Reduced capacitive baseline shift via mixing period adjustments

• US 10,372,276 B2
• Filed: 01/06/2017
• Issued: 08/06/2019
• Est. Priority Date: 01/06/2017
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: Bohannon, Eric Scott, Bell, Jr., Marshall J.
• Primary Examiner(s): Iluyomade, Ifedayo B
• Application Number:
  US15/400,681
• Publication Number:
  US 20180196542A1
• Time in Patent Office: 942 Days
• Field of Search: None
• 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 3/0443 using a single layer of sensing electrodes
• 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
• 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

A method and related processing system and input device are disclosed, the method comprising driving a first capacitive sensing signal with first sensing frequency onto a first group of a plurality of sensor electrodes, and acquiring first capacitive measurements of resulting signals received by a second group of the plurality of sensor electrodes. Acquiring first capacitive measurements comprises applying a first demodulation signal with a predefined first mixing period defined within a sensing period associated with the first sensing frequency. The method further comprises driving a second capacitive sensing signal having a second sensing frequency different than the first sensing frequency onto a third group of the plurality of sensor electrodes, and acquiring second capacitive measurements of resulting signals received by a fourth group of the plurality of sensor electrodes. Acquiring second capacitive measurements comprises applying a second demodulation signal having a different predefined second mixing period.

Claims

1. A method comprising:

driving, onto a first group of a plurality of sensor electrodes, a first capacitive sensing signal having a predefined first sensing frequency;

acquiring, based on the driven first capacitive sensing signal, first capacitive measurements of resulting signals received by a second group of the plurality of sensor electrodes, wherein acquiring first capacitive measurements comprises applying a first demodulation signal having a predefined first mixing period defined within a sensing period associated with the first sensing frequency;

driving, onto a third group of the plurality of sensor electrodes, a second capacitive sensing signal having a second sensing frequency different than the first sensing frequency; and

acquiring, based on the driven second capacitive sensing signal, second capacitive measurements of resulting signals received by a fourth group of the plurality of sensor electrodes,

wherein acquiring second capacitive measurements comprises applying a second demodulation signal having a predefined second mixing period within a sensing period associated with the second sensing frequency, the second mixing period different than the first mixing period, and

wherein the second mixing period is selected such that a second average current value for the second capacitive measurements has a substantially linear relation to a first average current value for the first capacitive measurements, the linear relation based on the first sensing frequency and the second sensing frequency.

2. The method of claim 1, wherein the second mixing period is selected such that a second average current value for the second capacitive measurements is substantially equal to a first average current value for the first capacitive measurements.

3. The method of claim 1, wherein each sensing period comprises a positive sensing half-cycle and a negative sensing half-cycle, wherein the positive sensing half-cycle and the negative sensing half-cycle each have a length corresponding to the first mixing period or the second mixing period.

4. The method of claim 3, wherein the first demodulation signal and the second demodulation signal are three-level demodulation signals having a positive level, a negative level, and a zero level,

wherein applying the first demodulation signal and applying the second demodulation signal each comprises:

applying the positive level during the positive sensing half-cycle;

applying the negative level during the negative sensing half-cycle; and

applying the zero level during a predefined period within the sensing period between the positive sensing half-cycle and the negative sensing half-cycle.

5. The method of claim 1, wherein the first sensing frequency and the second sensing frequency are included in a predefined plurality of sensing frequencies,

wherein the first mixing period and the second mixing period are included in a predefined plurality of mixing periods selected based on an identified one or more slowest sensor electrodes of the plurality of sensor electrodes.

6. The method of claim 5, wherein the predefined plurality of mixing periods are further selected based on one or more fastest sensing frequencies of the predefined plurality of sensing frequencies.

