Systems and methods for measuring resistive sensors

• US 10,006,828 B2
• Filed: 06/24/2015
• Issued: 06/26/2018
• Est. Priority Date: 06/24/2015
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Agarwal, Manu, Smith, John Stephen, Ranganathan, Sumant
• Primary Examiner(s): West, Paul
• Assistant Examiner(s): Shabman, Mark A
• Application Number:
  US14/749,571
• Publication Number:
  US 20160377501A1
• Time in Patent Office: 1,098 Days
• Field of Search: None
• CPC Class Codes: G01L 1/2281 for temperature variations
• CPC Class Codes: G01L 25/00 Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment

Abstract

Systems and methods for accurately and precisely measuring the resistance of a resistive sensor of a matched resistive sensor pair disposed on opposite surfaces of a substrate. Certain embodiments include coupled each sensor of the matched resistive sensors to a thermally-isolated pair of reference resistors contained within an integrated circuit so as to form a Wheatstone bridge. A controller associated with the integrated circuit can adjust the resistance of the thermally-isolated pair of reference resistors until the ratio of resistances matches to the ratio of resistances between the sensors of the matched pair.

Claims

1. An electronic device comprising:

a substrate comprising;

a top surface; and

a bottom surface;

a first resistive sensor coupled to the top surface and formed from a material with a strain-sensitive electrical property;

a second resistive sensor coupled to the bottom surface, positioned opposite the first resistive sensor and aligned with the first resistive sensor, and formed from a material sharing a thermal property with the material of the first resistive sensor;

an integrated circuit comprising;

a first digitally variable resistor; and

a second digitally variable resistor positioned adjacent to the first digitally variable resistor within the integrated circuit;

an addressing controller to couple the first resistive sensor, second resistive sensor, the first digitally variable resistor, and the second digitally variable resistor into a balancing network configuration; and

a calibration controller to balance the balancing network.

2. The electronic device of claim 1, wherein the thermal property shared by the first digitally variable resistor and the second digitally variable resistor is temperature.

3. The electronic device of claim 1, further comprising a processor coupled to the balancing network and configured to obtain both a differential property measurement and a common property measurement of the balancing network.

4. The electronic device of claim 3, wherein the processor obtains the differential property measurement and common property measurement of the balancing network substantially simultaneously.

5. The electronic device of claim 1, wherein the first and second resistive sensors are formed from the group consisting of carbon nanotubes, graphene, and indium tin oxide.

6. The electronic device of claim 1, wherein the substrate is formed from a rigid material.

7. The electronic device of claim 6, wherein the substrate is formed from a material from the group consisting of sapphire and glass.

8. The electronic device of claim 1, wherein the substrate is formed from a thermally conductive and mechanically rigid material.

9. The electronic device of claim 1, wherein the substrate and the first and second resistive sensors are each formed from an optically transparent material.

10. The electronic device of claim 1, wherein the first and second resistive sensors are formed from a piezoresistive material.

11. The electronic device of claim 1, wherein the first digitally variable resistor is positioned physically proximate the second digitally variable resistor within an integrated circuit such that a temperature of the first digitally variable resistor may be substantial equal to a temperature of the second digitally variable resistor.

12. The electronic device of claim 1, wherein integrated circuit is separated from the substrate.

13. An electronic device comprising:

a thermally-conductive substrate comprising;

a first surface; and

a second surface opposite the first surface;

a resistive sensor pair comprising;

a first resistive sensor disposed on the first surface; and

a second resistive sensor disposed on the second surface and aligned with the first resistive sensor;

an integrated circuit enclosing;

a first digitally-variable resistor; and

a second digitally-variable resistor;

a calibration controller in signal communication with the resistive sensor pair and the integrated circuit;

wherein

the resistive sensor pair and the first and second digitally-variable resistor are arranged in a balancing network; and

the calibration controller is configured to measure a voltage between a first node and a second node of the balancing network.

14. The electronic device of claim 13, wherein the first digitally-variable resistor comprises an arrangement of selectable resistors.

15. The electronic device of claim 13, wherein the integrated circuit is arranged such that the first digitally-variable resistor and the second digitally-variable resistor are disposed adjacent to one another.

16. The electronic device of claim 13, wherein the resistive sensor pair comprises carbon nanotubes, graphene, or indium tin oxide.

17. The electronic device of claim 13, wherein the substrate is formed from a rigid material.

18. The electronic device of claim 17, wherein the substrate is formed from a material from the group consisting of sapphire and glass.