Practical considerations of ADC circuits

Parameter	Explanation
Resolution	Perhaps the most important consideration of an ADC is its resolution. Resolution is the number of binary bits output by the converter. Because ADC circuits take in an analog signal, which is continuously variable, and resolve it into one of many discrete steps, it is important to know how many of these steps there are in total.... more on resolution
Conversion Rate	Another important consideration of ADC circuitry is its sample frequency, or conversion rate. This is simply the speed at which the converter outputs a new binary number.... more on sample frequency.
Step Recovery	Yet another measure of ADC performance is something called step recovery. This is a measure of how quickly an ADC changes its output to match a large, sudden change in the analog input. In some converter technologies especially, step recovery is a serious limitation. One example is the tracking converter, which has a typically fast update period but a disproportionately slow step recovery.

An ideal ADC has a great many bits for very fine resolution, samples at lightning-fast speeds, and recovers from steps instantly. It also, unfortunately, doesn't exist in the real world. Of course, any of these traits may be improved through additional circuit complexity, either in terms of increased component count and/or special circuit designs made to run at higher clock speeds. Different ADC technologies, though, have different strengths. Here is a summary of them ranked from best to worst:

Resolution/complexity ratio:

Single-slope integrating, dual-slope integrating, counter, tracking, successive approximation, flash.

Speed:

Flash, tracking, successive approximation, single-slope integrating & counter, dual-slope integrating.

Step recovery:

Flash, successive-approximation, single-slope integrating & counter, dual-slope integrating, tracking.

Please bear in mind that the rankings of these different ADC technologies depend on other factors. For instance, how an ADC rates on step recovery depends on the nature of the step change. A tracking ADC is equally slow to respond to all step changes, whereas a single-slope or counter ADC will register a high-to-low step change quicker than a low-to-high step change. Successive-approximation ADCs are almost equally fast at resolving any analog signal, but a tracking ADC will consistently beat a successive-approximation ADC if the signal is changing slower than one resolution step per clock pulse. I ranked integrating converters as having a greater resolution/complexity ratio than counter converters, but this assumes that precision analog integrator circuits are less complex to design and manufacture than precision DACs required within counter-based converters. Others may not agree with this assumption.