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I wanted to do falstad.com simulation of the circuit(link to schematic):

enter image description here

Falstad isn't familiar to me, so I'll be grateful for showing me how it should be drawn.

I think detector could be replaced by voltage generator.

I also wanted to know what is the idea of the third amplifier, that one which produces pulses with 500 \$\mu s\$ wide. Is it also amplifying the output? Why, I guess, non-inverting input of the amplifier is connected to 1/2 \$V_{cc}\$?

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  • \$\begingroup\$ Haven't you drawn the circuit? Don't you know why you used the third op-amp. If not then you need to provide details where you got the schematic from. Site rules. \$\endgroup\$
    – Andy aka
    Jan 17, 2022 at 19:54
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    \$\begingroup\$ @Andyaka - "you need to provide details where you got the schematic from. Site rules" FYI no, it isn't site rules to provide that info for questions, only for answers. It would be helpful for the OP to provide context, of course, but helpful =/= site rules. \$\endgroup\$
    – SamGibson
    Jan 17, 2022 at 20:02
  • \$\begingroup\$ That sounds like an arbitrary decision. \$\endgroup\$
    – Andy aka
    Jan 17, 2022 at 20:15
  • \$\begingroup\$ I think the third amplifier produces a more consistent and normalized pulse for counting purposes. I assume the point of this is to build a scintillation pulse counter, right? But I am not really sure. \$\endgroup\$
    – user57037
    Jan 17, 2022 at 22:12
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    \$\begingroup\$ @Andyaka - It's SE site-wide policy, so if you want to make a point about that, then Meta.SE is the right place for you to raise it. \$\endgroup\$
    – SamGibson
    Jan 19, 2022 at 12:44

2 Answers 2

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No, the detector should be a current source proportional to the incident light.

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That last op amp is a 2-pole low pass filter using a Sallen-Key configuration.

The detector can be replaced by a voltage generator. However, it's up to you to configure the voltage generator to behave like your detectorl

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