High-performance GaAs heterojunction bipolar transistor logarithmic IF amplifier

Abstract

A GaAs/AlGaAs heterojunction bipolar transistor (HBT) was used to synthesize a high-performance true logarithmic intermediate-frequency (IF) amplifier based on a silicon bipolar transistor dual-gain log-stage design. The HBT log IF amplifier monolithically integrates four log stages to achieve a piecewise-linear approximated log function for compression of wide-dynamic-range signals. A fabrication process based on metal-organic chemical vapor deposition (MOCVD) epitaxy and a 3- mu m emitter self-aligned base ohmic transistor was used. The true log IF amplifier's performance includes a DC-3-GHz IF/video bandwidth, 400-ps rise time, and les than +or-1-dB log error over about a 40-dB dynamic range at 3 GHz.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>