal of the driving transistor for receiving a reference voltage and for providing the reference voltage to the control terminal of the driving transistor according to the second scan control signal. The first light-emitting control circuit is coupled between the cathode terminal of the light-emitting element and the first terminal of the driving transistor for coupling the cathode terminal of the light-emitting element to the first terminal of the driving transistor according to the first light-emitting control signal . The second light-emitting control circuit is coupled to the first scan control circuit and the second end of the driving transistor for receiving a reference voltage and for providing the reference voltage to the second end of the driving transistor according to the second light-emitting control signal . The capacitor has a first terminal and a second terminal, wherein the first terminal of the capacitor is coupled to the control terminal of the driving transistor, and the second terminal of the capacitor is coupled to the anode terminal of the light emitting element.

In another embodiment of the present invention, a display device includes: a plurality of pixel compensation circuits, wherein each pixel compensation circuit has a light-emitting element and a driving circuit. The driving circuit is coupled to the light-emitting element to provide forward current to drive the light-emitting element to work in the linear rising region. The light-emitting element compensates for the current forward current of the light-emitting element according to the current temperature of the light-emitting element, so that the external quantum efficiency of the light-emitting element It is between N times and M times the preset external quantum efficiency, where M is greater than N, and M and N are positive real numbers.

In another embodiment of the present invention, the current forward current of the light emitting element is positively correlated with the current temperature, the preset external quantum efficiency corresponds to the preset forward current and the preset temperature, and the external quantum efficiency corresponds to the current forward current and Current Temperature.

In another embodiment of the present invention, the light emitting element has an anode terminal and a cathode terminal, and the anode terminal of the light emitting element is used to receive the power supply voltage.

In another embodiment of the present invention, the driving circuit includes a driving transistor having a control terminal, a first terminal, and a second terminal. The first terminal of the driving transistor is coupled to the cathode terminal of the light-emitting element to drive the second terminal of the transistor. The two terminals are used for receiving the reference voltage, and the driving transistor is used for generating a forward current according to the potential difference between the control terminal and the first terminal.

In another embodiment of the present invention, each pixel compensation circuit further has a control circuit. The control circuit is coupled to the driving circuit. The control circuit includes a pulse wave width modulation circuit and a pulse wave amplitude modulation circuit. The pulse width modulation circuit is coupled to the control terminal of the driving transistor, and is used to control the conduction time of the driving transistor according to the pulse width data. The pulse amplitude modulation circuit is coupled to the control terminal of the driving transistor, and is used to control the voltage amplitude applied to the control terminal of the driving transistor according to the pulse amplitude data.

The pixel compensation circuit and the display device provided by the embodiments of the present invention actively compensate the current variation caused by the threshold voltage deviation of the driving transistor through the compensation circuit, thereby maintaining the brightness of the light emitting diode from the threshold voltage deviation Impact. In addition, by redesigning the operating point of the light-emitting diode, the light-emitting diode has a self-compensation mechanism, so that the preset external quantum efficiency of the light-emitting diode is not changed by temperature changes, thereby maintaining the light-emitting diode The brightness is not affected by temperature. Thereby, the display panel on the display device is not affected by the threshold voltage shift and temperature change, and the phenomenon of uneven brightness of the display device is effectively improved.

The above description is only an overview of the technical solution of the present invention. In order to understand the technical means of the present invention more clearly, it can be implemented in accordance with the content of the specification, and to make the above and other objectives, features and advantages of the present invention more obvious and understandable. In the following, the preferred embodiments are cited in conjunction with the drawings, and the detailed description is as follows. In order to make the above and other objects, features and advantages of the present invention more comprehensible, the following specific examples are given in conjunction with the accompanying drawings to describe in detail as follows.

The pixel compensation circuit and display device provided by the embodiments of the present invention can be applied to electronic products such as displays, mobile phone screens, computer screens, or other electronic products that use light-emitting diodes as display devices. The pixel compensation circuit and the display device of the embodiment of the present invention mainly set the operating point of the characteristic curve of the external quantum efficiency (EQE) of the light emitting diode to the forward current (Forward Current, I _F ) In the linear rising region (the forward current rises with the rise of temperature, but the external quantum efficiency remains unchanged) and close to the saturation drop region (the forward current rises with the rise of temperature, but the external quantum efficiency increases with the temperature Rise and fall), so that the external quantum efficiency of the light-emitting diode does not change with temperature changes. For example, different temperatures will have different characteristic curves of external quantum efficiency versus forward current. When the operating point is set in the linear rising region, each characteristic curve preferably has the same external quantum efficiency. Conversely, when the operating point is set in the saturation drop zone, the external quantum efficiency of each characteristic curve is different. Therefore, in the embodiment of the present invention, the operating point of the characteristic curve of the external quantum efficiency of the light-emitting diode versus the forward current is set in the linear rising region, so that the light-emitting diode has characteristics that do not change with the increase in temperature. In this way, the uneven brightness of the light-emitting diode or the display device caused by the rise in temperature is improved.

