A 6-Gb/s CMOS imaging diversity receiver front-end employing select-best method

This paper presents an imaging diversity receiver front-end employing select-best method for free-space optical (FSO) communication. The imaging receiver consists of a seven channel transimpedance amplifier (TIA) array and a select-best circuit implemented in a 180 nm CMOS technology. This imaging receiver is designed for flip-chip bonding to a custom InGaAs MSM (metal-semiconductor-metal) photodetector array. Each single-channel front-end TIA provides a transimpedance gain of 60.2 dBOmega and a -3 dB bandwidth of 4.4 GHz for 250 fF photodiode capacitance. The select-best circuit employs a novel winner-take-all peak detector structure and demonstrates high-speed, high-precision reception. The resolution of the imaging receiver with select-best is about 2 muA near 20 muA input current and 4 muA near 400 muA input current at 6 Gb/s. The power dissipation for a single channel TIA is 8.2 mW, and for the select-best circuit is 26.6 mW from a single 1.8 V supply.