Feature: T&M


New hybrid ADC technology solves tough measurement challenges


By Grant M. Smith, technology writer F


or decades, DAQ (data acquisition) systems have been based on either delta- sigma ADCs or successive approximation (SAR) ADC types, each with its own


advantages and disadvantages. Whilst delta-sigma ADCs offer a


wide dynamic range, 24-bit resolution and built-in anti-aliasing capabilities, SAR ADCs offer higher bandwidth and excellent reproduction of impulse signals such as spikes and square waves. Delta- sigma ADCs were originally intended for the sinusoidal wave shapes found in nature, as in acoustic and vibration measurements, for example. They excel at these, but can exhibit hysteresis (i.e., “overshoot” or “ringing”) when fast- rising impulse signals are input. In addition, while SARs have the


advantage of higher sample rates and excellent handling of impulse signals, delta-sigma ADCs offer the highest possible dynamic range and built-in anti-aliasing filtering. Their dynamic range is so superior, in fact, that you


22 February 2022 www.electronicsworld.co.uk


Engineers choosing a DAQ system for their measurement applications have historically been forced to choose between speed and dynamic range


will rarely see a sound or vibration system that is not based on delta-sigma technology. It should be mentioned that each bit effectively doubles the resolution of an ADC, so 24 bits is not “50% better” than 16 bits. In fact, it provides 256 times as much resolution. Consider these numbers:


16-bit resolution: Data is quantised to one part in 65,536


24-bit resolution: Data is quantised data to one part in 16,777,216


Table 1: Basic pros and cons comparison of SAR vs. delta-sigma ADC technologies


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