In addition, the pixel compensation circuit and the display device of the embodiment of the present invention can be preliminarily divided into three implementation methods. The first implementation method is to control the driving transistor by the control method of pulse width modulation (PWM) and pulse amplitude modulation (PAM), so as to control the duration of the forward current and the forward current. Amplitude, thereby controlling the brightness of the light-emitting element. The second implementation method is that a pixel compensation circuit composed of six transistors and a capacitor (6T1C) controls the amplitude of the forward current by controlling the voltage amplitude applied to the control terminal of the driving transistor, thereby Control the brightness of the light-emitting element. The third implementation method is to apply the above-mentioned first implementation method or the second implementation method to the display device. When the temperature distribution of the display device is not uniform, the preset external quantum efficiency of all light-emitting diodes can still be maintained, thereby maintaining the uniformity of the brightness of the display device.

First, it is explained that the design of the operating point of the light emitting diode in the embodiment of the present invention. Traditionally, the operating points of light-emitting diodes are all designed in the saturation drop zone to obtain the highest external quantum efficiency and luminous brightness. However, when the temperature changes, the brightness of the light will also change. The temperature mentioned here includes the ambient temperature, the surface temperature of the light-emitting diode, and the junction temperature of the light-emitting diode (the temperature of the light-emitting layer). For example, when the ambient temperature rises, the forward voltage and external quantum efficiency of the light-emitting diode will decrease as the ambient temperature rises, and the forward current of the light-emitting diode will decrease as the forward voltage decreases. increase. At this time, the input electric power of the light-emitting diode itself will increase with the increase of the forward current, which not only causes the heat generated by the light-emitting diode itself to rise with the increase of the input electric power, but also causes the connection of the light-emitting diode. The surface temperature rises with the increase of the input electric power. At this moment, the ambient temperature and the junction temperature of the light-emitting diode continue to rise, and the light-emitting diode enters a vicious circle process, so that the external quantum efficiency increases with the continuous increase of the ambient temperature and the junction temperature of the light-emitting diode As a result, the light-emitting brightness of the light-emitting diode is greatly reduced, so that the brightness of the panel of the display device changes greatly with the change of temperature. Since the temperature distribution of the display panel on the display device is not uniform, the traditional design will cause unevenness in the overall luminous brightness. Therefore, the purpose of the embodiments of the present invention is to improve the above-mentioned deficiency.

Please refer to FIG. 1A. FIG. 1A is a schematic diagram of a characteristic curve of a light emitting diode's external quantum efficiency versus forward current according to an embodiment of the present invention. The operating point of the light-emitting diode of the embodiment of the present invention is set in the linear rising region, so that the multiple forward currents corresponding to the light-emitting diode at different temperatures preferably have the same preset external quantum efficiency (EQE _D ). For example, the light-emitting diode is 25°C at the first temperature (Temp 1), 85°C at the second temperature (Temp 2), and 150°C at the third temperature (Temp 3). At this time, the light-emitting diodes preferably have the same preset external quantum efficiency (EQE _D ), for example, 22%. Under this condition, the first temperature has a first forward current (I _F1 ) such as 5 mA, the second temperature has a second forward current (I _F2 ) such as 7.5 mA, and the third temperature has a third forward current ( I _F3 ) is 10 mA, for example. In other words, the forward current I _F will increase as the temperature rises, but the external quantum efficiency (EQE) does not decrease as the temperature rises, but remains unchanged. This effectively prevents the brightness of the light emitting diode from changing with temperature changes.

Furthermore, the LED is based on the current temperature of the LED to compensate the current forward current of the LED, so that the external quantum efficiency of the LED is within the preset external quantum efficiency of N Between times and M times, where M is greater than N, and M and N are positive real numbers. In one embodiment, N is preferably 0.75, and M is preferably 1.25. Please refer to FIGS. 1B to 1D. FIG. 1B is a schematic diagram of the characteristic curve of the external quantum efficiency of the light-emitting diode versus the forward current in a preset state according to an embodiment of the present invention. FIG. 1C is a schematic diagram of the characteristic curve of the external quantum efficiency of the light-emitting diode versus the forward current in the second temperature state according to an embodiment of the present invention. FIG. 1D is a schematic diagram of the characteristic curve of the external quantum efficiency of the light-emitting diode versus the forward current in the third temperature state according to an embodiment of the present invention.

For example, when the forward current when the light emitting diode is driven to work in the linear rising region is the preset forward current (I _FD ), the corresponding temperature at this time is the preset temperature (Temp D), such as 25°C, At this time, the corresponding external quantum efficiency is the preset external quantum efficiency (EQE _D ), for example, 22%. In other words, the preset external quantum efficiency (EQE _D ) corresponds to the preset forward current (I _FD ) and the preset temperature (Temp D). However, when the temperature continues to rise, the forward current of the light-emitting diode also rises as the temperature rises, but the external quantum efficiency remains within a specific range. At this time, the forward current of the light-emitting diode can be called the current forward current; the temperature of the light-emitting diode can be called the current temperature; and the external quantum efficiency of the light-emitting diode can be called the current external quantum efficiency. It can be seen that the current forward current of the light-emitting diode is positively correlated with the current temperature of the light-emitting diode. As shown in FIG. 1C, the second external quantum efficiency (EQE ₂ ) corresponds to the current forward current (I _F2 ) and the current temperature (Temp 2).

