equipments. Naturally these are only a subset of the use of ICs in telecommunications and cover a set of recent evolutions both in transmission system performance enhancement and in the solution of the addressing problem in switches and routers, which has been for a long time the bottleneck of the performances of such machines. There are a lot of other applications of microelectronics, like integrated switches and single cross-point implementation, control processors for element and network manage- ment and CPUs for protocol running. A few of these applications are in the field of general-purpose electronic systems, like the control board of the telecommunication equipments; others are consolidated technol- ogy, even if the continuous CMOS platform development leads to a continuous perfor- mance enhancement. However, the field of electronics application is SO large that for sure it can happen that the reader is interested in something that is not even cited here. More specific books on electronics for telecommunications surely will help the interested reader to go more in deep in this subject. [64,66,67]. 5.8.1 Low-Noise Receiver Front End Before reviewing digital signal processing applied to optical transmission, we will con- sider an important analog device that is present in all transmission systems: the low-noise amplifier that has the role of amplifying the photocurrent coming out from the photodiode up to a level suitable to be processed by the electronic receiver [32,68,69]. This amplifier noise characteristic determine almost completely the thermal noise per- formances of the receiver, since it is the first element of the electronic amplifier chain. In order to have a low noise figure, the input impedance of the amplifier has to be high, SO a high-impedance amplifier is suitable for this application. FIGURE 5.51 Electrical scheme of a high-impedance receiver front end. Technology for Telecommunications: Integrated Optics and Microelectronics Noise Ideal Diode circuit amplifier FIGURE 5.52 Equivalent circu