Amoled pixel driver circuit and pixel driving method

Patent metadata

Field	Value
Publication number	US-2018218681-A1
Application number	US-201615328494-A
Country	US
Kind code	A1
Filing date	Dec 16, 2016
Priority date	Sep 9, 2016
Publication date	Aug 2, 2018
Grant date	—

Abstract

The invention discloses an AMOLED pixel driver circuit and pixel driving method, by using a pixel driver circuit of 4T1C or 4T2C structure to effectively compensate threshold voltage of driving TFT in each pixel; through adding a third TFT (T 3 ) and a fourth TFT (T 4 ) and introducing the first scan signal (SEL 1 ) to control the third TFT (T 3 ) and the fourth TFT (T 4 ) to respectively writing the initialization signal (INI) to initialize the gate and the source of the driving TFT in reset phase so as to reduce the complexity of the power supply signal so that the circuit can use DC power supply directly; by adding a second capacitor (C 2 ) to regulate the influence on the source voltage of the driving TFT by the data signal (DATA) so as to reduce the data signal complexity. As a result, the data signal only needs to switch once.

First claim

What is claimed is:

1 . An active matrix organic light-emitting diode (AMOLED) pixel driver circuit, which comprises: a first thin film transistor (TFT), a second TFT, a third TFT, a fourth TFT, a first capacitor, and an organic light-emitting diode (OLED);
the first TFT having the gate connected to a first node, the source connected to a second node and the drain connected to the positive terminal of a direct current (DC) power supply; the second TFT having the gate connected to a second scan signal, the source connected to a data signal and the drain connected to the first node; the third TFT having the gate connected to a first scan signal, the source connected to an initialization signal and the drain connected to the first node; the fourth TFT having the gate connected to the first scan signal, the source connected to the initialization signal and the drain connected to the second node; the first capacitor having one end connected to the first node and the other end connected to the second node; the OLED having the anode connected to the second node and the cathode connected to the negative terminal of the DC power supply; and the initialization signal being a constant low level, and the data signal being a high level pulse.

2 . The AMOLED pixel driver circuit as claimed in claim 1 , wherein the AMOLED pixel driver circuit further comprises a second capacitor, with one end connected to the drain of the first TFT and the positive terminal of the DC power supply, and the other end connected to the source of the first TFT and the second node.

3 . The AMOLED pixel driver circuit as claimed in claim 1 , wherein the first TFT, the second TFT, the third TFT and the fourth TFT are all low temperature polysilicon (LTPS) TFTs, oxide semiconductor TFTs or amorphous silicon (a-Si) TFTs.

4 . The AMOLED pixel driver circuit as claimed in claim 1 , wherein the first scan signal, the second scan signal, the initialization signal and the data signal are all generated by an external timing controller.

5 . The AMOLED pixel driver circuit as claimed in claim 1 , wherein the first scan signal, the second scan signal and the data signal are combined to correspond in series to a reset phase, a threshold voltage detection phase, a threshold voltage compensation phase and a light-emitting phase;
in the reset phase, the first scan signal is high level, the second scan signal is low level, and the data signal is a reference low level; in the threshold voltage detection phase, the first scan signal is low level, the second scan signal is high level, and the data signal is the reference low level; in the threshold voltage compensation phase, the first scan signal is low level, the second scan signal is high level, and the data signal is a display data signal high level; and in the light-emitting phase, the first scan signal is low level, the second scan signal is low level, and the data signal is the reference low level.

