10.1 Noise in Components and Systems

Noise is of crucial concern in radio, since the higher a signal is above the noise, the higher will be its SNR and the farther away it can be detected with a desired BER. There are two primary classifications of noise: circuit generated and externally generated. Both are unavoidable and limit the possible gain of any receiver s amplifiers. However, noise can be minimized by careful and cautious circuit and systems design. For instance, if we employ LNAs and tight filtering in the front end of receivers, and decrease the noise contributions from local oscillators and the image frequency, and use proper shielding and layout techniques, we can significantly improve on the noise floor amplitude.

Noise manufactured within circuits and systems produces a haphazard and fluctuating voltage that varies widely in frequency. White noise (also referred to as Johnson or thermal noise) is created by a component s electrons randomly moving around under the influence of thermal energy. Shot noise, because of its characteristics, can also be considered another type of white noise, but is caused by electrons entering the collector or drain of a transistor, and by the haphazard movement...