A nanopower bandpass filter for detection of an acoustic signal in a wearable breathing detector.

This paper presents a nanopower programmable bandpass filter suitable to process biomedical signals. The filter proves to be very robust to mismatch and process variations even when it has been implemented using MOS transistors biased in the weak inversion region. The paper analyses design issues associated to matching and process variations for the chosen filter topology and constituent transconductor block. The design equations justify the choice of both when the main constraints are robustness and power. The sixth order, bandpass filter prototype consumes 70 nW of power, with a dynamic range greater than 47 dB and operates at 1-V power supply. The filter was designed as part of a wearable breathing detector but its wide programmability range makes it suitable for many other biomedical sensor interfaces that require steep low frequency rejection band as well as ultralow power and low voltage operation.