An algorithm for frequency-domain noise analysis in nonlinear systems

Many mixed-technology and mixed-signal designs require the assessment of the system's performance in the presence of signals that are best characterized as having continuous frequency spectra: for instance, the simulation of a circuit's behavior in the presence of electrical noise. This paper describes an algorithm for frequency-domain simulation of nonlinear systems capable of handling signals with continuous spectra. The algorithm is based on an orthogonal series expansion of the signals in the frequency domain. Thus it is, in a sense, the dual approach to frequency-domain simulation with respect to harmonic balance, which relies on a time-domain series expansion of the signals. Signal spectra are obtained from the solution of a system of nonlinear algebraic equations whose dimension increases with the desired spectral accuracy. Numerical results obtained on an optical amplifier are presented.