Trackpad sensitivity compensation

• US 20060290677A1
• Filed: 06/23/2005
• Published: 12/28/2006
• Est. Priority Date: 06/23/2005
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hotelling, Steve P., Lyon, Benjamin B.
• Granted Patent: US 9,298,311 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• 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 one electrode;

a storage device operatively connected to the first electrode;

a source operative to charge the at least one electrode;

a current source operatively connected to the storage device and sinking at least a portion of a current charging the storage device;

wherein

the storage device is charged from the first electrode; and

the current source acts to increase a sensitivity of the sensor circuit.

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 1, wherein the sensor circuit is a tracking sensor.

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

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

7. The sensor circuit of claim 5, wherein the tracking sensor operates in two dimensions.

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

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

10. The sensor circuit of claim 1, wherein the current sink 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 present 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 a first time from a first voltage negatively compensated by a current sink;

discharging the storage capacitor;

charging the storage capacitor 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; and

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

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

19. 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.

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

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

22. The method of claim 21, 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.

23. The method of claim 22, 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.