Smaller and cheaper products due to higher levels of integration and longer stand-by times are trends in receiver design for expanding portable wireless applications. Breems (Philips Research, Eindhoven, Netherlands) and Huijsing (Delft U. of Technology, Netherlands) review the relevant theory, design challenges, experimental results, and realization of continuous time sigma-delta modulators for analog- to-digital (A/D) conversion in radio receivers. Their thesis is that such conversions can be achieved with low power and high performance by combining a mixer with a continuous-time lowpass modulator. The volume concludes with a discussion of such test chips and A/D modulators in comparison to other designs. Illustrations include circuit designs, graphed modulator parameters, and a test chip micrograph