Harmonic distortion in switched-current sigma-delta modulators due to clock feedthrough

Harmonic distortion induced by the clock feedthrough in switched-current ΣΔ modulators is discussed. An expression is derived for the level of the second harmonic as a function of the parameters of the integrators. The results indicate that the level of the 2nd harmonic at the modulator output can be reduced with respect to that of SI cells and integrators by a factor of approximately the oversampling factor. SPICE simulations that confirm the results obtained have been performed using a special technique to take into account accurately the clock feedthrough effects