Display panel and its pixel circuit

Abstract

A display panel and its pixel circuit are proposed. The pixel circuit includes a driving transistor, a data writing circuit, a compensation circuit, a voltage control circuit, a laser switch, and a light-emitting element. The driving transistor receives a power supply voltage. The data writing circuit receives a first scan signal, a laser signal, and a write data signal, stores the write data signal according to the first scan signal, and provides the write data signal to the control terminal of the driving transistor. The compensation circuit has a first switch and a second switch coupled to each other at a relay terminal and controlled by a second scan signal. The voltage control circuit adjusts the voltage difference between the control terminal of the driving transistor and the relay terminal. The laser switch is coupled between a second terminal of the driving transistor and the light-emitting element and is controlled by the laser signal.

Description

Technical Field

[0001] This invention relates to a display panel and its pixel circuit, and more particularly to a display panel and its pixel circuit capable of stabilizing brightness stability. Background Technology

[0002] Pixel circuits are common circuits used to drive the light-emitting elements on display panels. To meet the demands of lighter, thinner, and more energy-efficient mobile terminal products, display panels are required to operate at lower frequencies. However, reducing the operating frequency can easily cause flickering in the light-emitting elements of the display panel. This flickering occurs because unstable leakage current in the pixel circuit leads to unstable voltage within the circuit, resulting in uneven brightness of the light-emitting elements. Stabilizing the leakage current and thereby achieving uniform brightness of the light-emitting elements is an important challenge for those skilled in the art. Summary of the Invention

[0003] This invention provides a display panel and its pixel circuit, which can improve the stability of the brightness of the light-emitting element.

[0004] The pixel circuit of this invention includes a driving transistor, a data writing circuit, a compensation circuit, a voltage control circuit, a laser switch, and a light-emitting element. The driving transistor has a first terminal for receiving a power supply voltage. The data writing circuit receives a first scan signal, a laser signal, and a write data signal, and stores the write data signal according to the first scan signal, providing the write data signal to the control terminal of the driving transistor. The compensation circuit has a first switch and a second switch connected in series between the control terminal and the second terminal of the driving transistor, and the first and second switches are coupled to a relay terminal and both controlled by the second scan signal. The voltage control circuit is coupled to the control terminal and the relay terminal of the driving transistor to adjust the voltage difference between the control terminal and the relay terminal. The laser switch is coupled between the second terminal of the driving transistor and the light-emitting element and is controlled by the laser signal.

[0005] The display panel of the present invention includes a plurality of the aforementioned pixel circuits. The pixel circuits are arranged in an array on the display panel.

[0006] Based on the above, the pixel circuit of the present invention uses a voltage control circuit and a compensation circuit to adjust the voltage difference between the control terminal and the relay terminal of the driving transistor, stabilize the leakage current flowing into the control terminal of the driving transistor, and thus achieve the effect of stabilizing the magnitude of the driving current. Attached Figure Description

[0007] Figure 1 A circuit diagram illustrating a pixel circuit according to an embodiment of the present invention is shown.

[0008] Figure 2A circuit diagram illustrating a pixel circuit according to another embodiment of the present invention is shown.

[0009] Figure 3A Draw Figure 2 A circuit diagram of one embodiment of the pixel circuit.

[0010] Figure 3B Draw Figure 3A The timing diagram of the implementation of the pixel circuit.

[0011] Figure 4 Draw Figure 2 A circuit diagram of another embodiment of the pixel circuit.

[0012] Figure 5 Draw Figure 2 A circuit diagram of another embodiment of the pixel circuit.

[0013] Figure 6 A circuit diagram illustrating a display panel according to an embodiment of the present invention is shown.

[0014] In the attached figures, the following labels are used:

[0015] 100, 200, PX: Pixel circuit

[0016] 110: Data writing circuit

[0017] 120: Voltage control circuit

[0018] 130: Compensation Circuit

[0019] 222: Impedance Provider

[0020] 600: Display panel

[0021] AD: Diode

[0022] AT: Transistor

[0023] ATVG: Control Voltage

[0024] C110, CpA: Capacitors

[0025] DTFT: Driving transistor

[0026] EM: Laser signal

[0027] I_LED: Drive current

[0028] LED1: Light-emitting element

[0029] P_COMP: Compensation time interval

[0030] P_EM: Laser time interval

[0031] P_RST: Reset time interval

[0032] RG_con: Resistor

[0033] S1, S2: Scan signals

[0034] SD: Write data signal

[0035] SW_EM: Laser switch

[0036] SW_RST: Reset switch

[0037] SW1, SW2: Switches

[0038] TR1, TR2: Switches

[0039] VDD: Power supply voltage

[0040] VN: Reference voltage terminal

[0041] VP: Operating voltage

[0042] VSS: Reference ground terminal Detailed Implementation

[0043] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the present invention.

