A 1.28-GHz sigma-delta modulator for video A/D-conversion

We describe a second-order sigma-delta modulator which is suitable for the A/D-conversion of signals with a large bandwidth. Test ICs using a 20 GHz f_T Si bipolar technology were fabricated and proven functional. One advantage of the sigma-delta principle is, that there is no anti-alias prefiltering required. In addition, it fits to the fact, that in general signals with a relatively small bandwidth like terrestrial broadcasting signals need a high signal-to-noise ratio while others with a larger bandwidth like satellite broadcasting signals need a lower SNR. Potential applications for this modulator on the way to a "one-chip TV" are therefore e.g. video A/D or digital IF conversion. Simulation results of the next version of the sigma-delta modulator promise a significant signalto- noise ratio improvement.