Method and system for noise immunity for automatically triggered impedance and capacitance sensors

1. A sensor system, comprising:

a receiver circuit including a receiver electrode;

a transmitter electrode; and

control logic;

wherein:

the receiver circuit is configured to oscillate when a capacitance measurement reaches a capacitance threshold;

the capacitance measurement is to include capacitance between the receiver electrode and the transmitter electrode, the capacitance to indicate a touch or proximity to the sensor system;

the capacitance measurement is to be performed while the transmitter electrode is deactivated; and

the control logic is configured to:

determine an amplitude of a transmitter electrode output signal;

based on a determination that the amplitude of the transmitter electrode output signal is greater than an amplitude threshold, determine a frequency of the transmitter electrode output signal;

determine whether the frequency of the transmitter electrode output signal is within an allowed frequency range; and

based on a determination that the frequency of the transmitter electrode output signal is not within the allowed frequency range, determine that noise is present in the system.

2. The sensor system of claim 1 , wherein the control logic is further configured to:

based on a determination that the frequency of the transmitter electrode output signal is within the allowed frequency range, determine an amplitude of a receiver electrode output signal; and

determine whether noise is present based upon the amplitude of the receiver electrode output signal.

3. The sensor system of claim 2 , wherein the control logic is further configured to:

determine whether the amplitude of the receiver electrode output signal is indicative of output saturation; and

based upon a determination that the receiver electrode output signal is indicative of output saturation, determine that noise is present in the system.

4. The sensor system of claim 2 , wherein the control logic is further configured to:

apply a zero-oscillation state impedance to the receiver electrode; and

determine whether the receiver electrode output signal indicates oscillation of the receiver electrode; and

determine that noise is present in the system based on an indication of oscillation of the receiver electrode.

5. The sensor system of claim 2 , wherein the control logic is further configured to:

apply a zero-oscillation state impedance to the receiver electrode;

determine whether the receiver electrode output signal indicates oscillation of the receiver electrode; and

determine that the capacitance measurement is correctly observed above the capacitance threshold based upon the determinations that the receiver electrode output signal indicates oscillation of the receiver electrode, and that the transmitter electrode output signal is within the allowed frequency range.

6. The sensor system of claim 5 , wherein the determination that the capacitance measurement is above the capacitance threshold is further based on a determination that the receiver electrode output signal is not indicative of output saturation.

7. The sensor system of claim 1 , wherein the control logic is further configured to:

determine that the amplitude of the transmitter electrode output signal is less than the amplitude threshold;

based on the determination that the amplitude of the transmitter electrode output signal is less than the amplitude threshold, determine whether a receiver electrode output signal is saturated; and

based on a determination that the receiver electrode output signal is not saturated, and upon the determination that the amplitude of the transmitter electrode output signal is less than the amplitude threshold, determine that the capacitance measurement is correctly observed below the capacitance threshold.

8. The sensor system of claim 1 , wherein the control logic is further configured to, based on a determination of noise in the sensor system:

apply a zero-oscillation state impedance to the receiver electrode; and

record the transmitter electrode output signal after application of the zero-oscillation state impedance to characterize the noise.

9. The sensor system of claim 8 , wherein the control logic is further configured to record a receiver electrode output signal after application of the zero-oscillation state impedance to characterize the noise.

10. A method of operating a sensor system with a transmitter electrode and a receiver electrode, the method comprising:

determining a capacitance measurement of a capacitance between a receiver electrode and a transmitter electrode, the capacitance to indicate a touch or proximity to the sensor system;

determining an amplitude of a transmitter electrode output signal;

based on a determination that the amplitude of the transmitter electrode output signal is greater than an amplitude threshold, determining a frequency of the transmitter electrode output signal;

determining whether the frequency of the transmitter electrode output signal is within an allowed frequency range; and

based on a determination that the frequency of the transmitter electrode output signal is not within the allowed frequency range, determining that noise is present in the system.

11. The method of claim 10 , further comprising:

based on a determination that the frequency of the transmitter electrode output signal is within the allowed frequency range, determining an amplitude of a receiver electrode output signal; and

determining whether noise is present based upon the amplitude of the receiver electrode output signal.

12. The method of claim 11 , further comprising:

determining whether the amplitude of the receiver electrode output signal is indicative of output saturation; and

based upon a determination that the receiver electrode output signal is indicative of output saturation, determining that noise is present in the system.

13. The method of claim 11 , further comprising:

applying a zero-oscillation state impedance to the receiver electrode; and

determining whether the receiver electrode output signal indicates oscillation of the receiver electrode; and

determining that noise is present in the system based on an indication of oscillation of the receiver electrode.

14. The method of claim 11 , further comprising:

applying a zero-oscillation state impedance to the receiver electrode;

determining whether the receiver electrode output signal indicates oscillation of the receiver electrode; and

determining that the capacitance measurement is correctly observed above the capacitance threshold based upon the determinations that the receiver electrode output signal indicates oscillation of the receiver electrode, and that the transmitter electrode output signal is within the allowed frequency range.

15. The method of claim 14 , the determination that the capacitance measurement is above the capacitance threshold is further based on a determination that the receiver electrode output signal is not indicative of output saturation.

16. The method of claim 10 , further comprising:

determining that the amplitude of the transmitter electrode output signal is less than the amplitude threshold;

based on the determination that the amplitude of the transmitter electrode output signal is less than the amplitude threshold, determining whether a receiver electrode output signal is saturated; and

based on a determination that the receiver electrode output signal is not saturated, and upon the determination that the amplitude of the transmitter electrode output signal is less than the amplitude threshold, determining that the capacitance measurement is correctly observed below the capacitance threshold.

17. The method of claim 10 , further comprising, based on a determination of noise in the sensor system:

applying a zero-oscillation state impedance to the receiver electrode; and

recording the transmitter electrode output signal after application of the zero-oscillation state impedance to characterize the noise.

18. The method of claim 17 , further comprising recording a receiver electrode output signal after application of the zero-oscillation state impedance to characterize the noise.