Practical approximations to the ideal raised-cosine transfer function for digital optical receivers and their effect on sensitivity

Computer analysis and SPICE circuit simulations have been employed to determine the effect of the -3 dB cutoff frequencies, fc₁ and fc₂, on the sensitivity of a receiver consisting of a FET front end transimpedance preamplifier cascaded with a simple 3rd order low pass filter. It has been shown that this configuration is relatively insensitive to fc₁ and fc₂ provided they are in the range B/2- B, where B is the bit rate. A fixed preamplifier stage has been demonstrated to be capable of operation over a 2.5:1 range of speeds by cascading the appropriate filter, incurring a 0.5 dB penalty in sensitivity over the optimum configuration