Touchscreen controller and method for charger noise reduction through noise shaping

摘要

Touch screen controllers and methods are presented for removing charger noise and other high frequency noise from touch screens in the presence of aliasing in which a digital low pass filter rejects the high frequency noise, a noise tracker determines whether noise is being aliased into the low pass filter pass band, and a noise shaper artificially induces or modifies aliasing in the system by adjusting an analog-to-digital converter sampling frequency and/or a panel scan frequency to try to move the aliased noise outside the low pass filter pass band.

主权项

1. A controller for interfacing a touch screen with a host system, the controller comprising:
a driver circuit operative in a scan mode to selectively provide one or more excitation signals to a connected touch screen; a sensing circuit operative in the scan mode to receive a plurality of input signals from the connected touch screen; an analog-to-digital converter operating at a sampling frequency to provide digital samples according to sampled input signals received by the sensing circuit; a digital low pass filter with a pass band defined by a cutoff frequency and operative to filter the digital samples and to provide filtered digital samples for detecting user actuation of one or more portions of the touch screen; a panel scan controller configured to control operation of the driver circuit and the sensing circuit to implement panel scanning to sequentially obtain a series of sets of digital samples at a panel scan frequency, the individual sets of digital samples corresponding to a plurality of locations of the touch screen; a noise tracker configured to compute a first set of statistics corresponding to the digital samples from the analog-to-digital converter and a second set of statistics corresponding to the filtered digital samples from the digital low pass filter; and a noise shaper configured to selectively adjust at least one of the sampling frequency of the analog-to-digital converter and the panel scan frequency of the panel scan controller if the first and second sets of statistics indicate the presence of noise aliased into the pass band of the digital low pass filter.