System and Method for Energy Efficient Measurement of Sensor Signal

• US 20140267157A1
• Filed: 03/11/2014
• Published: 09/18/2014
• Est. Priority Date: 03/15/2013
• Status: Active Grant

• Current Assignee: Microchip Technology Germany GmbH (Microchip Technology Incorporated)
• Original Assignee: Microchip Technology Incorporated
• Inventors: Dorfner, Andreas
• Granted Patent: US 9,946,410 B2
• Time in Patent Office: Days
• US Class Current: 345/174
• CPC Class Codes: G01D 5/24 by varying capacitance
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: H03K 17/955 using a capacitive detector
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03K 2217/96073 Amplitude comparison

Abstract

A method for improving robustness of a capacitive sensor system has the following steps: a) operating the capacitive sensor system, wherein received sensor signals are filtered by a band-pass filter having a band-pass having a first center frequency; b) polling sensor data at a first rate using the sensor system; c) determining whether a polled sensor value is meeting a predetermined threshold; d) if the predetermined threshold is met: d1) polling sensor data at a second rate being higher than the first rate using the sensor system; d2) verifying that sensor data polled at the second rate are consistent; d3) if the sensor data polled at the second rate are inconsistent, then repeating at least step d2) wherein said band-pass filter is controlled to have a second center frequency.

Claims

1. A method for improving robustness of a capacitive sensor system, said method comprising the steps of:

a) operating the capacitive sensor system, wherein received sensor signals are filtered by a band-pass filter having a band-pass having a first center frequency;

b) polling sensor data at a first rate using the sensor system;

c) determining whether a polled sensor value is meeting a predetermined threshold;

d) if the predetermined threshold is met;

d1) polling sensor data at a second rate being higher than the first rate using the sensor system;

d2) verifying that sensor data polled at the second rate are consistent;

d3) if the sensor data polled at the second rate are inconsistent, then repeating at least step d2) wherein said band-pass filter is controlled to have a second center frequency.

2. The method according to claim 1, wherein the sensor system is configured to be operated at a system frequency that matches a center frequency of the band-pass filter and further operable to switch between system frequencies that match said first and second center frequency.

3. The method according to claim 1, further including repeating steps b)-d) if the sensor data polled at the second rate are inconsistent in step d3).

4. The method according to claim 1, wherein if the sensor data polled at the second rate are consistent, then changing a state of a sensor output signal.

5. The method according to claim 1, wherein different threshold values are applied when determining a switch from a first state to a second state and a switch from a second state to a first state.

6. The method according to claim 2, wherein a system frequency is the first or second frequency, respectively.

7. The method according to claim 2, wherein s system frequency is within a pass-band of the band-pass filter.

8. The method according to claim 2, wherein the sensor system comprises a proximity sensor comprising a first transmission electrode receiving a carrier signal having the first or second frequency.

9. The method according to claim 8, wherein the sensor output signal indicates a touch or no-touch.

10. The method according to claim 1, wherein a first polling rate is between 20 ms and 200 ms or between 10 ms and 100 ms.

11. The method according to claim 10, wherein a second polling rate is lower than 10 ms.

12. The method according to claim 8, further comprising a reception electrode, wherein an quasi-static alternating electric field if formed between the transmission electrode and the reception electrode and an attenuation of the signal at the reception electrode is measured.

13. A capacitive sensor system comprising:

a capacitive sensor electrode arrangement;

a band-pass filter receiving sensor signals from said capacitive sensor electrode arrangement, wherein the band-pass filter having a band-pass with a first center frequency;

an evaluation unit configured;

to poll sensor data at a first rate using the capacitive sensor electrode arrangement;

determine whether a polled sensor value is meeting a predetermined threshold and if the predetermined threshold is met;

to poll sensor data at a second rate being higher than the first rate using the sensor system;

to verify that sensor data polled at the second rate are consistent and if the sensor data polled at the second rate are inconsistent, to control the band-pass filter to switch to a second center frequency.

14. The system according to claim 13, wherein the capacitive sensor electrode arrangement is configured to operate at a variable system frequency which can be switched to match said first or second center frequency.

15. The system according to claim 13, wherein a sensor output signal changes states if the sensor data polled at the second rate are consistent.

16. The system according to claim 15, wherein different threshold values are applied when determining a switch from a first state to a second state and a switch from a second state to a first state.

17. The system according to claim 14, wherein a system frequency is the first or second frequency, respectively.

18. The system according to claim 14, wherein a system frequency is selected to be within the band-pass of the band-pass filter.

19. The system according to claim 14, wherein the capacitive sensor electrode arrangement comprises a proximity sensor comprising a first transmission electrode receiving a carrier signal having the first or second frequency.

20. The system according to claim 19, wherein the sensor output signal indicates a touch or no-touch.

21. The system according to claim 13, wherein the first polling rate is between 20 ms and 200 ms or between 10 ms and 100 ms.

22. The system according to claim 21, wherein the second polling rate is less than 10 ms.

23. The system according to claim 19, further comprising a reception electrode, wherein an quasi-static alternating electric field if formed between the transmission electrode and the reception electrode and an attenuation of the signal at the reception electrode is measured.

24. A method for operating a portable device with a capacitive sensor system, said method comprising the steps of:

a) switching the device into a low power mode;

b) operating the capacitive sensor system at a first frequency, wherein received sensor signals are filtered by a band-pass filter having a band-pass matching said first frequency;

c) polling sensor data at a first rate using the sensor system operating at the first frequency;

d) determining whether a polled sensor value is meeting a predetermined threshold;

e) if the predetermined threshold is met;

e1) polling sensor data at a second rate being higher than the first rate using the sensor system operating at the first frequency;

e2) verifying that sensor data polled at the second rate are consistent;

e3) if the sensor data polled at the second rate are inconsistent, then repeating at least step e2) wherein the sensor system is operated at a second frequency and said band-pass filter is controlled to match said second frequency;

f) if in step e3) it has been verified that the sensor data polled at the second rate are consistent, then switching the portable device from a low power mode into a normal operating mode.