Analytical expressions for tuned feedback front end baseband optical receiver

Abstract

The incorrect interpretation of the noise expressions of modified front end optical receivers is becoming more common and persistent. This paper presents improved analytical expressions for the calculation of: — 3dB cut-off bandwidth, transimpedance, noise equivalent bandwidths and equivalent input noise current densities of simple tuned optical baseband receiver front end built with BJTs and p-i-n diode. Coloured noise in the typical TIA receiver design caused by amplifier noise being referred through input transistor and RC network formed by photodiode and input amplifier. In the case of tuned front end, this arrangement is altered. Hence, classic noise expressions become invalid, which typically leads to overly optimistic noise numbers. Two mathematical models have been used to predict receiver sensitivity and to calculate the total noise for non-tuned and tuned front end optical receivers. The numerical results show receiver sensitivity improvement of 1dB to 2.2dB. However, the significance of the work presented here is in development and validation of referring noise in tuned front end baseband optical receiver as well as optimising the transfer function of the tuned feedback transimpedance.