ABSTRACT
This chapter describes the principal sources of electric noise and discusses methods for the measurement of noise. Thermal noise or Johnson noise is generated by the random collision of charge carriers with a lattice under conditions of thermal equilibrium. Because these are independent of frequency, thermal noise is said to have a uniform or flat distribution. Such noise is also called white noise. Partition noise occurs when the charge carriers in a current have the possibility of dividing between two or more paths. The noise bandwidth of a filter can be measured with a white noise source with a known voltage spectral density. Noise equations derived by phasor analysis can be converted easily into equations for real signals. The noise factor can be measured with a calibrated white noise source driving the amplifier. Because noise signals are small, a low-noise amplifier is often required to boost the noise level sufficiently so that it can be measured.