6 . An active matrix organic light-emitting diode (AMOLED) pixel driving method, which comprises:
Step 1: providing an AMOLED pixel driver circuit, comprising: a first thin film transistor (TFT), a second TFT, a third TFT, a fourth TFT, a first capacitor, and an organic light-emitting diode (OLED); the first TFT having the gate connected to a first node, the source connected to a second node and the drain connected to the positive terminal of a direct current (DC) power supply; the second TFT having the gate connected to a second scan signal, the source connected to a data signal and the drain connected to the first node; the third TFT having the gate connected to a first scan signal, the source connected to an initialization signal and the drain connected to the first node; the fourth TFT having the gate connected to the first scan signal, the source connected to the initialization signal and the drain connected to the second node; the first capacitor having one end connected to the first node and the other end connected to the second node; the OLED having the anode connected to the second node and the cathode connected to the negative terminal of the DC power supply; and the initialization signal being a constant low level; Step 2: entering reset phase: the first scan signal providing high level, the second scan signal providing low level, the data signal providing a reference low level Vref, the second TFT cut off, the third TFT and the fourth TFT turned on, an initialization signal being written into the first node (i.e., the gate of the first TFT), an initialization signal being written into the second node (i.e., the source of the first TFT), and the first TFT cut off; Step 3: entering threshold voltage detection phase: the first scan signal transiting to low level, the second scan signal transiting to high level, and the data signal remaining the reference low level, the third TFT and the fourth TFT cut off, the second TFT turned on, the reference low level of the data signal being written into the first node (i.e., the gate of the first TFT), the second node (i.e., the source of the first TFT) changed to Vref−Vth, wherein Vth being threshold voltage of the first TFT; Step 4: entering threshold voltage compensation phase: the first scan signal first remaining low level, the second scan signal remaining high level, the data signal transiting to a display data signal high level, the third TFT and the fourth TFT cut off, the second TFT turned on, the data signal writing the display data signal high level via the second TFT into the first node (i.e., the gate of the first TFT) and the first capacitor, the second node (i.e., the source of the first TFT) transiting to Vref−Vth+ΔV, wherein ΔV being influence on the source voltage of the first TFT (i.e., the second node) caused by the display data signal high level voltage; and Step 5: entering light-emitting phase: the first scan signal remaining low level, the second scan signal transiting to low level, and the data signal voltage transiting to low level, the second TFT cut off, the second, third and fourth TFTs cut off, voltage difference between the first node (i.e., the gate of the first TFT) and the second node (i.e., the source of the first TFT) remaining unchanged due to storage effect of the first capacitor; the OLED emitting light and current flowing through the OLED independent of the threshold voltage of the first TFT.

7 . The AMOLED pixel driving method as claimed in claim 6 , the AMOLED pixel driver circuit provided in Step 1 further comprises a second capacitor, with one end connected to the drain of the first TFT and the positive terminal of the DC power supply, and the other end connected to the source of the first TFT and the second node.

8 . The AMOLED pixel driving method as claimed in claim 6 , wherein if the AMOLED pixel driver circuit provided in Step 1 does not comprise a second capacitor, the influence on the source voltage ΔV of the first TFT (i.e., the second node) caused by the display data signal high level voltage is:
Δ V =( V data− V ref)×( C 1/( C 1+ C OLED )),

wherein C OLED is the intrinsic capacitance of the OLED.

9 . The AMOLED pixel driving method as claimed in claim 6 , wherein if the AMOLED pixel driver circuit provided in Step 1 comprises a second capacitor, the influence on the source voltage ΔV of the first TFT (i.e., the second node) caused by the display data signal high level voltage is:
Δ V =( V data− V ref)×( C 1/( C 1+ C 2+ C OLED )),

wherein C OLED is the intrinsic capacitance of the OLED.

10 . The AMOLED pixel driving method as claimed in claim 6 , wherein the first TFT, the second TFT, the third TFT and the fourth TFT are all low temperature polys

Assignees

• Shenzhen China Star Optoelect

Inventors

• Cai Yuying

Classifications

• G09G3/3258 Primary

  with pixel circuitry controlling the voltage across the light-emitting element · CPC title

• G09G3/3275

  Details of drivers for data electrodes · CPC title

• G09G3/3266 Primary

  Details of drivers for scan electrodes · CPC title

• H01L27/3265

  Electricity · mapped topic

• H01L27/3276

  Electricity · mapped topic