Differential VCOM Resistance or Capacitance Tuning for Improved Image Quality

• US 20130328952A1
• Filed: 08/31/2012
• Published: 12/12/2013
• Est. Priority Date: 06/08/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Bae, Hopil
• Granted Patent: US 8,941,640 B2
• Time in Patent Office: Days
• US Class Current: 345/698
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G09G 2320/0219 Reducing feedthrough effects in active matrix panels, i.e. voltage changes on the scan electrode influencing the pixel voltage due to capacitive coupling
• CPC Class Codes: G09G 2320/0223 Compensation for problems related to R-C delay and attenuation in electrodes of matrix panels, e.g. in gate electrodes or on-substrate video signal electrodes
• 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 3/3655 Details of drivers for counter electrodes, e.g. common electrodes for pixel capacitors or supplementary storage capacitors

Abstract

Devices and methods for reducing a variation in voltage perturbation between common voltage layers (VCOMs) of a display in response to voltage interference are provided. In one example, a resistive element may be coupled to one of several VCOMs to increase the resistance value of the VCOM. The resistive element may cause a variation in voltage perturbations between the several VCOMs to become generally more uniform, thereby reducing or eliminating certain image artifacts.

Claims

1. An electronic display comprising:

a first pixel comprising a first common voltage layer (VCOM), wherein the first VCOM is configured to experience a first voltage perturbation in response to a pixel deactivation signal;

a second pixel comprising a second VCOM, wherein the second VCOM is configured to experience a second voltage perturbation in response to the pixel deactivation signal; and

a resistive device configured to be coupled to the first VCOM during at least a display phase of the electronic display, wherein the resistive device is configured to add resistance to the first VCOM so as to cause the first voltage perturbation to substantially match the second voltage perturbation, thereby reducing or eliminating image artifacts due to differences in VCOM voltage perturbation.

2. The electronic display of claim 1, wherein the resistive device comprises a resistor of constant value to add the resistance to the first VCOM.

3. The electronic display of claim 1, wherein the resistive device comprises a variable resistance configured to be tuned to the resistance added to the first VCOM.

4. The electronic display of claim 1, wherein the first VCOM is generally formed in a column perpendicular to a gate line configured to supply the pixel deactivation signal.

5. The electronic display of claim 1, wherein the second VCOM is electrically coupled to, but not physically contiguous with, at least one other VCOM, wherein the at least one other VCOM and the second VCOM are generally formed in a row parallel to a gate line configured to supply the pixel deactivation signal.

6. The electronic display of claim 1, wherein the first VCOM and the second VCOM are configured to have different parasitic capacitances with a gate line configured to supply the pixel deactivation signal.

7. An electronic device comprising:

a processor configured to generate an image signal, wherein the image signal comprises first and second data signals configured to cause two pixels to emit about the same amount of light; and

an electronic display configured to display the image signal, wherein the electronic display comprises;

a first pixel comprising a first common voltage layer (VCOM) that receives voltage from a first VCOM voltage supply through a discrete resistive element, capacitive element, or both, wherein the first pixel is configured to emit a first amount of light when programmed with the first data signal; and

a second pixel comprising a second VCOM receiving voltage from a second VCOM voltage supply, wherein the second pixel is configured to emit a second amount of light when programmed with the second data signal;

wherein the resistive element, the capacitive element, or both are configured to add to the resistance, capacitance, or both, of the first VCOM to cause a first transient voltage dissipation time associated with the first VCOM to substantially match a second transient voltage dissipation time associated with a second VCOM, such that the first amount of light and the second amount of light are about the same.

8. The electronic device of claim 7, wherein the resistive element, the capacitive element, or both, are configured to be applied while the electronic display is operating in a first state but not a second state.

9. The electronic device of claim 8, wherein the first state is a display phase of operation, during which the electronic display is configured to program the image signal onto the pixels of the display, and the second state is a touch phase of operation, during which the electronic display is configured to sense touches.

10. The electronic device of claim 7, wherein the first transient voltage dissipation associated with the first VCOM and the second transient voltage associated with the second VCOM are configured to occur when the first and second pixels are supplied a deactivation signal.

