Design of low-frequency low-pass filters for biomedical applications

This paper presents the design method of very low-frequency current-mode low-pass filters for biomedical applications. The double-output operational transconductance amplifiers and grounded capacitors (DO-OTA-Cs) are used to realize the proposed low-frequency low-pass filters. The theory focuses mainly on establishing a relationship between the cascaded DO-OTA-Cs and the multiple-loop feedback connections, which make the design formulas. For the implementation of large time constants of the proposed low-pass filters, both linearized DO-OTAs with reduced transconductance and impedance scaler scheme for grounded capacitors are employed. Physical chip design of a leapfrog low-frequency low-pass filter was fabricated by using TSMC 0.35-um 2P4M CMOS process. With an active area of 1240 um × 490 um and working at 1.5 V, the circuit dissipates about 96.5 nW and the -3 dB frequency is around 3.8 Hz. Also, the measurement results are presented to verify the theoretical analysis.