Increasing the dynamic range of an integrator based mutual-capacitance measurement circuit

Patent metadata

Field	Value
Publication number	US-9310924-B2
Application number	US-201213627028-A
Country	US
Kind code	B2
Filing date	Sep 26, 2012
Priority date	Sep 26, 2012
Publication date	Apr 12, 2016
Grant date	Apr 12, 2016

Abstract

In one embodiment, a method includes deactivating an integrator of a mutual-capacitive measurement circuit and configuring the mutual-capacitive measurement circuit according to a first voltage configuration. The first voltage configuration results in a charge on a sensor capacitor and a compensation capacitor when a supply voltage is applied to the mutual-capacitive measurement circuit. The method also includes adjusting a variable reference voltage input of the integrator to a first reference voltage, wherein the first reference voltage is selected to increase an output range of the mutual-capacitive measurement circuit. The method also includes applying the supply voltage to the mutual-capacitive measurement circuit and obtaining a first reference measurement from an analog-digital-converter coupled to an output of the mutual-capacitance measurement circuit.

First claim

What is claimed is:

1. A method of detecting a change in capacitance, comprising:
adjusting a variable reference voltage input of an integrator of a mutual-capacitive measurement circuit to a first reference voltage, wherein the first reference voltage is selected to increase a range of voltages that can be output by the mutual-capacitive measurement circuit during a first half of a differential measurement cycle;
configuring the mutual-capacitive measurement circuit for obtaining a first reference measurement during the first half of the differential measurement cycle;
obtaining the first reference measurement from an analog-digital-converter coupled to an output of the mutual-capacitance measurement circuit;
configuring the mutual-capacitive measurement circuit for obtaining a first output measurement during the first half of the differential measurement cycle;
obtaining the first output measurement from the analog-digital-converter;
adjusting the variable reference voltage input to a second reference voltage, wherein the second reference voltage is selected to increase the range of voltages that can be output by the mutual-capacitive measurement circuit during a second half of the differential measurement cycle;
configuring the mutual-capacitive measurement circuit for obtaining a second reference measurement during the second half of the differential measurement cycle;
obtaining the second reference measurement from the analog-digital-converter;
configuring the mutual-capacitive measurement circuit for obtaining a second output measurement during the second half of the differential measurement cycle;
obtaining the second output measurement from the analog-digital-converter; and
determining whether a touch or proximity event relative to a touch sensitive device has occurred based on calculating a differential measurement using a difference between the first reference measurement and the first output measurement and a difference between the second reference measurement and the second output measurement.

2. The method of claim 1 , wherein configuring the mutual-capacitive measurement circuit for obtaining a first reference measurement during the first half of the differential measurement cycle comprises:
deactivating the integrator of the mutual-capacitive measurement circuit;
configuring the mutual-capacitive measurement circuit according to a voltage configuration for obtaining the first reference measurement; and
applying a supply voltage to the mutual-capacitive measurement circuit.

3. The method of claim 1 , wherein configuring the mutual-capacitive measurement circuit for obtaining a first output measurement during the first half of the differential measurement cycle comprises:
activating the integrator of the mutual-capacitive measurement circuit;
configuring the mutual-capacitive measurement circuit according to a voltage configuration for obtaining the first output measurement; and
applying a supply voltage to the mutual-capacitive measurement circuit.

4. The method of claim 3 , wherein configuring the mutual-capacitive measurement circuit for obtaining a first output measurement during the first half of the differential measurement cycle further comprises calibrating a compensation capacitor of the mutual-capacitive measurement circuit.

5. The method of claim 1 , wherein configuring the mutual-capacitive measurement circuit for obtaining a second reference measurement during the second half of the differential measurement cycle comprises:
deactivating the integrator of the mutual-capacitive measurement circuit;
configuring the mutual-capacitive measurement circuit according to a voltage configuration for obtaining the second reference measurement; and
applying a supply voltage to the mutual-capacitive measurement circuit.

6. The method of claim 1 , wherein configuring the mutual-capacitive measurement circuit for obtaining a second output measurement during the second half of the differential measurement cycle comprises:
activating the integrator of the mutual-capacitive measurement circuit;
configuring the mutual-capacitive measurement circuit according to a voltage configuration for obtaining the second output measurement; and
applying a supply voltage to the mutual-capacitive measurement circuit.

7. The method of claim 6 , wherein configuring the mutual-capacitive measurement circuit for obtaining a second output measurement during the second half of the differential measurement cycle further comprises calibrating a compensation capacitor of the mutual-capacitive measurement circuit.

8. The method of claim 1 , further comprising detecting a proximity of an object relative to the touch sensitive device based on the differential measurement.

9. An apparatus comprising:
a mutual-capacitive measurement circuit comprising:
a mutual-capacitive sensor comprising a sensor capacitor and a compensation capacitor;
an integrator coupled to the mutual-capacitive sensor, the integrator having a variable reference voltage input capable of being adjusted to increase a range of voltages that can be output by the mutual-capacitive measurement circuit;
an analog-to-digital converter coupled to an output of the mutual-capacitive measurement circuit; and

a controller operable to:
dynamically adjust, over a plurality of measurement phases, the variable reference voltage input of the integrator; and
adjust the compensation capacitor until a voltage representing a charge share between the sensor capacitor and the compensation capacitor is equal to a particular reference voltage to which the variable reference voltage input is dynamically adjusted.

10. The apparatus of claim 9 , wherein the mutual-capacitive measurement circuit is embodied in a touch sensitive device.

11. The apparatus of claim 10 , wherein the controller is further operable to:
deactivate the integrator of the mutual-capacitive measurement circuit;
configure the mutual-capacitive measurement circuit according to a first voltage configuration, wherein the first voltage configuration results in a charge on the sensor capacitor and the compensation capacitor when a supply voltage is applied to the mutual-capacitive measurement circuit;
adjust the variable reference voltage input of the integrator to a first reference voltage, wherein the first reference voltage is selected to increase the range of voltages that can be output by the mutual-capacitive measurement circuit;
apply the supply voltage to the mutual-capacitive measurement circuit; and
obtain a first reference measurement from the analog-digital-converter.

12. The apparatus of claim 11 , wherein the controller is further operable to:
activate the integrator of the mutual-capacitive measurement circuit;
configure the mutual-capacitive measurement circuit according to a second voltage configuration, wherein the second voltage configuration results in a reversed polarity of the charge resulting from the first voltage configuration;
adjust the variable reference voltage input to the first reference voltage;
apply the supply voltage to the mutual-capacitive measurement circuit; and
obtain a first output measurement from the analog-digital-converter.

13. The apparatus of claim 12 , wherein the controller is further operable to:
deactivate the integrator of the mutual-capacitive measurement circuit;
configure the mutual-capacitive measurement circuit according to the second voltage configuration;
adjust the variable reference voltage input to a second reference voltage, wherein the second reference voltage is selected to increase the range of voltages that can be output by the mutual-capaci

Assignees

• Hanssen Ingar
• Whelan Rian
• Atmel Corp

Inventors

• Hanssen Ingar
• Whelan Rian

Classifications

• G06F3/0416 Primary

  Control or interface arrangements specially adapted for digitisers · CPC title

• H03K2217/960745

  Capacitive differential; e.g. comparison with reference capacitance · CPC title

• H03K2217/960725

  Charge-transfer · CPC title

• H03K17/9622

  using a plurality of detectors, e.g. keyboard · CPC title

• G01R27/2605

  Measuring capacitance (capacitive sensors G01D5/24) · CPC title