Systems and methods for indirect threshold voltage sensing in an electronic display

• US 10,573,209 B2
• Filed: 09/22/2016
• Issued: 02/25/2020
• Est. Priority Date: 10/09/2015
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Bi, Yafei, Wang, Xiaofeng, Li, Haifeng, Vahid Far, Mohammad B., Bae, Hopil, Lin, Hung Shen, Nho, Hyunwoo, Yao, Wei H.
• Primary Examiner(s): Sitta, Grant
• Application Number:
  US15/273,444
• Publication Number:
  US 20170103702A1
• Time in Patent Office: 1,251 Days
• CPC Class Codes: G09G 2300/0809 Several active elements per pixel in active matrix panels
• CPC Class Codes: G09G 2300/0814 used for selection purposes, e.g. logical AND for partial update
• CPC Class Codes: G09G 2300/0819 used for counteracting undesired variations, e.g. feedback or autozeroing
• CPC Class Codes: G09G 2310/0202 Addressing of scan or signal lines
• CPC Class Codes: G09G 2310/0291 Details of output amplifiers or buffers arranged for use in a driving circuit
• CPC Class Codes: G09G 2310/061 for resetting or blanking
• CPC Class Codes: G09G 2320/0233 Improving the luminance or brightness uniformity across the screen
• CPC Class Codes: G09G 2320/0295 by monitoring each display pixel
• CPC Class Codes: G09G 2320/045 Compensation of drifts in the characteristics of light emitting or modulating elements
• 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
• 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

Abstract

An electronic device includes a display panel with pixels arranged in at least one row and at least one column. The electronic device also includes a sensing channel coupled to the at least one column. The sensing channel indirectly calculates a threshold voltage of the plurality of pixels based on an application of a first current level and a second current level to a data line of a first column of the at least one column of the pixels.

Claims

1. An electronic device, comprising:

a display panel comprising a plurality of pixels arranged in at least one row and at least one column, wherein each pixel comprises a storage capacitor;

a sensing amplifier comprising a capacitance; and

a sensing channel coupled to the at least one column configured to indirectly calculate a threshold voltage of each of the plurality of pixels based on an application of a first current level and a second current level to a data line of a first column of the at least one column of the plurality of pixels, wherein the sensing amplifier receives from the sensing channel the first current level and the second current level, and wherein the threshold voltage is calculated using;

a first voltage and a second voltage of the storage capacitor corresponding to each of the plurality of pixels after providing the first current level and the second current level, respectively; and

a first voltage and a second voltage of the sensing amplifier associated with the first current level and the second current level, respectively such that the capacitance is cancelled out in calculation of the threshold voltage such that additional cancellation circuitry is not used.

2. The electronic device of claim 1, wherein the sensing channel is included within a source driver of the electronic device.

3. The electronic device of claim 1, comprising a plurality of sensing channels, wherein each of the plurality of sensing channels corresponds to a particular column of the at least one column of the plurality of pixels and is separate from others of the plurality of sensing channels.

4. The electronic device of claim 1, comprising:

a data voltage source amplified by a first amplifier within a gate driver of the electronic device; and

an initialization voltage source amplified by a second amplifier within a source driver integrated circuit (IC) of the electronic device.

5. The electronic device of claim 1, wherein the sensing channel comprises the sensing amplifier and the capacitance is configured as an integrating capacitor;

and

wherein the sensing amplifier and the integrating capacitor function together as an amplifier integrator capable of producing a signal representative of a current coming from at least one of the plurality of pixels.

6. The electronic device of claim 5, wherein the sensing channel comprises a plurality of switches that, upon being set a first configuration, cause a reset of the integrating capacitor.

7. The electronic device of claim 6, wherein an initialization voltage source, a pixel current, a panel current leakage, or any combination thereof is provided to a negative terminal of the sensing amplifier when one of the plurality of switches is closed.

8. The electronic device of claim 7, wherein a comparison voltage (Vcm) is provided to a positive terminal of the sensing amplifier.

9. The electronic device of claim 8, wherein an output of the sensing amplifier (Vsa) is provided to compensation circuitry of the electronic device, such that the compensation circuitry may compensate for the panel current leakage that is provided to the negative terminal of the sensing amplifier.

10. A computer-implemented method for calculating a threshold voltage (V_th) of a unit pixel of a system, comprising:

applying a first current on a data line at a first level from a sensing channel;

reading a first voltage output from a sensing amplifier and a first voltage of a storage capacitor for the first current at the first level;

applying a second current on the data line at a second level;

reading a second voltage output from the sensing amplifier and a second voltage of the storage capacitor of the unit pixel for the second current at the second level; and

calculating the threshold voltage based at least in part on the first voltage output from the sensing amplifier, the first voltage of the storage capacitor, the second voltage output from the sensing amplifier, and the second voltage of the storage capacitor such that a capacitance of the sensing channel is cancelled out and additional cancellation circuitry is not needed to calculate the threshold voltage.

11. The computer-implemented method of claim 10, wherein the first current on the data line at the first level is provided from a compensating current source of the sensing channel within an electronic device.

12. The computer-implemented method of claim 10, wherein the first voltage output is related to the threshold voltage according to:

V_SA1=T/C_fβ

(V_gs1−

V_th)²; and

wherein V_SA1 is the first voltage output for the first current, T is a temperature of the system, C_f is a capacitance of an integrating capacitor, β

is a constant, V_gs1 is the first voltage at the storage capacitor of the unit pixel during application of the first current at the first level, and V_th is the threshold voltage.

13. The computer-implemented method of claim 12, wherein the second voltage output is related to the threshold voltage according to:

V_SA2=T/C_fβ

(V_gs2−

V_th)²; and

wherein V_SA2 is the second voltage output for the second current, T is the temperature of the system, C_f is the capacitance of the integrating capacitor, β

is the constant, V_gs2 is the second voltage at the storage capacitor of the unit pixel during application of the second current at the second level, and V_th is the threshold voltage.

14. The computer-implemented method of claim 13, comprising calculating V_th in accordance with an equation:

15. The computer-implemented method of claim 10, wherein the second current at the second level is within 5%-15% higher or lower than the first current at the first level.

16. The computer-implemented method of claim 10, comprising calibrating an entire column of unit pixels based upon the threshold voltage.

17. A computer-implemented method to calculate a threshold voltage (V_th) of a unit pixel, comprising:

programming an integrating capacitor and a line capacitor, by discharging the integrating capacitor and charging the line capacitor to a voltage equal to a voltage of an initialization voltage source;

sensing a display panel leakage current of the unit pixel;

providing the display panel leakage current to compensation circuitry via a sensing amplifier;

re-programming the integrating capacitor and the line capacitor;

sensing a pixel current of the unit pixel and the display panel leakage current;

determining the threshold voltage based upon the sensed pixel current and the display panel leakage current, wherein through using the sensed pixel current and the display panel leakage current, the line capacitor is cancelled out such that additional cancellation circuitry is not needed in calculating the threshold voltage; and

calibrating a channel of associated unit pixels, based upon the threshold voltage.

18. The computer-implemented method of claim 17, comprising providing sensing values to an analog to digital controller, resulting in a digital output.

19. The computer-implemented method of claim 18, comprising calibrating the channel using the digital output.

20. The computer-implemented method of claim 17, comprising:

re-programming the integrating capacitor and the line capacitor a second time;

sensing a second pixel current and the display panel leakage current; and

determining the threshold voltage based upon the sensed pixel current, the second pixel current, and the display panel leakage current.