Mixed-mode universal filter using OTAs

This paper presents an electronically tunable versatile biquadratic filter. Unlike the typical voltage-mode and current-mode filter, the proposed filter can realize voltage-mode, current-mode, transconductance-mode and transresistance-mode transfer functions without changing the circuit topology, called a mixed-mode filter. The proposed structure employs six operational transconductance amplifiers, two grounded capacitors and one external resistor that provides following advantages: realization of low-pass, band-pass, high-pass, band-stop and all-pass filter responses; orthogonal control of the natural frequency and the quality factor; employment of grounded capacitors which is more suitable for integrated circuit implementation; low active and passive sensitivities. Simulation results are also given to confirm the presented theory.