Distortion analysis of bipolar transistor circuits

In the design of long-haul analog communication systems, it is essential to understand the nonlinear distortion behavior of the electronic circuit realization. Distortion analysis of weakly nonlinear circuits has been developed based on the well-known perturbation method. In the frequency domain, the nonlinearities of a transistor are shown to be equivalently represented by intermodulation distortion sources whose amplitudes and phases are iteratively determined by the linear circuit characteristics and the Taylor-series coefficients associated with the nonlinearities. For all practical purposes, only two iterations are sufficient to yield accurate results. An algorithm for computing the second- and third-order intermodulation distortions is described. This algorithm has been implemented in a program called NODAP (nonlinear distortion analysis program). NODAP computes the smallsignal nonlinear transistor model from the recently developed integral change-control model (ICM). It then passes this information through a linear circuit analysis program for distortion computations. Computer results for several transistor circuits using Western Electric highfrequency transistors are all in excellent agreement with the measured data over a wide range of bias conditions and frequencies. This demonstrates the validity of the approach treated in the paper.