7. A processing system comprising:

a sensing module comprising sensing circuitry and configured to;

drive, onto a first group of a plurality of sensor electrodes, a first capacitive sensing signal having a predefined first sensing frequency;

acquire, based on the driven first capacitive sensing signal, first capacitive measurements of resulting signals received by a second group of the plurality of sensor electrodes, wherein acquiring first capacitive measurements comprises applying a first demodulation signal having a predefined first mixing period defined within a sensing period associated with the first sensing frequency;

drive, onto a third group of the plurality of sensor electrodes, a second capacitive sensing signal having a second sensing frequency different than the first sensing frequency; and

acquire, based on the driven second capacitive sensing signal, second capacitive measurements of resulting signals received by a fourth group of the plurality of sensor electrodes,

wherein acquiring second capacitive measurements comprises applying a second demodulation signal having a predefined second mixing period within a sensing period associated with the second sensing frequency, the second mixing period different than the first mixing period, and

wherein the second mixing period is selected such that a second average current value for the second capacitive measurements has a substantially linear relation to a first average current value for the first capacitive measurements, the linear relation based on the first sensing frequency and the second sensing frequency.

8. The processing system of claim 7, wherein the second mixing period is selected such that a second average current value for the second capacitive measurements is substantially equal to a first average current value for the first capacitive measurements.

9. The processing system of claim 7, wherein each sensing period comprises a positive sensing half-cycle and a negative sensing half-cycle, wherein the positive sensing half-cycle and the negative sensing half-cycle each have a length corresponding to the first mixing period or the second mixing period.

10. The processing system of claim 9, wherein the first demodulation signal and the second demodulation signal are three-level demodulation signals having a positive level, a negative level, and a zero level,

wherein applying the first demodulation signal and applying the second demodulation signal each comprises:

applying the positive level during the positive sensing half-cycle;

applying the negative level during the negative sensing half-cycle; and

applying the zero level during a predefined period within the sensing period between the positive sensing half-cycle and the negative sensing half-cycle.

11. The processing system of claim 7, wherein the first sensing frequency and the second sensing frequency are included in a predefined plurality of sensing frequencies,

wherein the first mixing period and the second mixing period are included in a predefined plurality of mixing periods selected based on an identified one or more slowest sensor electrode of the plurality of sensor electrodes.

12. The processing system of claim 11, wherein the predefined plurality of mixing periods are further selected based on one or more fastest sensing frequencies of the predefined plurality of sensing frequencies.

13. An input device comprising:

a plurality of sensor electrodes; and

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

drive, onto a first group of a plurality of sensor electrodes, a first capacitive sensing signal having a predefined first sensing frequency;

acquire, based on the driven first capacitive sensing signal, first capacitive measurements of resulting signals received by a second group of the plurality of sensor electrodes, wherein acquiring first capacitive measurements comprises applying a first demodulation signal having a predefined first mixing period defined within a sensing period associated with the first sensing frequency;

drive, onto a third group of the plurality of sensor electrodes, a second capacitive sensing signal having a second sensing frequency different than the first sensing frequency; and

acquire, based on the driven second capacitive sensing signal, second capacitive measurements of resulting signals received by a fourth group of the plurality of sensor electrodes,

wherein acquiring second capacitive measurements comprises applying a second demodulation signal having a predefined second mixing period within a sensing period associated with the second sensing frequency, the second mixing period different than the first mixing period, and

wherein the second mixing period is selected such that a second average current value for the second capacitive measurements has a substantially linear relation to a first average current value for the first capacitive measurements, the linear relation based on the first sensing frequency and the second sensing frequency.

14. The input device of claim 13, wherein the second mixing period is selected such that a second average current value for the second capacitive measurements is substantially equal to a first average current value for the first capacitive measurements.

15. The input device of claim 13, wherein each sensing period comprises a positive sensing half-cycle and a negative sensing half-cycle, wherein the positive sensing half-cycle and the negative sensing half-cycle each have a length corresponding to the first mixing period or the second mixing period.

16. The input device of claim 15, wherein the first demodulation signal and the second demodulation signal are three-level demodulation signals having a positive level, a negative level, and a zero level,

wherein applying the first demodulation signal and applying the second demodulation signal each comprises:

applying the positive level during the positive sensing half-cycle;

applying the negative level during the negative sensing half-cycle; and

applying the zero level during a predefined period within the sensing period between the positive sensing half-cycle and the negative sensing half-cycle.

17. The input device of claim 13, wherein the first sensing frequency and the second sensing frequency are included in a predefined plurality of sensing frequencies,

wherein the first mixing period and the second mixing period are included in a predefined plurality of mixing periods selected based on an identified one or more slowest sensor electrodes of the plurality of sensor electrodes.