SYSTEM AND METHODS FOR EXTRACTION OF THRESHOLD AND MOBILITY PARAMETERS IN AMOLED DISPLAYS

• US 20140084932A1
• Filed: 12/02/2013
• Published: 03/27/2014
• Est. Priority Date: 05/20/2011
• Status: Active Grant

• Current Assignee: IGNIS Innovation Incorporated
• Original Assignee: IGNIS Innovation Incorporated
• Inventors: Chaji, Gholamreza, Azizi, Yaser, Ngan, Ricky Yik Hei, Zahirovic, Nino
• Granted Patent: US 9,799,246 B2
• Time in Patent Office: Days
• US Class Current: 324/414
• CPC Class Codes: G09G 2230/00 Details of flat display driving waveforms
• 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 2300/0819 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 2300/0861 with additional control of the display period without amending the charge stored in a pixel memory, e.g. by means of additional select electrodes
• CPC Class Codes: G09G 2310/0248 Precharge or discharge of column electrodes before or after applying exact column voltages
• CPC Class Codes: G09G 2310/0289 Details of voltage level shifters arranged for use in a driving circuit
• CPC Class Codes: G09G 2310/0291 Details of output amplifiers or buffers arranged for use in a driving circuit
• 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 2320/043 Preventing or counteracting the effects of ageing
• CPC Class Codes: G09G 2330/12 Test circuits or failure detection circuits included in a display system, as permanent part thereof
• 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

Abstract

A system reads a desired circuit parameter from a pixel circuit that includes a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal. One embodiment of the extraction system turns off the drive device and supplies a predetermined voltage from an external source to the light emitting device, discharges the light emitting device until the light emitting device turns off, and then reads the voltage on the light emitting device while that device is turned off. The voltages on the light emitting devices in a plurality of pixel circuits may be read via the same external line, at different times.

Claims

1. A method of extracting a circuit parameter from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the method comprising:

turning on the drive device so that the voltage of the light emitting device rises to a level higher than its turn-on voltage,

turning off the drive device so that the voltage on the light emitting device is discharged through the light emitting device until the light emitting device turns off, and

reading the voltage on the light emitting device while that device is turned off.

2. A method of extracting a circuit parameter from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the method comprising:

programming the pixel circuit,

turning on the drive device, and

extracting a parameter of the drive device by either

reading the current passing through the drive device while applying a predetermined voltage to the drive device, or

reading the voltage on the drive device while passing a predetermined current through the drive device.

3. A method of extracting a circuit parameter from a pixel circuit including a light emitting device, a drive transistor having gate, source and drain terminals to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the method comprising:

turning on the drive device and measuring the current and voltage of the drive transistor while changing the voltage between the gate and the source or drain of the drive transistor to operate the drive transistor in the linear regime during one time interval and in the saturated regime during a second time interval, and

extracting a parameter of the light emitting device from the relationship of the currents and voltages measured with the drive transistor operating in the two regimes.

4. A system for extracting a circuit parameter from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the system comprising

a controller coupled to the pixel circuit and supplying controlling input signals to the pixel circuit in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including

turning off the drive device and supplying a predetermined voltage from an external source to said light emitting device,

discharging said light emitting device until the light emitting device turns off, and

reading the voltage on the light emitting device while that device is turned off.

5. The system of claim 4 which includes a plurality of pixel circuits coupled to said external source via a common external line, and said reading of voltage on the light emitting devices in said plurality of pixel circuits is effected via said common external line at different times.

6. The system of claim 5 which includes

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;

and

a switch module including the 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 a plurality of electronic 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.

7. A system for extracting a circuit parameter from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the system comprising:

a controller coupled to the pixel circuit and supplying controlling input signals to the pixel circuit in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including

turning on the drive device so that the voltage of the light emitting device rises to a level higher than its turn-on voltage,

turning off the drive device so that the voltage on the light emitting device is discharged through the light emitting device until the light emitting device turns off, and

reading the voltage on the light emitting device while that device is turned off.

8. A system for extracting a circuit parameter from a pixel circuit including a light emitting device, a drive device to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the system comprising:

a controller coupled to the pixel circuit and supplying controlling input signals to the pixel circuit in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including

programming the pixel circuit,

turning on the drive device, and

extracting a parameter of the drive device by either

reading the current passing through the drive device while applying a predetermined voltage to the drive device, or

reading the voltage on the drive device while passing a predetermined current through the drive device.

9. A system for extracting a circuit parameter from a pixel circuit including a light emitting device, a drive transistor having gate, source and drain terminals to provide a programmable drive current to the light emitting device, a programming input, and a storage device to store a programming signal, the system comprising:

a controller coupled to the pixel circuit and supplying controlling input signals to the pixel circuit in a predetermined sequence to produce an output voltage value which is a function of a parameter of the pixel circuit, the sequence including

turning on the drive device and measuring the current and voltage of the drive transistor while changing the voltage between the gate and the source or drain of the drive transistor to operate the drive transistor in the linear regime during one time interval and in the saturated regime during a second time interval, and

extracting a parameter of the light emitting device from the relationship of the currents and voltages measured with the drive transistor operating in the two regimes.

