Current measurements at bandwidth of 400 Mhz

[gurras]

Hi,

I have a small problem. I need to measure currents (relatively small currents, ~20A)
Extremly fast, I need a bandwidth of around 400 MHz

I have a basedrive connected via a R || R-C network to the base of a BJT.
At the emitter I have now placed a small resistor to lead the current back to the basedrive. The problem is that my resistor (~0.05 ohm) is too large. and any lower the oscilloscope wouldn't be able to measure the current accuratley.

I wonder if you can give me any tips on low inductive, 0-resistive ways of measuring the current at these speeds?

 

[dick_freebird]

20A is not a small current. You may need to find (or make)
an inductive (current transformer) pickup and have it push
a good quality 50-ohm line directly.

Now if you made your sense resistor two parallel resistors,
such that the little one was (say) 2A at 20A net, you might
be able to use a generic CT-1 (or similar) that's made for
'scopes. Though I never tried to use them at that high a
frequency.

Knowing what they do and don't show, is probably the trick
where you're going.

Maybe you want a current transformer driving a RF amplifier
close-in, and cal-map it with whatever snappy current pulse
reference you can come up with.

 

[gurras]

thanks for your input. basically the same ideas I have..