Re: [SI-LIST] : Decoupling strategy on 622MHz devices

About this list Date view Thread view Subject view Author view

From: D. C. Sessions (dc.sessions@vlsi.com)
Date: Thu Apr 06 2000 - 17:49:46 PDT


Steeve Gaudreault wrote:
>
> Hi,
>
> I need a breakout strategy for the ASICs (BGA 383pins)
> that we have on the board. They all have lot 622MHz I/F.
> Those ASICs have a separate VDBB for those 622MHz I/Os.
> We put decoupling caps inside the device close to the die,
> but we also need a strategy for the decoupling on the board.
> At those frequencies/rise time (BTW rise time = 400ps), the
> effect of the parasitic becomes important when we do our
> decoupling strategy. I'd like to get some advice as for having
> decoupling between the ASIC and the board versus having the
> decoupling on the secondary side. I no for sure that manufacture
> won't like the first option but I'd like to get advises from the
> experts before I choose which way to go.

400 ps is nothing remarkable. All CMOS outputs from current technology
are in that range; if anything, 400ps is a bit slow.

The real issues are things you don't mention, such as whether you're
signaling differentially or single-ended, balanced or unbalanced codes,
shunt terminated or source-only, stuff like that.

> -----Original Message-----
> From: Chris Bobek [SMTP:cbobek@cadence.com]
> Sent: Wednesday, January 26, 2000 2:43 PM
> To: si-list@silab.eng.sun.com
> Subject: Re: [SI-LIST] : Decoupling capacitor resonance
>
> Hi,
>
> Thank you for all of your responses. So, are most of you saying
> that in my case, the 0.1uF is probably ok and to not bother purchasing
> 10pF
> caps for this
> application?
>
> Something I realized is that when this appnote tells you what caps
> to use for decoupling, they don't specify a package. So, they might say
> "use a 22uF and
> a 10pF", but they could be using through hole versions, while I'm
> using small SMT versions. My resonance will be entirely different from
> theirs (also
> because of layout differences). The same would be true if they were
> using 1206 and I'm using 0805.
>
> The bottom line for me is that the PLL is working great on our
> prototype with the 22uF and 0.1uF. We have 4 ground planes and there
> aren't
> any other
> signals around the PLL. I seriously doubt it's worth the trouble
> and complication of adding a brand new part to the BOM just to satisfy
> an
> appnote that
> happens to use different values.
>
> Thanks for all of your help, it will come in handy in the future,
>
> Chris
>
> **** To unsubscribe from si-list: send e-mail to
> majordomo@silab.eng.sun.com. 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
> ****
>
> **** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
> si-list archives are accessible at http://www.qsl.net/wb6tpu
> ****

-- 
D. C. Sessions
dc.sessions@vlsi.com

**** To unsubscribe from si-list or si-list-digest: send e-mail to majordomo@silab.eng.sun.com. In the BODY of message put: UNSUBSCRIBE si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP. si-list archives are accessible at http://www.qsl.net/wb6tpu ****


About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Thu Apr 20 2000 - 11:36:05 PDT