  We present a thorough theoretical analysis and experimental study of the shot
and electronic noise spectra of a balanced optical detector based on an
operational amplifier (OA) connected in a transimpedance scheme. We identify
and quantify the primary parameters responsible for the limitations of the
circuit, in particular the bandwidth and shot-to-electronic noise clearance. We
find that the shot noise spectrum can be made consistent with the second order
Butterworth filter, while the electronic noise grows linearly with the second
power of the frequency. Good agreement between the theory and experiment is
observed, however the capacitances of the operational amplifier input and the
photodiodes appear significantly higher than those specified in manufacturers'
datasheets. This observation is confirmed by independent tests.
