A Subhertz Nanopower Low-Pass Filter

This brief presents a first-order low-pass filter topology capable of providing cutoff frequencies down to 2 mHz with power consumption of 5 nW. The circuit is intended for signal conditioning applications, particularly for use with very low frequency physiological signals in low-power portable medical equipment. To achieve a low-frequency cutoff, the filter is based around the use of a clocked transconductor, which provides low transconductance while using a relatively high bias current level. The circuit is implemented in a 0.35-μm technology with a 1-V supply and has 32- μV_RMS measured noise and a 64-dB dynamic range. In terms of power consumption and cutoff frequency the reported filter outperforms previous filters from the literature.