[SI-LIST] Re: unused clocks
- From: "Ingraham, Andrew" <Andrew.Ingraham@xxxxxxxxxx>
- To: 'si-list' <si-list@xxxxxxxxxxxxx>
- Date: Thu, 30 Aug 2001 12:17:25 -0400
> i have a question.i have a clock buffer which o/p's 4 copies of 100mhz
> ttl clocks,i am using only 2 of them do i need to terminate the rest of
> the clocks which i am not using.if so which termination is good.if
> unconnected dont they radiate and upset the nearby traces.
Why do you think they would radiate? (Any more than with terminations?)
Terminating them makes the output current >0, so if anything there might be
more (magnetic) radiation.
If the outputs were complementary (differential), then you might need to
terminate both sides of each pair about the same, so that you don't upset
the current balance in the chip. Also I have seen an ECL chip where the
vendor wanted certain unused outputs terminated, in order to preserve clock
skews (on the order of 50ps).
Your best bet: ask the vendor.
Andy
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