[SI-LIST] Re: series term + fanout = noise?
- From: Ravinder Ajmani <ajmani@xxxxxxxxxx>
- To: "Si-list@freelists. org" <Si-list@xxxxxxxxxxxxx>
- Date: Wed, 23 Apr 2003 13:10:10 -0700
I believe this is in reference to the routing of differential pairs between
IC and R-pack. If IC and R-pack have identical pitch then the differential
pair can be routed with uniform spacing, otherwise the spacing will
increase when you are connecting to R-pack. I have seen similar pitch for
decoupling capacitors too. How important it is to do this is anybody's
guess.
Regards, Ravinder
Hitachi Global Storage Technologies
Email: ajmani@xxxxxxxxxx
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"Boris Yost"
<yost@rainbowdisp To: "Si-list@freelists.
org"
lays.com> <Si-list@xxxxxxxxxxxxx>
Sent by: cc:
si-list-bounce@fr Subject: [SI-LIST] series term
+ fanout = noise?
eelists.org
04/23/2003 09:01
AM
Please respond to
yost
Dear List:
I just read a very nice presentation. Most of it was
educational and I
believe it. One particular thing I really wonder about.
Assume a fine pitch IC (0.5mm) with ordinary TTL/CMOS output
(not something
differential or exotic), and resistor or ferrite packs for series
termination close to the IC. They assert that if the R-packs have the same
pitch as the IC, it will make less noise. If the IC must have fanout to
match the pitch of a slightly coarser Rpack, there will be more noise.
I unfortunately don't get it. The extra trace length before
the series
termination is going to be pretty small--we're not talking about fanout to
fit 1/4W through-hole resistors. And then after the R-pack, nothing can be
assumed about the trace length other than it must be reasonable for series
termination; the total length could be large compared with the tiny fanout
or stub.
It should be noted that the presentation authors manufacture
extra fine
pitch ferrite packs and SMD beads.
Can somebody explain this?
Boris
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