Fully-integrated, large-time-constant, low-pass, Gm-C filter based on current conveyors

This paper describes a low-power fully integrated CMOS low-pass filter with extremely low cut-off frequency range for use in implantable biomedical applications. The filter takes advantage of system-level properties of applying indirect negative feedback on an OTA to realize a low-cut-off frequency. It also features active capacitance multiplication using a second-generation current conveyor. Both of these techniques help reduce the silicon area of the proposed low-pass filter. Based on the proposed idea, a 1^st-order low-pass Gm-C filter was designed in a 0.5-μm standard CMOS process, occupying a core area of 0.0048mm². Cut-off frequency of the filter is tunable from 0.75Hz to 9.4Hz. Operated with ±1.5V supply voltages, power consumption of the filter ranges from 50nW to 740nW.