Wide dynamic range capacitive sensing

• US 9,201,547 B2
• Filed: 04/30/2012
• Issued: 12/01/2015
• Est. Priority Date: 04/30/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Elias, John Greer, Hotelling, Steven Porter
• Primary Examiner(s): PHAM, VIET DAVID
• Application Number:
  US13/460,620
• Publication Number:
  US 20130285971A1
• Time in Patent Office: 1,310 Days
• Field of Search: 345/173
• US Class Current: 1/1
• CPC Class Codes: G06F 2203/04101 2.5D-digitiser, i.e. digitiser detecting the X/Y position of the input means, finger or stylus, also when it does not touch, but is proximate to the digitiser's interaction surface and also measures the distance of the input means within a short range in the Z direction, possibly with a separate measurement setup
• CPC Class Codes: G06F 2203/04107 Shielding in digitiser, i.e. guard or shielding arrangements, mostly for capacitive touchscreens, e.g. driven shields, driven grounds
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• CPC Class Codes: H03K 17/955 using a capacitive detector

Abstract

A touch sensor panel configured to detect objects touching the panel as well as objects that are at a varying proximity to the touch sensor panel. The touch sensor panel includes circuitry that can configure the panel in a mutual capacitance (near field) architecture or a self-capacitance (far field and super far field) architecture. The touch sensor panel can also include circuitry that works to minimize an effect that a parasitic capacitance can have on the ability of the touch sensor panel to reliably detect touch and proximity events.

Claims

1. A method of sensing proximity events, comprising:

configuring a touch sensor panel to a self-capacitance architecture;

stimulating the touch sensor panel with one or more stimulation signals to generate one or more touch signals;

reducing an effect of a parasitic capacitance on the one or more touch signals received from the touch sensor panel by driving a shield with a shield signal of a same frequency and phase as the one or more stimulation signals, wherein the shield is a physical layer separate from other conductive structures in the touch sensor panel; and

determining if a proximity event has occurred based on the one or more reduced parasitic capacitance effect touch signals.

2. The method of claim 1, wherein reducing the effect of the parasitic capacitance includes offsetting the effect of the parasitic capacitance on a phase of the one or more touch signals.

3. The method of claim 1, wherein reducing the effect of parasitic capacitance includes attenuating an amount of parasitic capacitance in the touch sensor panel.

4. The method of claim 3, further comprising placing the shield in proximity to one or more touch sensor panel components and configuring the shield to carry the shield signal.

5. The method of claim 1, wherein reducing the effect of parasitic capacitance includes both offsetting the effect that the parasitic capacitance has on a phase of the one or more touch signals and attenuating an amount of parasitic capacitance in the touch sensor panel.

6. The method of claim 1, wherein configuring the touch sensor panel to the self-capacitance architecture includes switching a mutual capacitance touch detection hardware configuration into a self-capacitance touch detection hardware configuration.

7. The method of claim 1, further comprising:

scanning one or more electrodes in the touch sensor panel to obtain the one or more touch signals.

8. The method of claim 7, wherein determining if a proximity event has occurred further comprises:

determining a touch signal level of one or more of the reduced parasitic capacitance effect touch signals;

computing an average touch signal for one or more of the reduced parasitic capacitance effect touch signals; and

comparing the average touch signal with a pre-determined threshold value.

23. The method of claim 6, further comprising:

configuring a first set of multiple lines as sense electrodes in the self-capacitance touch detection hardware configuration by applying at least some of the one or more stimulation signals to the first set of multiple lines through one or more virtual ground charge amplifiers, and configuring the first set of multiple lines as drive lines in the mutual capacitance touch detection hardware configuration; and

configuring a second set of multiple lines as sense electrodes in either the self-capacitance touch detection hardware configuration or the mutual capacitance touch detection hardware configuration.

24. The method of claim 23, wherein configuring the first set of multiple lines as sense electrodes comprises coupling the one or more virtual ground charge amplifiers to the first set of multiple lines.

25. The method of claim 24, further comprising reducing the effect of parasitic capacitance by:

applying a sinusoidal signal to a positive input of at least one of the one or more virtual ground charge amplifiers; and

driving the shield with the shield signal having substantially the same frequency and phase as the sinusoidal signal.

9. An apparatus for detecting proximity events, comprising:

driving circuitry configured for stimulating a touch sensor panel with one or more stimulation signals to generate one or more touch signals indicative of changes in self-capacitance;

a parasitic capacitance reduction system configured for reducing an effect of parasitic capacitance on the one or more touch signals received from the touch sensor panel by causing the driving circuitry to drive a shield with a shield signal of a same frequency and phase as the one or more stimulation signals, wherein the shield is a physical layer separate from other conductive structures in the touch sensor panel; and

sensing circuitry capable of determining if a proximity event has occurred based on the one or more reduced parasitic capacitance effect touch signals.

10. The apparatus of claim 9, wherein the apparatus is further configured to be switchable to detect changes in mutual capacitance in the touch sensor panel.

