A Very Linear OTA with V-I Conversion based on Quasi-Floating MOS Resistor

This paper proposes a novel very linear tunable transconductor based on local feedback loops. The linear V-I conversion is accomplished using MOS resistors based on quasi-floating gate transistors. The absence of current mirrors in the signal path provides low sensitivity to transistor mismatch and decrease of nonlinear distortion. The OTA was designed in a 0.5 μm CMOS technology with ±1.65-V supply voltage. Simulation results show a THD of -80 dB at 100 kHz with 1 Vpp input signal. Good linearity of the OTA over a large tuning range is obtained.

I. Introduction

Modern communication systems require analog interfaces with high performance in terms of bandwidth and linearity. Operational Transconductance Amplifiers (OTAs) have proven to be efficient building blocks for this kind of systems. Although their open-loop operation mode allows them to work at very high frequencies, a modest linearity is usually obtained, which is a drawback for communication systems which continue employing the traditional opamp-RC topology to obtain a total harmonic distortion below −75 dB. Moreover, low distortion over a large input range is also difficult to achieve with present low supply voltage and the large nonidealities of small geometry devices.