Receiver Design

In this chapter we examine the problem of designing the electrical front end of the receiver, which consists of one or more photodetectors followed by a low-noise, wide-band preamplifier. The design of the preamplifier is challenging due to the high capacitance of large-area photodiodes and a potentially intense background light. The error performance of the entire system depends to a large degree on the ability of the preamplifier to amplify the detected signal over the desired bandwidth without adding undue noise. We show that it is always possible to make the preamplifier noise negligible in comparison to the background light shot noise. We show that, in practical cases, a PIN photodiode is preferable to an avalanche photodiode. We propose a transimpedance amplifier using a current-feedback pair, and present a detailed bandwidth and noise analysis. We present design procedures for two typical design scenarios. Numerical examples show that, using wide-gate FETs, low-noise operation over bandwidths near 100 MHz can be achieved for moderate detector areas near 1 cm2.