What are sample & hold circuits? 

Sample and hold circuits are a type of integrated circuit, or IC, that are primarily used to sample the continuous voltage of an input analogue signal so that the value is retained at a consistent level. The value, however, can only be retained for a set period of time as predefined by the user. 

Importance

Sample and hold circuits are important electrical components and semiconductors among data converters, which play a significant role in several different applications. They have crucial applications in linear systems where comparing voltage produced by a digital-to-analogue converter, or DAC, is required. Sample and hold circuits test values till the voltage being compared turns equal. The circuits use a sample clock to sample and hold the values. 

Applications

Sample and hold circuits are used extensively across industrial and non-industrial electrical workspaces. They are most commonly used in ADCs, or Analog-to-Digital Converters, to remove any existing variations from the input signal. These types of data converters are also used widely in applications like analogue signal processing, data conversion systems, and digital voltmeters. Some musical instruments such as synthesizers too use samples and hold circuits to impart effects.