Capacitance Super Multiplier for Sub-Hertz Low-Pass Integrated Filters

This brief addresses the design of tunable integrated low-pass filters for sub-Hertz frequencies. The required very large time constants are obtained by using the transconductance of MOS transistors with extremely low bias current and integrated capacitors whose value is augmented by a novel super multiplier circuit. Simulations at the transistor level using a 65-nm CMOS technology verify the effectiveness of the proposed techniques. It is shown that cut-off frequencies of 0.3 Hz require about 150 nA and 7 pF per single pole.