ABSTRACT
Despite its long history, apparent simplicity, and elegance, a sigma–delta modulator remains one of the most elusive circuits in microelectronics. This chapter presents the analysis and design methodology for a center frequency tunable continuous time bandpass (CT BP) sigma–delta modulator in the high-frequency (HF) signal range. It addresses some of outstanding problems related to this particular group of modulators, for example, loop delay compensation, center frequency tunability, and higher order stability. It appears that sigma–delta modulators have the potential to include a tunable frequency element, combined with frequency mixing, analog/digital (A/D) conversion, and a filtering function, in a single device. The chapter also focuses on the development of an analytical procedure for obtaining a closed-form transfer function for the loop filter of a tunable CT BP sigma–delta modulator. Analytical models for tunable fourth-order CT BP sigma–delta loop, both zero-delay and fractional-delay, are presented.
