Capacitive touch sensing system with interference rejection

摘要

An interference tolerant capacitive touch sensor readout circuit having improved power and area efficiency is disclosed. Interference rejection for the capacitive touch sensing system is realized by transferring charge between a capacitive touch sensor and the readout circuit at frequencies outside bands where a level of interference is unacceptable. Improved power and area efficient come from the simplicity of the readout circuit which comprises a switched-capacitor integrator, a comparator, a digital accumulator and number of switches for driving a touch sensor and a capacitive feedback loop. The readout circuit is capable of interfacing with both self and mutual capacitance sensor to achieve compatibility with a larger collection of sensors and provides additional sensing and diagnostic functionalities.

主权项

1. A method of sensing capacitance of a capacitive touch sensor and rejecting interference coupled-in through the capacitive touch sensor during a conversion cycle, the method comprising:
generating a driving signal, the driving signal driving the capacitive touch sensor during the conversion cycle; alternately storing charge transferred from the capacitive touch sensor to a switched-capacitor integrator during the conversion cycle; recording total charge accumulated in the switched-capacitor integrator during the conversion cycle; and wherein the recording step further includes modifying the switched-capacitor integrator by a fixed amount of charge using a feedback loop after charge stored in at least one capacitor of the switched-capacitor integrator exceeds a threshold level.