Force sensor interface for touch controller

• US 8,988,384 B2
• Filed: 09/23/2011
• Issued: 03/24/2015
• Est. Priority Date: 09/23/2011
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Krah, Christoph Horst, Shoykhet, Eugene Lvovich, Grunthaner, Martin Paul
• Primary Examiner(s): BOLOTIN, DMITRIY
• Application Number:
  US13/243,925
• Publication Number:
  US 20130076646A1
• Time in Patent Office: 1,278 Days
• Field of Search: 345156-184, 178/18.04, 178/18.06, 178/18.03, 178/18.05
• US Class Current: 345/174
• CPC Class Codes: G06F 3/04166 Details of scanning methods, e.g. sampling time, grouping of sub areas or time sharing with display driving Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally G06F3/04184
• CPC Class Codes: G06F 3/0446 using a grid-like structure of electrodes in at least two directions, e.g. using row and column electrodes
• 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

Abstract

A force sensor interface in a touch controller of a touch sensitive device is disclosed. The force sensor interface can couple to touch circuitry to integrate one or more force sensors with touch sensors of the device. The force sensor interface can include one portion to transmit stimulation signals generated by the touch circuitry to the force sensors to drive the sensors. The interface can also include another portion to receive force signals, indicative of a force applied to the device, from the force sensors for processing by the touch circuitry. The device can use the touch circuitry to concurrently and seamlessly operate both the force sensors and the touch sensors.

Claims

1. An interface for a touch controller comprising:

a first portion disposed between a first touch component of the touch controller and a force sensor to drive the force sensor with a differential input formed from a stimulation signal and an inverted stimulation signal to sense an applied force; and

a second portion disposed between a second touch component of the touch controller and the force sensor to process a force signal from the force sensor indicative of the applied force.

2. The interface of claim 1, wherein the first portion comprises:

a connector configured to connect the first touch component to the force sensor and to send a stimulation signal from the first touch component to the force sensor to drive the force sensor, wherein the first touch component comprises a touch buffer.

3. The interface of claim 1, wherein the first portion comprises:

a connector configured to connect the first touch component to the force sensor and to send the stimulation signal from the first touch component to the force sensor;

an inverter coupled to the first touch component and configured to receive the stimulation signal from the first touch component and to invert the stimulation signal; and

a force buffer coupled to the inverter and configured to send the inverted stimulation signal to the force sensor, wherein the first touch component comprises a touch buffer.

4. The interface of claim 1, wherein the first portion comprises:

a multiplexer coupled to the first touch component and configured to select the stimulation signal from the first touch component for sending to the force sensor;

a first force buffer coupled to the multiplexer and configured to send the stimulation signal to the force sensor;

an inverter coupled to the multiplexer and configured to receive the stimulation signal from the multiplexer and to invert the stimulation signal; and

a second force buffer coupled to the inverter and configured to send the inverted stimulation signal to the force sensor, wherein the first touch component comprises a stimulation signal generator.

5. An interface for a touch controller comprising:

a first portion disposed between a first touch component of the touch controller and a force sensor to drive the force sensor to sense an applied force; and

a second portion disposed between a second touch component of the touch controller and the force sensor to process a force signal from the force sensor indicative of the applied force, wherein the second portion comprises;

an amplifier coupled to the force sensor and configured to amplify the force signal; and

a mismatch circuit coupled to an output of the amplifier and the second touch component and configured to compensate for errors in an output signal value of the output, wherein the second touch component comprises a filter.

6. The interface of claim 5, wherein the amplifier is a differential amplifier, the differential amplifier outputting a first signal associated with the force signal to the mismatch circuit and a second signal associated with the force signal to the mismatch circuit, and wherein the mismatch circuit compensates for errors in the first and second signals.

7. The interface of claim 6, wherein the second portion comprises:

a converter coupled to the differential amplifier and the mismatch circuit and configured to convert the output of the differential amplifier and to send the converted output to the mismatch circuit to compensate for errors in the converted output.

