Electronic device with noise-cancelling force sensor

• US 9,246,486 B2
• Filed: 12/16/2011
• Issued: 01/26/2016
• Est. Priority Date: 12/16/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Yang, Bingrui, Grunthaner, Martin P., Hotelling, Steven P.
• Primary Examiner(s): Bolotin, Dmitriy
• Application Number:
  US13/329,133
• Publication Number:
  US 20130154998A1
• Time in Patent Office: 1,502 Days
• Field of Search: 345156-184, 178 1801- 2004
• US Class Current: 1/1
• CPC Class Codes: G01L 1/22 using resistance strain gauges
• CPC Class Codes: G01L 1/2262 involving simple electrical bridges
• CPC Class Codes: G06F 2203/04102 Flexible digitiser, i.e. constructional details for allowing the whole digitising part of a device to be flexed or rolled like a sheet of paper
• CPC Class Codes: G06F 2203/04105 Pressure sensors for measuring the pressure or force exerted on the touch surface without providing the touch position
• CPC Class Codes: G06F 3/0414 using force sensing means to determine a position
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means
• CPC Class Codes: G06F 3/045 using resistive elements, e.g. a single continuous surface or two parallel surfaces put in contact
• CPC Class Codes: G06F 3/047 using sets of wires, e.g. crossed wires
• CPC Class Codes: H03K 17/9625 using a force resistance transducer
• CPC Class Codes: H04M 1/0266 for a display module assembly
• CPC Class Codes: H04M 1/72466 with selection means, e.g. keys, having functions defined by the mode or the status of the device
• CPC Class Codes: H04M 1/72469 for operating the device by selecting functions from two or more displayed items, e.g. menus or icons

Abstract

An electronic device may have a housing in which components such as a display are mounted. A strain gauge may be mounted on a layer of the display such as a cover layer or may be mounted on a portion of the housing or other support structure. The layer of material on which the strain gauge is mounted may be configured to flex in response to pressure applied by a finger of a user. The strain gauge may serve as a button for the electronic device or may form part of other input circuitry. A differential amplifier and analog-to-digital converter circuit may be used to gather and process strain gauge signals. The strain gauge may be formed form variable resistor structures that make up part of a bridge circuit that is coupled to the differential amplifier. The bridge circuit may be configured to reduce the impact of capacitively coupled noise.

Claims

1. An electronic device, comprising:

a strain gauge having at least one variable resistor;

a differential amplifier that receives signals from the at least one variable resistor, wherein the electronic device comprises a layer of material, wherein the at least one variable resistor comprises first and second variable resistors in a bridge circuit, and wherein the first and second variable resistors are adjacent to each other on the layer of material; and

a display, wherein the at least one variable resistor comprises structures on the display.

2. The electronic device defined in claim 1 wherein the layer of material is a display cover layer of the display, and wherein the first and second variable resistors comprise patterned material on the display cover layer.

3. The electronic device defined in claim 2 wherein the display cover layer comprises a layer of cover glass having an exterior surface and an interior surface and wherein the patterned material comprises a meandering line on the interior surface.

4. The electronic device defined in claim 1 wherein the layer of material is configured to flex in response to pressure from a finger of a user, and wherein the at least one variable resistor comprises variable resistor structures formed on an interior surface of the layer of material.

5. The electronic device defined in claim 4 wherein the layer of material comprises glass.

6. The electronic device defined in claim 4 further comprising housing structures that include the layer of material.

7. The electronic device defined in claim 4 wherein the bridge circuit has a first node coupled to a first differential input of the differential amplifier and a second node coupled to a second differential input of the differential amplifier, wherein the variable resistor structures are coupled to the first and second differential inputs, and wherein the variable resistor structures are configured to balance how much noise is capacitively coupled to the first differential input from the finger with how much noise is capacitively coupled to the second differential input from the finger to reduce noise at an output of the differential amplifier.

8. The electronic device defined in claim 4 wherein the first and second variable resistors have the same shape and same area on the layer of material to balance how much noise is capacitively coupled to a first differential input of the differential amplifier from the finger with how much noise is capacitively coupled to a second differential input of the differential amplifier from the finger to reduce noise at an output of the differential amplifier.

9. The electronic device defined in claim 4 wherein the first and second variable resistors have meandering paths on the layer of material that run parallel to each other to balance how much noise is capacitively coupled to a first differential input of the differential amplifier from the finger with how much noise is capacitively coupled to a second differential input of the differential amplifier from the finger to reduce noise at an output of the differential amplifier.

10. The electronic device defined in claim 4 wherein the first and second variable resistors have different shapes and wherein the first and second variable resistors have equal size on the layer of material to balance how much noise is capacitively coupled to a first differential input of the differential amplifier from the finger with how much noise is capacitively coupled to a second differential input of the differential amplifier from the finger to reduce noise at an output of the differential amplifier.

11. The electronic device defined in claim 4 wherein the first and second variable resistors have different shapes and different sizes on the layer of material, the electronic device further comprising a coupling pad in the strain gauge that is coupled to the first variable resistor to balance how much noise is capacitively coupled to a first differential input of the differential amplifier from the finger with how much noise is capacitively coupled to a second differential input of the differential amplifier from the finger to reduce noise at an output of the differential amplifier.

12. The electronic device defined in claim 4 wherein the variable resistor structures are configured to balance how much noise is capacitively coupled from the finger of the user to a first differential input of the differential amplifier through the variable resistor structures with how much noise is capacitively coupled from the finger of the user to a second differential input of the differential amplifier through the variable resistor structures to reduce noise at an output of the differential amplifier.

13. The electronic device defined in claim 12 wherein the layer of material comprises a display cover layer having first and second opposing surfaces and wherein the variable resistor structures are formed on the second surface.

14. The electronic device defined in claim 13 wherein the display cover layer comprises a layer of cover glass and wherein the first surface comprises an external surface of the cover glass that is configured to flex inwardly in response to pressure from the finger.

15. The electronic device defined in claim 14 further comprising an analog-to-digital converter configured to digitize analog output signals received from the output of the differential amplifier.

16. The electronic device defined in claim 15 wherein the cover glass has first and second ends and wherein the variable resistor structures are located at the second end and are configured to serve as a button for the electronic device.

17. An electronic device, comprising:

a strain gauge having at least one variable resistor; and

a differential amplifier that receives signals from the at least one variable resistor, wherein the electronic device comprises a layer of material, wherein the at least one variable resistor comprises first and second variable resistors in a bridge circuit, wherein the first and second variable resistors are adjacent to each other on the layer of material, wherein the layer of material is configured to flex in response to pressure from a finger of a user, wherein the at least one variable resistor comprises variable resistor structures formed on an interior surface of the layer of material, and wherein the first and second variable resistors balance how much noise is capacitively coupled to a first differential input of the differential amplifier from the finger with how much noise is capacitively coupled to a second differential input of the differential amplifier from the finger to reduce noise at an output of the differential amplifier.

18. An electronic device, comprising:

a strain gauge having at least one variable resistor; and

a differential amplifier that receives signals from the at least one variable resistor, wherein the differential amplifier has first and second differential inputs, the electronic device further comprising a coupling pad in the strain gauge to balance how much noise is capacitively coupled to the first differential input with how much noise is capacitively coupled to the second differential input to reduce noise at an output of the differential amplifier.