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Principles of Low Noise Electronic Design This chapter details noise models and signal theory, such that the effect of noise in linear electronic systems can be ascertained. The results are directly applicable to nonlinear systems that can be approximated around an operating point by an affine function. An introductory section is included at the start of the chapter to provide an insight into the nature of Gaussian white noise — the most common form of noise encountered in electronics. This is followed by a description of the standard types of noise encountered in electronics and noise models for standard electronic components | Principles of Random Signal Analysis and Low Noise Design The Power Spectral Density and Its Applications. Roy M. Howard Copyright 2002 John Wiley Sons Inc. ISBN 0-471-22617-3 9 Principles of Low Noise Electronic Design 9.1 INTRODUCTION This chapter details noise models and signal theory such that the effect of noise in linear electronic systems can be ascertained. The results are directly applicable to nonlinear systems that can be approximated around an operating point by an affine function. An introductory section is included at the start of the chapter to provide an insight into the nature of Gaussian white noise the most common form of noise encountered in electronics. This is followed by a description of the standard types of noise encountered in electronics and noise models for standard electronic components. The central result of the chapter is a systematic explanation of the theory underpinning the standard method of characterizing noise in electronic systems namely through an input equivalent noise source or sources. Further the noise equivalent bandwidth of a system is defined. This method of characterizing a system simplifies noise analysis especially when a signal to noise ratio characterization is required. Finally the input equivalent noise of a passive network is discussed which is a generalization of Nyquist s theorem. General references for noise in electronics include Ambrozy 1982 Buckingham 1983 Engberg 1995 Fish 1993 Leach 1994 Motchenbacher 1993 and van der Ziel 1986 . 9.1.1 Notation and Assumptions When dealing with noise processes in linear time invariant systems an infinite timescale is often assumed so power spectral densities consistent with previous notation should be written in the form Grx f - However for notational 256 INTRODUCTION 257 Figure 9.1 Schematic diagram of signal source and amplifier. convenience the subscript is removed and power spectral densities are written as G f . Further the systems are assumed to be such that the .
