Investigation of HBT preamplification for high speed optical communication systems.

Abstract

A noise analysis for a Common-Collector-Cascode traveling wave HBT preamplifier is developed, resulting in an expression for the preamplifier's equivalent input noise current density. A photoreceiver, consisting of a P-I-N and GaAs HBT MMIC distributed amplifier, was implemented using Nortel's GaAs HBT (f T = 70GHz) process. The noise performance of the P-I-N preamplifier was predicted based on the noise analysis equations. The P-I-N preamplifier, having a measured bandwidth of 22GHz, displayed a measured average equivalent input noise current density of 24 pA/Hz . Good agreement was obtained between the predicted and measured noise performance. The analysis gives useful insight into the dominant noise contributions of the preamplifier. An 8-stage HBT distributed amplifier was successfully developed. By considering the various issues involved in its design, a design procedure for monolithic distributed amplifiers is presented. The implementation of the HBT preamplifier is described and its measured results are given. From the excellent agreement between the predicted and measured performance, the design method is considered validated. The successful operation of the distributed amplifier, which provides 15dB gain and 35GHz 3dB bandwidth, fulfills the objective of experimental verification. The implemented photoreceiver is the first to have a P-I-N mounted on the MMIC chip.