[sdiy] Noninverting precision half-wave rectifier?

[David G. Dixon]

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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