Noise Loading Analysis of a Third-Order Nonlinear System with Memory

This paper presents the noise loading analysis of a third-order nonlinear system characterized by Volterra kernels. The analysis is of practical interest since intermodulation distortion is often a limiting consideration in the design of solid-state long-haul broad-band frequency-division multiplexed transmission systems, and since speech on such systems is best represented by zero mean Gaussian noise. The analysis technique is amenable to digital computer calculation; as such, quantitive results are readily obtained. The analysis was applied to a single-stage transistor amplifier that was represented by a frequency-dependent nonlinear model. An excellent agreement between measured and calculated results was obtained. Portions of the program written for this example are readily applicable to the calculation of intermodulation distortion for any thirdorder nonlinear system (e.g., amplifier, repeater, or cascade of repeaters and cable sections) given the appropriate Volterra kernels.