Specifications and Architectures

Specifications and Architectures of Sample-and-Hold Amplifiers
Sample-and-Hold (S/H) amplifiers track an analog signal, and when given a ‘‘hold’’ command they hold the value of the input signal at the instant when the ‘‘hold’’ command was issued, thereby serving as an analog storage device. An ideal S/H amplifier would be able to track any kind of input signal, and upon being given a hold command store at its output, without delay, the precise value of the signal, and maintain this value indefinitely. Unfortunately, ideal S/H amps do not yet exist, and to be able to pick a S/H amp to suit a particular application, one must be familiar with how S/H amps are characterized, and how the S/H specifications will affect performance. In addition, it is helpful to be familiar with the common architectures that are used for S/H amps, as the architecture has a profound effect on the performance. In this application note, we discuss the meaning and signifiance of the various specifications for S/H amps, and we also discuss several common S/H architectures, and how the performance is influenced by the architectures. In the appendix, we give a table which lists the key specifications for a number of S/H amps. Since the primary use of S/Hs is in data conversion, we will refer to such applications when discussing some of the specifications.