Sigma-delta configurations for capacitance sensing

An input device, comprising:

• a first active integrator and an analog-to-digital (A/D) converter in series and configured to:
• actively drive a capacitive sensor electrode at a signal input of the active integrator with a periodic reference signal;
• and
• provide, at an output of the A/D converter, a digital representation of a sensing current resulting from driving the capacitive sensor electrode with the periodic reference signal,
• wherein the periodic reference signal is provided to a reference input of the first active integrator, and
• wherein a feedback path provides negative feedback of the digital representation of the sensing current to the signal input of the active integrator;
• and
• a demodulator configured to demodulate the digital representation of the sensing current using the periodic reference signal to obtain a digital measurement.

A method for operating an input device, comprising:

• obtaining a periodic reference signal;
• actively driving a capacitive sensor electrode at a signal input of a clocked comparator with the periodic reference signal;
• producing, by the clocked comparator, a digital representation of a sensing current based on a comparison of the signal input of the clocked comparator with the periodic reference signal;
• providing negative feedback of the digital representation of the sensing current to the signal input of the clocked comparator by a feedback path;
• and
• demodulating the digital representation of the sensing current using the periodic reference signal to obtain a digital measurement.