[0044] Please refer to Figure 1 , Figure 1 A schematic diagram of a pixel circuit 100 according to an embodiment of the present invention is shown. The pixel circuit 100 includes a data writing circuit 110, a voltage control circuit 120, a compensation circuit 130, a reset switch SW_RST, a driving transistor DTFT, a laser switch SW_EM, and a light-emitting element LED1.

[0045] In this embodiment, the data writing circuit 110 receives a scan signal S2, a laser signal EM, and a write data signal SD. A compensation circuit 130 is coupled between the data writing circuit 110 and the control terminal of the driving transistor DTFT. The compensation circuit 130 has switches SW1 and SW2, where switch SW1 is located between the output terminal of the data writing circuit 110 and the relay terminal A, and the first terminal of switch SW1 is coupled to the control terminal of the driving transistor DTFT. Switch SW2 is located between the relay terminal A and the second terminal of the driving transistor DTFT. Furthermore, the control terminals of both switches SW1 and SW2 receive the scan signal S2. A voltage control circuit 120 is coupled to the control terminal of the driving transistor DTFT and the relay terminal A.

[0046] Furthermore, the first terminal of the reset switch SW_RST is coupled between the relay terminal A and the reference voltage terminal VN, and the control terminal of the reset switch SW_RST receives the scan signal S1. The first terminal of the driving transistor DTFT is used to receive the power supply voltage VDD, and the second terminal of the driving transistor DTFT is coupled to the second terminal of the second switch SW2 and the first terminal of the laser switch SW_EM. The second terminal of the laser switch SW_EM is coupled between the light-emitting element LED1 and the reference ground terminal VSS. The control terminal of the laser switch SW_EM receives the laser signal EM. The light-emitting element LED1 is disposed between the second terminal of the laser switch SW_EM and the reference ground terminal VSS. Switches SW1, SW2, SW_RST, and SW_EM can all be transistor switches. In this embodiment, switches SW1, SW2, SW_RST, and SW_EM are transistor switches composed of P-type transistors.

[0047] In terms of operational details, the data writing circuit 110 can be turned on according to the scan signal S1, and the write data signal SD is written to the data writing circuit 110. On the other hand, the write data signal SD can be provided to the control terminal of the driving transistor DTFT via the data writing circuit 110. At the same time, the reset switch SW_RST can be turned on according to the scan signal S1, so that the voltage of the relay terminal A is equal to the voltage of the reference voltage terminal VN, and the voltage on the relay terminal A is reset.

[0048] On the other hand, switches SW1 and SW2 can be simultaneously turned on or off according to the scan signal S2. When switches SW1 and SW2 are turned on, information related to the threshold voltage of the driving transistor DTFT can be transmitted to the data writing circuit 110 via switches SW1 and SW2. In this way, the data writing circuit 110 can compensate the voltage at the control terminal of the driving transistor DTFT based on the received threshold voltage information.

[0049] Furthermore, the data writing circuit 110 can determine whether to receive the operating voltage VP based on the laser signal EM. The laser switch SW_EM can be turned on or off based on the laser signal EM, thereby controlling whether the drive current I_LED can flow to the light-emitting element LED1. In this embodiment, the voltage control circuit 120 is used to adjust the voltage difference between the control terminal of the driving transistor DTFT and the relay terminal A, and to stabilize the leakage current between the control terminal of the driving transistor DTFT and the relay terminal A, thereby stabilizing the voltage at the control terminal of the driving transistor DTFT and achieving a stable magnitude of the drive current I_LED.

[0050] Please note that when switches SW1 and SW2 are open-circuited, a leakage current exists between switches SW1 and SW2 and the control terminal of the driving transistor DTFT. This leakage current flows from relay terminal A through switch SW1 to the control terminal of the driving transistor DTFT. In this embodiment, the voltage control circuit 120 provides a path at the control terminal of the driving transistor DTFT and performs leakage current absorption through the aforementioned path. In this way, the impact of the leakage current on the voltage at the control terminal of the driving transistor DTFT can be effectively reduced, further stabilizing the magnitude of the driving current I_LED.