Assuming that the temperature rises from 25°C to 85°C, the LED will compensate the forward current of the LED according to the current temperature of the LED (85°C) to make it from the preset forward current (I _FD ) rises to the second forward current (I _F2 ) while maintaining the second external quantum efficiency (EQE ₂ ) of the light-emitting diode at the preset external quantum efficiency (EQE _D ), for example, 0.75 times of 22% To 1.25 times, that is, maintain between 16.5% and 27.5%. In the same way, suppose that when the temperature rises from 85°C to 150°C, the LED will compensate the forward current of the LED according to the current temperature (150°C) of the LED to make it from the second order. The forward current (I _F2 ) rises to the third forward current (I _F3 ) while maintaining the third external quantum efficiency (EQE ₃ ) of the light-emitting diode at the preset external quantum efficiency (EQE _D ), for example, 22% Between 0.75 times and 1.25 times, that is, between 16.5% and 27.5%. Conversely, when the temperature drops, and so on, the external quantum efficiency of the light-emitting diode can be maintained between 0.75 and 1.25 times the preset external quantum efficiency (EQE _D ), which will not be repeated here. In other words, the external quantum efficiency of light-emitting diodes (for example, the second external quantum efficiency (EQE ₂ ) and the third external quantum efficiency (EQE ₃ ) do not decrease drastically as the temperature rises, but are maintained in a specific range In this way, the brightness of the light-emitting diode is maintained uniform, and the brightness of the light-emitting diode is prevented from greatly changing with temperature changes.

What follows is a block diagram of a pixel compensation circuit according to an embodiment of the present invention. Please refer to FIG. 2, which is a block diagram of a pixel compensation circuit according to an embodiment of the present invention. A pixel compensation circuit 1 includes a light-emitting element 10 and a driving circuit 20 coupled to the light-emitting element 10. The light-emitting element 10 may be realized by a light-emitting diode. The operating point of the light-emitting element 10 is set in the linear rising region, so that the multiple forward currents I _F corresponding to the light-emitting element 10 at different temperatures preferably have the same preset external quantum efficiency (EQE _D ) For example, 20%. The driving circuit 20 may be realized by a transistor or a switching element. The driving circuit 20 is coupled to the light-emitting element 10 and used to provide a forward current I _F to drive the light-emitting element 10. The control circuit 30 may be realized by a discrete circuit or an integrated circuit. In addition, the pixel compensation circuit 1 further includes a control circuit 30 coupled to the driving circuit 20. The control circuit 30 can control the on-time of the driving circuit 20 according to the pulse width data Dw to determine the gray scale of the light emitting element 10, and can control the voltage amplitude applied to the driving circuit 20 according to the pulse amplitude data Da to determine the order The current amplitude of the current I _F.

Next, the first implementation manner of the embodiment of the present invention will be described. Please refer to FIG. 3, which is a partial circuit diagram of a pixel compensation circuit according to an embodiment of the present invention. A pixel compensation circuit 2 includes a light-emitting element 10 and a driving circuit 20. The light emitting element 10 includes a light emitting diode LED. The light emitting element 10 has an anode terminal and a cathode terminal, and the anode terminal of the light emitting element 10 is used to receive the power supply voltage VDD. The operating point of the light-emitting element 10 is set in the linear rising region, so that the multiple forward currents I _F corresponding to the light-emitting element 10 at different temperatures preferably have the same preset external quantum efficiency (EQE _D ) . Furthermore, when the temperature rises, the forward voltage (V _F ) of the light emitting diode will decrease as the temperature rises. The forward current I _F will increase as the forward voltage V _F decreases, but the external quantum efficiency (EQE) does not decrease with the increase in temperature, and it is better to maintain a fixed preset value (default External quantum efficiency EQE _D ). This effectively prevents the brightness of the light-emitting diode LED from changing with temperature changes. It is worth noting that, as mentioned above, the light-emitting diode LED is based on the current temperature of the light-emitting diode LED to compensate the current forward current of the light-emitting diode LED, so that the external quantum efficiency of the light-emitting diode LED ( EQE) is between N times and M times the preset external quantum efficiency, that is, maintained within a specific range. Thereby, the brightness of the light-emitting diode LED is maintained uniform, and the brightness of the light-emitting diode LED is prevented from greatly changing with temperature changes.

The driving circuit 20 includes a driving transistor T _D , for example, a P-type low temperature poly-silicon thin-film transistor with gate, source and drain. T _D driving transistor having a control terminal (gate), a first end (source) and the second terminal (drain), the driving transistor T _D a first terminal coupled to the cathode terminal of the light emitting element 10, the driving power T _D crystals of a second terminal for receiving a reference voltage VSS, and the driving transistor T _D according to a potential difference between the control terminal and the first terminal of the difference (V _GS), to produce the forward current I _F. For example, when the potential difference (V _GS ) is greater than the threshold voltage (Vth) of the driving transistor T _D , the P channel is formed and is in a conducting state to form a forward current I _F to drive the light emitting diode LED.

