The Design of DC Servos



In the section of this book dealing with input stages I have gone to some lengths to demonstrate that a plain unassisted amplifier - if designed with care - can provide DC offset voltages at an output that is are low enough for most practical purposes, without needing either an offset-nulling preset or a DC servo system. For example, the Trimodal amplifier can be expected not to exceed ±15 mV at the output. However, there may be premium applications where this is not good enough. In this case the choice is between manual adjustment and DC servo technology. As precision op-amps have got cheaper, the use of DC servos has increased.

DC Offset Trimming

Preset adjustment to null the offset voltage has the advantage ...

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