Subject: Bird 42 review by HyperLynx

From: Kellee Crisafulli <[email-masked]>
Date: Thu, 04 Jun 1998 17:53:08 -0700

Hi IBIS,

  We also reviewed the current-waveform bird 42 and found
the following:

1) After several revisions this is a well described bird (kudos to Kumar).
2) It seems to address the crowbar currents related to single pin
   not the die operating currents since it ties all the currents to an output pin.
   This would work for a buffer chip but would not address current
   spikes in the core of something like a video controller or CPU since they
   are not related to an output pin switching.
   It also doesn't deal with currents that result from PLL's on chip.
   (I hope we correctly interpreted the specification but we didn't see
   anything but output pin related currents).
3) DC Sessions has indicated that crow-bar current is for the most
   part not a critical problem with today's CMOS.  (If I am
   paraphrasing correctly).  
   Granted there is some overlap between an output changing and core logic but
   this bird seems to tie all the current changes to a pin change.
4) Crow-bar current is also handled to with the wave-tables.

If the assumption that today's CMOS doesn't present significant crow-bar
current is valid we recommend this bird be killed or modified to handle
core logic currents and ignore crow-bar currents.  The concept seems like it
could be applied to core logic currents perhaps with multiple
tables that can be used to indicate the clock frequency internally for which
they apply.
e.g. Table 1 applies if the PLL is set to 200Mhz, table 2 applies for 300Mhz,
     Table 3 applies at 400Mhz etc.

Kumar: I know you have worked very hard on this bird.  I would very much like
to see this bird reformed slightly into a core logic current specification.
What do you think?

Best wishes
Kellee

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Have a great day...
Kellee Crisafulli at HyperLynx
[email-masked]	http://www.hyperlynx.com
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