0.6-V, Sub-nW, second-order lowpass filters using flipped voltage followers

This paper presents a concept of using the flipped voltage follower as a 2nd-order lowpass filter. Combining two capacitors with the well-known two-transistor flipped voltage follower circuit, a single-branch transistorized gm-C filter, able to function from a low supply voltage, is obtained. Besides, the proposed filter can be configured as both single-ended and differential forms. Circuit simulation using 0.35-μm CMOS process shows that, to obtain a 100-Hz cutoff frequency with a 52.2-dB dynamic range, total capacitance of 36 pF and power consumption of 0.36 nW are required for the differential filter that operates in subthreshold region from a supply voltage of 0.6 V. Compared with the previously reported designs in the category of low-power biomedical filters, this proposed filter is the most power-efficient and operates from the lowest level of supply voltage.