[sdiy] Noninverting precision half-wave rectifier?

[David G. Dixon]

Yes, just one opamp, and it wasn't much of a thread, really; just me
thinking aloud on a "slow news day" (and trying to get the taste of that
last math-rant-which-devolved-into-an-ideological-crisis out of my mouth).

Your circuit is very cool.  I've added it to my archive, and I'm sure it
will find its way into some module or other.


> I havent followed this thread too closely... are you allowed only ONE
> opamp ?
> 
> If not try
> 
> http://www.edn.com/article/CA6339250.html
> 
> H^) harry  (/shameless self promotion mode)
> 
> ----- Original Message -----
> From: David G. Dixon <dixon at interchange.ubc.ca>
> To: Synth-diy at dropmix.xs4all.nl
> Sent: Sat, 26 Sep 2009 23:01:31 -0400 (EDT)
> Subject: RE: [sdiy] Noninverting precision half-wave rectifier?
> 
> It's not that big of a deal, Barry.  It's just that there are two ways to
> get precision half-wave rectification with an opamp: a (non-inverting)
> precision diode and an (inverting) precision half-wave rectifier.  The
> first
> has high input impedance but suffers from slew-rate distortion at high
> frequencies (depending on the opamp used).  The second is distortion-free
> but has finite input impedance.  This can complicate matters if you're
> feeding a signal through an attenuator, as you'll get a non-linear
> attenuation response.  Of course, in that case, you simply make the
> attenuation pot into a variable feedback resistor, and Bob's your uncle.
> 
> Anyway, I thought I had found a non-inverting precision half-wave
> rectifier,
> which would be distortion-free and have high input impedance.  However, it
> was too good to be true.  That's all.  It's a "don't believe everything
> you
> read" story, I think.
> 
> 
> > Ok I'll admit my ignorance.  I don't get what you are trying to achieve
> > or what the problems are exactly.  Is it your simulator that has the
> > issue?
> > Did you build a circuit on a breadboard to see if it behaves the same?
> > Why not just invert the input signal?
> > You can also use 2 diodes in the opamp feedback loop tied to a 3rd that
> is
> > switched to
> > ground or whatever that will clamp the output to a desired reference
> level
> > (not V- for example).
> 
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> --
> Harry Bissell & Nora Abdullah 4eva