MULTIPLE CHANNEL CAPACITIVE VOLTAGE DIVIDER SCANNING METHOD AND APPARATUS

• US 20150097583A1
• Filed: 10/01/2014
• Published: 04/09/2015
• Est. Priority Date: 10/04/2013
• Status: Active Grant

• Current Assignee: Microchip Technology Incorporated
• Original Assignee: Microchip Technology Incorporated
• Inventors: Gao, Xiang
• Granted Patent: US 9,857,394 B2
• Time in Patent Office: Days
• US Class Current: 324/679
• CPC Class Codes: G01R 1/30 Structural combination of electric measuring instruments with basic electronic circuits, e.g. with amplifier
• CPC Class Codes: G01R 15/002 Switches for altering the measuring range or for multitesters
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03M 1/1245 Details of sampling arrangements or methods

Abstract

Relative capacitance of a plurality of capacitive sensors may be monitored by using only one ADC conversion. A plurality of capacitive sensors individually charges a sample and hold capacitor. After all of the plurality of capacitive sensors have charged the sample and hold capacitor, a digital conversion of the resulting analog on the sample and hold capacitor is made and stored in a memory. This stored digital collective voltage is compared to a previously stored one and if different then a proximity/touch event may have occurred. Therefore, an entire panel of capacitive sensors may be quickly monitored for a change in the “group” capacitance thereof, or portions of the capacitive sensors may be monitored for a change in the “subgroup” capacitance thereof. By knowing which subgroup of capacitive sensors has changed its collective capacitive value, a more focused and selective capacitive sensor measurement can be made that uses less power.

Claims

1. A method for determining change in capacitance of at least one capacitive sensor of a plurality of capacitive sensors, said method comprising the steps of:

charging a plurality of capacitive sensors to a first voltage;

charging a sample and hold capacitor to a second voltage;

individually coupling each one of the plurality of capacitive sensors to the sample and hold capacitor, wherein electron charge from each of the individually coupled ones of the plurality of capacitive sensors is transferred to the sample and hold capacitor;

measuring a resulting voltage on the sample and hold capacitor after all of the plurality of capacitive sensors have been individually coupled to the sample and hold capacitor; and

comparing the measured resulting voltage to a previously measured resulting voltage, wherein if the measured resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value.

2. The method according to claim 1, further comprising the steps of:

(a) charging a first one of the plurality of capacitive sensors to the first voltage;

(b) charging the sample and hold capacitor to the second voltage;

(c) coupling the first one of the plurality of capacitive sensors to the sample and hold capacitor, wherein electron charge from the first one of the plurality of capacitive sensors is transferred to the sample and hold capacitor;

(d) measuring a resulting voltage on the sample and hold capacitor; and

(e) comparing the measured resulting voltage to a previously measured resulting voltage of the first one of the plurality of capacitive sensors, wherein if the measured resulting voltage is different than the previously measured resulting voltage then the first one of the plurality of capacitive sensors has changed capacitance value, if not then repeat steps (a) through (e) with another one of the plurality of capacitive sensors.

3. The method according to claim 1, further comprising the steps of:

charging a portion of the plurality of capacitive sensors to the first voltage;

charging the sample and hold capacitor to the second voltage;

individually coupling each one of the portion of the plurality of capacitive sensors to the sample and hold capacitor, wherein electron charge from each of the individually coupled ones of the portion of the plurality of capacitive sensors is transferred to the sample and hold capacitor;

measuring a resulting voltage on the sample and hold capacitor after all of the portion of the plurality of capacitive sensors have been individually coupled to the sample and hold capacitor; and

comparing the measured resulting voltage to a previously measured resulting voltage of the portion of the plurality of capacitive sensors, wherein if the measured resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the portion of the plurality of capacitive sensors has changed capacitance value.

4. The method according to claim 1, wherein the first voltage is more positive than the second voltage.

5. The method according to claim 1, wherein the second voltage is more positive than the first voltage.

6. The method according to claim 1, wherein the step of measuring the resulting voltage comprises the step of converting the resulting voltage on the sample and hold capacitor to a digital value with an analog-to-digital converter (ADC).

7. The method according to claim 6, wherein the step of comparing the measured resulting voltage to a previously measured resulting voltage comprises the steps of comparing the digital value go a previous digital value with a digital processor.

8. The method according to claim 7, further comprising the step of waking up the digital processor from a low power sleep mode when the measured resulting voltage is different from the previously measured resulting voltage.

18. An apparatus, operating in accordance with the method of claim 1, for determining change in capacitance of at least one capacitive sensor of a plurality of capacitive sensors, comprising:

a plurality of capacitive sensors;

a sample and hold capacitor;

a multiplexer having a plurality of inputs and an output;

a plurality of capacitive sensor switches coupled to the plurality of capacitive sensors, and adapted to selectively couple each of the plurality of capacitive sensors to the first voltage, the second voltage or a respective input of the multiplexer;

a sample and hold capacitor;

a sample and hold switch coupled between the output of the multiplexer and the sampler and hold capacitor;

an analog-to-digital converter (ADC) having an analog input coupled to the sample and hold capacitor; and

a digital processor coupled to an output of the ADC and adapted to control the plurality of capacitive sensor switches, multiplexer, and sample and hold switch.

