[sdiy] Noninverting precision half-wave rectifier?

[David G. Dixon]

Dave:

Yes, very useful document.  I had found this before, and the brilliant,
simple full-wave rectifier of Figure 6 (with a couple of artfully placed
18pF deglitching caps) is now the heart of the saw-to-triangle converter in
the Sowa-Hoshuyama 2164-Perfect-Tempco-Expo VCO I am currently laying out.
Hopefully I'll be in a position to unveil this little beauty in about one
week's time!

I was actually asking about a non-inverting half-wave rectifier without the
skew rate problems associated with the famous "precision diode".  However,
this document does not show such a beast (because it does not exist).

HOWEVER, I was finally able to lay my hands on a copy of the Hal Chamberlin
tome "Musical Applications of Microprocessors" today, and what should I see
on page 183 in Figure 6-9 (D) but yet another full-wave rectifier, of the
"classic... center-tap" variety, apparently, the configuration of which I
have never seen anywhere else.  Mr. Chamberlin has this to say about it (and
I quote): "This simple, open-loop rectifier is far superior to the usual
closed-loop rectifier found in op-amp application notes at the higher audio
frequencies."  Basically, the incoming sawtooth wave is split in two; one
branch goes through a diode, and the other branch goes through a unity-gain
inverter and a diode.  The two diodes are connected on the other side, and
this feeds another inverting opamp with a trimmed voltage reference on the +
terminal to adjust the triangle amplitude (including the diode drop).  In
other words, this is not a precision rectifier at all (although it kinda
looks like one at first glance).  Is this the standard way to convert saw to
triangle?


 
> David G. Dixon wrote:
> > Yes, just one opamp,
> Figure 7.
> 
> http://sound.westhost.com/appnotes/an001.htm
> 
> Relies on special characteristics of the chosen opamp, and uses the
> inverting input, so not sure if this meets all your constraints.
> 
> -Dave