8. The interface of claim 5, wherein the amplifier is a differential instrumentation amplifier, the differential instrumentation amplifier comprising a first amplifier to output a first signal associated with the force signal to the mismatch circuit and a second amplifier to output a second signal associated with the force signal to the mismatch circuit, and wherein the mismatch circuit compensates for errors in the first and second signals.

9. The interface of claim 5, wherein the amplifier is an instrumentation amplifier, the instrumentation amplifier comprising a first amplifier to output a first signal associated with the force signal, a second amplifier to output a second signal associated with the force signal, and a third amplifier to receive the first and second signals and to output a third signal based on the first and second signals to the mismatch circuit, and wherein the mismatch circuit compensates for errors in the third signal.

10. A touch controller comprising:

a transmit section configured to drive a touch sensor with a stimulation signal;

a receive section configured to process touch signals from the touch sensor in response to the stimulation signal; and

an interface integrated within the transmit section and the receive section to couple a force sensor thereto and configured to send the stimulation signal to the force sensor to drive the force sensor and to receive force signals from the force sensor in response to the stimulation signal, wherein the transmit section drives the touch sensor and the force sensor concurrently and the receive section processes the touch signals and the force signals concurrently, wherein the force sensor comprises a strain gauge, and wherein the force signals indicate a change in resistance of the strain gauge.

11. The controller of claim 10, wherein the transmit section comprises touch transmit circuitry configured to transmit the stimulation signal to the touch sensor, and wherein the receive section comprises touch receive circuitry configured to receive the touch signals from the touch sensor.

12. The controller of claim 10, wherein transmit section comprises touch transmit circuitry configured to transmit the stimulation signal to the force sensor via the interface, and wherein the receive section comprises touch receive circuitry configured to receive the force signals from the force sensor via the interface.

13. The controller of claim 12, wherein the touch receive circuitry comprises at least one of a bandpass filter or a low pass filter configured to reduce noise in the force signals.

14. The controller of claim 10, wherein the stimulation signal is configured to modulate so as to shift the force signals from the force sensor to a low noise frequency.

15. An integrated touch and force sensing device comprising:

at least one touch sensor that produces touch signals;

at least one force sensor that produces force signals, wherein the force sensor comprises a force sensor bridge configured to generate the force signals based on a resistance change at the bridge; and

a touch controller configured to integrally couple the touch sensor and the force sensor in the device, wherein the touch controller comprises;

touch circuitry that produces a stimulation signal; and

a signal path that conveys the stimulation signal to the touch sensor and the force sensor to produce the touch and force signals.

16. The device of claim 15, wherein the touch sensor comprises a touch panel configured to generate the touch signals based on a capacitance change at the panel.

17. The device of claim 15, wherein the bridge comprises four resistors, at least one of the resistors comprising a strain gauge.

18. The device of claim 17, wherein at least two of the resistors are part of the touch circuitry.

19. The device of claim 15, wherein the touch controller is configured to drive the force sensor with at least one of a single-ended stimulation signal or a differential stimulation signal.

20. The device of claim 15 incorporated into at least one of a mobile telephone, a digital media player, or a portable computer.

21. A method for sensing a touch and a force at a touch sensitive device comprising:

concurrently stimulating a touch sensor and a force sensor using touch circuitry;

generating a touch signal by the touch sensor, indicative of a touch at the touch sensor, and a force signal by the force sensor, indicative of a force applied at the force sensor, wherein the force signal indicates a resistance change in the force sensor due to the force applied at the force sensor;

scanning the touch sensor and the force sensor to capture the touch signal and the force signal respectively;

summing the touch signal and the force signal; and

processing the summed signal using the touch circuitry.

22. The method of claim 21, wherein scanning comprises:

concurrently scanning the touch sensor and the force sensor.

23. The method of claim 21, wherein scanning comprises:

scanning the touch sensor and the force sensor sequentially.

24. The method of claim 21, comprising:

triggering the scanning of at least one of the touch sensor or the force sensor based on a device condition.