Multiple-Input Single-Output Universal Biquad Filters Using Reduced Number of OTAs

This paper presents two three-input and single-output electronically controllable voltage-mode universal biquad filter configurations employing four single output operational transconductance amplifiers (OTAs) and two grounded capacitors (ideal for integrated circuit implementation and absorption of shunt parasitic capacitances). The presented structures provide second-order low pass filter (LPF), high pass filter (HPF), band pass filter (BPF), band reject filter (BRF) and all pass filter (APF) responses using appropriate selection(s) of three inputs. The cut-off frequency (omega(o)) and quality factor (Q(o)) can be tuned orthogonally through the transconductance of the OTAs. The proposed biquad filter configurations enjoy low active and passive sensitivities. The workability of multifunctional biquad filter topologies has been confirmed through PSPICE and MATLAB simulations.