Looking for ideas/suggestions on obtaining a DC output from an active half wave rectifier.

Thread Starter

Sycko

Joined Jul 11, 2019
23
Hello good people :)

I'm looking around for a way to obtain a DC output that closely follows the positive signal that comes off a half wave rectifier.
I was trying to do it using a low pass filter, but realized that was pointless and wouldn't achieve anything.

So, the input is a 1V AC signal around 14MHz, and the output is a half wave rectified signal shifted by +1.65V.
The screenshots here:

upload_2019-8-13_13-50-51.png


What i hope to achieve is something like this:
upload_2019-8-13_13-52-58.png

What sort of circuit should i add to the output of the half wave rectifier to obtain a Vout like the image above?

I thought about using a simple peak detector made out of a diode + resistor + capacitor, but that is not great since the 0.7 Voltage drop reduced the signal by a lot, not to mention the output of the op amp is already shifted by +1.65V so the diode won't do anything. (i think)

If anyone's got any suggestions I'd love to hear them! :D
 

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Thread Starter

Sycko

Joined Jul 11, 2019
23
I think i solved it, posting the solution for anyone who stumbles upon this in some distant future

It uses a 10k resistor to isolate the capacitor from becoming part of the op amp's feedback, and then a simple filtering capacitor.

upload_2019-8-13_14-16-40.png


upload_2019-8-13_14-17-7.png

It isn't quite following the purple wave from above (far from it) but i suppose this is the easiest solution.
 

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Thread Starter

Sycko

Joined Jul 11, 2019
23
Oh wow that is amazing Bordodynov!

So you've added a RC filter at the beggining and a Lowpass RC at the output?

If you have any reference material to that design I'd love to read it.

Thanks for showing me this!
 

AnalogKid

Joined Aug 1, 2013
8,229
What you are after is called an envelope detector, a variation of a peak detector. This is the heart of almost every broadcast AM receiver. Usually it is nothing more than a series diode and a shunt filter capacitor, with the downstream circuit impedance acting as the pull-down resistor. In your case you probably will need a fixed resistor like R4 above. With a fast enough diode, it should work for you.

Buffer (with or without gain) > diode > capacitor and resistor to GND > output

ak
 

Thread Starter

Sycko

Joined Jul 11, 2019
23
Oh the envelope detector, so that's the name of what I'm looking for!
Thanks for the suggestion!

But won't I have a problem with smaller signals (like for example 0.6V) since the diode has a forward voltage drop?
Otherwise it would be a perfect option, if there was a way to overcome this...
 
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