Quadrature demodulation for touch sensitive devices

• US 8,810,537 B2
• Filed: 02/15/2012
• Issued: 08/19/2014
• Est. Priority Date: 02/15/2012
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Yousefpor, Marduke, White, Kevin J., Krah, Christoph Horst
• Primary Examiner(s): Johnson, Ryan
• Application Number:
  US13/397,643
• Publication Number:
  US 20130207906A1
• Time in Patent Office: 916 Days
• Field of Search: 345/173, 345/174, 340/407.1, 178/18.01, 178/18.06, 329/304, 327/231, 327/233, 327/237, 327/238, 327/243, 327/254
• US Class Current: 345/173
• 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 3/0418 for error correction or compensation, e.g. based on parallax, calibration or alignment
• CPC Class Codes: G06F 3/04182 Filtering of noise external to the device and not generated by digitiser components
• CPC Class Codes: G06F 3/044 by capacitive means
• 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: H03D 2200/0029 Loop circuits with controlled phase shift

Abstract

Demodulation circuits and processes for demodulating touch signals from a touch sensor using the demodulation circuits are provided. The demodulation circuits can include circuitry configured to determine an adjustable phase delay based at least in part on a quadrature component of the touch signal or the phase-adjusted touch signal. The demodulation circuit can further include circuitry for applying the adjustable phase delay to the touch signal to compensate for phase delays in the touch signal caused by the touch sensor and/or other components. The demodulation circuit can dynamically change the adjustable phase delay to compensate for time-varying phase delays caused by the touch sensor and/or other components.

Claims

1. A demodulation circuit configured to:

determine an adjustable phase delay to be applied to a touch signal from a touch panel, the adjustable phase delay determined based at least in part on a phase-adjusted quadrature (Q) component of the touch signal; and

apply the adjustable phase delay to the touch signal to generate the phase-adjusted Q component of the touch signal.

2. The demodulation circuit of claim 1 further comprising:

a first integrator configured to output a phase-adjusted in-phase (I-phase) component of the touch signal; and

a second integrator configured to output the phase-adjusted Q-component of the touch signal.

3. The demodulation circuit of claim 2 further comprising:

a matrix circuit configured to multiply the phase-adjusted I-phase component of the touch signal by a matrix to generate a phase-adjusted touch signal representing a touch event on the touch panel.

4. The demodulation circuit of claim 1 further comprising:

a filter configured to filter the phase-adjusted quadrature (Q) component of the touch signal; and

a dither circuit coupled to an output of the filter, wherein the dither circuit is configured to dither the adjustable phase delay to determine a value of the adjustable phase delay corresponding to a minimum value of the phase-adjusted Q-component of the touch signal.

5. The demodulation circuit of claim 1, wherein the demodulation circuit is located within a touch-sensitive device, and wherein the touch-sensitive device comprises:

a touch panel comprising;

a plurality of drive lines, wherein a drive line of the plurality of drive lines is configured to receive a stimulation signal; and

a plurality of sense lines, wherein a sense line of the plurality of sense lines is configured to transmit the touch signal in response to the stimulation signal;

wherein the demodulation circuit is coupled to the sense line.

6. The demodulation circuit of claim 5, wherein the touch-sensitive device further comprises additional demodulation circuits coupled to each of the plurality of sense lines.

7. A demodulation circuit comprising:

a phase adjustment circuit configured to generate a first phase adjustment signal and a second phase adjustment signal, the first and second phase adjustment signals generated based at least in part on a quadrature (Q) component of a touch signal and an in-phase (I-phase) component of the touch signal; and

a mixing circuit configured to mix the I-phase component of the touch signal with the first phase adjustment signal and the Q-phase component of the touch signal with the second phase adjustment signal.

8. The demodulation circuit of claim 7, wherein the first phase adjustment signal is 90°

out of phase with the second phase adjustment signal.

9. The demodulation circuit of claim 7, wherein the mixing circuit comprises:

a first demodulation mixer configured to mix the I-phase component of the touch signal with the first phase adjustment signal; and

a second demodulation mixer configured to mix the Q component of the touch signal with the second phase adjustment signal.

