TWI891391B - AMOLED pixel compensation circuit, OLED display device and information processing device - Google Patents

Abstract

An AMOLED pixel compensation circuit includes a switching circuit, a PMOS transistor, a storage capacitor, and an OLED element. The switching circuit is configured to perform a switching operation to drive the PMOS transistor to generate a driving current to increase the brightness of the OLED element. The switching operation includes: setting a gate voltage of the PMOS transistor with a first initial voltage; The source voltage of the PMOS transistor is set with a positive DC supply voltage, and the anode voltage of the OLED element is set with a second initial voltage. The PMOS transistor and the storage capacitor are connected in series between a data voltage and the second initial voltage so that the voltage stored in the storage capacitor is the difference between the second initial voltage and the sum of the data voltage and the threshold voltage of the PMOS transistor. The drive current is generated by coupling two terminals of the storage capacitor to the gate and source of the PMOS transistor, respectively.

Description

AMOLED pixel compensation circuit, OLED display device, and information processing device

The present invention relates to the field of integrated circuits, and more particularly to an AMOLED pixel compensation circuit.

Each pixel in a typical AMOLED (active mode organic light emitting diode) display module is composed of a pixel circuit. This pixel circuit includes an OLED unit and a transistor circuit for generating a drive current to drive the OLED (organic light emitting diode) unit. This transistor circuit typically includes multiple transistors and a storage capacitor, such as a 7T1C (seven PMOS transistors and a storage capacitor) structure. A constant current is generated based on the display data voltage stored in the storage capacitor. The output time of this constant current is controlled by a pulse modulation signal to determine the equivalent value of the drive current, thereby driving the OLED unit to present a predetermined brightness.

However, due to process variations, the threshold voltages of the transistors in these pixel circuits may be uneven, resulting in uneven display brightness across pixels and causing mura (mura) on the display screen.

Furthermore, to increase the battery life of mobile devices, typical AMOLED display modules reduce the display refresh rate when displaying a static image to save power. However, when the display refresh rate is reduced, transistor leakage current in the transistor circuit causes the storage capacitor's voltage to drop, thereby affecting the display brightness of the OLED unit.

To solve the above problems, a novel AMOLED pixel compensation circuit architecture is urgently needed in this field.

One objective of the present invention is to provide an AMOLED pixel compensation circuit that can quickly equalize the source-gate voltage of the current source transistor of each OLED pixel during the display of a frame, thereby minimizing the short-term residual effect on the displayed image caused by the hysteresis voltage of the source-gate parasitic capacitance of the current source transistor.

Another object of the present invention is to provide an AMOLED pixel compensation circuit that can compensate the threshold voltage of a current source transistor to minimize display unevenness and mura caused by process variations and supply voltage drops.

Another object of the present invention is to disclose an AMOLED pixel compensation circuit that can extend the voltage retention time of a storage capacitor to support low screen refresh rates.

Another object of the present invention is to disclose an OLED display device that can minimize short-term afterimages on the display screen by using the aforementioned AMOLED pixel compensation circuit.

Another object of the present invention is to disclose an OLED display device that can minimize display unevenness and mura caused by process variations and supply voltage drops through the aforementioned AMOLED pixel compensation circuit, and extend the voltage retention time of the storage capacitor to support low refresh rates.

Another object of the present invention is to disclose an information processing device that can optimize display effects and support low refresh rates by using the aforementioned AMOLED pixel compensation circuit.

To achieve the aforementioned objectives, an AMOLED pixel compensation circuit is provided. The circuit comprises a switching circuit, a PMOS transistor, a storage capacitor, and an OLED element. The switching circuit is configured to perform a switching operation to drive the PMOS transistor to generate a driving current, thereby increasing the brightness of the OLED element. The switching operation comprises: setting the gate voltage of the PMOS transistor with a first initial voltage, setting the source voltage of the PMOS transistor with a positive DC supply voltage, and setting the anode voltage of the OLED element with a second initial voltage; The PMOS transistor and the storage capacitor are connected in series between a data voltage and the second initial voltage, such that the voltage stored in the storage capacitor is the difference between the second initial voltage and the sum of the data voltage and the threshold voltage of the PMOS transistor; and the two ends of the storage capacitor are respectively coupled to the gate and source of the PMOS transistor to generate the drive current.

