There are many dimensions of performance to analog-to-digital converter (ADC) technology. Some of which are listed in Table 1. These are common metrics for which ADCs may be selected and have value for certain areas of interest.

Article Tools

• 

Until the late 1980s, military requirements tended to drive data-converter markets. Military needs were driven by radar, communications applications and EMP^[1] detection. Often these converters were pushed in a single dimension of performance such as spurious-free dynamic range (SFDR) or sample rate. Occasionally, two dimensions may have been maximized, but rarely was this the case in multiple dimensions of performance. In fact, many of these dimensions were unimportant and were often sacrificed for the needed performance specification.

Today, designers, especially in commercial applications, expect multiple dimensions of converter performance, in many cases, up to four or five. Therefore, parameters such as power consumption, SNR, SFDR, input bandwidth and cost must all be optimized. High-speed converters once reserved for military and perhaps high-end test equipment are finding applications in industrial and consumer products. Notable applications include cellular infrastructure^[1,2] and a plethora of other wireless and wired applications such as DOCSIS, Wi-Fi, WiMAX and high-end consumer commercial broadcast receivers for HD, FM, AM and satellite broadcasts. The broad appeal for a well-rounded ADC is rooted in the fact that once the signal band of interest is digitized, signal processing can be optimized and tailored for nearly any application using software techniques as found in software-defined radio (SDR) or software-defined instrumentation.

ADC performance

As software-defined systems become more common, performance expectations for converters continue to increase, generally remaining one step ahead of actual converter performance. In general, significant upward pressure exists on SNR and SFDR and downward pressure on pricing. To a large degree, these market pressures are working as SNR performance is experiencing performance jumps not entirely predicted by reports by Walden^[3] and Le, et al.^[4] and others as a direct result of customer drive and increasing competitive pressures. Although not without performance penalties, cost for converters is falling as designs are moving from proprietary semiconductor processes to industry-standard CMOS processes that are generally much less expensive. Initially, SNR performance dropped back by as much as one-half of a bit during this process transition but recent improvements show signs that performance on standard CMOS processes are back in line with proprietary processes. SFDR is experiencing a slightly different trend. Performance for high-end ADCs has stalemated over the last few years and has experienced little forward progress indicating that basic linearity performance has not improved over the last few years. In order to move SFDR performance forward, a displacing technology will be required.

While performance will continue to improve in the varied dimensions, end users can affect the pace that these improvements occur by providing performance feedback to ADC manufacturers. Only when designers know exactly which specifications to target will they know how to optimize the designs, trading off one performance for another in a meaningful and useful manner.

What are the requirements?

While there are many dimesions of performance, there are always a few key specifications of interest. These specifications are key to a broad range of applications and offer a view into widely accepted parameters and how they enable certain features as well as how they interact with other parameters.