chapter  33

Noise Measurement

WithW. Marshall Leach

This chapter describes the principal sources of electric noise and discusses methods for the measurement of noise. The notations for voltages and currents correspond to the following conventions: dc quantities are indicated by an uppercase letter with uppercase subscripts, for example, V BE. Instantaneous small-signal ac quantities are indicated by a lowercase letter with lowercase subscripts, for example, v n. The mean-square value of a variable is denoted by a bar over the square 33-2of the variable, for example, v n 2 ¯ , where the bar indicates an arithmetic average of an ensemble of functions. The root-mean-square or rms value is the square root of the mean-square value. Phasors are indicated by an uppercase letter and lower case subscripts, for example, V n. Circuit symbols for independent sources are circular, symbols for controlled sources are diamond shaped, and symbols for noise sources are square. In the evaluation of noise equations, Boltzmann’s constant is k = 1.38 × 10−23 J K−1 and the electronic charge is q = 1.60 × 10−19 C. The standard temperature is denoted by T 0 and is taken to be T 0 = 290 K. For this value, 4kT 0 = 1.60 × 10−20 J and the thermal voltage is V T = kT 0/q = 0.025 V.