CMOS Gyrator-C Active Transformers

This paper presents a systematic approach to synthesize gyrator-C active transformers using MOS transistors. The self and mutual inductances of ideal and non-ideal active transformers are investigated in detailed and the intrinsic relation between the self and mutual inductances is derived. The configurations of gyrator-C active transformers with multiple primary and secondary windings are developed. Practical implementations of the proposed gyrator-C active transformers are realized in TSMC's 1.8V 0.18μm CMOS technology and their characteristics are analyzed using Spectre from Cadence Design Systems with BSIM3.3 device models. Simulation results are presented.

I. Introduction

CMOS on-chip spiral transformers have emerged recently [1], [2], [3]. The drawbacks of spiral inductors that are intrinsic to the spiral layout of the inductors, such as a low quality factor, a low self-resonant frequency, a non-tunable inductance, and large silicon area requirement, however, are inherited. In this paper, a systematic approach to synthesize transformers using MOS transistors is introduced. The proposed active transformers offer large and tunable self and mutual inductances and virtually no silicon area requirement. These transformers can be configured with either a positive or negative mutual inductance. Active transformers with multiple windings can also be constructed conveniently.