System and methods for extraction of threshold and mobility parameters in AMOLED displays

• US 9,799,248 B2
• Filed: 01/31/2017
• Issued: 10/24/2017
• Est. Priority Date: 05/20/2011
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza, Azizi, Yaser
• Primary Examiner(s): LEE, NICHOLAS J
• Application Number:
  US15/420,503
• Publication Number:
  US 20170140687A1
• Time in Patent Office: 266 Days
• Field of Search: None
• CPC Class Codes: G01R 19/0092 measuring current only all subgroups of G01R19/00 take precedence
• CPC Class Codes: G09G 2300/043 Compensation electrodes or other additional electrodes in matrix displays related to distortions or compensation signals, e.g. for modifying TFT threshold voltage in column driver
• CPC Class Codes: G09G 2300/0465 Improved aperture ratio, e.g. by size reduction of the pixel circuit, e.g. for improving the pixel density or the maximum displayable luminance or brightness
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2300/0842 forming a memory circuit, e.g. a dynamic memory with one capacitor
• CPC Class Codes: G09G 2300/0866 by means of changes in the pixel supply voltage
• CPC Class Codes: G09G 2310/0251 Precharge or discharge of pixel before applying new pixel voltage
• CPC Class Codes: G09G 2310/0291 Details of output amplifiers or buffers arranged for use in a driving circuit
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/029 by monitoring one or more pixels in the display panel, e.g. by monitoring a fixed reference pixel
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• CPC Class Codes: G09G 2330/028 Generation of voltages supplied to electrode drivers in a matrix display other than LCD
• CPC Class Codes: G09G 3/006 Electronic inspection or testing of displays and display drivers, e.g. of LED or LCD displays testing individual LED's G01R31/2635; testing lamps G01R31/44; testing of optical features of LCD displays G02F1/1309
• CPC Class Codes: G09G 3/3233 with pixel circuitry controlling the current through the light-emitting element
• CPC Class Codes: G09G 3/3258 with pixel circuitry controlling the voltage across the light-emitting element
• CPC Class Codes: G09G 3/3266 Details of drivers for scan electrodes
• CPC Class Codes: G09G 3/3291 in which the data driver supplies a variable data voltage for setting the current through, or the voltage across, the light-emitting elements
• CPC Class Codes: H03F 3/2171 : with field-effect devices H03F3/2173 - H03F3/2178 take precedence

Abstract

A system to improve the extraction of transistor and OLED parameters in an AMOLED display includes a pixel circuit having an organic light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input to provide the programming signal, and a storage device to store the programming signal. A charge-pump amplifier has a current input and a voltage output. The charge-pump amplifier includes an operational amplifier in negative feedback configuration. The feedback is provided by a capacitor connected between the output and the inverting input of the operational amplifier. A common-mode voltage source drives the non-inverting input of the operational amplifier. An electronic switch is coupled across the capacitor to reset the capacitor. A switch module including the input is coupled to the output of the pixel circuit and an output is coupled to the input of the charge-pump amplifier.

Claims

1. A data extraction system for an organic light emitting device (OLED) based display, the system comprising:

a pixel circuit including an organic light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input to provide a programming signal, and a storage device to store the programming signal;

a charge-pump amplifier having a current input and a voltage output, the charge-pump amplifier including an operational amplifier in negative feedback configuration, wherein the feedback is provided by a capacitor connected between the output and the inverting input of the operational amplifier, a common-mode voltage source to drive the non-inverting input of the operational amplifier, and an electronic switch coupled across the capacitor to reset the capacitor;

a switch module including an input coupled to the output of the pixel circuit and an output coupled to the input of the charge-pump amplifier; and

a controller coupled to the pixel circuit, charge-pump amplifier and the switch module, the controller controlling input signals to the pixel circuit, charge-pump amplifier and switch module in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including providing a program voltage to the programming input to pre-charge an internal capacitance of the pixel circuit to a charge level and transfer the charge to the charge-pump amplifier via the switch module to generate the output voltage value.

2. A data extraction system for an organic light emitting device (OLED) based display, the system comprising:

a pixel circuit including an organic light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input to provide a programming signal, and a storage device to store the programming signal;

a charge-pump amplifier having a current input and a voltage output, the charge-pump amplifier including an operational amplifier in negative feedback configuration, wherein the feedback is provided by a capacitor connected between the output and the inverting input of the operational amplifier, a common-mode voltage source to drive the non-inverting input of the operational amplifier, and an electronic switch coupled across the capacitor to reset the capacitor;

a switch module including an input coupled to the output of the pixel circuit and an output coupled to the input of the charge-pump amplifier and

a controller coupled to the pixel circuit, charge-pump amplifier and the switch module, the controller controlling input signals to the pixel circuit, charge-pump amplifier and switch module in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including providing a program voltage to the programming input to provide a current from the pixel circuit to the charge-pump amplifier via the switch module to produce the output voltage value by integration over a certain period of time.

