Patent ID: 8525798
Filing Date: 2013-09-03
Classification: G06F,H03K

Abstract:
1. An apparatus comprising: a plurality of capacitors each having a first electrode and a second electrode; signal generating circuitry coupled to the first electrodes; sensing circuitry coupled to the second electrodes, the sensing circuitry configured to detect changes in capacitance across the capacitors responsive to movement of an input object related to the apparatus, the sensing circuitry comprising a pseudo random signal generator configured to provide a drive signal to the first electrodes, the pseudo random signal generator varying a frequency of the drive signal at intervals; a demodulator coupled to the pseudo random signal generator and configured to receive the varying frequency therefrom and to select a passing frequency based on the varying frequency; a low pass filter to filter an output of the sensing circuitry; an analog to digital converter connected to the output of the low pass filter; and interpolating circuitry to identify which one of the capacitors is nearest to the input object according to the detected capacitance changes, wherein the demodulator dynamically varies the passing frequency to correspond with the varying frequency of the sensing circuitry output.