peak detector design

[Joe Wu]

Hi, I am building a peak detector and voltage comparator for my returning signal of the ultrasonic transducer.
Below are the circuit diagram of peak detector and voltage comparator:

And below are the screenshot of oscilloscope after peak detector and voltage comparator:


As you can see, it kind of works, it detect the peak at the very beginning, however, what I am interested is the returning signal after the first pulse (the signal that appears in the middle of the screen), and my peak detector is not able to detect it.
Any idea about how to do it?
Thank you.

 

[(*steve*)]

Google for a peak and hold circuit if you want something that will hold the peak value better.

Then reset the hold very briefly after the pulse has been sent. Another option is to hold it in reset while the signal is sent, lifting the reset after a small delay.

In general, a MOSFET or a bjt across the cap will work pretty well as a reset.

 

[Audioguru]

The duration of your peak detector is much too long for it to detect the return pulse. Shorten the duration by reducing the value of R1 to 47k or less. Then it will show the transmitted pulse, zero then the return pulse.

 

[Joe Wu]

The duration of your peak detector is much too long for it to detect the return pulse. Shorten the duration by reducing the value of R1 to 47k or less. Then it will show the transmitted pulse, zero then the return pulse.

I have tried, nothing changes. Thank you