3. A data extraction system for an organic light emitting device (OLED) based display, the system comprising:

a pixel circuit including a drive transistor, an organic light emitting device, and a programming input coupled to the gate of the drive transistor, the drive transistor having a source or a drain coupled to the OLED;

a charge-pump amplifier having an input and an integrated voltage output;

a switch module including an input coupled to the output of the pixel circuit and an output coupled to the input of the charge-pump amplifier, the switch module including switches to steer current in and out of the pixel circuit, provide a discharge path between the pixel circuit and the charge-pump amplifier and isolate the charge-pump amplifier from the pixel circuit; and

a controller coupled to the pixel circuit, charge-pump amplifier and the switch module, the controller controlling voltage inputs to the pixel circuit, charge-pump amplifier and switch module in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including providing a program voltage to the programming input to pre-charge a capacitance of the pixel circuit to a charge level and transfer the charge to the charge-pump amplifier via the switch module to generate the output voltage value.

4. A data extraction system for an organic light emitting device (OLED) based display, the system comprising:

a pixel circuit including a drive transistor, an organic light emitting device, and a programming input coupled to the gate of the drive transistor, the drive transistor having a source or a drain coupled to the OLED;

a charge-pump amplifier having an input and an integrated voltage output;

a switch module including an input coupled to the output of the pixel circuit and an output coupled to the input of the charge-pump amplifier, the switch module including switches to steer current in and out of the pixel circuit, provide a discharge path between the pixel circuit and the charge-pump amplifier and isolate the charge-pump amplifier from the pixel circuit; and

a controller coupled to the pixel circuit, charge-pump amplifier and the switch module, the controller controlling voltage inputs to the pixel circuit, charge-pump amplifier and switch module in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including providing a program voltage to the programming input to provide a current from the pixel circuit to the charge-pump amplifier via the switch module to produce the output voltage value by integration.

5. A method of extracting data from a pixel circuit including an organic light emitting device, a drive transistor to provide a programmable drive current to the light emitting device, a programming input to receive a programming signal, and a storage device to store the programming signal, the method comprising:

controlling input signals to the pixel circuit, a charge-pump amplifier having a current input and a voltage output, and a switch module including an input coupled to the output of the pixel circuit and an output coupled to the input of the charge-pump amplifier; and

providing a program voltage to the programming input to either;

pre-charge an internal capacitance of the pixel circuit to a charge level and transfer the charge to the charge-pump amplifier via the switch module to generate the output voltage value;

or

provide a current from the pixel circuit to the charge-pump amplifier via the switch module to produce the output voltage value by integration over a certain period of time, the program voltage provided to the programming input and the input signals comprising a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit.

6. The method of claim 5, further comprising:

allowing the stored charge of the internal capacitance to discharge through the switch module to the charge-pump amplifier until the gate-to-source drive-voltage of the drive transistor is equal to its threshold voltage,

wherein the parameter is the threshold voltage of the drive transistor, the internal capacitance of the pixel is pre-charged to a level that does not turn the OLED on, and the charge-pump amplifier'"'"'s output voltage value is a function of the threshold voltage, feedback capacitor, the OLED capacitance, and the programming input voltage.

7. The method of claim 5, further comprising:

allowing the stored charge of the internal capacitance to partially discharge through the switch module to the charge-pump amplifier over an integration time shorter than a substantially complete discharge time for the stored charge,

wherein the parameter is the mobility of the drive transistor, the internal capacitance of the pixel is pre-charged to a level that does not turn the OLED on, and the charge-pump amplifier'"'"'s output voltage value is a function of the drive transistor'"'"'s mobility, integration time, feedback capacitor, and the programming input voltage.

8. The method of claim 5, further comprising:

discharging the charge on the OLED capacitance through the OLED until it reaches the turn-on voltage of the OLED; and

transferring the remaining charge on the OLED capacitance through the switch module to the charge-pump amplifier,

wherein the parameter is the turn-on voltage of the OLED, the OLED capacitance is pre-charged to a level higher than the turn-on voltage of the OLED, and the amplifier output is a value of the turn-on voltage of the OLED as a function of the amplifier'"'"'s feedback capacitance and the OLED capacitance.

9. The method of claim 5, further comprising:

setting the program voltage to a proper level to turn the drive transistor on; and

steering the current of the drive transistor through the switch module into the charge-pump amplifier to be directly integrated for a certain amount of time,

wherein the parameters are the threshold voltage and mobility of the drive transistor and the amplifier output is a value of the threshold voltage and mobility as a function of the amplifier'"'"'s feedback capacitor, length of integration time, and the program voltage.

10. The system of claim 5, further comprising:

setting the program voltage to a proper level to operate the drive transistor as a switch; and

steering the current of the OLED through the switch module into the charge-pump amplifier to be directly integrated for a certain amount of time,

wherein the parameter is the turn-on voltage of the OLED and the amplifier output is a value of the OLED'"'"'s turn-on voltage as function of the amplifier'"'"'s feedback capacitor, length of integration time, and the common-mode voltage set at the non-inverting input of the amplifier.