[0051] It is worth mentioning that, in this embodiment, the operating voltage VP can be less than the maximum voltage of the write data signal SD, and the potential of the reference voltage terminal VN can be equal to the potential of the reference ground terminal VSS.

[0052] Please refer to Figure 2 , Figure 2 A circuit diagram illustrating a pixel circuit 200 according to another embodiment of the present invention is shown. The pixel circuit 200 includes a data writing circuit 210, a voltage control circuit 220, a compensation circuit 230, a driving transistor DTFT, a laser switch SW_EM, and a reset switch SW_RST.

[0053] exist Figure 2 In this circuit, the data writing circuit 210 includes a capacitor C110, transistors TR1 and TR2. The first terminal of transistor TR1 receives the operating voltage VP, the control terminal of transistor TR1 receives the laser signal EM, and the second terminal of transistor TR1 is coupled to the first terminal of capacitor C110. The first terminal of transistor TR2 is also coupled to the first terminal of capacitor C110, and the control terminal of transistor TR2 receives the scan signal S2, while the second terminal of transistor TR2 receives the write data signal SD. The second terminal of capacitor C110 is coupled to the control terminal of the driving transistor DTFT. The voltage control circuit 220 includes an impedance provider 222 and a capacitor CpA. The impedance provider 222 is coupled to the second terminal of capacitor C110. The first terminal of capacitor CpA receives the operating voltage VP, and the second terminal of capacitor CpA is coupled to the relay terminal A. The second terminal of capacitor C110 is coupled to the control terminal of the driving transistor DTFT.

[0054] In terms of operational details, when transistor TR2 is turned on according to the scan signal S2, the write data signal SD can be transmitted and stored in capacitor C110, and the write data signal SD can be transmitted to the control terminal of the driving transistor DTFT through capacitor C110. When transistor TR1 is turned on according to the laser signal EM, the first terminal of capacitor C110 can receive the operating voltage VP, and the second terminal of capacitor C110 (coupled to the control terminal of the driving transistor DTFT) can generate a voltage pump operation according to the operating voltage VP. It is worth noting that transistors TR1 and TR2 are not turned on simultaneously.

[0055] In the voltage control circuit 220, the impedance provider 222 can be used to draw the leakage current between the control terminal of the driving transistor DTFT and the relay terminal A, thereby stabilizing the voltage at the control terminal of the driving transistor DTFT. The leakage current flowing from the relay terminal A to the control terminal of the driving transistor DTFT can be discharged through the impedance provider 222, thus keeping the leakage current flowing from the relay terminal A to the control terminal of the driving transistor DTFT stable.

[0056] Capacitor CpA can be used as a voltage regulator on relay terminal A to stabilize the voltage on relay terminal A.

[0057] Please refer to Figure 3A and Figure 3B , Figure 3A Draw Figure 2 A circuit diagram of one embodiment of the pixel circuit. Figure 3B Draw Figure 3A The waveform diagram of the pixel circuit.

[0058] exist Figure 3A In the impedance provider 222, the transistor AT can be a transistor AT, and the first terminal of the transistor AT is coupled to the reference voltage terminal VN, the second terminal of the transistor AT is coupled to the control terminal voltage of the driving transistor DTFT, and the control voltage ATVG of the control terminal of the transistor AT can be either a bias voltage or a scan signal S1.

[0059] In terms of operational details, when the control terminal of transistor AT is selected to receive the bias voltage VGH, transistor AT can be made to have high impedance. When the control terminal of transistor AT is selected to receive the scan signal S1 and the light-emitting element LED1 illuminates, transistor AT is in an off-state, providing a leakage current discharge path at the control terminal of the driving transistor DTFT. It is worth mentioning that transistor AT can be any type of transistor. Figure 3A The transistor AT shown is a P-type transistor, which is merely an illustrative example and is not intended to limit the scope of the invention. In this embodiment, the transistor AT is, for example, a thin-film transistor.

[0060] Incidentally, the control terminal voltage ATVG of transistor AT can be the same as the scan signal S1, or a fixed bias voltage.