In one embodiment, the switch circuit and the PMOS transistor are fabricated using a low temperature polycrystalline oxide process.

In one embodiment, any transistor in the switch circuit is a transistor selected from the group consisting of PMOS transistors, NMOS transistors, and CMOS transistors.

To achieve the aforementioned objectives, the present invention further provides an OLED display device having an AMOLED panel having the aforementioned AMOLED pixel compensation circuit.

To achieve the aforementioned objectives, the present invention further provides an information processing device having a central processing unit and the aforementioned OLED display device, wherein the central processing unit is configured to communicate with the OLED display device.

In a possible embodiment, the information processing device may be a portable computer, a smart phone or a car computer.

In order to enable the Review Committee to further understand the structure, features, purpose, and advantages of this creation, we have attached diagrams and detailed descriptions of preferred specific embodiments as follows.

The principle of the present invention is:

(1) Using a switching circuit to uniformly control the source-gate voltage of the current source transistors of each OLED pixel during the initialization period of displaying a frame to minimize the difference in hysteresis voltage of the source-gate parasitic capacitance of each current source transistor, while simultaneously reverse biasing each OLED, thereby effectively reducing the short-term image sticking phenomenon of the displayed image;

(2) using the switch circuit to collect a linear combination voltage including an initial voltage, a data voltage, and a threshold voltage of a current source transistor, and pre-storing the linear combination voltage in a storage capacitor;

(3) using the switching circuit to drive the voltage of the storage capacitor to drive the current source transistor to generate a driving current that is independent of the threshold voltage; and

(4) A switching circuit manufactured using an oxide semiconductor process provides low leakage current to extend the voltage retention time of the storage capacitor.

In this way, the present invention can effectively reduce the short-term image sticking phenomenon of the display screen, minimize the impact of the threshold voltage on the driving current to optimize the display effect of the OLED panel, and support low screen refresh rates.

Please refer to Figure 1, which shows a circuit diagram of an embodiment of an AMOLED pixel compensation circuit according to the present invention. As shown in Figure 1, an AMOLED pixel compensation circuit 100 includes a first switch 111, a second switch 112, a third switch 113, a fourth switch 114, a fifth switch 115, a PMOS transistor 120, a first on-time modulation switch 121, a second on-time modulation switch 122, a third on-time modulation switch 123, a storage capacitor 130, and an OLED device 140. The PMOS transistor 120 and these switches can be fabricated using an LTPO (low temperature polycrystalline oxide) process.

The channel of the first switch 111 is coupled between a first node A and a second node B, and the first switch 111 is controlled by a first switching signal S1 to turn on and off the channel.

The channel of the second switch 112 is coupled between the second node B and a first initial voltage VINT1, and the second switch 112 is controlled by a second switching signal S2 to turn on and off the channel.

The channel of the third switch 113 is coupled between a data voltage VDATA and a third node C, and the conduction and disconnection of the channel of the third switch 113 are controlled by a third switch signal S3.

The channel of the fourth switch 114 is coupled between a fourth node D and a second initial voltage VINT2, and the fourth switch 114 is controlled by a fourth switching signal S4 to turn on and off the channel.

The channel of the fifth switch 115 is coupled between a fifth node E and the second initial voltage VINT2, and the conduction and disconnection of the channel of the fifth switch 115 are controlled by the fourth switch signal S4. Furthermore, the first switch 111 is preferably an NMOS transistor to provide good insulation when it is turned off, thereby extending the voltage retention time of the storage capacitor 130 to support low refresh rates, such as 1 _Hz .

