Direct capacitance measurement based capacitive disturbance detection system

Patent metadata

Field	Value
Publication number	US-11255889-B2
Application number	US-202016752792-A
Country	US
Kind code	B2
Filing date	Jan 27, 2020
Priority date	Sep 5, 2019
Publication date	Feb 22, 2022
Grant date	Feb 22, 2022

Abstract

An apparatus includes a first oscillator circuit coupled to a first electrode and a second oscillator circuit coupled to a second electrode. The first and second oscillator circuits oscillate synchronously in response to a capacitance between the first and second electrodes being greater than or equal to a threshold coupling capacitance and asynchronously in response to the capacitance being less than the threshold coupling capacitance. The first and second electrodes are separated by a distance, such that a disturbance within the distance increases the capacitance between the electrodes equal to or above the threshold coupling capacitance. The frequency of the first oscillator circuit is inversely proportional to a capacitance of the first electrode, and the frequency of the second oscillator circuit is inversely proportional to a capacitance of the second electrode.

First claim

What is claimed is:

1. An apparatus, comprising:
a first electrode having a first capacitance;
a second electrode having a second capacitance, and disposed in proximity to the first electrode;
a first oscillator circuit coupled to the first electrode, and configured to oscillate at a frequency inversely related to capacitance at the first electrode;
a second oscillator circuit coupled to the second electrode, and configured to oscillate at a frequency inversely related to capacitance at the second electrode;
and

a processing unit coupled to the first and second oscillator circuits and configured to:
determine whether the first and second oscillator circuits are oscillating synchronously or asynchronously;
detect a change between synchronous oscillation and asynchronous oscillation of the first and second oscillator circuits; and
responsive to detecting a change between synchronous and asynchronous oscillation, generate a control signal indicative of an external influence having changed capacitive coupling between the first electrode and the second electrode.

2. The apparatus of claim 1 , further comprising a capacitor coupled to the first and the second electrodes and having a capacitance less than the threshold coupling capacitance.

3. The apparatus of claim 1 , wherein the first and the second electrodes are separated by a distance, such that a disturbance within the distance increases the capacitance between the first and the second electrodes equal to or above the threshold coupling capacitance.

4. The apparatus of claim 1 , wherein the processing unit generates the control signal responsive to detecting a change from asynchronous oscillation to synchronous oscillation;
and wherein the control signal is indicative of the presence of an external influence coupling the first and second electrodes with a capacitance greater than a threshold coupling capacitance.

5. The apparatus of claim 1 , wherein the processing unit generates the control signal responsive to detecting a change from synchronous oscillation to asynchronous oscillation;
and wherein the control signal is indicative of the removal of an external influence coupling the first and second electrodes with a capacitance greater than a threshold coupling capacitance.

6. An apparatus, comprising:
a first electrode and a second electrode;
a first oscillator circuit coupled to the first electrode and comprising:
a first hysteresis buffer having a first input and a first output, wherein the first input is coupled to the first electrode;
a first inverter coupled to the first output, the first inverter having a first inverter output;
a first selector logic circuit having a first input coupled to a supply voltage node, a second input coupled to a ground node, a selection input coupled to the first inverter output, and a first selector logic output; and
a first resistor coupled to the first selector logic output and to the first input;

a second oscillator circuit coupled to the second electrode, wherein the first and second oscillator circuits are configured to:
oscillate synchronously in response to a capacitance between the first and second electrodes being greater than a threshold coupling capacitance, and
oscillate asynchronously in response to the capacitance between the first and second electrodes being less than a threshold coupling capacitance; and

a processing unit coupled to the first and second oscillator circuits and configured to:
determine whether the first and second oscillator circuits oscillate synchronously or asynchronously; and
generate a control signal indicative of a capacitive disturbance based on the determination whether the first and second oscillator circuits oscillate synchronously or asynchronously.

7. The apparatus of claim 6 , wherein the first hysteresis buffer comprises a Schmitt trigger.

8. The apparatus of claim 6 , wherein the second oscillator circuit comprises:
a second hysteresis buffer having a second input and a second output, wherein the second input is coupled to the second electrode;
a second inverter coupled to the second output, the second inverter having a second inverter output;
a second selector logic circuit having a third input coupled to a supply voltage node, a fourth input coupled to a ground node, a selection input coupled to the second inverter output, and a second selector logic output; and
a second resistor coupled to the second selector logic output and to the second input.

9. The apparatus of claim 8 , wherein the second hysteresis buffer comprises a Schmitt trigger.

10. A non-transitory computer-readable medium storing machine instructions which, when executed by one or more processing units, cause the one or more processing units to:
obtain a first oscillation frequency from a first oscillator circuit coupled to a first electrode and a second oscillation frequency from a second oscillator circuit coupled to a second electrode;
compare the first oscillation frequency and the second oscillation frequency to determine whether the first and the second oscillator circuits oscillate synchronously at substantially a same oscillation frequency or asynchronously at different oscillation frequencies; and
in response to the comparing of the first and second oscillation frequencies detecting a change between synchronous oscillation and asynchronous oscillation of the first and the second oscillator circuits, output a notification indicative of an external influence having changed a capacitance between the first and the second electrodes.

11. The non-transitory computer-readable medium of claim 10 , wherein the first oscillation frequency corresponds to a capacitance of the first electrode, and wherein the second oscillation frequency corresponds to a capacitance of the second electrode.

12. The non-transitory computer-readable medium of claim 11 , further comprising machine instructions which, when executed by the one or more processing units, cause the one or more processing units to:
determine a capacitance of the first electrode based on the first oscillation frequency; and
determine a capacitance of the second electrode based on the second oscillation frequency.

13. The non-transitory computer-readable medium of claim 10 , wherein the machine instructions, when executed, cause the one or more processing units to output the notification by:
in response to detecting a change from synchronous to asynchronous oscillation of the first and the second oscillator circuits, outputting a notification indicative of reduction of the capacitance between the first and the second electrodes to less than a threshold coupling capacitance.

14. The non-transitory computer-readable medium of claim 10 , wherein the machine instructions, when executed, cause the one or more processing units to output the notification by:
in response to detecting a change from asynchronous to synchronous oscillation of the first and the second oscillator circuits, outputting a notification indicative of an increase of the capacitance between the first and the second electrodes to greater than a threshold coupling capacitance.

15. The non-transitory computer-readable medium of claim 14 , wherein:
the first and the second electrodes are included in a touch interface;
the first and second electrodes are capacitively coupled in response to a touch on the touch interface; and
the capacitance of the first electrode and the capacitance of the second electrode vary based on a location of the touch.

16. The non-transitory computer-readable medium of claim 15 , further comprising machi

Assignees

• Texas Instruments Inc

Inventors

• Spevak Peter

Classifications

• G06F3/0412

  Digitisers structurally integrated in a display · CPC title

• G06F3/0416

  Control or interface arrangements specially adapted for digitisers · CPC title

• G01R27/2605 Primary

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

• G06F3/044

  by capacitive means · CPC title

• G06F3/0443 Primary

  using a single layer of sensing electrodes · CPC title