TWI847771B - AMOLED pixel compensation circuit, OLED display device and information processing device - Google Patents

Abstract

An AMOLED pixel compensation circuit has a switch circuit, a PMOS transistor, a storage capacitor and an OLED element. The switch circuit is used to execute a switch operation procedure to drive the PMOS transistor to generate a driving current so that the OLED element generates a brightness. The switch operation procedure includes: setting the gate voltage of the PMOS transistor and the anode voltage of the OLED element with a first DC voltage; setting the source voltage of the PMOS transistor with a second DC voltage; The voltage makes the difference between the gate voltage and the source voltage of the PMOS transistor equal to (the first DC voltage-the second DC voltage); the PMOS transistor and the storage capacitor are connected in series between a data voltage and a DC supply voltage so that the voltage stored in the storage capacitor is the difference between the DC supply 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.

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 of a general AMOLED (active mode organic light emitting diode) display module is composed of a pixel circuit, which includes an OLED unit and a transistor circuit for generating a driving current to drive the OLED (organic light emitting diode) unit. The transistor circuit generally includes a plurality of transistors and a storage capacitor, such as a 7T1C (seven PMOS transistors and a storage capacitor) structure, and generates a certain current according to the display data voltage stored in the storage capacitor, and controls the output time of the certain current according to a pulse modulation signal to determine the equivalent value of the driving current, thereby driving the OLED unit to present a predetermined brightness.

However, due to process variations, the transistors in the pixel circuits may have uneven threshold voltages, resulting in uneven display brightness of each pixel and causing Mura (mura) on the display screen.

In addition, to increase the battery life of mobile devices, when the displayed image is a static image, the general AMOLED display module will reduce the display scan refresh rate to save power. However, when the display scan refresh rate is reduced, the transistor leakage current in the transistor circuit will cause the storage voltage of the storage capacitor 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 the art.

One purpose of the present invention is to provide an AMOLED pixel compensation circuit, which can quickly equalize the source-gate voltage of the current source transistor of each OLED pixel in the process of displaying a frame, thereby minimizing the short-term afterimage caused by the hysteresis voltage of the source-gate parasitic capacitance of the current source transistor on the display image.

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 deviation and voltage drop of a supply voltage.

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

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

Another object of the present invention is to disclose an OLED display device, which can minimize display unevenness and Mura caused by process deviation and voltage drop of supply voltage through the aforementioned AMOLED pixel compensation circuit, and prolong the voltage holding time of the storage capacitor to support a low screen refresh rate.

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

To achieve the above-mentioned purpose, an AMOLED pixel compensation circuit is proposed, which 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: A first stage: setting the gate voltage of the PMOS transistor and the anode voltage of the OLED element with a first DC voltage; A second stage: setting the source voltage of the PMOS transistor with a second DC voltage so that the difference between the gate voltage and the source voltage of the PMOS transistor is equal to (the first DC voltage-the second DC voltage); A third stage: connecting the PMOS transistor and the storage capacitor in series between a data voltage and a DC supply voltage so that the voltage stored in the storage capacitor is the difference between the DC supply voltage and (the sum of the data voltage and the threshold voltage of the PMOS transistor); and A fourth stage: coupling the two ends of the storage capacitor to the gate and the source of the PMOS transistor respectively to generate the driving 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 object, the present invention further provides an OLED display device having an AMOLED panel. The AMOLED panel has the AMOLED pixel compensation circuit as described above.

To achieve the aforementioned object, 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 used to communicate with the OLED display device.

In possible embodiments, 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, the following are attached with diagrams and detailed descriptions of the preferred specific implementation examples.

The principle of the present invention is:

(i) using a switch circuit to uniformize the source-gate voltage of the current source transistor of each OLED pixel during the initialization period of displaying a frame of picture to minimize the difference in the hysteresis voltage of the source-gate parasitic capacitance of each current source transistor, thereby effectively reducing the short-term afterimage phenomenon of the displayed picture;

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

(iii) using the switch 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

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

Accordingly, the present invention can effectively reduce the short-term afterimage phenomenon of the display screen, minimize the influence of the threshold voltage on the driving current to optimize the display effect of the OLED panel, and support a low screen refresh rate.

Please refer to FIG. 1, which shows a circuit diagram of an embodiment of the AMOLED pixel compensation circuit of the present invention. As shown in FIG. 1, an AMOLED pixel compensation circuit 100 has 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 storage capacitor 130 and an OLED element 140, wherein the PMOS transistor 120 and the switches can be manufactured by a LTPO (low temperature polycrystalline oxide) process.