10. A method of extracting a parameter value from a pixel circuit including

a light emitting device,

an electrical power source for supplying electrical power to the light emitting device,

a drive transistor controllably coupling the power source to the light emitting device for supplying a controllable electrical current to the light emitting device, said drive transistor having a gate terminal, a source terminal and a drain terminal,

a first switching transistor controllably coupling a first signal line to the gate terminal of the drive transistor,

a second switching transistor for controllably coupling a second signal line to one of the source and drain terminals of the drive transistor, the other of the source and drain terminals connected to the light emitting device,

a third switching transistor or controllably coupling said power source to the terminal of the drive transistor that is coupled to the second switching transistor, and

a capacitor coupled between the gate terminal of the drive transistor and the terminal of the drive transistor that is coupled to the second switching transistor,

said method comprising:

supplying a reference voltage to said second signal line and turning on the second switching transistor to supply said reference voltage to the gate terminal of the drive transistor that is coupled to said second switching transistor,

supplying a programming voltage to said first signal line and turning on the first switching transistor to supply said programming voltage to the terminal of the drive transistor that is coupled to said second switching transistor,

turning off the second switching transistor so that the voltage at the terminal of the drive transistor that is coupled to said second switching transistor is adjusted by the charge on the capacitor, and

turning off the first switching transistor and turning on the third switching transistor to connect the power source to the drive transistor so that current flows from the power source to the light emitting device through the drive transistor, the magnitude of said current being controlled by the voltage applied to the gate terminal of the drive transistor by the capacitor.

11. A method of extracting a parameter value from a pixel circuit including a light emitting device,

an electrical power source for supplying electrical power to the light emitting device,

a drive transistor controllably coupling the power source to the light emitting device for supplying a controllable electrical current to the light emitting device, said drive transistor having a gate terminal, a source terminal and a drain terminal,

a first switching transistor controllably coupling a first signal line to the gate terminal of the drive transistor,

a second switching transistor for controllably coupling a second signal line to one of the source and drain terminals of the drive transistor, the other of the source and drain terminals connected to the light emitting device,

a third switching transistor or controllably coupling said power source to the terminal of the drive transistor that is coupled to the second switching transistor, and

a capacitor coupled between the gate terminal of the drive transistor and the terminal of the drive transistor that is coupled to the second switching transistor,

said method comprising:

supplying a reference voltage to said first signal line and turning on the first switching transistor to supply said reference voltage to the capacitor,

supplying a programming voltage to said second signal line and turning on the second switching transistor to supply said programming voltage to the terminal of the drive transistor that is coupled to the second switching transistor,

turning off the second switching transistor so that the voltage at the terminal of the drive transistor that is coupled to said second switching transistor is adjusted by the charge on the capacitor, and

turning off the first switching transistor and turning on the third switching transistor to connect the power source to the drive transistor so that current flows from the power source to the light emitting device through the drive transistor, the magnitude of said current being controlled by the voltage applied to the gate terminal of the drive transistor by the capacitor.

12. A method of extracting a parameter value from a pixel circuit including a light emitting device,

an electrical power source for supplying electrical power to the light emitting device,

a drive transistor controllably coupling the power source to the light emitting device for supplying a controllable electrical current to the light emitting device, said drive transistor having a gate terminal, a source terminal and a drain terminal,

a first switching transistor controllably coupling a first signal line to the gate terminal of the drive transistor,

a second switching transistor for controllably coupling a second signal line to one of the source and drain terminals of the drive transistor, the other of the source and drain terminals connected to the light emitting device,

a third switching transistor or controllably coupling said power source to the terminal of the drive transistor that is coupled to the second switching transistor, and

a capacitor coupled between the gate terminal of the drive transistor and the terminal of the drive transistor that is coupled to the second switching transistor,

said method comprising:

supplying a reference voltage to said second signal line and turning on the second switching transistor to supply said reference voltage to the gate terminal of the drive transistor that is coupled to said second switching transistor,

supplying a programming voltage to said first signal line and turning on the first switching transistor to supply said programming voltage to the capacitor,

turning off the second switching transistor so that the voltage at the terminal of the drive transistor that is coupled to said second switching transistor is adjusted by the charge on the capacitor,

discharging the capacitor for a preselected time period,

turning on the third switching transistor and turning on the third switching transistor, and

reading the current flowing through the drive transistor to the light emitting device.

13. A method of extracting a parameter value from a pixel circuit including a light emitting device,

an electrical power source for supplying electrical power to the light emitting device,

a drive transistor controllably coupling the power source to the light emitting device for supplying a controllable electrical current to the light emitting device, said drive transistor having a gate terminal, a source terminal and a drain terminal,

a first switching transistor controllably coupling a first signal line to the gate terminal of the drive transistor,

a second switching transistor for controllably coupling a second signal line to one of the source and drain terminals of the drive transistor, the other of the source and drain terminals connected to the light emitting device,

a third switching transistor or controllably coupling said power source to the terminal of the drive transistor that is coupled to the second switching transistor, and

a capacitor coupled between the gate terminal of the drive transistor and the terminal of the drive transistor that is coupled to the second switching transistor,

said method comprising:

supplying a reference voltage to said second signal line and turning on the second switching transistor to supply said reference voltage to the gate terminal of the drive transistor that is coupled to said second switching transistor,

supplying a programming voltage to said first signal line and turning on the first switching transistor to supply said programming voltage to the capacitor,

turning off the second switching transistor so that the voltage at the terminal of the drive transistor that is coupled to said second switching transistor is adjusted by the charge on the capacitor,

discharging the capacitor for a preselected time period, and

reading the voltage across the light emitting device via the drive transistor and the second switching transistor.