Touch-sensitive apparatus with improved noise immunity and method

Abstract

Described is a touch-sensitive apparatus for sensing the presence of an object relative to a touch-sensitive surface using capacitance measurements. The apparatus includes an electrode array comprising at least one electrode, the electrode array providing the touch-sensitive surface; a signal generating module for generating a time-varying drive signal to be applied to the electrode array; a differential amplifier comprising: a first input configured to receive a time-varying sensor signal from an electrode of the electrode array, the sensor signal indicative of a capacitive coupling associated with the at least one electrode; a second input configured to receive a time-varying reference signal; a first output configured to output a first output signal from the differential amplifier based on a difference between the time-varying sensor signal and the time-varying reference signal; and control circuitry configured to determine the presence of an object, wherein the apparatus further comprises a subtractor for subtracting a signal from the first output signal from the differential amplifier to generate a subtracted signal, wherein the control circuitry is configured to receive a signal based on the subtracted signal and to determine the presence of an object based on the received signal. Further disclosed is a method for sensing the presence of an object relative to a touch-sensitive surface using capacitance measurements of a touch sensitive apparatus.

Dependencies are inferred from the claim text.