he class of active devices used. zeros, 2Q is the peak SNR required for a given BER. For large SNR For a FET amplifier they are given by Equations 53.64 and 53.65. a good approximation of the error integral is based on the asymp- totic expansion, as in Equation 53.71 and for a BER of 10-9 Q=6. (53.64) (53.71) (53.65) Now in terms of Q the required optical power < Popi for a p-i-n receiver is given by Equation 53.72. D is a numerical constant with a typical value of 0.7 for silicon FETs, 1.75 for GaAs MESFETs and 1.0 for short channel silicon (53.72) MOSFETs. Then the noise spectral density referred to the input of the receiver is given by Equation 53.66 where R is either the load of the detector for high impedance input or the feedback resistor of a transimpedance amplifier. The value of the reviver noise depends on the front end device. For a FET amplifier it is given by Equation 53.73, where I2 and 13 are the values of the Personic integrals that are depended on the shapes of the incident and out pulses and B the bit rate. (53.66) (53.73) C1 is the total input capacitance, which consists of the detector and input parasitic capacitance, the gate-source and gate-drain FET capacitances and the parasitic capacitance of the load resistor R. The With an incident non-return to zero (NRZ) pulse and a full raised value of <e2 > is obtained by integrating Equation 53.66 over the cosine output pulse, I, = 0.562 and 13 = 0.0868. With a return to zero (RZ) pulse, I2 2 = 0.403 and I3 = 0.0984. It is clear that since the bandwidth of the receiver. For a bipolar transistor amplifier the optical power depends on the cube of the bit rate the receiver design noise spectral density is given by Equation 53.67. should minimise the CT With a bipolar front end receiver Equation 53.74 is obtained. (53.74) (53.67) capacitances CT and Cdf are given by Equations 53.68 and The receiver sensitivity equation for an APD detector is given by 53.69, where C is the parasitic detector capacitance and C and CH Equation 53.75, where the un-multipli