Mixed-Mode Universal Biquad Filter Using OTAs

This paper introduces an electronically tunable mixed-mode universal biquad filter configuration employing four single output operational transconductance amplifiers (OTAs), one dual output OTA and two grounded capacitors (GCs) (ideal for integrated circuit implementation and absorbing shunt parasitic capacitances). The presented structure can realize all second-order filter functions, namely, low pass (LP), high pass (HP), band pass (BP), band reject (BR) and all pass (AP) responses in voltage mode (VM), current mode (CM), transresistance mode (TRM) and transconductance mode (TCM) using appropriate selection(s) of input signals. The cut-off frequency (f(o)) and bandwidth (BW) of the realized filters can be tuned orthogonally through the transconductance (by varying the bias currents) of the OTAs. The proposed biquad configuration enjoys low active and passive sensitivities. The workability of this multifunctional biquad filter topology has been confirmed through simulations using MATLAB and Analog Design Environment (ADE) spectre tool provided by Cadence Virtuoso, using 0.18 mu m CMOS process parameter. The post-layout simulations have also been carried out to validate the theory.