In addition, the pixel compensation circuit 2 further includes a control circuit 30. The control circuit 30 is coupled to the driving circuit 20. The control circuit 30 includes a pulse width modulation circuit 301 and a pulse amplitude modulation circuit 302. It should be noted that the pulse width modulation circuit 301 and the pulse amplitude modulation circuit 302 can be implemented by discrete circuits or integrated circuits. Since there are thousands of circuit implementations of the pulse width modulation circuit 301 and the pulse amplitude modulation circuit 302, and they are well known to those with ordinary knowledge in the technical field to which the present invention pertains, they will not be repeated in this specification, but only Key overview. Pulse width modulation circuit 301 but is coupled to the control terminal of the driving transistor T _D, and for controlling the conduction time of the driving transistor T _D according to the pulse width data and Dw, to control the forward current I _F The duration determines the brightness of the LED grayscale. For example, the driving transistor T _D shorter conduction time, the shorter the duration of the forward current I _F of the LED light-emitting diode exhibited lower brightness gradation; conversely, the driving transistor T _D The longer the on-time and the longer the duration of the forward current I _F , the higher the brightness of the grayscale presented by the light-emitting diode LED. In addition, the pulse width modulation circuit 301 may include a coupling capacitor and two transistors (not shown in the figure). One end of the coupling capacitor is used to receive the pulse width data Dw, the other end of the coupling capacitor is coupled to the source terminal of the control transistor and the gate terminal of the inverting transistor, and the drain terminal of the control transistor is coupled to the inverting transistor. drain terminal, the source terminal of the inverting transistor for receiving the VDD supply voltage, the drain terminal of the inverting transistor coupled to a gate terminal connected to the driving transistor T _D, and electrically connected to the control terminal of the transistor gate pulse width in accordance coupled The control signal determines whether the control transistor is turned on or off.

Pulse amplitude modulation circuit 302 but is coupled to the control terminal of the driving transistor T _D, and according to the pulse wave amplitude data Da to control the voltage applied to the amplitude control terminal of the driving transistor T _D to control the forward The amplitude of the current I _F. For example, when a voltage is applied to an amplitude greater control terminal of the driving transistor T _D, the greater the current generated along I _F, the LED light-emitting diode exhibited higher luminance gray body. In addition, the pulse wave amplitude modulation circuit 302 may include a capacitor and a transistor (not shown in the figure). End of the capacitor is coupled to the driving transistor T _D is a source terminal, the other terminal of the capacitor is coupled to the driving transistor T _D and the gate terminal of the drain terminal of the transistor, the source terminal of the transistor for receiving the pulse wave amplitude data Da And according to the pulse amplitude control signal coupled to the gate terminal of the transistor to determine whether the transistor is turned on or off.

Next, the second implementation method of the embodiment of the present invention is to control the driving transistor through the control method of pulse wave amplitude modulation, thereby controlling the brightness of the light-emitting element. Please refer to FIGS. 4 and 5. FIG. 4 is a schematic circuit diagram of a pixel compensation circuit according to another embodiment of the present invention. 5 is a schematic diagram of signal timing of a pixel compensation circuit according to another embodiment of the invention.

A pixel compensation circuit 3 includes a light-emitting element 10 and a driving circuit 20 coupled to the light-emitting element 10. The light emitting element 10 includes a light emitting diode LED. The light-emitting element 10 has an anode terminal and a cathode terminal. The anode terminal of the light-emitting element 10 is used to receive the power supply voltage VDD, and the operating point of the light-emitting element 10 is set in the linear rising region, so that the light-emitting element 10 corresponds to each temperature at different temperatures. The multiple forward currents I _F preferably have the same preset external quantum efficiency. Furthermore, when the temperature rises, the forward voltage V _{F of the} light-emitting diode will decrease as the temperature rises. The forward current I _F will increase as the forward voltage V _F decreases, but the external quantum efficiency (EQE) does not decrease with the increase in temperature, but is maintained at a fixed preset value (default external quantum efficiency). Efficiency EQE _D ). This effectively prevents the brightness of the light-emitting diode LED from changing with temperature changes. It is worth noting that, as mentioned above, the light-emitting diode LED is based on the current temperature of the light-emitting diode LED to compensate the current forward current of the light-emitting diode LED, so that the external quantum efficiency of the light-emitting diode LED ( EQE) is between N times and M times the preset external quantum efficiency, that is, maintained within a specific range. In this way, the brightness of the light-emitting diode LED is maintained uniform, and the brightness of the light-emitting diode LED is prevented from greatly changing with temperature changes.

Driving circuit 20 includes a driving transistor having a control terminal T _D, the first and second ends, wherein the driving transistor T _D a first terminal coupled to the cathode terminal 10 of the light emitting element and the driving transistor T _D according to The potential difference between the control terminal and the first terminal drives the light-emitting element 10. In addition, the pixel compensation circuit 3 further includes a control circuit 30 coupled to the driving circuit 20. The control circuit 30 includes a data input circuit 303, a first scan control circuit 304, a second scan control circuit 305, a first light emission control circuit 306, a second light emission control circuit 307, and a capacitor C1.

The data input circuit 303 is coupled to the first end of the driving transistor T _D , and is used to provide pixel data DATA[m] to the driving transistor T _D according to the first scan control signal G[n] (nth stage) The first end. Furthermore, the data input circuit 303 includes a data input transistor T4, which has a control terminal, a first terminal, and a second terminal. The control terminal of the data input transistor T4 is coupled to the first scan control signal G[n], the first terminal of the data input transistor T4 is used to receive pixel data DATA[m], and the second terminal of the data input transistor T4 a first end coupled to the cathode terminal of the driving transistor T _D of the light emitting element 10.

First scanning control circuit 304 is coupled between the driving transistor T _D a second terminal and a control terminal, and configured to drive the transistor T _D is coupled to a first end of the [n] according to a first scanning control signal G To the control end of the drive transistor T _D. Furthermore, the first scan control circuit 304 includes a first scan control transistor T5, which has a control terminal, a first terminal, and a second terminal. The control terminal of the first scan control transistor T5 is coupled to the first scan control signal G[n], the first terminal of the first scan control transistor T5 is coupled to the control terminal of the drive transistor T _D , and the first scan control The second end of the transistor T5 is coupled to the first end of the driving transistor T _D.

