RE: Differential voltage probes 2

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

Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>

Hi Richard,

Note my other post were a single 150MHz amp does that differential stuff on 
chip ;-))  With single small 5000V SMD resistors now available, we might be 
able to really push this thing up into the MHz.

http://hot-streamer-dot-com/temp/DiffProbe11.gif

Also note that the inputs are "open" here for your uses too ;-))

Two things we probably won't have in that case are pots and range 
switches.  They would just be "complex impedances" at RF frequencies.  We 
would have to keep the signal paths very small and very short.  Everything 
would be surface mount...

Finn is also hinting that he could do boards if needed ;-)

I also plan on having one hook to the thing with a scope probe which solves 
all the impedance matching to the scope and adds another level of protection.

Probably time to stop talking, and start really working on it ;-))

Cheers,

         Terry

At 06:34 PM 6/28/2003 -0400, you wrote:
>Terry,list,
>
>Here is a quick diagram of a simple single IC four op amp differential
>instrumentation op amp based on a quad fet op amp.  The inputs are buffered
>and balanced.  Any input bias can be fairly well balanced with variable R
>on non-inverting input
>IC-3.  IC-4 reinverts output, allows amplification of small signals and
>buffers output.  (actually IC-4 can be left out, but signal will be
>inverted).  If you like TL082 (dual) then TL084 (quad) j-fet op amp with a
>few extra resistors will do the trick here.  Try it both ways with a single
>op amp and four op amps and you'll find a big difference.
>
>I agree -- keep it simple at first then get fancy later.  Maybe Dan could
>design a pcb for us later.
>
>RWW