How to build 40 MHz amplitude detector ?

[kekon]

I need to design peak detector for 40MHz sine wave. There are some fast operational amplifiers that could be used in the project. These are current feedback devices but I don't know how to design a peak detector by means of such amplifiers.

 

[jourval]

What is a problem?
40 MHz is not too high.....
Take this
**broken link removed**

for example

It is really straightforward

 

[kekon]

Come on... this circuit introduces an error caused by diode drop voltage !

 

[10kangstroms]

See below. You can substitute mmbth10 and mmbth81, or other high frequency transistors.

 

[preet]

hello kekon,
u can also do this by, frequency to voltage converter circuit

 

[10kangstroms]

hello kekon,
u can also do this by, frequency to voltage converter circuit

He wants to measure amplitude, not frequency.

 

[preet]

sorry,
for my previous post, but u can do it placing a capacitor in parallel to circuit,

 

[IanP]

Here is a concep of a simple peak detector using op-amp and diode connected between op-amps output and (-) input. Gain of the whole circuit is -1 ..

 

[lastdance]

A 40MHz sine wave oscillates at 25ns/cycle, therefore, for each half cycle, there's 12.5ns. Any amplifier used should rise in couple of nsecs to allow the peak to be registered on the holding capacitor?!

what is the range of amplitude that needs to be detected?
what is the amount of error that you can accomodate?

You should search for amplifiers with a slew rate that can follow a 40MHz sine wave with the value of holding capacitor you would be using. However, too fast an amplifier will cause overshooting, this u have to beware of.

Refer to manufacturer's datasheet for info on how to use CFA.

 

[bobcat1]

Hi

Simply use AD8307 log detector and a 40 MHz BPF in the front end

All the best


Bobi