Automatic Low Noise Frequency Selection

• US 20110063993A1
• Filed: 09/11/2009
• Published: 03/17/2011
• Est. Priority Date: 09/11/2009
• Status: Active Grant

• Current Assignee: Apple Inc.
• Original Assignee: Apple Inc.
• Inventors: Wilson, Thomas James, Krah, Christoph Horst
• Granted Patent: US 9,036,650 B2
• Time in Patent Office: Days
• US Class Current: 370/254
• CPC Class Codes: G06F 1/3262 Power saving in digitizer or tablet
• 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 3/044 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: H04L 27/2626 Arrangements specific to the transmitter only
• CPC Class Codes: H04L 27/2647 Arrangements specific to the receiver only equalisation H04L27/01
• CPC Class Codes: H04M 11/062 using different frequency bands for speech and other data

Abstract

Automatic low noise frequency selection for a touch sensitive device is disclosed. A low noise stimulation frequency can be automatically selected by device logic without intervention of the device processor to stimulate the device to sense a touch event at the device. The device logic can automatically select a set of low noise frequencies from among various frequencies based on the amount of noise introduced by the device at the various frequencies, where the frequencies with the lower noise amounts can be selected. The device logic can also automatically select a low noise frequency from among the selected set as the low noise stimulation frequency. The device logic can be implemented partially or entirely in hardware.

Claims

1. A circuit for automatically selecting a low noise frequency for use in a device comprising:

a plurality of sense channels, each sense channel configured to receive a signal;

a summing circuit coupled to the sense channels and configured to generate a sum of the signals;

a pair of magnitude circuits coupled to the summing circuit, one of the pair coupled to the summing circuit through a first mixer configured for demodulation with an in-phase (I) component of a demodulation frequency so as to calculate an in-phase magnitude value corresponding an amount of noise at the demodulation frequency, and the other of the pair coupled to the summing circuit through a second mixer configured for demodulation with a quadrature (Q) component of the demodulation frequency so as to calculate a quadrature magnitude value corresponding to the amount of noise at the demodulation frequency; and

frequency selection logic coupled to the calculation circuits and configured to select without intervention from a processor the demodulation frequency as a low noise frequency if the amount of noise is low.

2. The circuit of claim 1, wherein the frequency selection logic includes a noise calculator configured to calculate without intervention from the processor the amount of noise based on the in-phase magnitude value and the quadrature magnitude value.

3. The circuit of claim 1, wherein the frequency selection logic includes a noise comparator configured to compare without intervention from the processor the amount of noise to a threshold to determine whether the amount of noise is low.

4. The circuit of claim 1, wherein the frequency selection logic includes a frequency selector configured to select without intervention from the processor the demodulation frequency as the low noise frequency.

5. The circuit of claim 1, further comprising a memory configured to store data associated with the demodulation frequency.

6. The circuit of claim 1 incorporated into at least one of a mobile telephone, a digital media player, or a personal computer.

7. A method for automatically determining a low noise frequency for demodulating a signal, comprising:

selecting a plurality of demodulation frequencies at which low noise appears in a signal;

calculating a plurality of noise magnitudes at the selected demodulation frequencies, each noise magnitude based on an amount of noise in the signal at the corresponding demodulation frequency; and

determining a low noise magnitude and the corresponding demodulation frequency, the determined demodulation frequency being used to generate further signals,

wherein the selecting, the calculating, and the determining are without intervention of a processor.

8. The method of claim 7, wherein selecting comprises:

providing a range of demodulation frequencies;

generating a noise magnitude of the signal at each provided demodulation frequency;

sorting the noise magnitudes from lowest to highest; and

selecting the provided demodulation frequencies having the lowest noise magnitudes to be the selected plurality of demodulation frequencies.