Second scanning control circuit 305 is coupled to a control terminal of the first scan driver control circuit 304 and the transistor T _D. The second scan control circuit 305 is used to receive the reference voltage VSS, and is used to provide the reference voltage VSS to the driving transistor T according to the second scan control signal G[n-1] (level n-1; not shown in FIG. 5) _D' s control end. Furthermore, the second scan control circuit 305 includes a second scan control transistor T6 having a control terminal, a first terminal and a second terminal. The control end of the second scan control transistor T6 is coupled to the second scan control signal G[n-1], and the first end of the second scan control transistor T6 is coupled to the first end of the first scan control transistor T5 As with the control terminal of the driving transistor T _D , the second terminal of the second scan control transistor T6 is coupled to the reference voltage VSS.

A first light emitting control circuit 306 is coupled to the light emitting element and the cathode terminal of the driving transistor T _D 10 between a first terminal for the female terminal to the light emitting element 10 is electrically coupled to the driving according to the first emission control signal EM1 The first end of the crystal T _D. Furthermore, the first lighting control circuit 306 includes a first lighting control transistor T1, which has a control terminal, a first terminal, and a second terminal. The control terminal of the first emission control transistor T1 is coupled to the first emission control signal EM1, the first terminal of the first emission control transistor T1 is coupled to the cathode terminal of the light emitting element 10, and the first terminal of the first emission control transistor T1 is The two ends are coupled to the second end of the data input transistor T4 and the first end of the driving transistor T _D.

Second light emission control circuit 307 is coupled to a second terminal of the first scan driver control circuit 304 and the transistor T _D for receiving the reference voltage VSS, and is used to provide a reference voltage VSS to the light emission driving in accordance with a second control signal EM2 The second end of the transistor T _D. Furthermore, the second lighting control circuit 307 includes a second lighting control transistor T2, which has a control terminal, a first terminal and a second terminal. The control terminal of the second emission control transistor T2 is coupled to the second emission control signal EM2, and the first terminal of the second emission control transistor T2 is coupled to the second terminal of the first scan control transistor T5 and the driving transistor T The second terminal of _D , the second terminal of the second light-emitting control transistor T2 is coupled to the reference voltage VSS. In addition, the capacitor C1 has a first terminal and a second terminal. The first terminal of the capacitor C1 is coupled to the control terminal of the driving transistor TD, and the second terminal of the capacitor C1 is coupled to the anode terminal of the light emitting element 10.

Next, the first operation phase (reset phase) of the pixel compensation circuit 3 will be described. Please refer to FIG. 6A. FIG. 6A is a schematic diagram of the first operation stage of the pixel compensation circuit according to another embodiment of the present invention. In the reset phase, only the second scan control signal G[n-1] is low. In this case, only the second control transistor T6 and the scan driving transistor T _D is in a conductive state, while the remaining transistors are in an off state (in a double cross line crosses composition represented). In this way, the residual charge stored in the capacitor C1 in the previous stage is discharged.

Next, the second operation stage and the third operation stage (storage stage) of the pixel compensation circuit 3 will be described. Please refer to FIG. 6B and FIG. 6C. FIG. 6B is a schematic diagram of the second operation stage of the pixel compensation circuit according to another embodiment of the present invention. 6C is a schematic diagram illustrating the operation of the pixel compensation circuit in the third operation stage according to another embodiment of the present invention. In the second operation stage, only the first scan control signal G[n] is low. At this time, only the driving transistor T _D , the data input transistor T4 and the first scan control transistor T5 are in the on state, and the other transistors are in the off state. At this moment, the voltage at the control terminal of the driving transistor T _D is the voltage difference between the data voltage V _DATA (the voltage of the pixel data DATA[m]) and the threshold voltage Vth of the driving transistor T _D. In the third operation stage, the aforementioned voltage difference is stored in the capacitor C1.

Next, the fourth operation stage (voltage setting stage) of the pixel compensation circuit 3 will be described. Please refer to FIG. 6D. FIG. 6D is a schematic diagram of the fourth operation stage of the pixel compensation circuit according to another embodiment of the present invention. In the fourth operation stage, only the first light emission control signal EM1 is at a low level. In this case, only the drive transistor T _D of the first light emission control transistor T1 is in the ON state, while the remaining transistors are in an off state. The circuit at this time does not form a loop, so the forward current I _{F is} not formed. Therefore, the driving voltage of the first transistor T _D terminal (VS) approximating the supply voltage VDD or may be said to have the same potential as the power supply voltage VDD, while the voltage (VG) of the control terminal T _D crystal driving electric approximately V _DATA -Vth.

