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

We report theoretical, numerical, and experimental investigations of c lipping distortion in CATV systems. After reviewing Saleh's calculatio n of the carrier to nonlinear distortion ratio (CNLD), we extend its a pplicability 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 averag e or integrated spectra, but which spectrally resolves the clipping di stortion at intermodulation products (IMP) of all orders and frequenci es. 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 val idity of the various theoretical models, and we find that Saleh's mode l slightly over-estimates the numerical simulation results for the CNL D, while our new model is in essential agreement with the simulation f or all three distortion measures. We also performed experimental measu rements of the CSO, CTB, and CNLD over a 50-dB range in distortion. We obtained excellent agreement between the CSO, CTB, and CNLD measureme nts, 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.