A CMOS imaging diversity receiver for gigabit free-space optical MIMO

Authors:
V. M. Joyner;J. Zeng
Affiliations:
Department of Electrical and Computer Engineering, Tufts University, Medford, USA 02155;Department of Electrical and Computer Engineering, Tufts University, Medford, USA 02155
Venue:
Analog Integrated Circuits and Signal Processing
Year:
2011

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Abstract

A 7-channel imaging diversity receiver based on current-summing is implemented in a 180 nm CMOS technology for broadband free-space optical (FSO) multi-input/multi-output (MIMO) communication. Each channel employs a low input-impedance current mirror (CM) as the input stage, which allows the implementation of direct current-summing for equal-gain combining (EGC). The summed current signal drives a second stage transimpedance amplifier (TIA) to generate the output voltage. Electrical characterization was performed using a photodiode emulation circuit and chip-on-board FR-4 assembly, demonstrating a total transimpedance gain of 62 dB驴, 驴3 dB bandwidth of 1.2 GHz, and eye diagrams up to 2 Gb/s for 0.25 pF photodiode capacitance. The theoretical sensitivity of the imaging receiver is 驴16.8 dBm for a bit error rate (BER) of 10驴9 at a photodetector responsivity of 0.4 A/W. The simulated power consumption for a single front-end amplifier circuit is 4.2 mW, and for the second stage TIA is 10.3 mW from a single 1.8 V supply. The diversity receiver is flip-chip compatible to enable hybrid integration to a custom InGaAs photodetector array.