On the design of low-frequency filters using CMOS OTAs operating in the subthreshold region

Abstract

Design considerations on a circuit technique based on subthreshold operation of MOS transistors is described for the realization of low-frequency OTA-C active filters with small capacitance values of the order of 25–400 pF. The circuit technique described is applied to the α (8–12 Hz), β (13–40 Hz), θ (4–8 Hz) and δ (1–4 Hz) band filters for EEG signals. Because of small capacitance values the filter circuit is suitable for realization on a single VLSI chip using the CMOS technology, and enables the user to implement the circuit on implantable biotelemetric applications.