farjamit@eecs.cs.pdx.edu (Tom Farjami) (05/17/91)
Greetings, I have a question about effect of offset voltage in operation of a simple 5 transistor trans-amp. I appreciate any comments in this regard. Basically for a open loop trans-amp, vout = gain . (V+ - V-) + offset However when we cause the unity feedback, that is when used as a follower, math tells me that, Vout = ( gain /(gain +1) ) . Vin + offset/gain It seems too good to be true. My question is that would the offset be divided by the gain of the open loop trans-amp or not ? How does offset show up in the follower operation? . thank you. Sincerely, Tom Farjami farjamit@eecs.ee.pdx.edu
jgk@osc.COM (Joe Keane) (05/23/91)
It is true that output offset is much less when using a follower configuration than just open-loop. However, note that offset is almost always referred to the input. In the follower the input offset and output offset are the same, so you just use that number. In the open-loop situation the input offset must be _multiplied_ by the gain to get the correct output offset. -- Joe Keane, amateur electronics hacker jgk@osc.com (...!uunet!stratus!osc!jgk)