The PMOS transistor 120 has a source, a gate, and a drain. The source is coupled to the third node C, the gate is coupled to the first node A, and the drain is coupled to the second node B. The PMOS transistor 120 is configured to output a driving current to the OLED element 140 via the drain.

The first on-time modulation switch 121 is coupled between a positive DC supply voltage ELVDD and the third node C, and the on-time of the first on-time modulation switch 121 is controlled according to a first PWM signal EM1.

The second on-time modulation switch 122 is coupled between the second node B and the fifth node E, and the on-time of the second on-time modulation switch 122 is controlled according to a second PWM signal EM2.

The third on-time modulation switch 123 is coupled between the positive DC supply voltage ELVDD and the fourth node D, and the on-time of the third on-time modulation switch 123 is controlled according to the second PWM signal EM2.

The storage capacitor 130 is coupled between the first node A and the fourth node D to store a voltage to provide a voltage difference between the source and the gate of the PMOS transistor 120 to generate the driving current.

The OLED element 140 is coupled between the fifth node E and a negative DC voltage ELVSS, and generates a corresponding brightness according to the driving current.

During operation, the AMOLED pixel compensation circuit 100 performs the following steps in sequence:

(1) First stage: (first switch 111, second switch 112, third switch 113, fourth switch 114, fifth switch 115, first on-time modulation switch 121, second on-time modulation switch 122, third on-time modulation switch 123) are made to present (on, on, off, on, on, on, on, off, off) correspondingly, so that the first node A, The voltages of the second node B, the third node C, the fourth node D, and the fifth node E are respectively the first initial voltage VINT1, the first initial voltage VINT1, the positive DC supply voltage ELVDD, the second initial voltage VINT2, and the second initial voltage VINT2, thereby initializing the voltage of the storage capacitor 130 and the anode voltage of the OLED element 140. Please refer to Figure 2a for the situation. In this way, each OLED element 140 of a display panel can be reverse-biased, and the source-gate voltage of the PMOS transistor 120 in each pixel compensation circuit of the display panel can be uniformed to (ELVDD-VINT1), thereby minimizing the difference in hysteresis voltage of the source-gate parasitic capacitance of the PMOS transistor 120 and effectively reducing the short-term image sticking phenomenon of the display screen.

(2) Second stage: (the first switch 111, the second switch 112, the third switch 113, the fourth switch 114, the fifth switch 115, the first on-time modulation switch 121, the second on-time modulation switch 122, the third on-time modulation switch 123) are made to present (on, on, off, on, on, off, off, off), so that the voltages of the first node A, the second node B, the third node C, the fourth node D, and the fifth node E are respectively the first initial voltage VINT1, the first initial voltage VINT1, floating, the second initial voltage VINT2, and the second initial voltage VINT2, thereby maintaining the voltage of the storage capacitor 130 at (VINT2- VINT1) and maintain the anode voltage of the OLED element 140 at VINT2. Please refer to FIG. 2b for the situation.

(3) Phase III: The first switch 111, the second switch 112, the third switch 113, the fourth switch 114, the fifth switch 115, the first on-time modulation switch 121, the second on-time modulation switch 122, and the third on-time modulation switch 123 are caused to respectively present the states (on, off, on, on, on, on, off, off, off), so that the voltages of the first node A, the second node B, the third node C, the fourth node D, and the fifth node E are (VDATA+VTH), (VDATA+VTH), VDATA, the second initial voltage VINT2, and the second initial voltage VINT2, respectively. VTH is the threshold voltage of the PMOS transistor 120. Please refer to FIG. 2c for the situation. At this time, the voltage stored in the storage capacitor 130 is the difference between VINT2 and (VDATA+VTH). That is, the voltage stored in the storage capacitor 130 includes the threshold voltage of the PMOS transistor 120, which can be used to compensate the threshold voltage of the PMOS transistor 120 when driving the PMOS transistor 120 to generate the driving current.

