ideal diode (precion rectifier) with voltage follower in feedback?

[SArepairman]

What is the point of adding a voltage follower into the feedback loop of a precision rectifier?

Output -> Diode -> Voltage follower (buffer op amp) > negative opamp terminal

Does this have something to do with improving the response time of the circuit?

http://upload.wikimedia.org/wikipedia/commons/6/60/Op-Amp_Precision_Rectifier.svg with a buffer in the feedback loop after the diode
the diode is a 1n4248

does this allow you to use a crap diode at the expense of an amplifier?

[Odysseus]

Is the attached schematic what you're thinking of?

If so, I don't think it's going to improve the transient response of the amplifier since the first op-amp is still going to go open loop and enter saturation.

The only benefit I can see is the prevention of any subsequent circuitry from offsetting the voltage at which it rectifies.

[KJDS]

Dave did one of his videos on this a few weeks ago, might be worth a check.

[SArepairman]

so it would remove the offset error created by  the next op-amp in line?

wont the voltage followers offset cause an offset anyway?

 

[Odysseus]

The precision rectifier goes flat when the current in the diode drops to zero.  The issue is if your load has a significant bias current.  Then the point at which the diode current is zero is no long the same as zero voltage.  The extra op-amp is just a buffer to prevent this. 

This doesn't really explain why the second op-amp is inside the feedback loop of the first.  I see no advantage.

[SArepairman]

The precision rectifier goes flat when the current in the diode drops to zero.  The issue is if your load has a significant bias current.  Then the point at which the diode current is zero is no long the same as zero voltage.  The extra op-amp is just a buffer to prevent this. 

This doesn't really explain why the second op-amp is inside the feedback loop of the first.  I see no advantage.

this is the digitizer circuit on a spectrum analyzers video signal if it makes any difference.

looks like a peak detector circuit