High Precision Full-Wave Rectifier for those interested.

[Transmogrifox]

I was surfing the web for high-speed comparators and found an IC by AD that seems to fit my taste for what I'm doing.  While browsing the datasheet, I noticed they have a schematic for a high-precision rectifier in their app notes:

http://www.analog.com/UploadedFiles/Data_Sheets/258917749AD790_d.pdf

The rectifier is on page 7.  

The op-amp polarity in the schematic is reversed (A simple typo error, I assume).  If you use this schematic exactly, it won't work...but all you need to do is configure the opamp in a standard linear amplifier scheme as would be implied by the schematic, not by the +/- signs on the op amp.

These are good in pitch-shifters, ring modulators, wave-form generators and envelope followers.  Unless you are making a high-performance audio compressor, I don't suppose this is as beneficial in an envelope follower.

[mikeb]

It would be interesting to know how well it works in 'real life' - are you going to give the datasheet schematic a shot?

Eeep, those AD790s are US$7 each from Digikey!

Mike

[R.G.]

The rectifier is on page 7.

Yep, that's the synchronous rectifier, as portrayed in "The Polarity Reverser" from January 2001 at GEO. They're using the unique characteristics of their comparator to make it work. In the schematic, the AD790 is deriving the +1/-1 signal shown for the synchronous rectifier.

[Brian Marshall]

i have a schematic arround here for a full wave active opamp rectifier....  it is supposed to work extreemly well.... at least from a mathematical standpoint... it has NO crossover drop out, which could be good or bad.... that would mean no gating, which means more noise, but a more natural decay.

Its in a book, ill see if i can find it.

[mikeb]

The best ones I have found (in theory, haven't had a chance to build them) are the ones by Harry Bissel and also the one on Rene's DIY synth page. One day I'll get a chance to play with them - OTOH, the simple approach of the MutronIII has worked pretty well for a while now!

Mike