VLSI implementation of Gm-C filter using modified Nauta OTA with double CMOS pair

Abstract

In the literature, a modified Nauta's OTA has been proposed for achieving higher PSRR and CMRR. In this paper, a modified Nauta's OTA with double CMOS pair is proposed and is used for implementing a programmable Gm-C filter. The double CMOS pair enables the transconductance to be varied by varying the bias voltages at high impedance nodes. This in turn results in programmability of the filter (F-tuning). For the purpose of comparison, the proposed OTA and Nauta's OTA reported in the literature are implemented in UMC-0.18µm CMOS process and studied through simulation. The proposed OTA results in 11 dB increase in the PSRR and 21 dB increase in the CMRR compared to the Nauta's OTA. The tunable second order Gm-C band pass filter using the proposed OTA is implemented and studied. Simulation of filter is done with BSIM3V3 parameters under (±0.9V) supply voltage and (±1.4V) supply voltage for biasing of double CMOS pair. It is verified from the post-layout simulation that the filter can be tuned over the range (10MHz–300MHz).