Optimum preamplification and shaping of signals delivered by photodetectors without internal amplification: A theoretical analysis

The use of photodetectors without internal amplification is an appealing ch oice in the design of low-cost solid-state optical instrumentation. However , once photodiodes are used in the detection unit, the instrument sensitivi ty is related not only to the photodetector characteristics, but mainly to the front-end electronics noise performance. Therefore, great care has to b e taken in the design of the preamplification and shaping electronics in or der to minimize their noise contribution. The present paper introduces, fro m the theoretical point of view the optimum front-end electronics to proces s signals delivered by photodetectors without internal amplification. In th e analysis performed, with simple formalism, the optimum signal-to-noise ra tio and the minimum detectable signal have been calculated, Moreover some p ractical realizations, which approximate the optimum signal processor, are presented.