mula p=hwR./8, where E is the electron charge, the instantaneous power of the shot noise signal beat is Transmission Systems Architectures and Performances (6.27) where Be is the front-end, electrical bandwidth P is the instantaneous received optical power 6.2.3.4.2 Detector Noise The detector noise depends on the photodiode that is used. Starting from a PIN photodiode, the electrical noise introduced by the photodiode with its front-end signal amplifier depends essentially on the electronic structure of the front- end amplifier (see Chapter 5). Here we will summarize all the parameters of the front end in the so-called noise factor, called Far SO that we have the following expression for the total noise: (6.28) where R is the front-end input resistance. The Boltzmann constant is indicated with RB and S is the absolute temperature. In Equation 6.28, the contribution due to the spectral increase of the electronic noise at very low frequencies, the so-called 1/f noise, is neglected. Both for this reason and for coupling reason with the other electronic circuits of the receiver, practical front ends generally exhibit a minimum passband frequency, provided by an input inductive impedance. Below the minimum passband, the electrical signal is eliminated. A minimum passband frequency around 100kHz, for example, does affect neither the modulated signal nor the residual carrier (that has to be preserved for the sampling syn- chronization), and allows low frequency noise to be virtually eliminated. Besides the thermal noise, practical PIN-based receivers exhibit another form of electri- cal noise that could give a relevant contribution in specific cases. It is the dark current noise (see Chapter 5) that depends on the fact that, even in the absence of detected radiation, a real PIN photodiode under inverse polarization is traversed by a small current, called dark current, whose amplitude is a random process SO that it is seen as another noise source during signal detection. In case of the use of an avalanche photodiode (AP