CFDITA-Based Mixed-Mode Biquad Filter with Grounded Capacitors and Independent Q Control

Abstract

This work introduces a compact multi-mode biquad filter utilizing a Current Follower Differential Input Transconductance Amplifier (CFDITA). The suggested circuit design is resistor less and incorporates two CFDITAs along with two grounded capacitors exclusively. It functions in all four possible modes: voltage-mode (VM), current-mode (CM), transadmittance-mode (TAM), and transimpedance-mode (TIM). In CM, the proposed circuit achieves all filtering functions, including low-pass, high-pass, band-pass, band-reject and all-pass responses. Consequently, the suggested circuit serves as a universal filter in CM. The main characteristic of the proposed multi-mode filter includes the use of minimal, grounded passive components, which removes the requirement for input matching conditions. It sustains low input impedances for current inputs and high input impedances for voltage inputs, making it ideal for cascading. It operates effectively at higher frequencies (10.3 MHz), uses low supply voltages (±1.25 V), and consumes low power (1.32 mW). Additionally, it allows for independent and electronic control of the pole frequency and quality factor through the bias currents of the CFDITA. PSPICE simulation results utilizing 0.18 µm CMOS technology confirm the theoretical findings. Furthermore, the proposed circuit is experimentally verified for a voltage-mode low-pass filter response.