Row column architecture for strain sensing

• US 10,444,091 B2
• Filed: 04/11/2017
• Issued: 10/15/2019
• Est. Priority Date: 04/11/2017
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hu, Jason C., Agarwal, Manu
• Primary Examiner(s): Bibbins, LaTanya
• Application Number:
  US15/484,958
• Publication Number:
  US 20180292933A1
• Time in Patent Office: 917 Days
• CPC Class Codes: G01L 1/205 using distributed sensing elements
• CPC Class Codes: G01L 1/2262 involving simple electrical bridges
• CPC Class Codes: G01L 5/22 for measuring the force applied to control members, e.g. control members of vehicles, triggers
• CPC Class Codes: G06F 3/04144 using an array of force sensing means position sensing using the local deformation of sensor cells G06F3/0447
• CPC Class Codes: G06F 3/0416 Control or interface arrangements specially adapted for digitisers

Abstract

Disclosed herein are structures, devices, and methods for sensing physical parameters, such as strain in a surface, using resistance-based parameter sensors and current sensing. An applied strain can cause a differential change in one or more currents from two resistors configured in parallel in the sensor. Strain can be inferred from a ratio of the difference of the two currents to a sum of the two currents. These structures and methods can be adapted to measure strain or other parameters using an array of sensors, with common voltages applied to rows of the array, and currents being summed in column in the array so that fewer receivers are needed.

Claims

1. A resistance-based sensing structure operable to determine a physical parameter, comprising:

a resistance-based parameter sensor comprising;

a first parameter-sensitive element; and

a second parameter-sensitive element connected in parallel with the first parameter-sensitive element;

drive circuitry coupled to the resistance-based parameter sensor and operative to apply a source signal to the resistance-based parameter sensor; and

current sensing circuitry coupled to the resistance-based parameter sensor and operative to concurrently and separately,

receive and measure a first current from the first parameter-sensitive element; and

receive and measure a second current from the second parameter-sensitive element;

wherein the current sensing circuitry is operable to estimate the physical parameter based on the separate measurements of the first current and the second current.

2. The resistance-based sensing structure of claim 1, wherein:

the physical parameter is a strain;

the first parameter-sensitive element is a first strain-sensitive element;

the second parameter-sensitive element is a second strain-sensitive element; and

the first strain-sensitive element and the second strain-sensitive element each comprise one of a conductive material or a piezoresistive material.

3. The resistance-based sensing structure of claim 2, wherein the first strain-sensitive element is on a first side of the resistance-based strain sensor, and the second strain-sensitive element is on a second side of the resistance-based strain sensor that is opposite to the first side.

4. The resistance-based sensing structure of claim 1, wherein:

the source signal is applied at an input node connected to the first parameter-sensitive element and the second parameter-sensitive element;

the first current is received from a first output node connected to a first output electrode of the first parameter-sensitive element; and

the second current is received from a second output node connected to a second output electrode of the second parameter-sensitive element, the second output electrode of the second parameter-sensitive element being electrically separated from the first output electrode of the first parameter-sensitive element.

5. The resistance-based sensing structure of claim 4, wherein the source signal is a voltage signal.

6. The resistance-based sensing structure of claim 4, further comprising:

a first current sink connected to the first output node; and

a second current sink connected to the second output node.

7. The resistance-based sensing structure of claim 6, wherein the current sensing circuitry comprises an amplifier configured to receive the first current and the second current.

8. The resistance-based sensing structure of claim 6, wherein the current sensing circuitry comprises:

a first amplifier having a first input junction that receives the first current and a first feedback of a first output signal of the first amplifier; and

a second amplifier having a second input junction that receives the second current and a second feedback of a second output signal of the second amplifier.

9. The resistance-based sensing structure of claim 1 wherein a value of the physical parameter is determined at least in part by a ratio of a difference between the first current and the second current to a sum of the first current and the second current.

10. A method of determining a physical parameter by a resistance-based parameter sensor comprising a first parameter-sensitive element and a second parameter-sensitive element connected in parallel, the method comprising:

applying a signal to the resistance-based parameter sensor;

receiving, separately and concurrently,

a first current from a first output electrode of the first parameter-sensitive element; and

a second current from a second output electrode of the second parameter-sensitive element;

separately obtaining measurements of the first current and the second current;

determining the physical parameter using the measurements of the first current and the second current.

