Hüseyin Rahmi Seren said:
Hello again,
Mr Hobbs,
I built one of your circuits (Fig-3 in the paper "Ultrasensitive laser
measurements without tears"). In principal it worked. However, I see
lots of internal oscillations which can be considered as noise. For
example whenever the signal beam becomes zero an oscillation around
1.5 MHz appears. Also, there is another oscillation which periodically
appears and exponentially diminishes. Do you have any suggestions or
experience about this?
Thanks very much.
Best wishes.
Just saw this now...my news provider (supernews.com) is dropping a lot
of posts.
Your feedback loop is oscillating. This could be due to inadequate
bypassing, poor layout, or even hanging a coaxial cable on the output of
an op amp with no isolation resistor.
If you can send me an actual schematic, I'll have a look at it, but that
exact circuit works very well--the New Focus "Nirvana" detector is just
that circuit in a nice box, for which they'll charge you $1500. (The
email address above actually works, spam block and all.)
Cheers,
Phil Hobbs
