# How to practically find the amplitude of a high frequency signal?

I had initially planned to use a standard peak detector circuit with an op amp of a much lower bandwidth than the signal I want to measure - my assumption was that given a high enough time domain the low bandwidth wouldn't matter "some" of the signal would make it through and I would read the correct value eventually. I'm now starting to doubt this based on some articles such as this from Analog Devices that claims inaccuracies at high frequencies.

This is for a pico driven function generator using an AD9833 module, that needs to be able to sample peak to peak for closed-loop gain control of the signal amplifier. I'm using a DAC with more than enough accuracy for my purposes (<5 mV steps over the 24 V range I'm using) to provide the reading, I just require a way to process a signal to convert the peak to DC - though I'm open to other solutions for how to solve this. I plan to potentially use a calibration curve, so some inaccuracy can be dealt with but wanted to ask some more qualified people how to solve this problem.

The signal will be anywhere from ~1-24V p-p and (hopefully) useful within ~0.05 Hz to 10 MHz, though feel free to tell me if this is a lofty goal.

• Is anything preventing you from doing this digitally? Jun 22 at 21:54
• You mean sampling so fast I can figure it out that way, or calculating the amplitude based off my understanding of the circuit? For the first is speed - I don't believe I'll be able to sample fast enough on the pico. For the second, I plan to, but want closed loop control to (hopefully) provide better accuracy Edit: let me know if the idea of closed loop control for such a circuit is silly - i honestly have no clue Jun 22 at 22:09
• If your circuit is generating the signal, shouldn't you know the amplitude? Jul 1 at 15:18
• In theory yes, but in practice a lot of the components have changing impedance over the frequency range - and being able to measure directly would allow for a far quicker production of calibration data versus the use of the oscilloscope I have Jul 3 at 13:39