Design considerations on a circuit technique based on subthreshold operatio
n 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. T
he circuit technique described is applied to the alpha (8-12 Hz), beta (13-
40 Hz), theta (4-8 Hz) and delta (1-4 Hz) band filters for EEG signals. Bec
ause of small capacitance values the filter circuit is suitable for realiza
tion on a single VLSI chip using the CMOS technology, and enables the user
to implement the circuit on implantable biotelemetric applications. (C) 199
8 Elsevier Science Ltd. All rights reserved.