regards
Andreas
-----Urspr=FCngliche Nachricht-----
Von: owner-si-list@silab.eng.sun.com
[mailto:owner-si-list@silab.eng.sun.com]Im Auftrag von Ingraham, Andrew
Gesendet am: Freitag, 21. Mai 1999 14:06
An: 'si-list@silab.eng.sun.com'
Betreff: RE: [SI-LIST] : What speed scope should I consider?
>Also note that the loading of the probe on the cirucit isn't just the DC
>impedance of the probe. A 10 MOhm, 10 pF probe represents an input
>impedance of
>26.5 Ohms at 600 MHz. (unless I've done the math wrong)
Your math is right, but it may be even worse than this.
I don't have a reference handy, but I have read or been told that many
10Mohm, x10 probes also have a significant resistive loss or shunt factor
(perhaps due to dielectric losses?) at high frequencies. Thus the input
impedance is something much less than 10Mohm in parallel with 10pF.
I haven't used a x10 probe in a very long time.
Get good probes, then pay utmost attention to grounding and probe leads. =
1"
is too much.
Regards,
Andy
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