Commonly the transfer function of the photodiodes is modeled as an equation which describes the generation of the electron-hole pairs and the drift of the carriers in the depletion layer. Using a network synthesis, the ideal frequency response of a MSM, Metal-Semiconductor-Metal Photodiode, is described as a simple RLC electrical circuit. The modeling of the frequency response to a lumped elements equivalent circuit allows an easy implementation in CAD systems such as PSPICE or ADS (Advanced Design system) and to combine it with other devices like amplifiers and filters for computer simulation.