(IV) Fourth stage: The first switch 111, the second switch 112, the third switch 113, the fourth switch 114, the fifth switch 115, the first on-time modulation switch 121, the second on-time modulation switch 122, and the third on-time modulation switch 123 are caused to respectively present the states (off, off, off, off, off, off, on, on, on), so that the voltages at the third node C, the fourth node D, and the first node A are ELVDD, ELVDD, and (ELVDD + VDATA + VTH - VINT2), respectively. Please refer to FIG2d for the situation. In this way, the voltage stored in the storage capacitor 130 can be used to bias the gate and source of the PMOS transistor 120 to generate the driving current. The driving current then flows through the OLED element 140, causing the OLED element 140 to emit light. The driving current is independent of the threshold voltage of the PMOS transistor 120. The driving current can be expressed by the following formula:

, where I _OLED represents the driving current, W represents the channel width, and C _OX represents the oxide dielectric capacitance. represents the carrier mobility, and L represents the channel length.

Please refer to Figure 2e, which shows an operating timing diagram of the AMOLED pixel compensation circuit 100 in Figure 1. As shown in Figure 2d, T1 represents the first phase, T2 represents the second phase, T3 represents the third phase, and T4 represents the fourth phase.

In T1, (EM1, EM2, S1, S2, S3, S4) present (low potential, high potential, high potential, low potential, high potential, low potential), causing (first switch 111, second switch 112, third switch 113, fourth switch 114, fifth switch 115, first on-time modulation switch 121, second on-time modulation switch 122, third on-time modulation switch 123) to present (on, on, off, on, on, on, off, off).

In T2, (EM1, EM2, S1, S2, S3, S4) present (high voltage, high voltage, high voltage, low voltage, high voltage, low voltage) correspondingly, causing (first switch 111, second switch 112, third switch 113, fourth switch 114, fifth switch 115, first on-time modulation switch 121, second on-time modulation switch 122, third on-time modulation switch 123) to present (on, on, off, on, on, off, off, off) correspondingly.

In T3, (EM1, EM2, S1, S2, S3, S4) present (high voltage, high voltage, high voltage, high voltage, low voltage, low voltage) correspondingly, causing (first switch 111, second switch 112, third switch 113, fourth switch 114, fifth switch 115, first on-time modulation switch 121, second on-time modulation switch 122, third on-time modulation switch 123) to present (on, off, on, on, on, off, off, off).

In T4, (EM1, EM2, S1, S2, S3, S4) present (low potential, low potential, low potential, high potential, high potential, high potential) correspondingly, causing (the first switch 111, the second switch 112, the third switch 113, the fourth switch 114, the fifth switch 115, the first on-time modulation switch 121, the second on-time modulation switch 122, the third on-time modulation switch 123) to present (off, off, off, off, off, on, on, on) correspondingly.

As can be seen from the above description, the present invention discloses an AMOLED pixel compensation circuit, which has a switching circuit, a PMOS transistor, a storage capacitor and an OLED element. The switching circuit is used to perform a switching operation process to drive the PMOS transistor to generate a driving current so that the OLED element generates a brightness, and the switching operation process includes: setting the gate voltage of the PMOS transistor with a first initial voltage, setting the positive DC supply voltage with a positive DC supply voltage, and The source voltage of the PMOS transistor is set, and the anode voltage of the OLED element is set with a second initial voltage; the PMOS transistor and the storage capacitor are connected in series between a data voltage and the second initial voltage so that the voltage stored in the storage capacitor is the difference between the second initial voltage and the sum of the data voltage and the threshold voltage of the PMOS transistor; and the two ends of the storage capacitor are respectively coupled to the gate and the source of the PMOS transistor to generate the driving current.

In a possible embodiment, the switch circuit and the PMOS transistor can be manufactured by a low temperature polycrystalline oxide process. In addition, any transistor in the switch circuit can be a PMOS transistor, an NMOS transistor or a CMOS transistor.