11. The apparatus of claim 9, wherein the parasitic capacitance reduction system includes a phase noise calibration system for calibrating out an effect of the parasitic capacitance on a phase of the one or more touch signals.

12. The apparatus of claim 9, wherein the parasitic capacitance reduction system includes a parasitic capacitance attenuation system for lowering a magnitude of the parasitic capacitance present in the touch sensor panel.

13. The apparatus of claim 9, wherein the parasitic capacitance reduction system includes:

a phase noise calibration system for calibrating out an effect of the parasitic capacitance on a phase of the one or more touch signals; and

a parasitic capacitance reduction system for lowering a magnitude of the parasitic capacitance present in the touch sensor panel.

14. The apparatus of claim 9, wherein the sensing circuitry is further capable of scanning one or more electrodes in the touch sensor panel to obtain the one or more touch signals.

15. The apparatus of claim 9, wherein the sensing circuitry is further capable of determining the occurrence of the proximity event by determining a touch signal level indicative of a proximity event, computing an average touch sensor panel signal level, and comparing the computed average touch panel signal level with the determined touch signal level.

26. The apparatus of claim 10, further comprising:

a plurality of input/output (I/O) lines for connecting to the touch sensor panel;

wherein the sensing circuitry includes one or more sense amplifiers configured for receiving sense signals through at least some of the plurality of I/O lines;

wherein the driving circuitry is couplable to the one or more sense amplifiers and configurable for providing the one or more stimulation signals to at least some of the plurality of I/O lines in a self-capacitance configuration; and

wherein the apparatus further comprises switching circuitry coupled to the plurality of I/O lines, a plurality of drivers, and the one or more sense amplifiers, the switching circuitry configured for coupling the plurality of drivers to at least some of the plurality of I/O lines in a mutual capacitance configuration, and for coupling the one or more sense amplifiers to at least some of the plurality of I/O lines and applying the one or more stimulation signals to at least some of the plurality of I/O lines through the one or more sense amplifiers in the self-capacitance configuration.

16. A non-transitory computer readable storage medium having stored thereon a set of instructions for detecting proximity events in a touch sensor panel, that when executed by a processor causes the processor to:

configure a touch sensor panel to detect changes in a self-capacitance on a plurality of electrodes in the touch sensor panel;

stimulate the touch sensor panel with one or more stimulation signals to generate one or more touch signals indicative of the changes in self-capacitance;

reduce a parasitic capacitance effect on the one or more touch signals received from the plurality of electrodes by driving a shield with a shield signal of a same frequency and phase as the one or more stimulation signals, wherein the shield is a physical layer separate from other conductive structures in the touch sensor panel; and

determine if a proximity event has occurred based on the one or more reduced parasitic capacitive effect touch signals.

17. The non-transitory computer readable storage medium of claim 16, wherein configuring the touch sensor panel includes switching the touch sensor panel from a mutual capacitance touch sensor panel to a self-capacitance touch sensor panel.

18. The non-transitory computer readable storage medium of claim 16, wherein reducing the parasitic capacitance effect includes calibrating out an effect of the parasitic capacitance on a phase of the one or more touch signals.

19. The non-transitory computer readable storage medium of claim 16, wherein reducing the parasitic capacitance effect includes attenuating an amount of parasitic capacitance in a touch sensor panel.

20. The non-transitory computer readable storage medium of claim 16, wherein reducing the parasitic capacitance effect includes both attenuating an amount of parasitic capacitance in the touch sensor panel and calibrating out an effect of the parasitic capacitance on a phase of the one or more touch signals.

21. The non-transitory computer readable storage medium of claim 16, further comprising scanning one or more electrodes in the touch sensor panel to obtain the one or more touch signals.

22. The non-transitory computer readable storage medium of claim 16, wherein determining if the proximity event has occurred includes:

determining a touch signal value indicative of a proximity event;

computing an average electrode signal value for one or more of the reduced parasitic capacitance effect touch signals; and

comparing the average signal value with the determined touch signal value.

27. The non-transitory computer readable storage medium of claim 17, the method further comprising:

configuring a first set of multiple lines as sense electrodes in a self-capacitance touch detection hardware configuration by applying at least some of the one or more stimulation signals to the first set of multiple lines through one or more virtual ground charge amplifiers, and configuring the first set of multiple lines as drive lines in a mutual capacitance touch detection hardware configuration; and

configuring a second set of multiple lines as sense electrodes in either the self-capacitance touch detection hardware configuration or the mutual capacitance touch detection hardware configuration.

28. The non-transitory computer readable storage medium of claim 27, wherein configuring the first set of multiple lines as sense electrodes comprises coupling the one or more virtual ground charge amplifiers to the first set of multiple lines.

29. The non-transitory computer readable storage medium of claim 28, the method further comprising reducing the effect of parasitic capacitance by:

applying a sinusoidal signal to a positive input of at least one of the one or more virtual ground charge amplifiers; and

driving the shield with the shield signal having substantially the same frequency and phase as the sinusoidal signal.