[sdiy] D.C. Level Shifting question

[Dan Gendreau]

> ...this is called a "precision rectifier", every text on op amps
> will have some discussion of this, if you mean that the positive
> range of the signal is left as it is.

Here is a link to a college electronics lab on rectifiers and it shows how
to make a full wave precision rectifier. (part 9 and 10 at the bottom of the
page)

http://www.swarthmore.edu/NatSci/echeeve1/Class/e72/E72L3/Lab3(Diodes).html

All you need is an appropriate low-pass filter after that to make an
envelope follower.

-Dan G.