9. The method of claim 7, wherein calculating comprises:

calculating an in-phase magnitude corresponding to an in-phase amount of noise at the corresponding demodulation frequency;

calculating a quadrature magnitude corresponding to a quadrature amount of noise at the corresponding demodulation frequency; and

calculating the noise magnitude at the corresponding demodulation frequency as a function of the in-phase magnitude and the quadrature magnitude.

10. The method of claim 7, wherein determining comprises:

comparing the noise magnitudes to a threshold until one of the noise magnitudes is determined to be lower than the threshold; and

selecting the demodulation frequency corresponding to the determined noise magnitude to be used to generate further signals.

11. The method of claim 7, further comprising storing data representing the selected plurality of demodulation frequencies in a lookup table in memory.

12. A touch sensitive device comprising:

at least one sense channel configured to sense a touch event at the device;

scan logic couplable to the at least one sense channel and configured to perform a scan sequence on the device to determine the occurrence of the touch event; and

frequency selection logic couplable to the scan logic and configured to select without intervention from a processor a low noise frequency to be used during the scan sequence, the low noise frequency selectable from among a plurality of signal frequencies.

13. The device of claim 12, wherein the scan logic comprises spectral scan logic configured to perform the scan sequence on the device when there is no occurrence of a touch event to determine an amount of noise introduced by the device, and wherein the frequency selection logic selects the low noise frequency as the signal frequency that produces a low amount of noise during the scan sequence.

14. The device of claim 12, wherein the frequency selection logic is configured to send a signal to the processor to initiate the scan sequence by the scan logic when the low noise frequency is not selected.

15. The device of claim 12, wherein the at least one sense channel comprises a bandpass filter to filter a touch signal indicative of the sensed touch event, and the device comprises a memory configured to store data associated with the low noise frequency for applying to the bandpass filter for filtering the touch signal.

16. The device of claim 12, further comprising a demodulation section configured to demodulate a touch signal indicative of the sensed touch event with the low noise frequency, and a memory configured to store data associated with the low noise frequency for applying to the demodulation section for demodulating the touch signal.

17. A touch circuit comprising:

a noise calculator configured to calculate a plurality of noise magnitudes, each noise magnitude based on in-phase and quadrature magnitudes associated with an amount of noise at a corresponding demodulation frequency of an input signal, each demodulation frequency selectably determined as a low noise frequency; and

a frequency selector configured to select a low noise magnitude and the demodulation frequency corresponding to the selected low noise magnitude for operating the circuit at the selected demodulation frequency,

the noise calculator and the frequency selector operable without intervention from a processor.

18. The touch circuit of claim 17, comprising at least one sense channel configured to transmit the input signal, the sense channel having a gain.

19. The touch circuit of claim 18, comprising a noise scaler configured to scale the noise magnitudes to account for frequency dependencies associated with the sense channel gain.

20. The touch circuit of claim 18, wherein the sense channel is configured to bypass certain components thereof to account from frequency dependencies associated with the sense channel gain.

21. The touch circuit of claim 17, comprising a math engine including

a single multiplier configured to perform demodulation, scaling, and squaring of the input signal, and

a single accumulator configured to accumulate the in-phase and quadrature magnitudes and to accumulate phase data for an oscillator function.

22. The touch circuit of claim 17, wherein the frequency selector is configured to periodically reorder the noise magnitudes for selecting the low noise magnitude when the amount of selection processing reaches a certain level.

23. A method comprising:

selecting a low noise frequency for operating a device;

dynamically populating a memory with data corresponding to the selected low noise frequency, the data selectable from another memory comprising a plurality of data associated with a plurality of low noise frequencies; and

selecting from the memory at least some of the data to apply to the device for operating the device at the low noise frequency.

24. The method of claim 23, wherein the data comprises phase adjustments to signals having the low noise frequency to correct for signal delays, and wherein dynamically populating the memory comprises populating a lookup table in the memory with the phase adjustments.

25. The method of claim 23, wherein the data comprises baseline data to be subtracted from signals having the low noise frequency to normalize the signals, and wherein dynamically populating the memory comprises populating the memory with the baseline data.