Re: [SI-LIST] : LVDS signal observation

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From: greg kimball (gkimball@indra.com)
Date: Wed Feb 02 2000 - 21:03:22 PST


Joe-
I'll second the motion re passive probes being of value at hundreds to GHz
range. Take a note of the Xc of the TEK P6248 - At 500MHz(0.7ns tr), the 1.5pF
differential input capacitance is 212 ohms!! I believe the passive probe
design Howie Johnson mentions in his High Speed Digital Design book
is about 1K and a fraction of a pF I believe, and much better usable voltage
range. BUT, on the downside - it is only single-ended.

Does anyone know of a truly balanced passive diff probe design??

Regards,
Greg Kimball
TI Storage Product GP

jjcahill@us.ibm.com wrote:

> FET probes can be had with very low input C and reasonably high input R,
> and very nice BW. I prefer passive probes however. They are 5X cheaper,
> they can be had with 1kOhm input R and they usually fit in smaller places
> than the good active probes. Another benefit is that nobody else wants them
> so the lab thieves leave them right where I put them down :-)
>
> If you are going to do any debugging buy a scope with a high single trigger
> sample rate, and watch out for specs based upon interleaving digitizers.
> The CSA series scopes will do very nicely if your signal is repetitive, but
> if your 'oddity' only occurs once a second you will never see it with
> anything but a trigger crafted for the oddity and a high sample rate single
> shot scope. The high end Infinium and the Tek TDS684 and TDS694 are the
> instruments I am familiar with.
>
> Joe
>
> CEC Analysis and I/O Design
> Phone: 507.253.0762 Fax: 507.253.4966
> jjcahill@us.ibm.com
>
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