A new method for measuring the performance of weakly nonlinear systems

Real transmission systems are only approximately linear. Their actual performance can be described by a model consisting of an ideal linear subsystem and a nonlinear one. A method is presented for measuring the complex transfer function of the linear part and simultaneously the power density spectrum of the noise produced by the nonlinear subsystem. The procedure has been implemented using an integrated signal processor under PC control. Its performance is demonstrated with results found for digital filters, working with limited wordlength, quantizers, and limiters. They are in excellent agreement with those based on theoretical considerations. The method works very fast and yields extremely accurate results even in the stopband of filters