21 - Circuits and systems for digital front-ends to support multiple wireless standards

Summary

Introduction

While the migration of RF circuits running at multi-gigahertz frequencies to low-cost deep-submicron CMOS process has made single-chip wireless transceivers a reality, the proliferation of multiple wireless standards has imposed new challenges of integrating multiple wireless standards on the same hardware. One of the challenges in multi-standard radios is the need to support multiple frequency bands ranging from less than 1 GHz to more than 5 GHz. In this chapter, we will discuss the design of digital front-end (DFE) circuits that are applicable to at least two wireless standards: these include GSM/GPRS/EDGE (GGE) and WCDMA. We will also show how to extend the design to support LTE. Restricting the coverage to only three wireless standards is primarily for the amount of analysis that needs to be performed for each standard.

In the context of a receiver, we will use digital front-end (DFE) to describe digital circuits that bridge the output of an A/D converter (ADC) to a digital base-band (DBB) processor. We will also restrict discussion in this chapter to the case of implementation-friendly direct-conversion receiver (DCR) architecture. This will assume zero intermediate frequency (ZIF) for WCDMA and LTE signals but will allow for very low IF (VLIF) for GGE.