Multipoint touch surface controller

• US 8,279,180 B2
• Filed: 05/02/2006
• Issued: 10/02/2012
• Est. Priority Date: 05/02/2006
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Hotelling, Steven P., Krah, Christoph H., Huppi, Brian Quentin
• Primary Examiner(s): Lefkowitz, Sumati
• Assistant Examiner(s): HORNER, JONATHAN R
• Application Number:
  US11/381,313
• Publication Number:
  US 20070257890A1
• Time in Patent Office: 2,345 Days
• Field of Search: 345173-178
• 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 touch surface, the touch surface having a plurality of drive electrodes and at least one sense electrode, a plurality of nodes formed at intersections of the plurality of drive electrodes and the at least one sense electrode, the controller comprising:

output circuitry operatively connected to the plurality of drive electrodes, the output circuitry being configured to generate timing signals used to generate drive waveforms for the touch surface, each drive waveform including a plurality of bursts in a single stimulation sequence for stimulating the drive electrodes in a single scan of the nodes in the touch surface, the plurality of bursts including

a first periodic waveform having a first predetermined frequency, and

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

wherein at least one of the drive electrodes is stimulated consecutively with the plurality of bursts including periodic waveforms having different predetermined frequencies before one of the other drive electrodes is stimulated in the single scan.

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 touch surface.

3. The controller of claim 2 wherein the decoding and level shifting circuitry are part of the single application specific integrated circuit.

4. The controller of claim 1 wherein the at least one additional periodic waveform comprises 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.

5. 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 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.

6. The controller of claim 5 wherein the charge amplifier further comprises a resistor coupled between the 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.

7. The controller of claim 5 wherein the non-inverting input of the amplifier is coupled to ground.

8. 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 drive electrode and the sense electrode.

9. The controller of claim 5 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 drive electrode and the sense electrode.

10. 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 drive electrode and the sense electrode with a demodulation waveform.

11. The controller of claim 5 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 drive electrode and the sense electrode, with a demodulation waveform.

12. The controller of claim 11 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 drive electrode and the sense electrode.

13. The controller of claim 8 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 drive electrode and the sense electrode, with a demodulation waveform.

14. The controller of claim 10, wherein the demodulation waveform is determined with reference to a lookup table.

15. The controller of claim 14 wherein the demodulation waveform is a Gaussian-enveloped sine wave.

16. The controller of claim 1, 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.

17. The controller of claim 16 wherein the analog to digital converter is a sigma-delta converter.

18. A method of operating a touch surface, the touch surface comprising a plurality of drive electrodes and at least one sense electrode, a plurality of nodes formed at intersections of the plurality of drive electrodes and the at least one sense electrode, the method comprising:

stimulating the drive electrodes with a plurality of bursts in a single stimulation sequence in a single scan of the nodes in the touch surface, the plurality of bursts including 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;

reading the at least one sense electrode after the drive electrodes have been stimulated with the first periodic waveform during the single scan to determine a first capacitance of the nodes formed at the intersection of the drive electrodes and the at least one sense electrode;

reading the at least one sense electrode after the drive electrodes have been stimulated with an additional periodic waveform during the single scan to determine at least one additional capacitance of the node formed at the intersection of the drive electrode and the at least one sense electrode; and

combining the first capacitance with the at least one additional capacitance to determine a capacitance of the node,

wherein at least one of the drive electrodes is stimulated consecutively with the plurality of bursts including periodic waveforms having different predetermined frequencies before one of the other drive electrodes is stimulated in the single scan.

19. The method of claim 18 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.

20. The method of claim 19 wherein combining the first capacitance with the at least one additional capacitance comprises taking an average of the capacitances.

21. The method of claim 19 wherein combining the first capacitance with the at least one additional capacitance comprises applying a majority rules algorithm to the capacitances.

22. The method of claim 19 wherein combining the first capacitance with the at least one additional capacitance comprises taking the median of the capacitances determined by the first, second, and third stimuli.

28. The method of claim 18, wherein combining includes performing one of applying a majority rules algorithm, selecting a median value, or averaging the capacitive coupling.

23. A method of operating a touch surface, the touch surface comprising a plurality of drive electrodes and at least one sense electrode, a plurality of nodes formed at intersections of the plurality of drive electrodes and the at least one sense electrode, the method comprising:

stimulating the drive electrodes with a plurality of bursts in a single stimulation sequence in a single scan of the nodes in the touch surface, the plurality of bursts including a first drive waveform having a first predetermined frequency and at least one additional drive waveform having at least one additional predetermined frequency different from the first predetermined frequency;

detecting a first waveform on the at least one sense electrode caused by capacitive coupling of the first drive waveform at the nodes;

detecting at least one additional waveform on the at least one sense electrode caused by capacitive coupling of the at least one additional drive waveform at the nodes;

amplifying the detected waveforms;

demodulating each of the first waveform and the at least one additional waveform; and

determining a capacitance at the nodes to detect an object located proximate the nodes,

wherein at least one of the drive electrodes is stimulated consecutively by the plurality of bursts including periodic waveforms having different predetermined frequencies before one of the other drive electrodes is stimulated in the single scan.

24. The method of claim 23, further comprising subtracting an offset from the amplified waveforms, the offset being determined as a function of the capacitance of the nodes, wherein the demodulating of the amplified waveform takes place subsequent to subtracting the offset.

25. The method of claim 23, wherein demodulating each of the first waveform and the at least one additional waveform comprises mixing the waveforms with a Gaussian enveloped sine wave.

26. The method of claim 23, wherein demodulating each of the first waveform and the at least one additional waveform further comprises delaying a demodulating signal by a predetermined amount to compensate for phase delay in the touch panel.

27. The method of claim 23, further comprising adjusting programmable elements of detecting and amplifying circuitry by predetermined amounts to compensate for node-to-node variations.