This chapter describes some common analog building blocks other than those already presented. Specifically, circuits to realize sample-and-holds, and translinear gain cells and multipliers are discussed. A sample-and-hold (S/H) is used to sample an analog signal and to store its value for some length of time. A translinear gain cell is commonly used to create an amplifier whose gain can be adjusted through the use of a controlling input current. Finally, a translinear multiplier is realized by interconnecting two gain cells and finds a variety of uses in applications such as a modulator (in a communication system) or a phase detector (in a phase-locked loop).


An important analog building block, especially in data-converter systems, is the sample-and-hold circuit. Before proceeding, it is worthwhile to mention that sample-and-hold circuits are also often referred to as “track-and-hold” circuits. Normally, these two terms are synonymous except for a few particular switched-capacitor sample-and-hold circuits that do not have a phase where the output signal is tracking the input signal. Sample-and-hold circuits are necessary components in many data-acquisition systems such as A/D converters. In many cases, the use of a sample-and-hold (at the front of the data converter) can greatly minimize errors due to slightly different delay times ...

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