AUTOMATIC LOW NOISE FREQUENCY SELECTION

摘要

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.

主权项

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 from a touch sensor panel; a summing circuit coupled to the plurality of 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 of magnitude circuits 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 to an amount of noise at the demodulation frequency, and the other of the pair of magnitude circuits 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 pair of magnitude circuits and configured to select without intervention from a processor the demodulation frequency as a low noise frequency if the amount of noise is lower than an amount of noise at another demodulation frequency, wherein the processor is configured to identify one or more touch events on the touch sensor panel.