Attenuating CMOS low-frequency capacitive sensor interface

We present a circuit for strain and vibration sensing from piezoelectric film elements (PVDF). The target application is the monitoring of low-frequency vibration in a biomedical wearable device. Since standard PVDF sensors produce an open-circuit voltage that is too large for direct amplification on an integrated circuit, the circuit performs input signal folding as well as output voltage attenuation. Measured results are reported for a chip fabricated in 180nm technology with 1.8 V supply. Attenuation is 28.6 dB for an effective input range of up to ±14 V at 100 Hz and the measured bandwidth is 0.2 Hz to 1 kHz. The core occupies 0.006 mm
²
and consumes 55.4 μW.