Analog Versus Digital Design: When and Where to Make the Cut

Abstract

System designers are frequently asked to create circuits that measure and control the analog world. One of the the challenges in these types of designs is to know when to convert the signal signal from the analog domain to the digital domain. In the analog domain, signal conditioning techniques such as gain, offset, and filtering are used to quickly modify the incoming signal. Alternatively, mathematical algorithms are used in the digital domain to implement similar functions. Every system design is unique and requires custom solutions for each case, but there are some general guidelines that can help the designer make the right decisions concerning where to draw the line. Two circuit scenarios will be discussed in this paper. With each of the two systems, the question of when and where to use analog signal conditioning strategies as opposed to digital techniques will be answered. The first scenario that will be used in this discussion is a simple RTD(Resistance Temperature Detectors) temperature sensing circuit. With this system, digital versus analog calibration, gain and offset techniques will be under evaluation.Filtering techniques is the second scenario that will be evaluated. Discussions will show that all circuit designs require a degree of analog filtering whether or not the input analog signal is DC or AC. From this premise, the advantages of analog versus digital filter designs will be investigated.