On the design of low-noise current-mode optical preamplifiers

Abstract

Classical designs of optical transimpedance amplifiers for p-i-n photodiode receiver circuits generally employ common-emitter or common-source input stages. In this paper we explore the design of a new class of low-noise “current-mode” optical preamplifier based upon common-base and common-gate input stages. Two current-mode designs are considered, firstly an improved bipolar common-base configuration and secondly a GaAs MESFET common-gate configuration. Both designs employ current-feedback techniques to achieve higher transimpedance gains than is obtained with classical voltage-feedback structures for the same operating bandwidth. A theoretical noise analysis of the new current-mode designs confirms the expected low noise performance. Finally, experimental noise measurements at 100-MHz bandwidth indicates that under certain conditions electrical noise improvements of up to 4 dBs over classical designs can be obtained with the new current-mode circuits.