CMOS Data Converters for Communications / Edition 1

by Mikael Gustavsson, J. Jacob Wikner, Nianxiong Tan

Overview

CMOS Data Converters for Communications distinguishes itself from other data converter books by emphasizing system-related aspects of the design and frequency-domain measures. It explains in detail how to derive data converter requirements for a given communication system (baseband, passband, and multi-carrier systems). The authors also review CMOS data converter architectures and discuss their suitability for communications. The rest of the book is dedicated to high-performance CMOS data converter architecture and circuit design. Pipelined ADCs, parallel ADCs with an improved passive sampling technique, and oversampling ADCs are the focus for ADC architectures, while current-steering DAC modeling and implementation are the focus for DAC architectures. The principles of the switched-current and the switched-capacitor techniques are reviewed and their applications to crucial functional blocks such as multiplying DACs and integrators are detailed. The book outlines the design of the basic building blocks such as operational amplifiers, comparators, and reference generators with emphasis on the practical aspects. To operate analog circuits at a reduced supply voltage, special circuit techniques are needed. Low-voltage techniques are also discussed in this book.
CMOS Data Converters for Communications can be used as a reference book by analog circuit designers to understand the data converter requirements for communication applications. It can also be used by telecommunication system designers to understand the difficulties of certain performance requirements on data converters. It is also an excellent resource to prepare analog students for the new challenges ahead.

Product Details

ISBN-13:	9780792377801
Publisher:	Springer US
Publication date:	01/31/2000
Series:	The Springer International Series in Engineering and Computer Science , #543
Edition description:	2000
Pages:	378
Product dimensions:	6.10(w) x 9.25(h) x 0.36(d)

Read an Excerpt

Chapter 4: Overview of D/a Converter architectures

Introduction

In this chapter we present different techniques for converting a digital signal into an analog signal representation. The approaches differ in speed, chip area, power efficiency, achievable accuracy, etc. It is therefore necessary to understand which converter algorithms or architectures to choose for the specific application. For example, when the conversion bandwidth is relatively small, it could be advantageous to use a higher sampling ratio and some oversampling technique to reduce the noise energy within the signal band. If very high speeds are required, a flash converter architecture should be used. However, the trade-off in converter design is normally between resolution and bandwidth (or the update frequency over signal frequency ratio). The higher bandwidth the lower resolution is generally achievable.

In Sec. 4.2 we discuss the concept of Nyquist-rate conversion, and in Sec. 4.3 to Sec. 4.8 we show different implementations for Nyquist-rate DaCs. There is a limited number of DaC architectures that are good candidates for high-speed and high-performance applications. One is the current-steering DaC, which uses a number of binary scaled elements which generate the output value.

In Sec. 4.9, we discuss the concept of oversampling D/a conversion. In this book we refer to an oversampling DaC (OSDaC) to a converter operating at a higher update frequency and also containing a noise shaping loop. Often, the OSDaC utilizes some kind of a Nyquist-rate converter (with a lower nominal resolution) together with digital modulators and analog filters.

To further increase the performance of DaCs, some special enhancement techniques can be used, as for example dynamic randomization and dynamic element matching (DEM) techniques. This is discussed in Sec. 4.10.

In Sec. 4.11 we compare a number of DaC architectures reported in the literature and in data sheets from vendors. We present an overview of the performance in terms of linearity vs. update and signal frequencies.

Nyquist Rate D/a Converters

In general the Nyquist-rate converter is required for wide band applications where oversampling techniques are impossible due to the high clocking frequency. In for example, audio applications an oversampling D/a converter (OSDaC) is preferred. Since a Nyquist-rate converter also is used in most OSDaCs we first present some general and common Nyquist-rate DaC architectures. We discuss application areas and highlight some of the advantages and disadvantages with the different types of converter architectures. The architectures that are discussed, are the binary weighted, thermometer coded, and encoded DaC architectures. The different architectures can be combined into hybrid DaCs where the advantages of different individual architectures are used.

We are considering DaCs for telecommunication applications and therefore we focus on candidates suitable for high speed and high resolution. However, lower-speed DaCs such as the algorithmic DaC are also briefly presented. These lower-speed DaCs can be used in pipeline DaCs where the throughput is increased by pipelining.

To illustrate the principle of the DaC, usually single-ended circuits are used. In a real implementation they are differential circuits to improve linearity and SNR. In this chapter, we consider only binary offset coded inputs. To represent a negative output of the converter, the reference elements of the most significant bit get the opposite sign, i.e., a 2's complement coded input.

We use three modes of circuit technology; voltage-mode, current-mode, and chargeredistribution mode. We associate voltage-mode with a DaC where the element values are given by voltage levels as for example in a resistor-string which divides a voltage reference level into a number of different amplitude levels. With current-mode the DaC elements are currents, as for example switched current sources or resistors dividing a major current into weighted subcurrents. Finally, charge-redistribution DaCs are using the switched-capacitor technique (SC). Note that the SC technique usually is refered to as a voltage-mode technique as well...

Table of Contents

Characterization of Data Converters.- Data Converter Requirements for Communications.- Overview of High-Speed A/D Converter Architectures.- Overview of D/A Converter Architectures.- Overview of Circuit Techniques.- Analog Functional Blocks.- Basic Analog Circuit Design.- Low-Voltage Analog Techniques.- Pipelined A/D Converters.- Time-Interleaved A/D Converters.- Oversampling A/D Converters.- Modeling of Nyquist D/A Converters.- Implementation of CMOS Current-Steering D/A Converters.

Editorial Reviews

‘ ...an excellent introduction to the field of data converters for communications. Moreover, it can be used by system designers to trade off the various performance and requirement issues, especially in wireless and wire-bound front-ends. In addition, expers will benefit from this reference book in numerous ways, be it on circuit, systems, or measurement issues. Overall, this book is very delightful to read and understand. It gives deep insight into the field of data converters for communcations, from the system perspective as well as from the circuit and measurement viewpoint. A must in every engineer's bookshelf!'
Circuits & Devices (2000)

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