A 0.25 mW 13 b passive /spl Sigma//spl Delta/ modulator for a 10 MHz IF input

Combining /spl Sigma//spl Delta/ modulator with mixing achieves frequency translation and A/D conversion in a single step, simplifying analog circuitry and saving power. Further power efficiency can be achieved by a /spl Sigma//spl Delta/ modulator with a passive loop filter. Because this involves direct conversion, the signal is always mixed down to dc irrespective of the pole locations of loop filter and therefore the null position of the quantization noise power spectrum density is insensitive to the parasitics. A passive switched-capacitor modulator with a built-in passive mixer digitizes a 10 MHz IF signal. Due to the lack of gain in the passive loop filter, a switch-only gain-boost network provides gain without using active circuitry.