I am trying to make an envelope detector for an OOK signal, but my comparator is not working properly.

I tried various models for the comparator but for some reason the output is staying relatively saturated.

It should go from 0 to 3.3V, it is detecting the envelope but the signal variation is not too much.

Does anyone know anything about this? The frequency of operation is 915MHz.

The circuit waveforms are as follows:

The circuit diagram is as attached below:

enter image description here

The LTspice simulation file used is here.

  • \$\begingroup\$ The discharge path for huge C4 depends on leakage current of D6, D5. This could be quite slow if those diodes are cold. \$\endgroup\$
    – glen_geek
    May 30, 2023 at 12:55

1 Answer 1


It seems that Vref2 is 0.236V when output is 3.3V and the Vdiode2 is not crossing this voltage hence, the output always stays high. Increasing the amplitude of OFK will help toggle the comparator output to 0V when the sine wave starts.

However, I think the output may not go to 3.3V again because Vref2 will become 0V after detection of envelope and Vdiode2 will not go lower than 0V. So, you need to correct your reference voltage scheme in my view.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.