Detection of low noise frequencies for multiple frequency sensor panel stimulation

• US 8,120,591 B2
• Filed: 10/13/2010
• Issued: 02/21/2012
• Est. Priority Date: 06/13/2007
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Krah, Christoph Horst, Hotelling, Steve Porter, O'Connor, Sean Erik, Westerman, Wayne Carl
• Primary Examiner(s): Eisen, Alexander
• Assistant Examiner(s): YEUNG, MATTHEW M
• Application Number:
  US12/904,012
• Publication Number:
  US 20110025634A1
• Time in Patent Office: 496 Days
• Field of Search: None
• US Class Current: 345/173
• CPC Class Codes: G02F 1/13338 Input devices, e.g. touch panels
• CPC Class Codes: G06F 3/0412 Digitisers structurally integrated in a display
• 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 3/04184 Synchronisation with the driving of the display or the backlighting unit to avoid interferences generated internally
• CPC Class Codes: G06F 3/0445 using two or more layers of sensing electrodes, e.g. using two layers of electrodes separated by a dielectric layer

Abstract

The identification of low noise stimulation frequencies for detecting and localizing touch events on a touch sensor panel is disclosed. Each of a plurality of sense channels can be coupled to a separate sense line in a touch sensor panel and can have multiple mixers, each mixer using a demodulation frequency of a particular frequency, phase and delay. With no stimulation signal applied to any drive lines in the touch sensor panel, pairs of mixers can demodulate the sum of the output of all sense channels using the in-phase (I) and quadrature (Q) signals of a particular frequency. The demodulated outputs of each mixer pair can be used to calculate the magnitude of the noise at that particular frequency, wherein the lower the magnitude, the lower the noise at that frequency. Several low noise frequencies can be selected for use in a subsequent touch sensor panel scan function.

Claims

1. A method for determining low noise stimulation frequencies for use in generating an image of touch, comprising:

demodulating a combined noise signal from a plurality of sense lines in an unstimulated touch sensor panel with in-phase (I) and quadrature (Q) components of a first plurality of frequencies;

accumulating the I and Q components of the demodulated noise signal for each of the first plurality of frequencies;

calculating a magnitude of the accumulated I and Q components of the demodulated noise signal for each of the first plurality of frequencies; and

determining the low noise frequencies by selecting those frequencies whose generated magnitudes are smallest.

2. The method of claim 1 further comprising demodulating the combined noise signal with I and Q components of one or more different pluralities of frequencies, and accumulating the I and Q components of the demodulated noise signal for each of the one or more different plurality of frequencies.

3. The method of claim 1, further comprising generating the plurality of noise values and determining the low noise frequencies during the vertical blanking phase of a liquid crystal display (LCD) adjacent to the touch sensor panel.

4. An apparatus for determining low noise stimulation frequencies for use in generating an image of touch, comprising:

a summing circuit coupled for receiving a noise signal from a plurality of sense lines in an unstimulated touch sensor panel and generating a combined noise signal;

a plurality of pairs of mixers, each pair of mixers for demodulating the combined noise signal with in-phase (I) and quadrature (Q) components of a particular demodulation frequency;

one accumulator coupled to each of the plurality of mixers for generating an accumulated mixer output; and

a plurality of magnitude calculator circuits, each magnitude calculator circuit coupled for receiving the accumulated mixer outputs from a particular pair accumulators associated with a particular pair of mixers, each magnitude calculator circuit generating a magnitude value corresponding to an amount of noise at the demodulation frequency for the particular pair of mixers.

5. The apparatus of claim 4, further comprising a frequency generator circuit coupled to each mixer for generating the demodulation frequency.

6. The apparatus of claim 5, one or more of the frequency generator circuits comprising a numerically controlled oscillator (NCO).

7. The apparatus of claim 4, further comprising memory for storing the plurality of magnitude values generated by each magnitude calculator circuit.

8. A computing system comprising the apparatus of claim 4.

9. A mobile telephone comprising the computing system of claim 8.

10. A digital audio player comprising the computing system of claim 8.

11. A mobile telephone including an apparatus for determining low noise stimulation frequencies for use in generating an image of touch, the apparatus comprising:

a summing circuit coupled for receiving a noise signal from a plurality of sense lines in an unstimulated touch sensor panel and generating a combined noise signal;

a plurality of pairs of mixers, each pair of mixers for demodulating the combined noise signal with in-phase (I) and quadrature (Q) components of a particular demodulation frequency;

one accumulator coupled to each of the plurality of mixers for generating an accumulated mixer output; and

a plurality of magnitude calculator circuits, each magnitude calculator circuit coupled for receiving the accumulated mixer outputs from a particular pair accumulators associated with a particular pair of mixers, each magnitude calculator circuit generating a magnitude value corresponding to an amount of noise at the demodulation frequency for the particular pair of mixers.

12. A digital audio player including an apparatus for determining low noise stimulation frequencies for use in generating an image of touch, the apparatus comprising:

a summing circuit coupled for receiving a noise signal from a plurality of sense lines in an unstimulated touch sensor panel and generating a combined noise signal;

a plurality of pairs of mixers, each pair of mixers for demodulating the combined noise signal with in-phase (I) and quadrature (Q) components of a particular demodulation frequency;

one accumulator coupled to each of the plurality of mixers for generating an accumulated mixer output; and

a plurality of magnitude calculator circuits, each magnitude calculator circuit coupled for receiving the accumulated mixer outputs from a particular pair accumulators associated with a particular pair of mixers, each magnitude calculator circuit generating a magnitude value corresponding to an amount of noise at the demodulation frequency for the particular pair of mixers.

13. A method for operating a touchscreen, the touchscreen having a touch sensor panel and a display device, the method comprising:

updating the display device during an active period of the display device; and

determining low noise stimulation frequencies for use in generating an image of touch from the touch sensor panel by demodulating a combined noise signal at a plurality of frequencies from a plurality of sense lines when the touch sensor panel is unstimulated during a vertical blanking phase of the display device.

14. The method of claim 13, wherein the display device is a liquid crystal display (LCD).