Based on the above description, the present invention further provides an OLED display device. Please refer to Figure 3, which shows a block diagram of one embodiment of the OLED display device of the present invention. As shown in Figure 3, an OLED display device 200 comprises a driver circuit 210 and an AMOLED panel 220. AMOLED panel 220 includes multiple AMOLED pixel compensation circuits 221. AMOLED pixel compensation circuits 221 are implemented using AMOLED pixel compensation circuit 100. Driver circuit 210 is configured to cause each AMOLED pixel compensation circuit 221 to illuminate the OLED element according to the aforementioned operating sequence.

Based on the above description, the present invention further provides an information processing device. Please refer to FIG. 4 , which shows a block diagram of an embodiment of the information processing device of the present invention. As shown in FIG. 4 , an information processing device 300 includes a central processing unit 310 and an OLED display device 320 . The central processing unit 310 is configured to communicate with the OLED display device 320 , which is implemented by the OLED display device 200 .

In addition, the information processing device 300 can be a portable computer, a smart phone, or a car computer.

Through the design disclosed above, the present invention has the following advantages:

(1) The AMOLED pixel compensation circuit of the present invention can quickly equalize the source-gate voltage of the current source transistor of each OLED pixel during the display of a frame, thereby minimizing the short-term residual effect on the display caused by the hysteresis voltage of the source-gate parasitic capacitance of the current source transistor;

(2) The AMOLED pixel compensation circuit of the present invention can compensate for the threshold voltage of the current source transistor to minimize display unevenness and mura caused by process deviation and supply voltage drop;

(3) The AMOLED pixel compensation circuit of the present invention can extend the voltage retention time of the storage capacitor to support low screen refresh rates;

(4) The OLED display device of the present invention can minimize short-term image sticking on the display screen through the aforementioned AMOLED pixel compensation circuit;

(5) The OLED display device of the present invention can minimize display unevenness and mura caused by process deviation and supply voltage drop through the aforementioned AMOLED pixel compensation circuit, and extend the voltage retention time of the storage capacitor to support low screen refresh rates; and

(6) The information processing device of the present invention can optimize the display effect and support low screen refresh rate through the aforementioned AMOLED pixel compensation circuit.

The present invention discloses only one preferred embodiment. Any partial changes or modifications based on the technical concept of the present invention and easily inferred by a person skilled in the art do not deviate from the scope of the patent rights of the present invention.

In summary, this case demonstrates significant differences from known technologies in terms of purpose, means, and effectiveness. Furthermore, its first invention is practical and truly meets the patent requirements for invention. We earnestly request the Review Commission to examine this matter and grant a patent to this application as soon as possible to benefit society. This is our utmost prayer.

100: AMOLED pixel compensation circuit 111: First switch 112: Second switch 113: Third switch 114: Fourth switch 115: Fifth switch 120: PMOS transistor 121: First on-time modulation switch 122: Second on-time modulation switch 123: Third on-time modulation switch 130: Storage capacitor 140: OLED element 200: OLED display device 210: Driver circuit 220: AMOLED panel 221: AMOLED pixel compensation circuit 300: Information processing device 310: Central processing unit 320: OLED display device

Figure 1 shows a circuit diagram of an embodiment of an AMOLED pixel compensation circuit of the present invention. Figure 2a shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of Figure 1 operating in a first phase. Figure 2b shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of Figure 1 operating in a second phase. Figure 2c shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of Figure 1 operating in a third phase. Figure 2d shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of Figure 1 operating in a fourth phase. Figure 2e shows an operating timing diagram of the AMOLED pixel compensation circuit of Figure 1. Figure 3 shows a block diagram of an embodiment of an OLED display device of the present invention. Figure 4 shows a block diagram of an embodiment of the information processing device of the present invention.