11. An electronic display comprising:

a plurality of pixels configured to emit light when provided with , some of the pixels being associated with a first common voltage layer (VCOM) and some of pixels being associated with a second VCOM; and

a resistive element, a capacitive element, or both, coupled to the first VCOM and configured to add to the resistance, the capacitance, or both of the first VCOM to increase a rise time of a transient voltage response of the first VCOM, wherein the resistive element, the capacitive element, or both are configured to cause the plurality of pixels to emit substantially the same amount of light when provided the same data signals.

12. The electronic display of claim 11, wherein the first VCOM and the second VCOM are configured to experience transient voltage responses, wherein the resistive element, the capacitive element, or both are configured to cause a voltage difference programmed in the plurality of pixels to be approximately the same as of a time when the pixels are deactivated when provided the same data signals.

13. A method comprising:

coupling a resistive element to a first common voltage layer (VCOM) associated with a first set of pixels in an electronic display when the electronic display is in a first state; and

decoupling the resistive element from the first VCOM when the electronic display is in a second state.

14. The method of claim 13, wherein the resistive element is coupled and decoupled to the first VCOM using a resistance controller configured to switch between a resistive path comprising the resistive element and a non-resistive path lacking the resistive element.

15. The method of claim 13, wherein the first state comprises a display mode of operation and the second state comprises a touch mode of operation.

16. The method of claim 13, wherein the first VCOM is coupled to the resistive element such that a first transient voltage response time of the first VCOM substantially matches a second transient voltage response time of a second VCOM not coupled to the resistive element.

17. A method, comprising:

monitoring an electronic display for visual artifacts in response to TFT deactivation;

determining if a visual artifact is present in the electronic display; and

adjusting a resistance value of a resistance device associated with a common voltage layer (VCOM) of the display when a visual artifact is present to reduce or eliminate the visual artifact.

18. The method of claim 17, comprising increasing the resistance value of the resistive element when a visual artifact is present.

19. The method of claim 17, wherein monitoring the electronic display for visual artifacts comprises:

supplying an activation signal to a row of pixels;

supplying a known display signal to the row of pixels;

removing the activation signal from the row of pixels;

detecting a display output from the row of pixels; and

analyzing the display output for visual artifacts.

20. The method of claim 17, wherein detecting and analyzing the display output is performed by a human operator.

21. The method of claim 17, wherein detecting and analyzing the display output is performed by a machine.

22. A method of manufacturing an electronic display comprising:

providing a first common voltage layer (VCOM) associated with a row of pixels, wherein the first VCOM is configured to experience a first transient voltage when the row of pixels is activated, thereby causing a programmed voltage value of a first group of the pixels to vary by a first voltage difference;

providing a second VCOM associated with the row of pixels but not electrically connected to the first VCOM, wherein the wherein the second VCOM is configured to experience a second transient voltage when the row of pixels is activated, thereby causing a programmed voltage value of a second group of the pixels to vary by a second voltage difference; and

providing a resistive element, a capacitive element, or both coupled to the first VCOM, wherein the resistive element, the capacitive element, or both are configured to cause the first VCOM to dissipate the first transient voltage such that the first voltage difference and the second voltage difference are substantially the same when programmed with the same voltages.

23. The method of claim 22, wherein the first VCOM provided is generally formed in a column perpendicular to the row of pixels.

24. The method of claim 22, wherein the second VCOM provided is generally formed in a row parallel to the row of pixels.

25. The method of claim 24, wherein the second VCOM provided is generally formed from a plurality of non-contiguous, but electrically connected, segments extending parallel with the row of pixels.

26. An electronic device comprising:

a processor configured to generate image signals; and

an electronic display configured to display the image signals, the electronic display comprising;

a first pixel associated with a first common voltage layer (VCOM);

a second pixel associated with a second VCOM; and

a resistive device configured to couple to the first VCOM to cause a first transient voltage on the first VCOM to dissipate at approximately the same rate as a second transient voltage on the second VCOM, thereby reducing or eliminating image artifacts caused by differences in VCOM transient voltages.