Re: Differential voltage probes 3

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Paul Benham by way of Terry Fritz <teslalist-at-qwest-dot-net>" <paulb-at-woodanddouglas.co.uk>

Terry,

Can you connect the differential output up to the scope input if the whole
thing is floating?  This will reduce down the distortion products and noise
from the IC that are coupled into the scope.  It seems that this would be
better that use it with a single ended output.

Cheers,

Paul.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, June 29, 2003 2:46 AM
Subject: RE: Differential voltage probes 3


 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi,
 >
 > Ok, using bleeding edge, oh!, I mean leading edge parts...  I got it back
 > down to one IC.
 >
 > http://hot-streamer-dot-com/temp/DiffProbe21.gif
 >
 > The fabulous Ti THS4151ID apparently does all the power supply offsets and
 > CMRR fixing internally.  That chip is basically the whole enchaladia!   So
 > I just added Ohmite's little 5kV resistors, some 1% 1K resistors, some big
 > NPO caps and it's done.  It would almost fit on a quarter ;-)
 >
 > There are some relatively expensive parts now, but the total cost is not
 > that much.  The input resistors are $4 each, the IC is $9, the NPO caps
are
 > $2...  But I think the total cost would be about $45.  Yes, it is all that
 > little surface mount stuff and you have to be careful since the high
 > voltage is very near.  Probably a good candidate for HV conformal
coating...
 >
 > The input resistors are 5%, but hopefully they are somewhat matched as
they
 > come off the reel.  The PCB around those resistors would have to be routed
 > out to insure voltage standoff.
 >
 > I have no idea what the frequency response would be, but it "should" be
 > pretty darn high!  The IC is 150MHz and I am feeding it just like it
 > wants.  With the input resistors being so small, a LOT of response
problems
 > just vanish.  Caps across the 1k resistors could limit the frequency
 > response if needed.
 >
 > Unless someone has a better idea, I think I will give this one a try.
 >
 > Cheers,
 >
 > Terry
 >
 >
 >
 >
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