Free space optical front-end receiver’s bandwidth enhancement employing micro-electro mechanical systems variable feedback capacitor

Abstract

Free space optical front-end receiver usually suffers high photodetector input capacitance which limits the bandwidth of the system. This is due to the large detection area required to collect as much optical radiant power as possible to increase the system’s sensitivity. In this work, the bootstrap transimpedance amplifier (BTA) is adopted as an alternative approach for free space optical front-end receiver design. This technique offers the usual advantages of the transimpedance amplifier (TIA) together with the effective capacitance reduction technique. An improved photodetector model and the both front-end structures; TIA and BTA have been simulated using harmonic balance technique offers by Microwave Office, and the results show that the design improves the system bandwidth by 6.7 times in average. However, the performance of the BTA was found limited to a certain photodetector input capacitance. In order for the front-end structure to adapt with various photodetectors capacitance, MEMS variable capacitor (varicap) is introduced as a tunable feedback element for the bootstrap loop for an optimum performance. The MEMS varicap have been designed and modeled using CoventorWare and found to be practical for circuit implementation. The implementation of MEMS varicap with the design BTA optical front-end receiver was verified using the CoventorWare ARCHITECT. The simulation of the BTA employing MEMS variable capacitor as the feedback capacitor shows the improvement in bandwidth by 1.04 times in average for various photodetector input capacitance.