In wireless communication, ?? modulators are widely used as data converters to construct oversampled ADCs and DACs and they play an integral part in modern frequency synthesis. ?? modulators operate at higher conversion or sampling rates than would be required by the Nyquist criterion. For this reason these types of data converters are known as oversampling converters. Despite their popularity, ?? converters have yet to be adopted in SDR radios that employ IF sampling architecture. The obvious reasons are the required dynamic range and increased sampling rate required to support a multistandard multimode operation at IF. However, in wireless architectures that rely on quadrature demodulation such as direct conversion, low-IF, and superheterodyne, ?? converters have presented viable low-power, low-cost data conversion solutions.

This chapter is divided into six major sections. Section 9.1 presents an overview of the signal processing operation of ?? converters. Section 9.2 compares the performance of continuous-time versus discrete-time converters. The SQNR performance for first and higher order loops is given in Section 9.3. Section 9.4 discusses bandpass of ?? converters. Section 9.5 discusses common converter architectures such as modulators with multibit quantizers and the MASH architecture. The chapter concludes with a small section on the nonidealities of ?? converters.