Next, the fifth operation stage (light emitting stage) of the pixel compensation circuit 3 will be described. Please refer to FIG. 6E. FIG. 6E is a schematic diagram of the fifth operation stage of the pixel compensation circuit according to another embodiment of the present invention. In the fifth operation stage, only the first light-emitting control signal EM1 and the second light-emitting control signal EM2 are at a low level. At this time, only the driving transistor T _D , the first light-emitting control transistor T1 and the second light-emitting control transistor T2 are in the on state, and the remaining transistors are in the off state. At this time, the driving voltage of the first transistor T _D terminal (VS) approximates the power supply voltage VDD-V _F, the voltage (VG) of the control terminal T _D crystal driving electric approximately V _DATA -Vth. At this time, the forward current I _F = k (VG-VS+Vth) ² = k [(V _DATA -Vth)-( VDD-V _F ) +Vth] ² = k(V _DATA -VDD+ V _F ), where k is a physical structure parameter value related to the driving transistor T _D. It can be seen, the threshold voltage value Vth forward current I _F of the driving transistor T _D is irrelevant. Therefore, the amount of variation caused by the deviation of the threshold voltage Vth is greatly reduced, and the difference of the forward current I _F is effectively reduced, thereby improving the brightness of the light-emitting diode caused by the deviation of the threshold voltage Vth. The phenomenon of mutation.

Next, it is explained that the third implementation manner of the embodiment of the present invention can be implemented simultaneously with the foregoing first implementation manner or the second implementation manner. Generally speaking, due to internal or external environmental factors, the display panel on the display device will have different temperature distributions among various blocks, resulting in uneven brightness of the display device, and various traces. Therefore, the purpose of the third implementation manner of the embodiment of the present invention is to improve the above-mentioned deficiency. Please refer to FIG. 7, which is a schematic diagram of a display device according to an embodiment of the present invention.

A display device 4 includes a plurality of pixel compensation circuits PX (display panel). It should be noted that the pixel compensation circuit PX can be implemented by the pixel compensation circuit 2 in the first implementation mode, the pixel compensation circuit 3 in the second implementation mode, or the pixel compensation circuit 1. Since the circuit structure and operation mode of the pixel compensation circuits 1, 2, and 3 have been described in detail in the foregoing embodiment, they will not be repeated here, and only an overview is given. Each pixel compensation circuit PX has a light emitting element 10 and a driving circuit 20. The driving circuit 20 is coupled to the light-emitting element 10 to provide a forward current I _F to drive the light-emitting element 10, and the operating point of the light-emitting element 10 (for example, a light-emitting diode) is set in the linear rising region, so that the light-emitting element 10 The multiple forward currents I _F corresponding to different temperatures preferably have the same preset external quantum efficiency (EQE _D ). It is worth noting that, as mentioned above, the light-emitting diode LED is based on the current temperature of the light-emitting diode LED to compensate the current forward current of the light-emitting diode LED, so that the external quantum efficiency of the light-emitting diode LED ( EQE) is between N times and M times the preset external quantum efficiency, that is, maintained within a specific range. In this way, the brightness of the light-emitting diode LED is maintained uniform, and the brightness of the light-emitting diode is prevented from greatly changing with temperature changes. In addition, each pixel compensation circuit PX further has a control circuit 30 which is coupled to the driving circuit 20. The control circuit 30 comprises a pulse width modulation circuit 301 and the pulse amplitude modulation circuit 302, and configured to control the conduction time of the driving transistor T _D according to the pulse width data and the pulse wave amplitude in the drive data applied Transistor T _D controls the voltage amplitude at the terminal.

Please refer to FIG. 8. FIG. 8 is a schematic diagram of the temperature distribution of the display device according to an embodiment of the present invention. Assume that the temperature distribution of the display device 4 includes two regions, one is a high temperature region 41 and the other is a low temperature region 42. For example, the high-temperature area 41 may be an area closer to the heat source, such as a chip or component with a higher temperature on a circuit board. Conversely, the low-temperature area 42 may be an area far away from the heat source, such as a chip or component with a lower temperature on a circuit board. It is worth noting that the actual temperature distribution of the display device 4 may include multiple regions, and the temperature distribution is, for example, 30°C, 50°C, 85°C, 100°C, and 150°C.

What follows is the mode of operation of temperature compensation. Assuming a chip, component or other heat source with a higher temperature on the circuit board, most of the heat generated is transferred to the area (high temperature area 41) of the display device 4 closer to the heat source, so that the temperature of the high temperature area 41 rises from 30°C, for example To 150°C. At this time, the forward voltage V _F of the light-emitting diodes in the high temperature region 41 will decrease as the temperature increases, and the forward current I _F will increase as the forward voltage V _F decreases. Since the operating points of these light-emitting diodes are set in the linear rising region, and it is preferable to set these light-emitting diodes to have the same preset external quantum efficiency (EQE _D ), the outside of these light-emitting diodes The quantum efficiency (EQE) does not decrease as the temperature rises (for example, from 34% to 25%), but is preferably maintained at a fixed preset value (that is, the preset external quantum efficiency EQE _D ), for example 22%, so that the brightness of these light-emitting diodes will not decrease as the temperature rises.

Conversely, a small part of the heat may be transferred to the region (low temperature region 42) of the display device 4 away from the heat source, so that the temperature of the low temperature region 42 rises from 30°C to 50°C, for example. At this time, the forward voltage V _F of the light-emitting diodes in the low temperature region 42 will decrease as the temperature increases, and the forward current I _F will increase as the forward voltage V _F decreases. Since the operating points of these light-emitting diodes are set in the linear rising region, and it is preferable to set these light-emitting diodes to have the same preset external quantum efficiency (EQE _D ), the outside of these light-emitting diodes The quantum efficiency (EQE) does not decrease with the increase in temperature (for example, from 34% to 30%), but is preferably maintained at a fixed preset value (that is, the preset external quantum efficiency (EQE _D ), for example 22%), so that the brightness of these light-emitting diodes will not decrease with the increase in temperature.