11. The method of claim 10, wherein determining the physical parameter using the measurements of the first current and the second current comprises:

determining a difference of the measurements of the first current and the second current;

determining a sum of the measurements of the first current and the second current; and

determining a ratio of the difference and the sum.

12. The method of claim 10, wherein the signal is a time-varying voltage signal.

13. The method of claim 10, further comprising:

receiving the first current and the second current in a current sensing circuit, wherein the current sensing circuit comprises a first amplifier and a second amplifier;

amplifying the first current with the first amplifier; and

amplifying the second current with the second amplifier.

14. The method of claim 13, further comprising:

providing a first current sink at the first output electrode of the first parameter-sensitive element and shunting a first offset current from the first current; and

providing a second current sink at the second output electrode of the second parameter-sensitive element and shunting a second offset current from the second current.

15. An electronic device comprising:

an input surface;

a first resistance-based strain sensor positioned beneath the input surface, comprising;

a first signal input electrode;

a first strain-sensitive element connected to the first signal input electrode; and

a second strain-sensitive element connected to the first signal input electrode in parallel with the first strain-sensitive element;

a second resistance-based strain sensor positioned beneath the input surface, comprising;

a second signal input electrode;

a third strain-sensitive element connected to the second signal input electrode; and

a fourth strain-sensitive element connected to the second signal input electrode in parallel with the third strain-sensitive element;

a first signal source operative to apply a first signal to the first signal input electrode;

a second signal source operative to apply a second signal to the second signal input electrode;

a first current junction configured to receive a first current from the first strain-sensitive element and a second current from the third strain-sensitive element;

a second current junction configured to receive a third current from the second strain-sensitive element and a fourth current from the fourth strain-sensitive element;

current sensing circuitry coupled to first current junction and the second current junction; and

a processing structure operative to determine a force applied to the input surface using a sum of the first current and the second current and a sum of the third current and the fourth current,

wherein the sum of the first current and the second current is measured separately from the sum of the third current and the fourth current.

16. The electronic device of claim 15, wherein the first signal source and the second signal source respectively apply the first signal and the second signal alternately.

17. The electronic device of claim 15, further comprising:

a third resistance-based strain sensor positioned beneath the input surface and comprising;

a third signal input electrode;

a fifth strain-sensitive element connected to the third signal input electrode; and

a sixth strain-sensitive element connected to the third signal input electrode in parallel with the fifth strain-sensitive element;

a fourth resistance-based strain sensor positioned beneath the input surface and comprising;

a fourth signal input electrode;

a seventh strain-sensitive element connected to the fourth signal input electrode; and

an eighth strain-sensitive element connected to the fourth signal input electrode in parallel with the seventh strain-sensitive element;

a third current junction configured to receive a fifth current from the fifth strain-sensitive element and a sixth current from the seventh strain-sensitive element;

a fourth current junction configured to receive a seventh current from the sixth strain-sensitive element and an eighth current from the eighth strain-sensitive element;

wherein;

the first signal source is operative to apply the first signal to the third signal input electrode;

the second signal source is operative to apply the second signal to the fourth signal input electrode; and

the processing structure is operative to determine the force on the input surface using a sum of the fifth current and the seventh current and a sum of the sixth current and the eighth current.

18. The electronic device of claim 17, wherein:

the first signal source is operative to apply a third signal to the first signal input electrode and to the third signal input electrode;

the second signal source is operative to apply a fourth signal to the second signal input electrode and to the fourth signal input electrode;

the third signal and the fourth signal are applied simultaneously; and

the third signal and the fourth signal have opposite polarity.

19. The electronic device of claim 18, wherein the force on the input surface is determined using a change in value of at least one of the first, third, fifth, or seventh currents.

20. The electronic device of claim 17, wherein the first signal and the second signal are applied simultaneously with the same polarity.

21. The electronic device of claim 20, wherein the processing structure separately determines a first force applied to the input surface at a first location using the first, second, third, and fourth currents, and a second force applied to the input surface at a second location using the fifth, sixth, seventh and eighth currents.

22. The electronic device of claim 15, wherein:

the first signal source and the second signal source are positioned on a first plane beneath the input surface of the electronic device;

the first current junction and the second current junction are positioned on a second plane beneath the input surface, the second plane being parallel to the first plane and the input surface; and

a first conducting via connects the first strain-sensitive element to the first current junction;

a second conducting via connects the second strain-sensitive element to the second current junction;

a third conducting via connects the third strain-sensitive element to the first current junction; and

a fourth conducting via connects the fourth strain-sensitive element to the second current junction.