The channel of the first switch 111 is coupled between a positive DC voltage V _INI and a first node A, and the first switch 111 is controlled by a first switch signal SW1 to turn on and off the channel.

The channel of the second switch 112 is coupled between the first node A and a common voltage V _COM , and the conduction and disconnection of the channel of the second switch 112 are controlled by a second switch signal SW2.

The channel of the third switch 113 is coupled between a data voltage V _DATA and a second node B, and the conduction and disconnection of the channel of the third switch 113 are controlled by a third switch signal SW3.

The channel of the fourth switch 114 is coupled between a third node C and a fourth node D, and the conduction and disconnection of the channel of the fourth switch 114 are controlled by a fourth switch signal SW4.

The channel of the fifth switch 115 is coupled between the first node A and the third node C, and the fifth switch 115 is controlled by a fifth switch signal SW5 to turn on and off the channel. In addition, preferably, the fourth switch 114 and the fifth switch 115 can both be NMOS transistors to provide a good insulation effect when they are disconnected, thereby extending the voltage holding time of the storage capacitor 130 to support a low screen refresh rate, such as a 1 _Hz screen refresh rate.

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

The first on-time modulation switch 121 is coupled between the first node A and a fifth node E, and the on-time of the first on-time modulation switch 121 is controlled according to a PWM signal EM. In addition, the fifth node E is coupled to a DC supply voltage ELVDD.

The second on-time modulation switch 122 is coupled between the second node B and the fourth node D, and the on-time of the second on-time modulation switch 122 is controlled according to the PWM signal EM.

The storage capacitor 130 is coupled between the third node C and the fifth node E, and is used 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 fourth node D and a negative DC voltage ELVSS, and generates corresponding brightness according to the driving current.

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

(i) The first 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) are made to present (on, off, off, on, on, off, off) correspondingly, so that the voltages of the first node A, the third node C and the fourth node D are all positive DC voltages _VINI to initialize the gate voltage of the PMOS transistor 120 and the anode voltage of the OLED element 140. Please refer to FIG. 2a for the situation;

(ii) The 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) are made to present (off, on, off, off, off, off, off, off), so that the voltage of the third node C is the positive DC voltage V _INI , and the voltage of the first node A is the common voltage V _COM , as shown in FIG. 2 b ; accordingly, the gate-source voltage of the PMOS transistor 120 of the pixel compensation circuit in the plurality of pixels of a display panel is uniformly (V _INI -V _COM ), thereby minimizing the difference in hysteresis voltage of the source-gate parasitic capacitance of the PMOS transistor 120 and effectively reducing the short-term afterimage phenomenon of the display screen;

(III) The third 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) are made to present (off, off, on, off, on, off, off) correspondingly, so that the voltage of the third node C and the voltage of the first node A are both (V _DATA +V _th ), wherein V _th is the threshold voltage of the PMOS transistor 120, and the situation is shown in FIG. 2c ; at this time, the voltage stored in the storage capacitor 130 is ELVDD and (V _DATA +V _th ), 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 the PMOS transistor 120 is driven to generate the driving current; and

(IV) The 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 are made to present (off, off, off, off, off, on, on) correspondingly, so that the voltage of the third node C is (V _DATA +V _TH ), and the voltage of the first node A is ELVDD, please refer to FIG. 2d; accordingly, the voltage stored in the storage capacitor 130 can be used to bias the gate and the source of the PMOS transistor 120 to generate the driving current, and the driving current flows through the OLED element 140 to make the OLED element 140 emit light, and the driving current is independent of the threshold voltage of the PMOS transistor 120. The driving current can be expressed by the following formula: I _OLED =(WC _OX μ/2L)(V _gs -V _th ) ² =(WC _OX μ/2L)(V _DATA +V _th -ELVDD-V _th ) ² =(WC _OX μ/2L)(V _DATA -ELVDD) ² , wherein I _OLED represents the driving current, W represents the channel width, C _OX represents the oxide layer dielectric capacitance, μ represents the carrier mobility, and L represents the channel length.

Please refer to FIG. 2e, which shows a working timing diagram of the AMOLED pixel compensation circuit 100 of FIG. 1. As shown in FIG. 2d, T1 represents the first stage, T2 represents the second stage, T3 represents the third stage, and T4 represents the fourth stage. The first switch 111 is a PMOS transistor, the second switch 112 is a PMOS transistor, the third switch 113 is a PMOS transistor, the fourth switch 114 is an NMOS transistor, the fifth switch 115 is an NMOS transistor, the first on-time modulation switch 121 is a PMOS transistor, and the second on-time modulation switch 122 is a PMOS transistor.

