Radio-Frequency Digital-to-Analog Converters

Chapter 4

RF front-end (RFDAC) of the polar transmitter*

Abstract

This chapter focuses on the RFDAC (also termed as DPA) for the polar transmitter. The RFDAC also serves as a mixer combining amplitude and phase modulation. A digital clock, running at RF carrier with phase modulation, contains the phase information generated by the DCO. The RFDAC achieves its amplitude modulation by using a combination of integer and fractional transistors. The transistors are switched at a rate represented by the DCO clock. Fractional resolution is achieved using second-order Sigma-Delta modulator. Dynamic Element Matching (DEM) is used to randomize the mismatches between integer transistors. Any systematic mismatch between integer and fractional transistors ...