It can be seen that regardless of whether the temperature distribution of the display device 4 is uniform or not, the external quantum efficiency (EQE) of each light-emitting diode of the display device 4 will not decrease as the temperature rises, but all remain at a fixed preset Value (that is, the preset external quantum efficiency EQE _D ). Thereby, the phenomenon of uneven brightness of the display device 4 caused by the influence of temperature is improved.

In summary, the pixel compensation circuit and display device provided by the embodiments of the present invention actively compensate for the current variation caused by the threshold voltage deviation of the driving transistor through the compensation circuit, thereby maintaining the brightness of the light emitting diode. Affected by the threshold voltage shift. In addition, by redesigning the operating point of the light-emitting diode, the light-emitting diode has a self-compensation mechanism, so that the preset external quantum efficiency of the light-emitting diode is not changed by temperature changes, thereby maintaining the light-emitting diode The brightness is not affected by temperature. Thereby, the display panel on the display device is not affected by the threshold voltage shift and temperature change, and the phenomenon of uneven brightness of the display device is effectively improved.

Although the present invention has been disclosed in the above embodiments, it is not intended to limit the present invention. Those with ordinary knowledge in the technical field to which the present invention pertains can make some changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to those defined by the attached patent application scope.

1, 2, 3: pixel compensation circuit 4: display device 10: light-emitting element 20: drive circuit 30: control circuit 301: pulse width modulation circuit 302: pulse amplitude modulation circuit 303: data input circuit 304 : First scan control circuit 305: second scan control circuit 306: first light emission control circuit 307: second light emission control circuit C1: capacitance Da: pulse wave amplitude data DATA[m]: pixel data Dw: pulse wave width data EM1: first light emission control signal EM2: second light emission control signal EQE: external quantum efficiency EQE ₁ : first external quantum efficiency EQE ₂ : second external quantum efficiency EQE ₃ : third external quantum efficiency EQE _D : preset external quantum Efficiency G[0]: the first scan control signal of level 0 G[1]: the first scan control signal of level 1 G[n]: the first scan control signal G[n-1]: the second scan control Signal I _F : forward current I _F1 : first forward current I _F2 : second forward current I _F3 : third forward current LED: light emitting diode PX: pixel compensation circuit VDD: power supply voltage V _DATA : Data voltage V _F : Forward voltage VG: Control terminal voltage V _GS : Potential difference VS: First terminal voltage VSS: Reference voltage Vth: Threshold voltage T1: First light-emitting control transistor T2: Second light-emitting control transistor T4: Data input transistor T5: first scan control transistor T6: second scan control transistor T _D : drive transistor Temp 1: first temperature Temp 2: second temperature Temp 3: third temperature Temp D: preset temperature

FIG. 1A is a schematic diagram of the characteristic curve of the external quantum efficiency of the light-emitting diode versus the forward current according to an embodiment of the present invention. FIG. 1B is a schematic diagram of a characteristic curve of the external quantum efficiency of a light-emitting diode versus forward current in a preset state according to an embodiment of the present invention. FIG. 1C is a schematic diagram of the characteristic curve of the external quantum efficiency of the light-emitting diode versus the forward current in the second temperature state according to an embodiment of the present invention. FIG. 1D is a schematic diagram of the characteristic curve of the external quantum efficiency of the light-emitting diode versus the forward current in the third temperature state according to an embodiment of the present invention. 2 is a block diagram of a pixel compensation circuit according to an embodiment of the invention. FIG. 3 is a schematic partial circuit diagram of a pixel compensation circuit according to an embodiment of the invention. 4 is a schematic circuit diagram of a pixel compensation circuit according to another embodiment of the invention. 5 is a schematic diagram of signal timing of a pixel compensation circuit according to another embodiment of the invention. 6A is a schematic diagram of the operation of the pixel compensation circuit in the first operation stage according to another embodiment of the invention. 6B is a schematic diagram illustrating the operation of the pixel compensation circuit in the second operation stage according to another embodiment of the present invention. 6C is a schematic diagram illustrating the operation of the pixel compensation circuit in the third operation stage according to another embodiment of the present invention. 6D is a schematic diagram of the operation of the pixel compensation circuit in the fourth operation stage according to another embodiment of the present invention. 6E is a schematic diagram of the operation of the pixel compensation circuit in the fifth operation stage according to another embodiment of the invention. FIG. 7 is a schematic diagram of a display device according to another embodiment of the invention. FIG. 8 is a schematic diagram of temperature distribution of a display device according to another embodiment of the invention.

