Synaptics Incorporated
Sigma-delta configurations for capacitance sensing

Abstract:

An input device includes a clocked comparator configured to actively drive a capacitive sensor electrode at a signal input of the clocked comparator with a first periodic reference voltage, and provide a digital representation of a sensing current resulting from driving the capacitive sensor electrode with the first periodic reference signal. The clocked comparator produces the digital representation of the sensing current based on a comparison of the signal input of the clocked generator with the first periodic reference signal. A feedback path provides negative feedback of the digital representation of the sensing current to the signal input of the clocked comparator. The input device further includes a demodulator configured to demodulate the digital representation of the sensing current using the first periodic reference signal to obtain a first digital measurement.