Design of switched capacitor biquad filter with quality factor tunability

Abstract

A high selectivity switched capacitor bandpass filter is introduced in this paper which is derived from Fleischer and Laker switched capacitor biquad [1]. High quality factors are obtained by means of a proposed Q-factor tuning technique that is applied by changing the effective sampling frequency of the clock signals of a positive feedback switched capacitor branch. The center frequency is 17.4 KHz and Q-factor ranges from 0.53–27.04. Spice simulations are provided for the filters. Active blocks are used to realize switched capacitor filters where an Operational Amplifier is used for simulation, The op-amp used in the design stage is a two-stage compensated op-amp where a 0.25µm transistor model is used with a supply voltage Vdd and Vss of ±2.5V respectively