CLIPPING DISTORTION IN LIGHTWAVE CATV SYSTEMS - MODELS, SIMULATIONS, AND MEASUREMENTS

We report theoretical, numerical, and experimental investigations of clipping distortion in CATV systems. After reviewing Saleh's calculation of the carrier to nonlinear distortion ratio (CNLD), we extend its applicability by incorporating a more precise spectral analysis by Mazo and further analytic results of our own. We also present a new model, the effective transfer function model, which is not limited to average or integrated spectra, but which spectrally resolves the clipping distortion at intermodulation products (IMP) of all orders and frequencies. This model features closed-form analytic calculation of the second- and third-order distortions (CSO and CTB) from basic principles, as well as the CNLD. Numerical simulations were performed to test the validity of the various theoretical models, and we find that Saleh's model slightly over-estimates the numerical simulation results for the CNLD, while our new model is in essential agreement with the simulation for all three distortion measures. We also performed experimental measurements of the CSO, CTB, and CNLD over a 50-dB range in distortion. We obtained excellent agreement between the CSO, CTB, and CNLD measurements, the simulations, and the new model over the entire 50 dB range we investigated, giving the first reported agreement between theoretical models, numerical simulations, and experimental measurements for all three CATV distortion indices, as well as the best reported agreement between measurement and theory. The unified nature of the model allows standard CATV CSO and CTB measurements to be theoretically connected to the CNLD and clipping boundary.