Trackpad sensitivity compensation

• US 9,298,311 B2
• Filed: 06/23/2005
• Issued: 03/29/2016
• Est. Priority Date: 06/23/2005
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Lyon, Benjamin B., Hotelling, Steve P.
• Primary Examiner(s): Pappas, Claire X
• Assistant Examiner(s): STONE, ROBERT M
• Application Number:
  US11/165,951
• Publication Number:
  US 20060290677A1
• Time in Patent Office: 3,932 Days
• Field of Search: 345/156, 345/173, 345/174, 178 1801- 1907, 463/37
• US Class Current: 1/1
• CPC Class Codes: G06F 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• 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: H03K 2217/96073 Amplitude comparison

Abstract

A device compensating for a loss in sensitivity of a sensor, such as a trackpad. The device may be standalone, integrated with the trackpad itself, or within the associated integrated circuit designed to measure relative electrode capacitances. The embodiment generally employs a current source to negatively compensate for the current available to charge at least one capacitor (or other storage device) in the trackpad.

Claims

1. A sensor circuit, comprising:

at least a first electrode;

a storage device operatively connected to the first electrode;

a source operative to charge at least the first electrode; and

a current source operatively connected to the storage device and sinking a portion of a current while a remainder of the current is charging the storage device;

wherein

the storage device is charged from the first electrode.

2. The sensor circuit of claim 1, wherein the storage device is a capacitor.

3. The sensor circuit of claim 1, further comprising:

a surface overlaying the at least one electrode;

wherein

the surface is operative to capacitively couple a finger touching the surface to the first electrode.

4. The sensor circuit of claim 3, wherein the tracking sensor operates in at least one dimension.

5. The sensor circuit of claim 1, wherein the sensor circuit is a tracking sensor.

6. The sensor circuit of claim 1, wherein the sensor is a touch button.

7. The sensor circuit of claim 6, wherein the tracking sensor operates in two dimensions.

8. The sensor circuit of claim 1, wherein the current source comprises a switched capacitor.

9. The sensor circuit of claim 1, wherein the current source comprises a switched resistor.

10. The sensor circuit of claim 1, wherein the current source comprises a current follower.

11. The sensor circuit of claim 1, wherein the sensor circuit comprises an active current sink.

12. The sensor circuit of claim 1, further comprising a comparator operatively connected to the storage device.

13. The sensor circuit of claim 12, further comprising a switch operatively connected to the storage device.

14. The sensor circuit of claim 13, wherein:

the comparator is operative to close the switch when the storage device reaches a preset voltage; and

the switch is operative to drain a voltage from the storage device when the switch closes.

15. The sensor circuit of claim 14, further comprising:

a first switch connected between the first electrode and the voltage source; and

a second switch connected between the first electrode and second electrode;

wherein

the opening and closing of the first and second switches is operative to charge the first and second electrodes at a given frequency.

16. A method for determining a presence of a finger, comprising:

charging a storage capacitor for a first time while a first voltage is negatively compensated by a current sink by sinking a portion of a current while a remainder of the current charges the storage capacitor;

discharging the storage capacitor;

charging the storage capacitor for a second time;

comparing the first time to the second time; and

in the event the second time is less than the first time, concluding a finger is present.

17. The method of claim 16, wherein the step of charging a capacitor a first time comprises:

charging the storage capacitor from a current generated by a sense capacitor at a given frequency.

18. The method of claim 17, wherein the step of charging the storage capacitor a second time comprises:

charging the storage capacitor from a current generated by a sense capacitor at a given frequency; and

negatively compensating the current before the current charges the storage capacitor.

19. The method of claim 18, further comprising charging the sense capacitor at a given frequency from a voltage source.

20. The method of claim 19, wherein the application of the negative compensation to the current increases a sensitivity of the sense capacitor to the presence of a finger.

21. The method of claim 20, further comprising:

determining whether a voltage of the storage capacitor exceeds a threshold voltage;

in the event the voltage of the storage capacitor exceeds the threshold voltage, closing a switch; and

in response to closing the switch, resetting the voltage of the storage capacitor.

22. The method of claim 21, wherein:

the operation of negatively compensating the current comprises;

connecting the current source and the storage capacitor to a common node; and

draining at least a portion of the current from the common node such that the drained portion of the current cannot charge the storage capacitor.

23. The method of claim 16, wherein the current is negatively compensated by applying a current source to the current.