A Floating-gate Based Low-Power Capacitive Sensing Interface Circuit

This paper describes a high signal-to-noise ratio capacitive sensing circuit topology based on a capacitive feedback charge amplifier with high power and area efficiency. When the circuit is used in an audio MEMS sensor, 78.6dB SNR in audio band is measured with less than 0.5 muW power consumption. With a MOS-BJT pseudo-resistor feedback scheme, this topology has also been applied to a capacitive micromachined ultrasonic transducer (CMUT) operating around 1MHz. An adaptation scheme using Fowler-Nordheim tunneling and channel hot electron injection mechanisms is also employed to stabilize the output DC voltage in an audio MEMS microphone sensor. The measured noise spectrums show that this slow-time scale adaptation does not degrade the performance of the circuit. Therefore, this simple topology can be employed in many capacitive sensing applications and can achieve high performance with high efficiency