Analog Circuit Design

18

Bias voltage and current sense circuits for avalanche photodiodesFeeding and reading the APD

Jim Williams

Introduction

Avalanche photodiodes (APDs) are widely utilized in laser based fiberoptic systems to convert optical data into electrical form. The APD is usually packaged with a signal conditioning amplifier in a small module. An APD receiver module and attendant circuitry appears in Figure 18.1. The APD module (figure right) contains the APD and a trans-impedance (e.g., current-to-voltage) amplifier. An optical port permits interfacing fiberoptic cable to the APD’s photosensitive portion. The module’s compact construction facilitates a direct, low loss connection between the APD and the amplifier, necessary because of the extremely high speed ...