In T1, EM is at a high potential, SW1 is at a low potential, SW2 is at a high potential, SW3 is at a high potential, SW4 is at a high potential, and SW5 is at a high potential, so that (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, and the second on-time modulation switch 122) are displayed correspondingly (on, off, off, on, on, off, off).

In T2, EM is at a high potential, SW1 is at a high potential, SW2 is at a low potential, SW3 is at a high potential, SW4 is at a low potential, and SW5 is at a low potential, so that (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, and the second on-time modulation switch 122) are displayed correspondingly (disconnect, conduct, disconnect, disconnect, disconnect, disconnect, disconnect, disconnect).

In T3, EM is at a high potential, SW1 is at a high potential, SW2 is at a high potential, SW3 is at a low potential, SW4 is at a low potential, and SW5 is at a high potential, so that (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) are displayed correspondingly (disconnect, disconnect, conduct, disconnect, conduct, disconnect, disconnect).

In T4, EM is at a low potential, SW1 is at a high potential, SW2 is at a high potential, SW3 is at a high potential, SW4 is at a low potential, and SW5 is at a low potential, so that (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, and the second on-time modulation switch 122) are displayed correspondingly (off, off, off, off, off, on, on).

As can be seen from the above description, the present invention discloses an AMOLED pixel compensation circuit, which has a switch circuit, a PMOS transistor, a storage capacitor and an OLED element. The switch circuit is used to execute a switch operation procedure to drive the PMOS transistor to generate a driving current so that the OLED element generates a brightness, and the switch operation procedure includes: setting the gate voltage of the PMOS transistor and the anode voltage of the OLED element with a first DC voltage; setting the PM with a second DC voltage. The source voltage of the OS transistor makes the difference between the gate voltage and the source voltage of the PMOS transistor equal to (the first DC voltage - the second DC voltage); the PMOS transistor and the storage capacitor are connected in series between a data voltage and a DC supply voltage so that the voltage stored in the storage capacitor is the difference between the DC supply 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.

According to the above description, the present invention further proposes an OLED display device. Please refer to FIG. 3, which shows a block diagram of an embodiment of the OLED display device of the present invention. As shown in FIG. 3, an OLED display device 200 has a driving circuit 210 and an AMOLED panel 220, and the AMOLED panel 220 has a plurality of AMOLED pixel compensation circuits 221, wherein the AMOLED pixel compensation circuit 221 is implemented by the AMOLED pixel compensation circuit 100, and the driving circuit 210 is used to make each AMOLED pixel compensation circuit 221 light up the OLED element according to the aforementioned working sequence.

According to the above description, the present invention further proposes 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 has a central processing unit 310 and an OLED display device 320, wherein the central processing unit 310 is used to communicate with the OLED display device 320, and the OLED display device 320 is implemented by the OLED display device 200.

In addition, the information processing device 300 may 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 in the process of displaying a frame, thereby minimizing the short-term residual effect of the hysteresis voltage of the source-gate parasitic capacitance of the current source transistor on the display image.

2. The AMOLED pixel compensation circuit of the present invention can compensate the threshold voltage of the current source transistor to minimize the display unevenness and Mura phenomenon caused by process deviation and supply voltage drop.

3. The AMOLED pixel compensation circuit of the present invention can extend the voltage holding time of the storage capacitor to support low screen refresh rate.

4. The OLED display device of the present invention can minimize the short-term afterimage of the display screen through the aforementioned AMOLED pixel compensation circuit.

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

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 invention disclosed is one of the preferred embodiments. Any partial changes or modifications that are derived from the technical concept of the invention and are easily inferred by those familiar with the art do not deviate from the scope of the patent right of the invention.

In summary, this case shows that it is very different from the known technology in terms of purpose, means and effect, and it is the first invention that is practical and indeed meets the patent requirements for invention. We sincerely ask the review committee to examine it carefully and grant a patent as soon as possible to benefit the society. This is our utmost prayer.

100:AMOLED pixel compensation circuit

111: First switch

112: Second switch

113: The third switch

114: The fourth switch

115: The fifth switch

120: PMOS transistor

121: First on-time modulation switch

122: Second on-time modulation switch

130: Storage capacitor

140:OLED components

200:OLED display device

210:Drive circuit

220:AMOLED panel

221: AMOLED pixel compensation circuit

300: Information processing device

310: Central processing unit

320:OLED display device

FIG. 1 shows a circuit diagram of an embodiment of the AMOLED pixel compensation circuit of the present invention; FIG. 2a shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of FIG. 1 operating in a first stage. FIG. 2b shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of FIG. 1 operating in a second stage. FIG. 2c shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of FIG. 1 operating in a third stage. FIG. 2d shows an equivalent circuit diagram of the AMOLED pixel compensation circuit of FIG. 1 operating in a fourth stage. FIG. 2e shows a working timing diagram of the AMOLED pixel compensation circuit of FIG. 1. FIG. 3 shows a block diagram of an embodiment of the OLED display device of the present invention. FIG4 is a block diagram showing an embodiment of the information processing device of the present invention.