[0061] exist Figure 3B In the process, the control terminal voltage ATVG of transistor AT is the same as the scan signal S1. During the reset time interval P_RST, the control voltage ATVG, scan signals S1 and S2 are all at the first voltage (logic low voltage), while the laser signal EM is at the second voltage (logic high voltage), where the first voltage is lower than the second voltage. At this time, the reset switch SW_RST and transistor TR2 are turned on according to the scan signal S1; transistor AT is turned on according to the control terminal voltage ATVG; switches SW1 and SW2 in compensation circuit 230 are turned on according to the scan signal S2; and transistor TR1 and laser switch SW_EM are turned off according to the laser signal EM. The turn on of reset switch SW_RST makes the voltage of relay terminal A the same as the voltage of reference voltage terminal VN (equal to the reference ground voltage). Since switches SW1 and SW2 are turned on, the control terminal and the second terminal of driving transistor DTFT can be reset to the reference ground voltage. At the same time, the write data signal SD can be transmitted through the turned-on transistor TR2 and stored in capacitor C110.

[0062] Next, during the compensation time interval P_COMP (between the reset time interval P_RST and the laser time interval P_EM), the control voltage ATVG and the scan signal S1 rise to the second voltage, as does the laser signal EM, while only the scan signal S2 maintains the first voltage. In the pixel circuit 200, only transistor TR2, switch SW1, and switch SW2 are turned on, while the remaining transistors are off. The conduction of transistor TR2 causes the write data signal SD to be continuously transmitted to the first terminal of capacitor C110 via transistor TR2. The conduction of switches SW1 and SW2 causes the critical voltage of the driving transistor DTFT to be compensated from the second terminal of the driving transistor DTFT to the control terminal of the driving transistor DTFT. Therefore, the voltage difference between the first and second terminals of capacitor C110 is the critical voltage between the write data signal SD and the driving transistor DTFT.

[0063] During the laser time interval P_EM, the control voltage ATVG, scanning signals S1 and S2 are all second voltages, while the laser signal EM is the first voltage. The reset switch SW_RST, transistor TR2, transistor AT, and switches SW1 and SW2 in the compensation circuit 230 are all open circuits, while transistor TR1 and the laser switch SW_EM are on. When transistor TR1 and the laser switch SW_EM are on, the DC signal of the operating voltage VP is received by capacitor C110, and the critical voltage value compensated to the control terminal of the driving transistor DTFT is canceled by the driving transistor DTFT. The driving current I_LED is transmitted through the laser switch SW_EM to the driving light-emitting element LED1, causing LED1 to emit light.

[0064] During the laser time interval P_EM, because the voltage at relay terminal A is higher than the voltage at the control terminal of the driving transistor DTFT, leakage current flows from relay terminal A to the control terminal of the driving transistor DTFT, potentially causing the voltage at the control terminal of the driving transistor DTFT to rise, thereby reducing the driving current I_LED. If the leakage current and the voltage change at the control terminal of the driving transistor DTFT are too drastic, it will affect the magnitude of the driving current I_LED, resulting in uneven brightness of the light-emitting element LED1. Therefore, this embodiment of the invention includes a transistor AT. Since the voltage at the control terminal of the driving transistor DTFT is greater than the potential of the reference voltage terminal VN coupled to transistor AT, another leakage current flows from the control terminal of the driving transistor DTFT through transistor AT to the reference voltage terminal VN, stabilizing the leakage current flowing from relay terminal A to the control terminal of the driving transistor DTFT, thereby stabilizing the voltage at the control terminal of the driving transistor DTFT and achieving the purpose of stabilizing the driving current I_LED.

[0065] Please refer to Figure 4 , Figure 4 Draw Figure 2 A circuit diagram of another embodiment of the pixel circuit. Figure 4 In this circuit, the impedance provider 222 can be a diode AD, with the anode of the diode AD coupled to the reference voltage terminal VN, and the cathode of the diode AD receiving the control terminal voltage of the driving transistor DTFT. The anode of the diode AD being coupled to the reference voltage terminal VN ensures that when the light-emitting element LED1 emits light, the diode AD is in an open-circuit state, allowing a leakage current to flow through the diode AD, thereby maintaining a stable leakage current flowing from the relay terminal A to the control terminal of the driving transistor DTFT.

