Analog-to-Digital Conversion in the Early Twenty-First Century
Published Online: 15 SEP 2008
Copyright © 2007 by John Wiley & Sons, Inc.
Wiley Encyclopedia of Computer Science and Engineering
How to Cite
Walden, R. H. 2008. Analog-to-Digital Conversion in the Early Twenty-First Century. Wiley Encyclopedia of Computer Science and Engineering. 1–14.
- Published Online: 15 SEP 2008
Analog-to-digital converters (ADCs) continue to be important components of signal-processing systems, such as those for mobile communications, software radio, radar, satellite communications, and others. This article revisits the state-of-the-art of ADCs and includes recent data on experimental converters and commercially available parts. Converter performances have improved significantly since previous surveys were published (1999–2005). Specifically, aperture uncertainty (jitter) and power dissipation have both decreased substantially during the early 2000s. The lowest jitter value has fallen from approximately 1 picosecond in 1999 to < 100 femtoseconds for the very best of current ADCs. In addition, the lowest values for the IEEE Figure of Merit (which is proportional to the product of jitter and power dissipation) have also decreased by an order of magnitude. For converters that operate at multi-GSPS rates, the speed of the fastest ADC IC device technologies e.g., InP, GaAs, is the main limitation to performance; as measured by device transit-time frequency, fT, has roughly tripled since 1999. ADC architectures used in high-performance broadband circuits include pipelined (successive approximation, multistage flash) and parallel (time-interleaved, filter-bank) with the former leading to lower power operation and the latter being applied to high-sample rate converters. Bandpass ADCs based on delta-sigma modulation are being applied to narrow band applications with ever increasing center frequencies. CMOS has become a mainstream ADC IC technology because (1) it enables designs with low power dissipation and (2) it allows for significant amounts of digital signal-processing to be included on-chip. DSP enables correction of conversion errors, improved channel matching in parallel structures, and provides filtering required for delta-sigma converters. Finally, a performance projection based on a trend in aperture jitter predicts 25 fs in approximately 10 years, which would imply performance of 12 ENOB at nearly 1-GHz bandwidth.
- analog-to-digital converters;
- signal-to-noise ratio;
- aperture jitter;
- input-referred noise;
- comparator ambiguity;
- spurious-free dynamic range;