enter image description here

I feel that I have a semi-solid understanding of op-amps (and the circuit above) after reading quite a few explanations online. Where I'm starting to get quite lost is the function of the two diodes in the schematic above. My understanding is that diodes are meant to inhibit the flow of current into one particular direction. If op-amps have (ideally) infinite impedance at the inputs and outputs, what are the diodes doing below? Why is the output of IC1-B (right side of image) connected to the voltage divider at the positive input of IC1-A?

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    \$\begingroup\$ I'm assuming that you haven't simulated the circuit? \$\endgroup\$
    – user103380
    Feb 10, 2018 at 18:31
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    \$\begingroup\$ Ideal opamps have zero output impedance, not infinite. \$\endgroup\$
    – pjc50
    Feb 10, 2018 at 18:34
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    \$\begingroup\$ @Jasen I think pjc50 is correct, ideal op amps have zero output impedance and infinite input impedance. \$\endgroup\$
    – John D
    Feb 10, 2018 at 18:48
  • \$\begingroup\$ you're right. deleted bad comment. \$\endgroup\$ Feb 10, 2018 at 19:05
  • \$\begingroup\$ This is a VCO - Voltage Controlled Oscillator. You need to analyze the entire idea of the circuit to find the role of diodes. The right side is an integrator providing a voltage ramp. When voltage gets above 0.7V, the first OPA changes the level of input to the integrator, which likely starts driving its output in opposite way, and the cycle repeats. Or something along this way. The frequency depends on "Control voltage input" level. \$\endgroup\$ Feb 10, 2018 at 19:27

1 Answer 1


The bottom diode provides positive feedback to the first opamp so it oscillates.


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