MULTIPOINT TOUCH SURFACE CONTROLLER

• US 20070257890A1
• Filed: 05/02/2006
• Published: 11/08/2007
• Est. Priority Date: 05/02/2006
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Krah, Christoph, Huppi, Brian, Hotelling, Steven
• Granted Patent: US 8,279,180 B2
• Time in Patent Office: Days
• US Class Current: 345/173
• CPC Class Codes: G06F 2203/04104 Multi-touch detection in digitiser, i.e. details about the simultaneous detection of a plurality of touching locations, e.g. multiple fingers or pen and finger
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/0443 using a single layer of sensing electrodes
• 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

Abstract

A multipoint touch surface controller is disclosed herein. The controller includes an integrated circuit including output circuitry for driving a capacitive multi-touch sensor and input circuitry for reading the sensor. Also disclosed herein are various noise rejection and dynamic range enhancement techniques that permit the controller to be used with various sensors in various conditions without reconfiguring hardware.

Claims

1. A controller for a multi-touch surface, the multi-touch surface having at least one drive electrode, at least one sense electrode, and at least one node disposed at an intersection of the at least one drive electrode and the at least one sense electrode, the controller comprising:

output circuitry operatively connected to the at least one drive electrode, the output circuitry being configured to generate timing signals that may be used to generate drive waveforms for the multi-touch surface; and

input circuitry operatively connected to the at least one sense electrode, the input circuitry being configured to determine proximity of an object at each node by measuring capacitive coupling of the drive waveforms from the drive electrode to the sense electrode;

wherein the output circuitry and input circuitry are part of a single application specific integrated circuit.

2. The controller of claim 1 further comprising decoding and level shifting circuitry connected between the output circuitry and the drive electrode, the decoding and level shifting circuitry being configured to receive the timing signals and generate drive waveforms for the multi-touch surface.

3. The controller of claim 1 wherein the decoding and level shifting circuitry are part of the single application specific integrated circuit.

4. The controller of claim 1 wherein the drive waveforms comprise:

a first periodic waveform having a first predetermined frequency; and

at least one additional periodic waveform having an additional predetermined frequency different from the first predetermined frequency;

wherein the first periodic waveform and at least one additional periodic waveforms are applied sequentially to the drive electrode.

5. The controller of claim 4 wherein the at least one additional periodic waveforms comprise a second periodic waveform having a second predetermined frequency and a third periodic waveform having a third predetermined frequency, each of the second predetermined frequency and the third predetermined frequency being different from the first predetermined frequency and different from each other.

6. The controller of claim 1 wherein the input circuitry comprises a charge amplifier, the charge amplifier further comprising:

an operational amplifier having an inverting input terminal, a non-inverting input terminal, and an output terminal, wherein the non-inverting input terminal is operatively connected to the at least one sense electrode;

a feedback capacitor connected between the output terminal and the inverting input terminal, wherein the feedback capacitor is programmable to take on a range of values; and

a feedback resistor connected between the output terminal and the inverting input terminal, wherein the feedback resistor is programmable to take on a range of values.

7. The controller of claim 6 wherein the charge amplifier further comprises a resistor coupled between the non-inverting input terminal and the at least one sense electrode to form an anti-aliasing filter in combination with the feedback resistor and feedback capacitor.

8. The controller of claim 6 wherein the non-inverting input of the amplifier is coupled to ground.

9. The controller of claim 1 wherein the input circuitry comprises an offset compensator, the offset compensator comprising:

a programmable offset digital to analog converter adapted to generate an offset signal corresponding to a static component of the capacitive coupling between the drive electrode and the sense electrode; and

a subtractor circuit configured to subtract the offset signal from a measured signal indicative of the capacitive coupling between the at least one drive electrode and the at least one sense electrode.

10. The controller of claim 6 wherein the input circuitry further comprises an offset compensator, the offset compensator comprising:

a programmable offset digital to analog converter adapted to generate an offset signal corresponding to a static component of the capacitive coupling between the drive electrode and the sense electrode; and

a subtractor circuit configured to subtract the offset signal from an output signal of the charge amplifier, the output signal being indicative of the capacitive coupling between the at least one drive electrode and the at least one sense electrode.

11. The controller of claim 1 wherein the input circuitry comprises a demodulator, the demodulator comprising a multiplier configured to mix a signal indicative of a capacitive coupling between the at least one drive electrode and the at least one sense electrode with a demodulation waveform.

12. The controller of claim 6 wherein the input circuitry further comprises a demodulator, the demodulator comprising a multiplier configured to mix an output signal of the operational amplifier, said output signal being indicative of a capacitive coupling between the at least one drive electrode and the at least one sense electrode, with a demodulation waveform.

13. The controller of claim 12 wherein the input circuitry further comprises an offset compensator, the offset compensator comprising:

a programmable offset digital to analog converter adapted to generate an offset signal corresponding to a static component of the capacitive coupling between the drive electrode and the sense electrode; and

a subtractor circuit configured to subtract the offset signal from the output signal of the demodulator, said output signal being indicative of the capacitive coupling between the at least one drive electrode and the at least one sense electrode.

14. The controller of claim 9 wherein the input circuitry further comprises a demodulator, the demodulator comprising a multiplier configured to mix an output signal of the offset compensator, said output signal being indicative of a capacitive coupling between the at least one drive electrode and the at least one sense electrode, with a demodulation waveform.