100: AMOLED pixel compensation circuit

111: First switch

112: Second switch

113: Third switch

114: The fourth switch

115: Fifth Switch

120: PMOS transistor

121: First on-time modulation switch

122: Second on-time modulation switch

123: Third on-time modulation switch

130: Storage capacitor

140:OLED components

Claims (7)

An AMOLED pixel compensation circuit has a switching circuit, a PMOS transistor, a storage capacitor and an OLED element. The switching circuit is used to perform a switching operation procedure to drive the PMOS transistor to generate a driving current so that the OLED element generates a brightness. The switching operation procedure includes: setting the gate voltage of the PMOS transistor with a first initial voltage, setting the source voltage of the PMOS transistor with a positive DC supply voltage, and setting the anode voltage of the OLED element with a second initial voltage; The PMOS transistor and the storage capacitor are connected in series between a data voltage and the second initial voltage so that the voltage stored in the storage capacitor is the difference between the second initial voltage and (the sum of the data voltage and the threshold voltage of the PMOS transistor); and the two ends of the storage capacitor are respectively coupled to the gate and the source of the PMOS transistor to generate the driving current;        wherein the switching circuit and the PMOS transistor are manufactured by a low temperature polycrystalline oxide process. The AMOLED pixel compensation circuit as described in claim 1, wherein any transistor in the switching circuit is a transistor selected from the group consisting of PMOS transistors, NMOS transistors and CMOS transistors. An OLED display device has an AMOLED panel, the AMOLED panel has a plurality of AMOLED pixel compensation circuits, each of the AMOLED pixel compensation circuits has a switching circuit, a PMOS transistor, a storage capacitor and an OLED element, the switching circuit is used to perform a switching operation procedure to drive the PMOS transistor to generate a driving current so that the OLED element generates a brightness, the switching operation procedure includes: setting the gate voltage of the PMOS transistor with a first initial voltage, setting the source voltage of the PMOS transistor with a positive DC supply voltage, and setting the anode voltage of the OLED element with a second initial voltage; The PMOS transistor and the storage capacitor are connected in series between a data voltage and the second initial voltage so that the voltage stored in the storage capacitor is the difference between the second initial voltage and (the sum of the data voltage and the threshold voltage of the PMOS transistor); and the two ends of the storage capacitor are respectively coupled to the gate and the source of the PMOS transistor to generate the driving current; wherein the switching circuit and the PMOS transistor are manufactured by a low temperature polycrystalline oxide process. The OLED display device as described in claim 3, wherein any transistor in the switch circuit is a transistor selected from the group consisting of PMOS transistors, NMOS transistors and CMOS transistors. An information processing device has a central processing unit and an OLED display device. The central processing unit is used to communicate with the OLED display device. The OLED display device has an AMOLED panel. The AMOLED panel has multiple AMOLED pixel compensation circuits. Each of the AMOLED pixel compensation circuits has a switching circuit, a PMOS transistor, a storage capacitor and an OLED element. The switching circuit is used to execute a switching operation procedure to drive the PMOS transistor to generate a driving current so that the OLED element generates a brightness. The switching operation procedure includes: The gate voltage of the PMOS transistor is set with a first initial voltage, the source voltage of the PMOS transistor is set with a positive DC supply voltage, and the anode voltage of the OLED element is set with a second initial voltage; the PMOS transistor and the storage capacitor are connected in series between a data voltage and the second initial voltage so that the voltage stored in the storage capacitor is the difference between the second initial voltage and (the sum of the data voltage and the threshold voltage of the PMOS transistor); and the two ends of the storage capacitor are respectively coupled to the gate and the source of the PMOS transistor to generate the driving current; The switch circuit and the PMOS transistor are manufactured by a low temperature polycrystalline oxide process. The information processing device as described in claim 5, wherein any transistor in the switch circuit is a transistor selected from the group consisting of PMOS transistors, NMOS transistors and CMOS transistors. The information processing device as described in any one of claims 5 to 6 is a device selected from the group consisting of a portable computer, a smart phone and a car computer.