[SI-LIST] Effect of Driving current

  • From: "Ched-Chang Chai" <ched_chang@xxxxxxxxxxx>
  • To: si-list@xxxxxxxxxxxxx
  • Date: Tue, 14 May 2002 21:53:40 +0800

Dear all,
I have a situation where an ASIC is connected to DDR-SDRAM.
We have 2 IBIS models for the ASIC. The differences of the 2 IBIS models 
are:
- IBIS 1 has larger pullup and pulldown currents than IBIS 2.
- IBIS 1 has faster rising and falling edges than IBIS 2.

Simulations have been carried out with the ASIC as the driver and DDR-SDRAM 
as receiver. The overall results are:
(1) The receiver waveform amplitude is smaller if IBIS 1 is used.
(2) The signal delay is not much different for either IBIS models.

I expect the amplitude of the receiver waveform to be larger if IBIS 1 is 
used (higher pullup and pulldown). But I got it the other way round.
It seems like my thinking maybe wrong all the while.
Also, do pullup and pulldown currents affect the signal delay?

Can someone please explain this to me?

Thank you very much.
--
Rgds,
Chai




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