EQE _D : preset external quantum efficiency

I _F1 : the first forward current

I _F2 : second forward current

I _F3 : third forward current

Temp 1: the first temperature

Temp 2: second temperature

Temp 3: third temperature

Claims (13)

A pixel compensation circuit includes: a light-emitting element; and a driving circuit, coupled to the light-emitting element, for providing a forward current to drive the light-emitting element to work in a linear rising region; wherein the light-emitting element emits light according to the A current temperature of the element compensates for a current forward current of the light-emitting element, so that an external quantum efficiency of the light-emitting element is between N times and M times a predetermined external quantum efficiency, where M is greater than N, and M is N is a positive real number. In the pixel compensation circuit described in item 1 of the scope of patent application, the current forward current of the light-emitting element is positively correlated with the current temperature, and the predetermined external quantum efficiency corresponds to a predetermined forward current and a predetermined Temperature, the external quantum efficiency corresponds to the current forward current and the current temperature. In the pixel compensation circuit described in claim 1, wherein the light-emitting element has an anode terminal and a cathode terminal, and the anode terminal of the light-emitting element is used for receiving a power supply voltage. The pixel compensation circuit described in item 3 of the scope of patent application, wherein the driving circuit includes a driving transistor, having a control terminal, a first terminal and a second terminal, and the first terminal of the driving transistor is coupled Connected to the cathode terminal of the light-emitting element, the second terminal of the driving transistor is used to receive a reference voltage, and the driving transistor is used to generate a voltage according to a potential difference between the control terminal and the first terminal The forward current. The pixel compensation circuit described in item 4 of the scope of patent application further includes a control circuit, the control circuit is coupled to the drive circuit, wherein the control circuit includes: A pulse width modulation circuit, coupled to the control terminal of the driving transistor, and used for controlling the on-time of the driving transistor according to a pulse width data; and a pulse amplitude modulation circuit, It is coupled to the control terminal of the driving transistor and used for controlling the voltage amplitude applied to the control terminal of the driving transistor according to a pulse amplitude data. A pixel compensation circuit includes: a light-emitting element having an anode end and a cathode end, wherein the anode end of the light-emitting element is used to receive a power supply voltage; and a driving transistor having a control end and a first end And a second terminal, wherein the first terminal of the driving transistor is coupled to the cathode terminal of the light-emitting element, and the driving transistor is used for driving according to a potential difference between the control terminal and the first terminal The light-emitting element works in a linear rising region; wherein, the light-emitting element compensates for a current forward current of the light-emitting element according to a current temperature of the light-emitting element, so that an external quantum efficiency of the light-emitting element is within a predetermined external quantum efficiency The efficiency is between N and M times, where M is greater than N, and M and N are positive real numbers. For the pixel compensation circuit described in item 6 of the scope of patent application, wherein the current forward current of the light-emitting element is positively correlated with the current temperature, and the predetermined external quantum efficiency corresponds to a predetermined forward current and a predetermined Temperature, the external quantum efficiency corresponds to the current forward current and the current temperature. The pixel compensation circuit described in item 6 of the scope of patent application further includes: a data input circuit coupled to the first end of the driving transistor for providing a pixel according to a first scan control signal Data to the first end of the driving transistor; A first scan control circuit, coupled between the second end of the driving transistor and the control end, for coupling the first end of the driving transistor to the driving transistor according to the first scan control signal The control terminal of the driving transistor; a second scan control circuit, coupled to the first scan control circuit and the control terminal of the driving transistor, for receiving a reference voltage and for controlling according to a second scan Signal to provide the reference voltage to the control terminal of the driving transistor; a first light-emitting control circuit, coupled between the cathode terminal of the light-emitting element and the first terminal of the driving transistor, is used according to a The first light-emitting control signal is used to couple the cathode end of the light-emitting element to the first end of the driving transistor; a second light-emitting control circuit is coupled to the first scan control circuit and the driving transistor The second terminal is used for receiving the reference voltage and used for providing the reference voltage to the second terminal of the driving transistor according to a second light-emitting control signal; and a capacitor having a first terminal and a second terminal Wherein the first terminal of the capacitor is coupled to the control terminal of the driving transistor, and the second terminal of the capacitor is coupled to the anode terminal of the light-emitting element. A display device includes a plurality of pixel compensation circuits, wherein each pixel compensation circuit has a light-emitting element and a driving circuit, the driving circuit is coupled to the light-emitting element for providing a forward current to drive the light-emitting The element works in a linear rising region, and the light-emitting element compensates for a current forward current of the light-emitting element according to a current temperature of the light-emitting element, so that an external quantum efficiency of the light-emitting element is N times a preset external quantum efficiency To M times, where M is greater than N, and M and N are positive real numbers. For the display device described in claim 9, wherein the current forward current of the light-emitting element is positively correlated with the current temperature, and the predetermined external quantum efficiency corresponds to a predetermined forward current The forward current and a preset temperature, and the external quantum efficiency corresponds to the current forward current and the current temperature. According to the display device described in claim 9, wherein the light-emitting element has an anode terminal and a cathode terminal, and the anode terminal of the light-emitting element is used to receive a power supply voltage. The display device according to claim 11, wherein the driving circuit includes a driving transistor having a control terminal, a first terminal and a second terminal, and the first terminal of the driving transistor is coupled to The cathode terminal of the light-emitting element, the second terminal of the driving transistor are used to receive a reference voltage, and the driving transistor is used to generate the forward sequence according to a potential difference between the control terminal and the first terminal To current. For the display device described in claim 12, each of the pixel compensation circuits further has a control circuit, the control circuit is coupled to the drive circuit, and the control circuit includes: a pulse width modulation circuit , Coupled to the control terminal of the driving transistor, and used to control the on-time of the driving transistor according to a pulse width data; and a pulse amplitude modulation circuit, coupled to the driving transistor The control terminal is used for controlling the voltage amplitude applied to the control terminal of the driving transistor according to a pulse amplitude data.

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