From: Degerstrom, Michael J. (firstname.lastname@example.org)
Date: Wed Feb 02 2000 - 11:55:45 PST
I also like to us a good high bandwidth 10X probe instead of a FET probe.
However, the user must be very careful as a 10X probe looks like
500 ohms to ground to the LVDS output. When you only have 3-4ma
of current swings you do not want 1.2/500 = 2.4ma pulled to ground.
Depending on the LVDS design you won't just get reduced swings you
may get nothing if the buffer is pulled out of its bias range. Luckily
I have always have control of the bit pattern coming out of
the LVDS buffer. Therefore I simply apply a well balanced
2^N-1 PRBS code so I can use AC coupling from my 10X probe into
my 50 ohm oscilloscope to do my evaluations.
Mike Degerstrom Email: email@example.com
200 1st Street SW
Gugg. Bldg. RM 1042A Phone: (507) 284-3292
Rochester, MN 55905 FAX: (507) 284-9171
> -----Original Message-----
> From: Tom Dagostino [mailto:firstname.lastname@example.org]
> Sent: Wednesday, February 02, 2000 12:39 PM
> To: email@example.com
> Subject: RE: [SI-LIST] : LVDS signal observation
> Be more concerned about the C loading of the probe than the
> input R. I'd
> much rather use 150 fF of input C from a good 10X 500 ohm
> passive probe than
> 400 fF 100K Ohms from and active probe. 1 pF at 1 GHz is
> about 160 Ohms.
> Tom Dagostino
> ICX Modeling Group
**** To unsubscribe from si-list: send e-mail to firstname.lastname@example.org. In the BODY of message put: UNSUBSCRIBE si-list, for more help, put HELP.
si-list archives are accessible at http://www.qsl.net/wb6tpu
This archive was generated by hypermail 2b29 : Thu Apr 20 2000 - 11:34:52 PDT