The Spectral Products Created by Nonlinear Intersymbol Interference in NRZ Data

In two-level noise-shaped D/A conversion, a delta-sigma modulator quantizes a bandlimited discrete-time signal into a binary drive for a two-level D/A converter that then outputs a nominally clean NRZ data waveform with the quantization-noise spectrum shaped to be very low in the signal band. Nonlinear intersymbol interference in the final two-level conversion can, however, corrupt the signal band with intermodulation noise. Here a nonlinear model of that two-level conversion is used to derive its output spectrum for test data that are either periodic or random with i.i.d. bits, results that can enable laboratory measurement of model parameters and guide needed circuit improvements