High-Input Impedance Voltage-Mode Multifunction Filter with Three-Input Single-Output Based on Simple CMOS OTAs

A new voltage-mode three inputs and one output universal biquadratic filter with high-input impedance employing six simple operational transconductance amplifiers (OTAs) and two grounded capacitors is presented. The proposed circuit offers the following features: realization of all the standard filter functions, that is, highpass, bandpass, lowpass, bandstop, and allpass filters; electronically tunable of the angular frequency through adjusting the bias currents/voltages of OTAs; no requirements for component matching conditions; high-input impedance good for cascadability for the voltage-mode circuits; the use of only grounded capacitors and require no resistor; low active and passive sensitivities. PSPICE simulation results that confirm the theoretical predictions are given.