Mitigation of parasitic capacitance

• US 9,086,768 B2
• Filed: 04/30/2012
• Issued: 07/21/2015
• 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:
  US13/460,652
• Publication Number:
  US 20130285973A1
• Time in Patent Office: 1,177 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 3/041662 using alternate mutual and self-capacitive scanning
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer

Abstract

A touch sensor panel configured to mitigate the effect of parasitic capacitance on the ability of a capacitive touch sensor panel to reliably detect touch and proximity events. The touch sensor panel includes circuitry that can electrically drive a set of conductive shields that partially encapsulate various conductive components of the touch sensor panel. The touch sensor panel can also include circuitry that work to calibrate the touch sensor panel against variations in signal phase due to a parasitic capacitance.

Claims

1. A method of reducing an effect of parasitic capacitance on a touch input device, the method comprising:

generating a plurality of periodic signals different from a touch sense circuitry output signal, the plurality of periodic signals having a same frequency as the touch sense circuitry output signal;

initializing a gain of the plurality of periodic signals;

combining the plurality of periodic signals with the touch sense circuitry output signal; and

adjusting the gain of the plurality of periodic signals until the combination of the plurality of periodic signals and the touch sense circuitry output signal is approximately zero.

2. The method of claim 1, wherein generating the plurality of periodic signals includes using a plurality of multiplying digital to analog converters.

3. The method of claim 2, wherein the multiplying digital to analog converters are configured to generate the plurality of periodic signals with a frequency that is substantially identical to the touch sense circuitry output signal.

4. The method of claim 1, wherein combining the plurality of periodic signals with the touch sense circuitry output signal includes summing the signals.

5. The method of claim 4, wherein summing the signals includes using voltage summation to sum the signals.

6. The method of claim 4, wherein summing the signals includes using current summation to sum the signals.

7. The method of claim 1, wherein the touch sense circuitry output is generated without a touch or proximity event occurring on the touch input device.

8. The method of claim 1, further comprising:

attenuating an amount of parasitic capacitance on the touch sensor panel.

9. An apparatus for reducing an effect of parasitic capacitance on a touch input device, the apparatus comprising:

a plurality of signal generators configured to generate a plurality of periodic signals different from an output of touch sensor circuitry;

a signal combiner configured to combine the plurality of periodic signals with the output of the touch sensor circuitry; and

a processor capable of determining an output of the signal combiner and adjusting a gain of the plurality of periodic signals if the output of the signal combiner is above a pre-determined threshold.

10. The apparatus of claim 9, wherein the plurality of signal generators include a plurality of multiplying digital to analog converters configured to generate the plurality of periodic signals with a particular frequency and phase.

11. The apparatus of claim 9, wherein frequencies of the plurality of periodic signals are set to substantially the same frequency as the output of the touch sensor circuitry.

12. The apparatus of claim 9, wherein the signal combiner includes a voltage summer configured to sum voltages of the plurality of periodic signals with the output of the touch sensor circuitry.

13. The apparatus of claim 9, wherein the signal combiner includes a junction in which currents of the plurality of periodic signals are combined with a current from the output of the touch sensor circuitry to perform current summation.

14. The apparatus of claim 9, wherein the processor can determine the output of the signal combiner by determining an output of a demodulator in which an input of the demodulator is driven by the output of the signal combiner.

15. The apparatus of claim 10, wherein the processor can adjust the gain of the plurality of periodic signals by adjusting an input of the plurality of multiplying digital to analog converters.

16. The apparatus of claim 9, further comprising a parasitic capacitance attenuation circuit configured to attenuate parasitic capacitance in the touch input device.

17. 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:

determine a frequency of a touch sense circuitry output signal;

generate a plurality of signals different from the touch sense circuitry output signal, the plurality of signals having the same frequency as the determined frequency of the touch sense circuitry output signal;

combine the plurality of signals with the touch sense circuitry output signal;

determine if a magnitude of the combination is below a pre-determined threshold; and

adjust a gain of the signals until the combination is below a pre-determined threshold.

18. The non-transitory computer readable storage medium of claim 17, wherein generating the plurality of signals includes configuring a plurality of inputs on a plurality of multiplying digital to analog converters.

19. The non-transitory computer readable storage medium of claim 17, wherein combining the plurality of signals includes performing a voltage summation of the plurality of signals and the touch sense circuitry output signal.

20. The non-transitory computer readable storage medium of claim 17, wherein combining the plurality of signals includes performing a current summation of the plurality of signals and the touch sense circuitry output signal.

21. The non-transitory computer readable storage medium of claim 17, wherein the touch sensing circuitry output is generated in an absence of a touch or proximity event.

22. The non-transitory computer readable storage medium of claim 18, wherein adjusting the gain of the signals includes configuring a plurality of inputs on the plurality of multiplying digital to analog converters.

23. A computing device including an apparatus for reducing an effect of parasitic capacitance on a touch input device, the apparatus comprising:

a plurality of signal generators configured to generate a plurality of periodic signals different from an output of touch sensor circuitry;

a signal combiner configured to combine the plurality of periodic signals with the output of the touch sensor circuitry; and

a processor capable of determining an output of the signal combiner and adjusting a gain of the plurality of periodic signals if the output of the signal combiner is above a pre-determined threshold.