[0066] Please refer to Figure 5 , Figure 5 Draw Figure 2 A circuit diagram of another embodiment of the pixel circuit. Figure 5In contrast to Figures 3 and 4, the impedance provider 222 can be a resistor RG_CON, which is coupled between the reference voltage terminal VN and the control terminal of the driving transistor DTFT. Furthermore, the resistor RG_CON can be a polysilicon (POLY) resistor with a high impedance value, or it can be constructed using other semiconductor materials that provide high resistance values; there are no specific limitations.

[0067] Please refer to Figure 6 , Figure 6 A circuit diagram illustrating a display panel 600 according to an embodiment of the present invention is shown. The display panel 600 includes a plurality of pixel circuits PX, which are arranged in an array on the display panel 600. The pixel circuits PX can be implemented using the pixel circuits 100 or 200 of the foregoing embodiments. The implementation details of the pixel circuits PX have been described in detail in the foregoing embodiments, and will not be repeated hereafter.

[0068] In summary, the pixel circuit of the present invention provides a voltage control circuit to generate a leakage current discharge path at the control terminal of the driving transistor, thereby stabilizing the voltage difference between the control terminal and the relay terminal of the driving transistor, so that the voltage at the control terminal of the driving transistor can be kept stable, effectively improving the brightness uniformity of the light-emitting element.

[0069] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the appended claims.

Claims

1. A pixel circuit, characterized in that, include: A driving transistor having a first terminal to receive a power supply voltage; A data writing circuit receives a first scan signal, a laser signal, and a write data signal, stores the write data signal according to the first scan signal, and provides the write data signal to the control terminal of the driving transistor. A compensation circuit has a first switch and a second switch connected in series between the control terminal and the second terminal of the driving transistor. The first switch and the second switch are coupled to a relay terminal and are both controlled by a second scan signal. A voltage control circuit is coupled to the control terminal of the driving transistor and the relay terminal to adjust the voltage difference between the control terminal of the driving transistor and the relay terminal. as well as A laser switch is coupled between the second terminal of the driving transistor and a light-emitting element, and is controlled by the laser signal; The voltage control circuit includes: An impedance provider, coupled to the output of the data writing circuit, is used to stabilize the voltage level at the output of the data writing circuit. as well as A capacitor is coupled to the relay terminal and used to receive an operating voltage.

2. The pixel circuit as described in claim 1, characterized in that, The impedance-providing circuit is a transistor, and the control terminal of the transistor receives a bias voltage or the second scan signal.

3. The pixel circuit as described in claim 1, characterized in that, The impedance-providing circuit is a diode, the cathode of which is coupled to the control terminal of the driving transistor, and the anode of which is coupled to a reference voltage terminal.

4. The pixel circuit as described in claim 1, characterized in that, The impedance is provided by a resistor.

5. The pixel circuit as described in claim 1, characterized in that, The data writing circuit includes: A capacitor having a first terminal coupled to the control terminal of the driving transistor; A first transistor having a first terminal receiving an operating voltage, a control terminal receiving the laser signal, and a second terminal for coupling to the second terminal of a capacitor; and A second transistor has a first terminal coupled to the second terminal of the capacitor, a control terminal of the second transistor receiving the first scan signal, and a second terminal of the second transistor receiving the write data signal.

6. The pixel circuit as described in claim 1, characterized in that, The compensation circuit includes: The first switch is disposed between the output terminal of the data writing circuit and the relay endpoint; and The second switch is located between the relay terminal and the second terminal of the driving transistor. Both the first switch and the second switch are controlled by the first scan signal.

7. The pixel circuit as described in claim 5, characterized in that, It also includes a reset switch coupled between the relay terminal and a reference voltage terminal, the reset switch being controlled by the second scan signal.

8. The pixel circuit as described in claim 7, characterized in that, During a reset time interval, the reset switch is turned on according to the second scan signal, coupling the relay terminal to the reference voltage terminal. The second transistor is turned on according to the second scan signal, and the write data signal is written to the capacitor. During a compensation time interval, the first switch and the second switch are turned on according to the first scan signal, and the data writing circuit stores the write data signal. During a laser time interval, the laser switch is turned on according to the laser signal, grounding the second terminal of the driving transistor and providing a driving current to drive the light-emitting element. The compensation time interval is located between the reset time interval and the laser time interval.

9. A display panel, characterized in that, include: Multiple pixel circuits as described in claim 1, wherein the pixel circuits are arranged in an array on the display panel.

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