J
Joerg
Hello Phil,
[ ... ]
Maybe I am too obsessed with noise here then. Gain stability won't be
such a problem because it's only changes we have to detect. The absolute
current value doesn't have to be logged since that is handled in the DC
section.
It's the OPA847. That thing can do a GHz. Basically the new ones are all
too fast for this application. But that could be tuned down via Cf.
[ ... ]
If you have 300 uA to work with, life is easy. A 200-ohm load will get
you to the shot noise limit--so something like a Mini Circuits T4-1
transformer running into a garden variety 50-ohm amplifier (with no load
resistor) will be the bee's knees from a SNR point of view. Gain
stability will probably be the limitation then.
Maybe I am too obsessed with noise here then. Gain stability won't be
such a problem because it's only changes we have to detect. The absolute
current value doesn't have to be logged since that is handled in the DC
section.
A cascode stage running into the summing junction of a current-feedback
amp would be another approach. That AD847 doesn't look as though it has
the GBW for a 100-MHz application.
It's the OPA847. That thing can do a GHz. Basically the new ones are all
too fast for this application. But that could be tuned down via Cf.