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I'm designing a peak sinusoidal and impulse detector, based on the old design of a peak voltmeter designed by Haefely. I have the schematic, but I can't understand how this circuit works. The large number of elements in the feedback branch confuses me.

I would like help or an explanation on this circuit so I can understand how it works, mainly the feedback loop.

What I know this about the circuit is that it's purpose is to receive an impulse or sinusoidal waveform (attenuated by a previous stage) and obtain a DC or square pulse with amplitude proportional to the peak of input signal. The user can select if they want to see the positive or negative peak, using the relay on the A2 inputs. The output value is stored in C7.

Also, this circuit is a module inside an instrument that I know how to use and that works very well.

enter image description here

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    \$\begingroup\$ juliancaba - Thanks for naming the company whose schematic you copied into the question. However as you see in the site rule, for books & other sources which are not online, it says: "For non-web-based citations, include the source to the best of your ability (title, author, page number, etc)." Can you please add more detail? Adding the document's title, author(s), publisher, page number and any other known details, would help. Even if it's not perfect, the aim is to give a "best effort" good faith citation. Thanks. \$\endgroup\$
    – SamGibson ♦
    Commented Nov 4, 2023 at 17:49
  • \$\begingroup\$ FYI: The HP5082-2800 is a Schottky diode, equivalent to a 1N5711 according to one website. \$\endgroup\$
    – Mattman944
    Commented Nov 4, 2023 at 23:21
  • \$\begingroup\$ @SamGibson Thanks to your comment, I digitized the complete manual. Do you know which would be the most convenient place to upload the pdf? \$\endgroup\$
    – juliancaba
    Commented Nov 11, 2023 at 3:22

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The feedback circuit create a precision half wave rectifier, a small amount of filtering, perhaps some compensation for the diodes, and as you say a voltage peak storage on C7. For reference here is a bit more info on precision rectifier circuits.

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  • \$\begingroup\$ OK, but this circuit isn't close to any of the precision rectifier circuits that you referenced. What are V1 and V2 for, and why are they Schottky diodes? What is C8 for? \$\endgroup\$
    – Mattman944
    Commented Nov 6, 2023 at 17:58
  • \$\begingroup\$ @Mattman944 - If you were to remove some of the extra caps and resistors the circuit is very close to the two diode precision rectifier circuit on page 5 of the link, the difference being that the polarity here is negative so the diodes are reversed. The second op-amp is just being used as a buffer. I don't see a V1 or V2. Might you be referring to the variable resistors R1 & R2? These are likely just offset adjustments for each op-amp. I wasn't able to find much info on the Burr-Brown 3400B except that it is an old obsolete high speed op-amp. \$\endgroup\$
    – Nedd
    Commented Nov 7, 2023 at 2:42
  • \$\begingroup\$ @Mattman944 - To continue: This circuit also uses two series Schottky diodes on the inner line rather than just one. Schottky diodes can be very fast, using two in series may help to reduce the series capacitance and further improve the high speed operation. Not so sure about C8 or the 10k resistors on either side, they may be another method to speed up the Schottky diode pair or they may be to add just a little RC filtering. \$\endgroup\$
    – Nedd
    Commented Nov 7, 2023 at 2:46
  • \$\begingroup\$ @Mattman944 Yes R1 and R2 potentiometer are for offset adjustment. I can't find the datasheet, but adjustment process of the instrument indicate use this for offset adjustment. \$\endgroup\$
    – juliancaba
    Commented Nov 11, 2023 at 3:25

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