[sdiy] Noninverting precision half-wave rectifier?

[Jerry Gray-Eskue]

<<And no, it does not rectify!>>

You got me curious about this so I set it up on a breadboard like this, and
it is a precision Inverting half wave rectifier. With the diodes facing as
shown the output is Negative, reverse both diodes and it is Positive
output - and a match for Coughlin and Driscoll, 2nd ed. fig 7-2 pg 134. I
did observe the "Rail Hitting" behavior with the diode polarities "miss
matched".

The simplest way I see to make a Noninverting precision half-wave rectifier
requires two op amps.



Sig In-RRR--+-----RRR--------------+--------> Vout
> >         |                      |
> >         +--|<|----------+--|<|--
> >         |               |
> >         +-|(-)          |
> >           |op amp-------+
> >         +-|(+)
> >         |
> >         Grnd

- Jerry

-----Original Message-----
From: David G. Dixon [mailto:dixon at interchange.ubc.ca]
Sent: Saturday, September 26, 2009 5:55 PM
To: 'David G. Dixon'; 'Jerry Gray-Eskue'; Synth-diy at dropmix.xs4all.nl
Subject: RE: [sdiy] Noninverting precision half-wave rectifier?


Of course, I meant "-10V" in my last message...


> Jerry,
>
> Yes, I've got Coughlin and Driscoll, 2nd ed. (one of the very best books
> on
> opamp applications, in my experience).  The first half of the full-wave
> rectifier circuit shown in Figure 7-9, page 141 is exactly the same
> circuit
> given in Figure 16.6, page 16-6 of Stout and Kaufman.
>
> And no, it does not rectify!
>
> If equal resistors are used (thus giving a gain of 2 in non-inverting
> mode),
> then feeding a +/- 5V sine wave gives an asymmetrical wave out with upper
> lobes to +5V and lower lobes to +10V from the "Inverting" output (as shown
> in your figure below), and a wave with upper lobes to +(5 + D)V and lower
> lobes to -(10 + D)V from the "Non Inverting" output (as shown in your
> figure
> below), where D = one diode drop.
>
> The full-wave rectifier of Figure 7-9 works perfectly, of course (assuming
> precision resistors are used).
>
> Sorry, Jerry!
>
>
> > Try this:
> >
> > V1-RRR--+-----RRR--------------+--------> Vout Inverting
> >         |                      |
> >         +--|<|----------+--|<|--
> >         |               |
> >         +-|(-)          |
> >           |op amp-------+--> Vout Non Inverting
> >         +-|(+)
> >         |
> >         V2
> >
> > RRR   = resistors
> > -|<|- = Diode cathode on left
> >
> > V1 and V2 signal and ground these can be used either signal to - in or
> > signal to + in.
> >
> > V1 signal in look at Vout Non Inverting
> > V2 signal in look at Vout Inverting
> >
> > If you have the books:
> >
> > Part of the Full Wave rectifier Figure 7-9 pg 141 - Shows + input
> > Operational Amplifiers and Linear Integrated Circuits - Coughlin/Driscol
> > 2nd
> > edition
> >
> >
> > Figure 10.4 Pg 589 Analysis and Design of Analog Integrated Circuits -
> > Gray/Meyer 2nd edition
> > Shows - input
> >
> > - Jerry
> >
> > -----Original Message-----
> > From: synth-diy-bounces at dropmix.xs4all.nl
> > [mailto:synth-diy-bounces at dropmix.xs4all.nl]On Behalf Of David G. Dixon
> > Sent: Saturday, September 26, 2009 12:59 AM
> > To: 'Synth-DIY DIY'
> > Subject: [sdiy] Noninverting precision half-wave rectifier?
> >
> >
> > Most of you are probably aware of the inverting precision half-wave
> > rectifier (inverting opamp with two artfully placed diodes).  Well, I'm
> > looking this old book "Handbook of Operational Amplifier Circuit
> Design",
> > and it's also got a schematic of a NON-inverting precision half-wave
> > rectifier (Fig. 16.6 on page 16-6).  It is basically the non-inverting
> > analogue of the inverting rectifier.  I'm thinking, "Wow, this is great:
> > an
> > active rectifier with high input impedance which isn't severely slew-
> rate
> > limited.  Why haven't the other books mentioned this great circuit?!?"
> > However, when I simulate it in Multisim, it doesn't rectify.
> >
> > There isn't really any such thing, is there?  Only the crappy, severely
> > slew-rate limited one-diode version which Horowitz and Hill warns us
> > against
> > (but which I've used on several occasions anyway).  The book is wrong.
> >
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