CURRENT FEEDBACK TECHNIQUES FOR CAPACITIVE SENSING

• US 20160091999A1
• Filed: 09/30/2014
• Published: 03/31/2016
• Est. Priority Date: 09/30/2014
• Status: Active Grant

• Current Assignee: Synaptics Incorporated
• Original Assignee: Synaptics Incorporated
• Inventors: DATTALO, Tracy Scott
• Granted Patent: US 9,891,763 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G06F 3/0383 Signal control means within the pointing device
• CPC Class Codes: G06F 3/041662 using alternate mutual and self-capacitive scanning
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• 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
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/96073 Amplitude comparison
• CPC Class Codes: H03K 2217/960745 Capacitive differential; e.g. comparison with reference capacitance

Abstract

Examples of the present disclosure generally provide current feedback techniques for capacitive sensing with an input device. A processing system for an input device includes an operational amplifier having a non-inverting input, an inverting input, and an output. A voltage source is coupled to the non-inverting input. A first voltage-controlled current source is coupled between the output and the inverting input to form a feedback path. A second voltage-controlled current source is coupled to the output and configured for modifying a charge on a capacitor based on a control voltage at the output. A determination module is coupled to the capacitor and configured for determining a capacitance measurement at the inverting input based on the charge on the capacitor.

Claims

1. A processing system for an input device, comprising:

an operational amplifier having a non-inverting input, an inverting input, and an output;

a voltage source coupled to the non-inverting input;

a first voltage-controlled current source coupled between the output and the inverting input to form a feedback path;

a second voltage-controlled current source coupled to the output and configured for modifying a charge on a capacitor based on a control voltage at the output; and

a determination module coupled to the capacitor and configured for determining a capacitance measurement at the inverting input based on the charge on the capacitor.

2. The processing system of claim 1, wherein the first voltage-controlled current source is configured for driving an input sensing signal onto a sensor electrode based on the control voltage while the second voltage-controlled current source is modifying the charge on the capacitor.

3. The processing system of claim 2, wherein the voltage source is configured for driving an input voltage onto the non-inverting input to cause the first voltage-controlled current source to drive the input sensing signal onto the sensor electrode.

4. The processing system of claim 2, wherein the capacitance measurement comprises a capacitance between the sensor electrode and an input object.

5. The processing system of claim 2, wherein the capacitance measurement comprises a first capacitance between the sensor electrode and an input object and a second capacitance between the sensor electrode and a receiver electrode.

6. The processing system of claim 1, wherein the first voltage-controlled current source is configured for coupling to a sensor electrode, and the capacitance measurement comprises a capacitance between the sensor electrode and a transmitter electrode.

7. The processing system of claim 6, wherein the voltage source is configured for driving a substantially constant input voltage onto the non-inverting input during a mutual capacitance sensing time period.

8. The processing system of claim 7, wherein the first voltage-controlled current source is configured for driving an input sensing signal onto the sensor electrode based on the control voltage during a self capacitance sensing time period.

9. The processing system of claim 1, wherein a capacitance of the capacitor is substantially constant.

10. An input device for capacitive sensing, comprising:

a plurality of sensor electrodes; and

a processing system coupled to the plurality of sensor electrodes, the processing system comprising;

an operational amplifier having a non-inverting input, an inverting input, and an output;

a voltage source coupled to the non-inverting input;

a first voltage-controlled current source coupled between the output and the inverting input to form a feedback path;

a second voltage-controlled current source coupled to the output and configured to modify a charge on a capacitor based on a control voltage at the output; and

a determination module coupled to the capacitor and configured to;

determine a capacitance measurement associated with a sensor electrode included in the plurality of sensor electrodes and coupled to the inverting input based on the charge on the capacitor; and

determine positional information based on the capacitance measurement.

11. The input device of claim 10, wherein the first voltage-controlled current source is coupled to the sensor electrode and configured to drive an input sensing signal onto the sensor electrode based on the control voltage while the second voltage-controlled current source modifies the charge on the capacitor.

12. The input device of claim 11, wherein the voltage source is configured to drive an input voltage onto the non-inverting input to cause the first voltage-controlled current source to drive the input sensing signal onto the sensor electrode.

13. The input device of claim 11, wherein the capacitance measurement comprises a capacitance between the sensor electrode and an input object.

14. The input device of claim 11, wherein the capacitance measurement comprises a first capacitance between the sensor electrode and an input object and a second capacitance between the sensor electrode and a receiver electrode.

15. The input device of claim 10, wherein the voltage source is configured to drive a substantially constant input voltage onto the non-inverting input during a mutual capacitance sensing time period, and the capacitance measurement comprises a capacitance between the sensor electrode and a transmitter electrode during the mutual capacitance sensing time period.

16. The input device of claim 15, wherein the first voltage-controlled current source is configured to drive an input sensing signal onto the sensor electrode based on the control voltage during a self capacitance sensing time period.

17. A method of input sensing with a sensor electrode, the method comprising:

driving an input voltage onto a non-inverting input of an operational amplifier, wherein a first voltage-controlled current source is coupled between an output of the operational amplifier and an inverting input of the operational amplifier to form a feedback path;

modifying, via a second voltage-controlled current source coupled to the output, a charge on a capacitor based on a control voltage at the output; and

determining a capacitance measurement associated with a sensor electrode coupled to the inverting input based on the charge on the capacitor.

18. The method of claim 17, wherein driving the input voltage onto the non-inverting input causes the first voltage-controlled current source to drive an input sensing signal onto the sensor electrode while the second voltage-controlled current source modifies the charge on the capacitor.

19. The method of claim 18, wherein the capacitance measurement comprises a capacitance between the sensor electrode and an input object.

20. The method of claim 18, wherein the capacitance measurement comprises a first capacitance between the sensor electrode and an input object and a second capacitance between the sensor electrode and a receiver electrode.

21. The method of claim 17, wherein the capacitance measurement comprises a capacitance between the sensor electrode and a transmitter electrode.

22. The method of claim 21, further comprising driving a substantially constant input voltage onto the non-inverting input during a mutual capacitance sensing time period.

23. The method of claim 22, wherein driving the input voltage onto the non-inverting input causes the first voltage-controlled current source to drive an input sensing signal onto the sensor electrode during a self capacitance sensing time period.