The MICROMIXER: a highly linear variant of the Gilbert mixer using a bisymmetric Class-AB input stage

TLDR

The paper develops a highly linear variant of the Gilbert mixer. The mixer replaces the conventional BJT differential pair input stage with a bisymmetric Class‑AB translinear topology, and inductive degeneration enables narrowband matching at microwave frequencies. The resulting mixer exhibits no inherent gain compression, supports high signal levels with two‑tone intercepts up to +30 dBm, operates on 2.2 V supplies with under 5 mW consumption, offers controllable 50 Ω input impedance, and delivers acceptable noise figures (≈6.5 dB for narrowband microwave variants) while remaining highly linear.

Abstract

This paper outlines the basic theory of a development of the Gilbert mixer. The bipolar junction transistor (BJT) differential pair widely used as the RF input stage is replaced by a bisymmetric Class-AB topology based on translinear principles. It does not have inherent gain compression, affording a greatly extended signal capacity. The linearity of variants of the basic form is excellent, providing two-tone intermodulation intercepts as high as +30 dBm, without the expenditure of high bias currents. It can operate on supplies as low as 2.2 V, with a power consumption of under 5 mW. The input impedance of this mixer is accurately controllable (typically 50 /spl Omega/) and provides a true broadband match. The noise figure depends on design details and is generally not as low as in mixers specifically optimized for noise performance, although acceptable for many receiver applications. Inductively degenerated variants can be tuned to a narrowband match at microwave frequencies and provide full-mixing SSB noise figures as low as 6.5 dB, Practical realizations are in use in applications to 1.9 GHz.