A cross-coupled symmetric floating impedance scaler with enhanced bandwidth and accuracy

Capacitors realized using symmetric floating impedance scaling (SFIS) are area efficient. They are preferred for the implementation of fully differential filters for biomedical applications. The SFIS reported in the literature has poor accuracy and lower effective bandwidth. In this paper, a cross coupled symmetric floating impedance scaling (CC-SFIS) with enhanced bandwidth and accuracy is proposed. To evaluate its performance, a 500 pF capacitor is implemented in UMC 180 nm CMOS technology with a base capacitor (Cb) of 10 pF using both CC-SFIS and source follower based SFIS (SF-SFIS). The magnitude and phase of the impedance of the capacitor realized using CC-SFIS and SF-SFIS are obtained through post-layout simulations. CC-SFIS requires 53.68% lower area, 62.39% lower power consumption, and 88% higher accuracy than SF-SFIS. Fully differential 2nd order Butterworth low pass filters with cutoff frequency of 100Hz are implemented in UMC 180 nm technology using both CC-SFIS and SF-SFIS capacitors. Their performances are evaluated through simulation. From this, it is found that the deviation in the cut off frequency of the filter using CC-SFIS is smaller (2%) compared to that using SF-SFIS (40%) circuit.