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

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) multiinput/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 dBX, -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 -16.8 dBm for a bit error rate (BER) of 10 -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.

Transmitter and receiver technologies for optical wireless

“…Examples of array receivers can be found in [18,99]. For both the transmitter and the receiver, the challenge is the implementation complexity, as individual drive circuitry is required for each source, and receiver circuitry for each detector in the respective arrays.…”

“…At the receiver, arrays of detectors can enable large collection areas and high bandwidth, as each individual detector in the array can have low capacitance and thus high bandwidth. Examples of array receivers can be found in [18,99]. For both the transmitter and the receiver, the challenge is the implementation complexity, as individual drive circuitry is required for each source, and receiver circuitry for each detector in the respective arrays.…”