On 10/14/05, Harold Hallikainen <harold@hallikainen.com> wrote:
> I've got a project where we need to watch a pulse on another piece of
> equipment. We do not want to load the circuit in the other piece of
> equipment. Running a piece of coax to my equipment results in considerable
> ringing, since the coax is not terminated. So, the question comes up, how
> does a scope probe get away with a 1M load in the scope?

 For less than 100Mhz poor. For less than 500MHz and passive probe
very poor. For 1GHz passive probe, lousy poor = impossible
measurement.
For a correct pulse measurement you need a LVDO driver on the board 1
and a LVDO receiver on the board2. Between board1 and board2 a
differential connection.
Then what you'll measure on board2 can be sure it's exactly what you
have on board1.
Take a look at Maxim site. There are drivers up to 5000V/us. A 10:1
scope probe is the greatest cheating thing. Try for example a noise
measurement with it and you'll understand what I'm saying.

cheers,
Vasile



I doubt that's
> terminating the coax with its characteristic impedance. The idea of a 10X
> probe with compensation is pretty clear... the trick is how do they deal
> with the lack of termination?
>
> Ideas?
>
> THANKS!
>
> Harold
>
>
>
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