Re: need some info.....

Nirmal Jain (
Wed, 10 Jan 96 12:35:25 EST

>Hi folks,
> I am a VLSI circuit designer and hence a novice when it comes to the
>emagnetics. I do have a question for you:
> In most of the high performance and large chips, the power supply and
>some of the critical signals are routed in metal lines which are wide. There
>was also a paper by one of the alpha designers about the inductance effects of
> the wide power bus lines inside their alpha chips. So Instead of having a
>single wide line, how about having a bunch of narrow strips of the metal lines
>such that the total width of all the narrow strips equals the width of single
>wide line with maybe even shorting bars in the perpendicular direction at some
>predetermined intervals?
>Would this reduce the inductance effects? Would this bunch of the narrow
>metal strips behave similar to a single wide line if the distance (pitch)
>of seperation between the individual strips? What would be an acceptable pitch
>relatively speaking ( no hard numbers needed)?
> I know doing this might increase the area. But if i dont care about the area
>of the wiring so much, is there any other alternate ways? better ways?

I think :

The best solution would be adding GND/PWR planes and dropping
vias to GND/PWR planes close to your I/O buffers. But if you can
not add seperate GND/PWR planes and if you donot have area constraint
in your design then above approach of splitting your
single wide line into bunch of lines would be really neat and
moreover you can optimally route those lines so that IO switching
current pathlenght are minimized. BTW the effective inductance
of the single wide strip would be definitely higher than the
bunch of narrow strips ( total width and thicknesses are same )

Hope it helps, regards


>This may already have been discussed before on this forum, if so I would
>appreciate any info about this in the archives or if you could send me any
>info by email to me instead of the forum please do so to
>Thank you

Nirmal Jain					    ANSOFT CORPORATION
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