[SI-LIST] Re: Undershoot on a cPCI Bus
- From: steve weir <weirsi@xxxxxxxxxx>
- To: bfields@xxxxxxxx, <si-list@xxxxxxxxxxxxx>
- Date: Fri, 07 Oct 2005 13:45:55 -0700
Brian,
You can:
Try putting damping resistors 1/3 and 2/3 the way along the back
plane. 15-24 ohms are decent starting values.
Steve.
At 10:13 AM 10/7/2005 -0600, Fields, Brian wrote:
>I'm simulating a Compact PCI backplane, and have found that the signals
>show an undershoot of which is outside the manufacturers maximum
>operating conditions. The FPGA devices on the bus all have internal
>clamping diodes, however the voltage at which they start to conduct is
>also outside the operating range.=20
>
>Simulations with external Schottky clamping diodes show that the
>transient ringing which produces the undershoot lasts for about 2ns, too
>fast for the external diodes to respond. There are 10ohm series
>resistors on each of the daughter cards signal lines, per the spec, and
>any termination scheme would have to be implemented on the backplane.
>
>Any ideas? I'm stumped.
>
>
>Thanks,
>
>Brian Fields
>Ball Aerospace & Technologies Corp.
>bfields@xxxxxxxx
>(303) 939-4036
>
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