100:AMOLED pixel compensation circuit

111: First switch

112: Second switch

113: The third switch

114: The fourth switch

115: The fifth switch

120: PMOS transistor

121: First on-time modulation switch

122: Second on-time modulation switch

130: Storage capacitor

140:OLED components

Claims (10)

An AMOLED pixel compensation circuit has a switch circuit, a PMOS transistor, a storage capacitor and an OLED element. The switch circuit is used to execute a switch operation procedure to drive the PMOS transistor to generate a driving current so that the OLED element generates a brightness. The switch operation procedure includes: A first stage: setting the gate voltage of the PMOS transistor and the anode voltage of the OLED element with a first DC voltage; A second stage: setting the source voltage of the PMOS transistor with a second DC voltage so that the difference between the gate voltage and the source voltage of the PMOS transistor is equal to (the first DC voltage - the second DC voltage); A third stage: connecting the PMOS transistor and the storage capacitor in series between a data voltage and a DC supply voltage so that the voltage stored in the storage capacitor is the difference between the DC supply voltage and (the sum of the data voltage and the threshold voltage of the PMOS transistor); and A fourth stage: coupling the two ends of the storage capacitor to the gate and the source of the PMOS transistor respectively to generate the driving current. An AMOLED pixel compensation circuit as described in claim 1, wherein the switch circuit and the PMOS transistor are manufactured by a low temperature polycrystalline oxide process. An AMOLED pixel compensation circuit as described in claim 2, wherein any transistor in the switch circuit is a transistor selected from a 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 switch circuit, a PMOS transistor, a storage capacitor and an OLED element, the switch circuit is used to execute a switch operation procedure to drive the PMOS transistor to generate a drive current so that the OLED element generates a brightness, the switch operation procedure includes: A first stage: setting the gate voltage of the PMOS transistor and the anode voltage of the OLED element with a first DC voltage; A second stage: setting the source voltage of the PMOS transistor with a second DC voltage so that the difference between the gate voltage and the source voltage of the PMOS transistor is equal to (the first DC voltage - the second DC voltage); A third stage: connecting the PMOS transistor and the storage capacitor in series between a data voltage and a DC supply voltage so that the voltage stored in the storage capacitor is the difference between the DC supply voltage and (the sum of the data voltage and the threshold voltage of the PMOS transistor); and A fourth stage: coupling the two ends of the storage capacitor to the gate and the source of the PMOS transistor respectively to generate the driving current. An OLED display device as described in claim 4, wherein the switch circuit and the PMOS transistor are manufactured by a low-temperature polycrystalline oxide process. An OLED display device as described in claim 5, wherein any transistor in the switch circuit is a transistor selected from a 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 switch circuit, a PMOS transistor, a storage capacitor and an OLED element. The switch circuit is used to execute a switch operation procedure to drive the PMOS transistor to generate a drive current so that the OLED element generates a brightness. The switch operation procedure includes: A first stage: setting the gate voltage of the PMOS transistor and the anode voltage of the OLED element with a first DC voltage; A second stage: setting the source voltage of the PMOS transistor with a second DC voltage so that the difference between the gate voltage and the source voltage of the PMOS transistor is equal to (the first DC voltage - the second DC voltage); A third stage: connecting the PMOS transistor and the storage capacitor in series between a data voltage and a DC supply voltage so that the voltage stored in the storage capacitor is the difference between the DC supply voltage and (the sum of the data voltage and the threshold voltage of the PMOS transistor); and A fourth stage: coupling the two ends of the storage capacitor to the gate and the source of the PMOS transistor respectively to generate the driving current. An information processing device as described in claim 7, wherein the switch circuit and the PMOS transistor are manufactured by a low temperature polycrystalline oxide process. An information processing device as described in claim 8, wherein any transistor in the switch circuit is a transistor selected from a group consisting of PMOS transistors, NMOS transistors and CMOS transistors. The information processing device as described in any one of claims 7 to 9 is a device selected from the group consisting of a portable computer, a smart phone and a car computer.

Images