19. The apparatus according to claim 18, wherein the plurality of capacitive sensor switches, the multiplexer, the sample and hold capacitor, the ADC and the digital processor are provided in a microcontroller.

20. The apparatus according to claim 19, further comprising a capacitive sensor scan controller for performing the steps of claim 1 while the digital processor is in a low power sleep mode.

21. The apparatus according to claim 20, wherein the capacitive sensor scan controller wakes up the digital processor from the low power sleep mode when the at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value.

9. A method for determining change in capacitance of at least one capacitive sensor of a plurality of capacitive sensors, said method comprising the steps of:

charging a plurality of capacitive sensors to a first voltage;

charging a sample and hold capacitor to a second voltage;

coupling the plurality of capacitive sensors to the sample and hold capacitor, wherein electron charge from the plurality of capacitive sensors is transferred to the sample and hold capacitor;

measuring a resulting voltage on the sample and hold capacitor; and

comparing the resulting voltage to a previously measured resulting voltage, wherein if the resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value.

10. The method according to claim 9, further comprising the steps of:

charging a portion of the plurality of capacitive sensors to the first voltage;

charging the sample and hold capacitor to the second voltage;

coupling the portion of the plurality of capacitive sensors to the sample and hold capacitor, wherein electron charge from the portion of the plurality of capacitive sensors is transferred to the sample and hold capacitor;

measuring a resulting voltage on the sample and hold capacitor; and

comparing the measured resulting voltage to a previously measured resulting voltage of the portion of the plurality of capacitive sensors, wherein if the measured resulting voltage is different than the previously measured resulting voltage then at least one capacitive sensor of the portion of the plurality of capacitive sensors has changed capacitance value.

11. The method according to claim 10, further comprising if the measured resulting voltage is not substantially different than the previously measured resulting voltage then perform the steps of:

charging another portion of the plurality of capacitive sensors to the first voltage;

charging the sample and hold capacitor to the second voltage;

coupling the another portion of the plurality of capacitive sensors to the sample and hold capacitor, wherein electron charge from the another portion of the plurality of capacitive sensors is transferred to the sample and hold capacitor;

measuring another resulting voltage on the sample and hold capacitor; and

comparing the another resulting voltage to a previously measured another resulting voltage of the another portion of the plurality of capacitive sensors, wherein if the resulting another voltage is different than the previously measured another resulting voltage then at least one capacitive sensor of the another portion of the plurality of capacitive sensors has changed capacitance value.

12. The method according to claim 10, further comprising the steps of:

(a) charging a first one of the portion of the plurality of capacitive sensors to the first voltage;

(b) charging the sample and hold capacitor to the second voltage;

(c) coupling the first one of the portion of the plurality of capacitive sensors to the sample and hold capacitor, wherein electron charge from the first one of the portion of the plurality of capacitive sensors is transferred to the sample and hold capacitor;

(d) measuring a resulting voltage on the sample and hold capacitor; and

(e) comparing the measured resulting voltage to a previously measured resulting voltage of the first one of the portion of the plurality of capacitive sensors, wherein if the measured resulting voltage is different than the previously measured resulting voltage then the first one of the portion of the plurality of capacitive sensors has changed capacitance value, if not repeat steps (a) through (e) with another one of the portion of the plurality of capacitive sensors.

13. The method according to claim 9, wherein the first voltage is more positive than the second voltage.

14. The method according to claim 9, wherein the second voltage is more positive than the first voltage.

15. The method according to claim 9, wherein the step of measuring the resulting voltage comprises the step of converting the resulting voltage on the sample and hold capacitor to a digital value with an analog-to-digital converter (ADC).

16. The method according to claim 15, wherein the step of comparing the measured resulting voltage to a previously measured resulting voltage comprises the steps of comparing the digital value to a previous digital value with a digital processor.

17. The method according to claim 16, further comprising the step of waking up the digital processor from a low power sleep mode when the measured resulting voltage is different from the previously measured resulting voltage.

22. An apparatus, operating in accordance with the method of claim 9, for determining change in capacitance of at least one capacitive sensor of a plurality of capacitive sensors, comprising:

a plurality of capacitive sensors;

a sample and hold capacitor;

a multiplexer having a plurality of inputs and an output;

a plurality of capacitive sensor switches coupled to the plurality of capacitive sensors, and adapted to couple the plurality of capacitive sensors to the first voltage, the second voltage or an input of the multiplexer;

a sample and hold capacitor;

a sample and hold switch coupled between the output of the multiplexer and the sampler and hold capacitor;

an analog-to-digital converter (ADC) having an analog input coupled to the sample and hold capacitor; and

a digital processor coupled to an output of the ADC and adapted to control the plurality of capacitive sensor switches, multiplexer, and sample and hold switch.

23. The apparatus according to claim 22, wherein the plurality of capacitive sensor switches, the multiplexer, the sample and hold capacitor, the ADC and the digital processor are provided in a microcontroller.

24. The apparatus according to claim 23, further comprising a capacitive sensor scan controller for performing the steps of claim 9 while the digital processor is in a low power sleep mode.

25. The apparatus according to claim 24, wherein the capacitive sensor scan controller wakes up the digital processor from the low power sleep mode when the at least one capacitive sensor of the plurality of capacitive sensors has changed capacitance value.