Asynchronous interference detection in a capacitive sensing system

• US 10,126,884 B2
• Filed: 12/22/2014
• Issued: 11/13/2018
• Est. Priority Date: 12/22/2014
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Schwartz, Adam
• Primary Examiner(s): Shah, Neel
• Application Number:
  US14/579,533
• Publication Number:
  US 20160179243A1
• Time in Patent Office: 1,422 Days
• Field of Search: 345173-178, 324686, 178 1801, 178 1803, 178 1806
• CPC Class Codes: G06F 3/03547 Touch pads, in which fingers can move on a surface
• CPC Class Codes: G06F 3/04162 for exchanging data with external devices, e.g. smart pens, via the digitiser sensing hardware
• CPC Class Codes: G06F 3/04164 Connections between sensors and controllers, e.g. routing lines between electrodes and connection pads
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/0442 using active external devices, e.g. active pens, for transmitting changes in electrical potential to be received by the digitiser
• 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

Abstract

In an example, a processing system for a capacitive sensing device includes a sensor module and a determination module. The sensor module comprises a receiver, coupled to a sensor electrode, configured to receive a capacitive sensing signal. The receiver includes an in-phase channel and a quadrature channel. The in-phase channel is configured to mix the capacitive sensing signal with a local oscillator signal substantially in phase with the capacitive sensing signal. The quadrature channel is configured to mix the capacitive sensing signal with a phase-shifted signal near ninety degrees out of phase with the capacitive sensing signal. The determination module is configured to measure a change in capacitance in response to a demodulated signal of the in-phase channel concurrently with measuring a non-coherent signal in response to a demodulated signal of the quadrature channel.

Claims

1. A processing system for a capacitive sensing device, comprising:

a sensor module coupled to a sensor electrode, and configured to receive a capacitive sensing signal by driving the sensor electrode based on a clock signal having a sensing frequency, the sensor module comprises a receiver including;

an in-phase channel configured to mix the capacitive sensing signal with a local oscillator signal generated based on the clock signal, having the sensing frequency and being substantially in phase with the capacitive sensing signal; and

a quadrature channel configured to mix the capacitive sensing signal with a phase-shifted signal generated based on the clock signal, having the sensing frequency and being near ninety degrees out of phase with the capacitive sensing signal; and

a determination module configured to;

measure a change in capacitance in response to a demodulated signal output by the in-phase channel; and

measure a non-coherent signal in response to a demodulated signal output by the quadrature channel concurrently with measuring the change in capacitance, wherein the non-coherent signal comprises effects of interference or effects of a signal transmitted by an active pen proximate the capacitive sensing device, and

wherein the sensor module is configured to shift the sensing frequency of the clock signal based on the non-coherent signal.

2. The processing system of claim 1, wherein the capacitive sensing signal comprises a sinusoidal signal, and wherein the determination module is configured to measure a change in capacitance using a square root of a sum of squares of the demodulated signals of the in-phase channel and the quadrature channel.

3. The processing system of claim 1, wherein the local oscillator signal comprises a continuous-time signal, and wherein the receiver further comprises a phase-shift circuit configured to generate the phase-shifted signal, the phase-shift circuit comprising one of an RC filter, a Hilbert transform filter, or a Weaver mixer.

4. The processing system of claim 1, wherein the local oscillator signal comprises a discrete-time signal generated by stepping through a lookup table, and wherein the receiver is configured to generate the phase-shifted signal by stepping through another lookup table or by stepping through the lookup table with an offset.

5. The processing system of claim 1, wherein the local oscillator signal comprises one of a sinusoidal signal, a square wave signal, or a multi-level harmonic-reject signal.

6. The processing system of claim 1, wherein the in-phase channel comprises a first mixer configured to mix the capacitive sensing signal with the local oscillator signal and a first low-pass filter configured to filter output of the first mixer, and wherein the quadrature channel comprises a second mixer configured to mix the capacitive sensing signal with the phase-shifted signal and a second low-pass filter configured to filter output of the second mixer.

7. The processing system of claim 6, wherein a bandwidth of the second low-pass filter is different than a bandwidth of the first low-pass filter.

8. The processing system of claim 1, wherein the sensor module is configured to enter a high-noise mode based on the non-coherent signal.

9. The processing system of claim 1, wherein the receiver is configured to shift a phase of the local oscillator signal with respect to a phase of the capacitive sensing signal to compensate for transmission line effects of the sensor electrodes.

10. An input device, comprising:

a plurality of sensor electrodes;

a processing system, coupled to the plurality of sensor electrodes, the processing system configured to;

receive capacitive sensing signals by driving one of the plurality of sensor electrodes based on a clock signal having a sensing frequency;

mix the capacitive sensing signal with a local oscillator signal generated based on the clock signal, having the sensing frequency and being substantially in phase with the capacitive sensing signal to generate in-phase demodulated signals; and

mix the capacitive sensing signal with a phase-shifted signal generated based on the clock signal, having the sensing frequency and being near ninety degrees out of phase with the capacitive sensing signal to generate quadrature demodulated signals;

measure changes in capacitance in response to the in-phase demodulated signals;

measure non-coherent signals in response to the quadrature demodulated signals concurrently with measuring the changes in capacitance, wherein the non-coherent signals comprise effects of interference or effects of a signal transmitted by an active pen proximate the input device; and

shift the sensing frequency of the clock signal based on the non-coherent signals.

11. The input device of claim 10, wherein the processing system is further configured to enter a high-noise mode based on the non-coherent signals.

12. The input device of claim 10, wherein the processing system is configured to shift a phase of the local oscillator signal with respect to a phase of the capacitive sensing signal to compensate for transmission line effects of the sensor electrodes.

13. A method of operating a capacitive sensing device having a plurality of sensor electrodes, the method comprising:

receiving capacitive sensing signals received from the plurality of sensor electrodes by driving one of the plurality of sensor electrodes based on a clock signal having a sensing frequency;

mixing the capacitive sensing signals with a local oscillator signal generated based on the clock signal, having the sensing frequency and being substantially in-phase with the capacitive sensing signals to generate in-phase demodulated signals;

mixing the capacitive sensing signals with a phase-shifted signal generated based on the clock signal, having the sensing frequency and being near ninety degrees out of phase with the capacitive sensing signals to generate quadrature demodulated signals;

measuring changes in capacitance in response to the in-phase demodulated signals;

measuring non-coherent signals in response to the quadrature demodulated signals concurrently with measuring the changes in capacitance, wherein the non-coherent signals comprise effects of a signal transmitted by an active pen proximate the capacitive sensing device; and

shifting the sensing frequency of the clock signal based on the non-coherent signals.

14. The method of claim 13, further comprising:

entering a high-noise mode based on the non-coherent signals.

15. The method of claim 13, further comprising:

shifting a phase of the local oscillator signal with respect to a phase of the capacitive sensing signal to compensate for transmission line effects of the sensor electrodes.