Capacitive sensor with differential shield

• US 9,739,816 B2
• Filed: 10/29/2014
• Issued: 08/22/2017
• Est. Priority Date: 11/27/2013
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Flanagan, Adrian Anthony
• Primary Examiner(s): Nguyen, Tung X
• Assistant Examiner(s): HAWKINS, DOMINIC E
• Application Number:
  US14/526,872
• Publication Number:
  US 20150145537A1
• Time in Patent Office: 1,028 Days
• Field of Search: 324686
• CPC Class Codes: G01R 27/2605 Measuring capacitance capacitive sensors G01D5/24
• CPC Class Codes: H03K 17/9622 using a plurality of detectors, e.g. keyboard
• CPC Class Codes: H03K 2217/960705 Safety of capacitive touch and proximity switches, e.g. increasing reliability, fail-safe
• CPC Class Codes: H03K 2217/960745 Capacitive differential; e.g. comparison with reference capacitance
• CPC Class Codes: H03K 2217/960765 Details of shielding arrangements

Abstract

The present disclosure describes a differential shield capacitive sensor design. The sensor design uses a differential measurement to measure capacitance and a pair of traces are used to differentially reject the response of the sensor traces and balance any parasitic capacitances. In some embodiments, the sensor design includes a differential sensor design on a bottom side of a flex circuit to differentially balance the environment and reject noise coupling to the sensor. The top side of the flex circuit can include a single ended design for proper environment sensing. The spatial arrangement and size of the sensors may vary depending on the application.

Claims

1. A capacitive sensor for sensing an environment of the capacitive sensor, wherein the capacitive sensor comprises:

a single-ended portion;

a segmented sensing differential shield portion having multiple segments; and

a pair of traces coupled to two terminals of a differential sampling circuitry respectively for differential sampling;

wherein the single-ended portion is connected to a first one of the traces, a first subset of the segments of the segmented sensing differential shield portion is connected to the first one of the traces, and a second subset of the segments is connected to a second one of the traces.

2. The capacitive sensor of claim 1, wherein:

the first subset of the segments has the same area or charge contribution as the second subset of the segments.

3. The capacitive sensor of claim 1, wherein:

the first subset of the segments are arranged in an alternating fashion with the second subset of the segments.

4. The capacitive sensor of claim 1, wherein:

the single-ended portion is on a first side of an insulating layer; and

the segmented sensing differential shield portion is on a second side of the insulating layer.

5. The capacitive sensor of claim 1, wherein:

the single-ended portion is on a first side of an insulating layer; and

the segmented sensing differential shield portion is on the first side of the insulating layer and on the second side of the insulating layer.

6. The capacitive sensor of claim 1, wherein the single-ended portion spans a smaller area than the segmented sensing differential shield portion.

7. The capacitive sensor of claim 1, wherein the single-ended portion is centered with respect to the segmented sensing differential shield portion.

8. The capacitive sensor of claim 1, wherein:

the single-ended portion and the first subset of segments are driven by a first one of a pair of differential signals; and

the second subset of the segments are driven by a second one of the pair of differential signals.

9. The capacitive sensor of claim 1, wherein the differential sampling circuitry substantially simultaneously samples a differential signal present on the pair of traces.

10. The capacitive sensor of claim 1, wherein:

the single-ended portion is adapted to sense the environment; and

the segmented sensing differential shield portion is adapted to differentially balance the environment and reject noise coupled to the segmented sensing differential shield portion.

11. The capacitive sensor of claim 1, wherein:

the single ended portion has a circular shape; and

the segmented sensing differential shield portion has a circular shape.

12. A system for sensing an environment of a capacitive sensor using differential sampling, the system comprising:

the capacitive sensor comprising;

a single-ended portion;

a segmented sensing differential shield portion having multiple segments; and

a pair of traces;

wherein the single-ended portion is connected to a first one of the traces, a first subset of the segments of the segmented sensing differential shield portion is connected to the first one of the traces, and a second subset of the segments is connected to a second one of the traces, and

a circuitry having two terminals connected to the pair of traces for differentially charging the capacitive sensor and substantially simultaneous sampling the capacitive sensor to obtain two differential measurement signals representative of the environment.

13. The system of claim 12, wherein:

the circuitry comprises a differential integrator for integrating the difference between the two differential signals present at the two terminals.

14. The system of claim 12, wherein:

the circuitry rejects noise coupled to the segmented sensing differential shield portion.

15. The system of claim 12, wherein the circuitry comprises:

switches configurable to connect the two terminals to a differential signal for charging the capacitive sensor; and

switches configurable to connect the two terminals to the inputs of a differential integrator for amplifying the difference between the two differential signals present at the two terminals.

16. The system of claim 12, further comprising:

an insulating layer;

wherein the single-ended portion is on a first side of an insulating layer and the segmented sensing differential shield portion is on at least a second side of the insulating layer.

17. The system of claim 16, wherein the insulating layer comprises a circuit board, flexible plastic substrate of a flexible circuit, and/or electrically insulating material.

18. A method for sensing an environment of a capacitive sensor using differential sampling, the method comprising:

differentially charging the capacitive sensor by connecting a first terminal and a second terminal to a first one of a differential signal and a second one of the differential signal respectively, wherein the first terminal and the second terminal are connected to a first trace and a second trace respectively, the first trace is connected to a single ended portion of the capacitive sensor and a first subset of segments of a segmented sensing differential shield portion of the capacitive sensor, and the second trace is connected to a second subset of segments of the segmented sensing differential shield portion of the capacitive sensor; and

substantially simultaneously sampling two differential measurement signals present at the first terminal and the second terminal.

19. The method of claim 18, further comprising:

rejecting noise and parasitic capacitances coupled to the segmented sensing differential shield portion through differential signaling.

20. The method of claim 18, further comprising:

rejecting a common mode signal of the two differential signals generated by the capacitive sensor.