Electronic circuits for wireless optical LANs - I

Abstract

This is the first of two papers discussing practical issues and results on the implementation of low-cost transceivers for several wireless optical LANs, covering most physical layer elements. Target optical LANs under consideration have bit-rates varying between 4Mbps and 25Mbps, and input photodiode capacitance may vary between 10pF and 50pF. PPM modulation, either in a 4-PPM or 16-PPM format, istypically used in the physical layer. Several differential front-end topologies are presented bothin discrete and integrated (CMOS) implementations, targeting different LANs. Strategies for bandwidth improvement, interference reduction and dynamic range improvement have been used in some of these topologies. These strategies lead to a switched-gain transceiver with a transimpedance gain*bandwidth of 25THzΩ , achieved witha 10pF capacitance photodiode.