Track-and-hold amplifier

Track-and-hold amplifiers are used to store incoming signals briefly for an ADC, particularly when several signals have to be stored simultaneously and then... 

Figure 23.34. Track-and-hold amplifier. From S. P. Perone and D. O. Jones, Digital Computers in Scientific Instrumentation, New York McGraw-Hill, 1973, by permission of the publisher. Copyright 1973 by McGraw-Hill, Inc.

Using Track-and Hold Amplifiers. The tracking capabilities of even a high-speed ADC are relatively limited. To substantially improve the tracking features of a data-acquisition system, a track-and-hold (T/H) amplifier should precede the ADC. 

Note however, that the amplifier gain must be dynamically changed depending on signal amplitude, which leads to discontinuities. Kriz also points out the slew rate problems in the track and hold. His solution was to use a DC feedback loop with an analog integrator. 

Schematics of the amplification block composed of three stages (1) head stage, (2) voltage-gain difference amplifier, and (3) track-and-hold circuit. Here, an instrumentation amplifier topology, AMPl and AMP2, and compensation switches Mj and Mj are adopted for the head stage.

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