10. The demodulation circuit of claim 7, wherein the phase adjustment circuit is further configured to determine an adjustable phase delay based at least in part on the Q component of the touch signal and the I-phase component of the touch signal.

11. The demodulation circuit of claim 7, wherein the demodulation circuit further comprises a filter configured to filter the first and second phase adjustment signals.

12. A touch-sensitive device comprising:

a touch panel configured to receive a stimulation signal to drive the touch panel and to transmit a touch signal in response to the stimulation signal; and

a demodulation circuit comprising;

a filter configured to filter a phase-adjusted quadrature (Q) component of a touch signal generated by the touch panel; and

a dither circuit coupled to an output of the filter, wherein the dither circuit is configured to dither an adjustable phase delay to determine a value of the adjustable phase delay corresponding to a minimum value of the phase-adjusted Q-component of the touch signal.

13. The touch-sensitive device of claim 12, wherein the filter is a low-pass filter having a bandwidth below 60 Hz.

14. The touch-sensitive device of claim 12, wherein the filter and the dither circuit are integrated within a processor.

15. The touch-sensitive device of claim 12, wherein the dither circuit is configured to dither the adjustable phase delay during periods of time when no touch events are occurring on the touch panel.

16. The touch-sensitive device of claim 12, wherein the dither circuit is configured to maintain the value of the adjustable phase delay during periods of time when touch events are occurring on the touch panel.

17. A method for adjusting a phase delay of a touch signal from a touch panel, the method comprising:

receiving a touch signal from a touch panel;

generating a first phase adjustment signal and a second phase adjustment signal, wherein the first and second phase adjustment signals are generated based at least in part on an in-phase (I-phase) component of the touch signal and a quadrature (Q) component of the touch signal;

applying the first phase adjustment signal to the I-phase component of the touch signal to generate a phase-adjusted I-phase component of the touch signal; and

applying the second phase adjustment signal to the Q component of the touch signal to generate a phase-adjusted Q component of the touch signal.

18. The method of claim 17, wherein applying the first phase adjustment signal to the I-phase component of the touch signal comprising mixing the first phase adjustment signal with the I-phase component of the touch signal, and wherein applying the second phase adjustment signal to the Q component of the touch signal comprising mixing the second phase adjustment signal with the Q component of the touch signal.

19. The method of claim 17 further comprising:

integrating the phase-adjusted I-phase component of the touch signal with the phase-adjusted Q component of the touch signal to generate an integrated phase-adjusted touch signal; and

multiplying the integrated phase-adjusted touch signal with a matrix to generate a phase-adjusted touch signal that is representative of a proximity of an object to the touch panel.

20. The method of claim 17 further comprising:

prior to applying the first phase adjustment signal to the I-phase component of the touch signal, multiplying the I-phase component of the touch signal by a first matrix;

prior to applying the second phase adjustment signal to the Q component of the touch signal, multiplying the Q component of the touch signal by a second matrix; and

integrating the phase-adjusted I-phase component of the touch signal with the phase-adjusted Q component of the touch signal to generate a phase-adjusted touch signal that is representative of a proximity of an object to the touch panel.

21. A method for adjusting a phase delay of a touch signal from a touch panel, the method comprising:

receiving a touch signal from a touch panel;

determining an adjustable phase delay based at least in part on a phase-adjusted quadrature (Q) component of a touch signal; and

applying the adjustable phase delay to the touch signal to generate the phase-adjusted Q component of the touch signal.

22. The method of claim 21, wherein the applying the adjustable phase delay to the touch signal comprises causing a phase delay in the touch signal equal to the adjustable phase delay.

23. The method of claim 21, wherein the touch signal is generated by the touch panel in response to a stimulation signal, and wherein the applying the adjustable phase delay to the touch signal comprises:

causing a phase delay in the stimulation signal equal to the adjustable phase delay; and

mixing the phase-delayed stimulation signal with the touch signal.

24. The method of claim 21 further comprising multiplying a phase-adjusted in-phase (I-phase) component of the touch signal by a matrix to generate a phase-adjusted touch signal that is representative of a proximity of an object to the touch panel.

25. The method of claim 21 further comprising applying a constant phase delay to the touch signal, wherein the constant phase delay represents a phase difference between a desired component of the touch signal and an undesired component of the touch signal.