15. The controller of claim 11, 12, 13, or 14 wherein the demodulation waveform is determined with reference to a lookup table.

16. The controller of claim 15 wherein the demodulation waveform is a Gaussian-enveloped sine wave.

17. The controller of claim 1, 6, 9, 10, 11, 12, 13, or 14, wherein the input circuitry further comprises an analog to digital converter configured to produce a digital output from the measured capacitive coupling of the drive waveforms from the drive electrode to the sense electrode.

18. The controller of claim 17 wherein the analog to digital converter is a sigma-delta converter.

19. A method of operating a multi-touch surface, the multi-touch surface comprising at least one drive electrode, at least one sense electrode, and at least one node disposed at an intersection of the at least one drive electrode and the at least one sense electrode, the method comprising:

stimulating the at least one drive electrode with a first periodic waveform having a first predetermined frequency;

reading the at least one sense electrode to determine a capacitance of the node disposed at the intersection of the at least one drive electrode and the at least one sense electrode;

stimulating the at least one drive electrode with at least one additional periodic waveform having an additional predetermined frequency different from the first predetermined frequency;

reading the at least one drive electrode to determine a capacitance of the node disposed at the intersection of the at least one drive electrode and the at least one sense electrode; and

comparing the capacitance determined by the first stimulus with the capacitance determined by the at least one additional stimulus to determine the true capacitance of the node.

20. The method of claim 19 wherein stimulating the at least one drive electrode with at least one additional periodic waveform having an additional predetermined frequency different from the first predetermined frequency comprises:

stimulating the at least one drive electrode with a second periodic waveform having a second predetermined frequency; and

stimulating the at least one drive electrode with a third periodic waveform having a third predetermined frequency;

wherein the second and third predetermined frequencies are different from the first predetermined frequency and different from each other.

21. The method of claim 20 wherein comparing the capacitance determined by the first stimulus with the capacitance determined by the at least one additional stimulus to determine the true capacitance of the node comprises taking an average of the capacitances determined by the first, second, and third stimuli.

22. The method of claim 20 wherein comparing the capacitance determined by the first stimulus with the capacitance determined by the at least one additional stimulus to determine the true capacitance of the node comprises applying a majority rules algorithm to the capacitances determined by the first, second, and third stimuli.

23. The method of claim 20 wherein comparing the capacitance determined by the first stimulus with the capacitance determined by the at least one additional stimulus to determine the true capacitance of the node comprises taking the median of the capacitances determined by the first, second, and third stimuli.

24. A charge amplifier comprising:

an operational amplifier having an inverting input terminal, a non-inverting input terminal, and an output terminal;

a feedback capacitor connected between the output terminal and the inverting input terminal, wherein the feedback capacitor is programmable to take on a range of values; and

a feedback resistor connected between the output terminal and the inverting input terminal, wherein the feedback resistor is programmable to take on a range of values.

25. The charge amplifier of claim 24 wherein the charge amplifier further comprises a resistor coupled between the non-inverting input terminal and an input to form an anti-aliasing filter in combination with the feedback resistor and capacitor.

26. The charge amplifier of claim 24 wherein the non-inverting input of the amplifier is coupled to ground.

27. A method of operating a multi-touch surface, the multi-touch surface comprising at least one drive electrode, at least one sense electrode, and at least one node disposed at an intersection of the at least one drive electrode and the at least one sense electrode, the method comprising:

detecting a waveform on the at least one sense electrode caused by capacitive coupling of a drive waveform at the at least one node, said drive waveform having been applied to the at least one drive electrode;

amplifying the detected waveform; and

demodulating the amplified waveform to detect an object located proximate the at least one node.

28. The method of claim 27 further comprising subtracting an offset from the amplified waveform, the offset being determined as a function of the static capacitance of the at least one node, wherein the step of demodulating the amplified waveform takes place subsequent to subtracting the offset.

29. The method of claim 27 wherein:

detecting a waveform on the at least one sense electrode comprises;

detecting a first waveform on the at least one sense electrode caused by capacitive coupling of a first drive waveform at the at least one node, the first drive waveform having been applied to the at least one drive electrode and having a first predetermined frequency; and

detecting at least one additional waveform on the at least one sense electrode caused by capacitive coupling of at least one additional drive waveform at the at least one node, the at least one additional drive waveform having been applied to the at least one drive electrode and having an additional predetermined frequency; and

demodulating the amplified waveform comprises;

demodulating each of the first waveform and the at least one additional waveform and comparing the demodulated waveforms to determine a capacitance of the node.

30. The method of claim 29 wherein comparing the demodulated waveforms comprises taking an average.

31. The method of claim 29 wherein comparing the demodulated waveforms comprises selecting a median.

32. The method of claim 29 wherein comparing the demodulated waveforms comprises applying a majority rules algorithm.

33. The method of claim 27 wherein demodulating the amplified waveform comprises mixing the amplified waveform with a Gaussian enveloped sine wave.

34. An offset compensation circuit for use in conjunction with a capacitive touch sensor, wherein the capacitive touch sensor is operated by measuring capacitive coupling of a drive waveform from a drive electrode to a sense electrode, the offset compensation circuit comprising:

a programmable offset digital to analog converter adapted to generate an offset signal corresponding to a static component of the capacitive coupling between the drive electrode and the sense electrode; and

a subtractor circuit configured to subtract the offset signal from a measured signal indicative of the capacitive coupling between the at least one drive electrode and the at least one sense electrode.