Systems and Methods for Measuring Resistive Sensors

Patent metadata

Field	Value
Publication number	US-2016377501-A1
Application number	US-201514749571-A
Country	US
Kind code	A1
Filing date	Jun 24, 2015
Priority date	Jun 24, 2015
Publication date	Dec 29, 2016
Grant date	—

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.

First claim

What is claimed is:

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 formed from a material sharing a thermal property with the material of the first resistive sensor; a first digitally variable resistor; and a second digitally variable resistor disposed so as to share a thermal property with the first digitally variable resistor; 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 , wherein the first digitally variable resistor and the second digitally variable resistor are disposed within an integrated circuit.

4 . 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.

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

6 . 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.

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

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

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

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

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

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

13 . A method of calibrating a force sensor comprising a first and second resistive strain sensors arranged on opposite sides of a substrate and electrically coupled as a first voltage divider, the method comprising:
coupling a first digitally-controlled resistor to a second digitally controlled resistor as a second voltage divider; coupling the first voltage divider to the second voltage divider to form a balancing network; adjusting the resistance of the first digitally-controlled resistor and the resistance of the second digitally-controlled strain sensors until the balancing network is balanced; and storing the resistance of the first digitally-controlled resistor and the second digitally-controlled strain sensor.

14 . The method of claim 13 , wherein the first and second resistive strain sensors are formed from an optically transparent material.

15 . The method of claim 13 , further comprising:
determining that the force sensor is experiencing a known force magnitude prior to adjusting the resistance of the first digitally-controlled resistor and the resistance of the second digitally-controlled strain sensors until the balancing network is balanced.

16 . The method of claim 15 , wherein the known force magnitude comprises a force having a magnitude greater than zero.

17 . The method of claim 15 , wherein the known force magnitude comprises a force having a magnitude functionally equal to zero.

18 . A method of reading a force sensor comprising a first and second resistive strain sensors arranged on opposite sides of a substrate and electrically coupled as a first voltage divider, the method comprising:
coupling a first digitally-controlled resistor to a second digitally controlled resistor as a second voltage divider, coupling the first voltage divider to the second voltage divider to form a balancing network; setting the resistance of the first and second digitally controlled resistor based on a first and second calibration value; and obtaining a measurement of a voltage between midpoints of the balancing network

19 . The method of claim 18 , wherein the substrate comprises glass.

20 . The method of claim 18 , wherein:
the substrate is formed from glass; and the resistive strain sensors are formed from a piezoresistive material.

21 . The method of claim 18 , further comprising associating the voltage between midpoints of the balancing network with a magnitude of force applied to the substrate.

22 . A method of manufacturing an integrated circuit for measuring changes in a resistive strain sensor pair, the method comprising:
determining a resistance and manufacturing tolerance for each resistive strain sensor within the resistive strain sensor pair; forming a first plurality of individual resistors onto a substrate such that the total series resistance of the plurality of individual resistors is greater than the manufacturing tolerance; forming a first plurality of switching transistors onto the substrate, each switching transistor electrically coupled to a respective one sensor of the first plurality of individual sensors; forming a second plurality of individual resistors adjacent to the first plurality of individual resistors, the second plurality of individual resistors formed onto the substrate such that the total series resistance of the plurality of individual resistors is greater than the manufacturing tolerance; and forming a second plurality of switching transistors onto the substrate, each switching transistor electrically coupled to a respective one sensor of the second plurality of individual sensors.

Assignees

• Apple Inc

Inventors

• Agarwal Manu
• Smith John Stephen
• Ranganathan Sumant

Classifications

• G01L1/18

  using properties of piezo-resistive materials, i.e. materials of which the ohmic resistance varies according to changes in magnitude or direction of force applied to the material · CPC title

• G01L25/00 Primary

  Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency · CPC title

• G06F3/0418

  for error correction or compensation, e.g. based on parallax, calibration or alignment · CPC title

• G01L1/2281

  for temperature variations · CPC title