Re: [IBIS] Rfixture value

Hi Sudarshan:

It is OK and reasonable to increase the resistor to a
higher value for two reasons:

1, The buffer is slow, so high speed issues are not really
a factor.  So Transmission line characteristic impedance
modeling should have minimal impact on the simulation.

2, If the Buffer is weak, a large resistor allows you to
extract the table over a larger swing to correspond
to how the part may operate (in a mostly infinite
to small capacitive load.

If you have to use 10,000 ohms, then do so, but it would
be better to use a smaller value.  Perhaps 500 ohms or
1,000 ohms might be better as long as there is a
reasonable voltage swing (such as 30 - 50 percent of the Vdd-Gnd
rail.)  While, for example, on the rising edge, the response
to a load to Vdd will remain fast, a smaller resistor load
should capture some buffer speed reduction better if it
is actually connected with a termination load to Gnd.

Bob

Sudarshan Honnudike wrote:
> 
> Hello Experts,
> 
> One of my IO buffer is very slow and i need to increase R_fixture to 
> considerably high value to
> make the V-t curves attains steady state. I actually increased to 
> 10k(10,000).
> 
> Will this have any major effect during SI simulations or is it ok to 
> have this big load also.?  
> 
> 
> Best Regards,
> 
> Sudarshan HN
> NXP Semiconductors/CTO /PLT
> C-4, Manyata Tech Park, Nagawara
> Bangalore-560 045 , India.    
> Ph:+91-80-40247073  
> Fax: +91-80-4026 7855
> seri:sudarsha@inpsblr
> E-mail: sudarshan.honnudike@nxp.com
> -- 
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-- 
Bob Ross
Teraspeed Consulting Group LLC     Teraspeed Labs
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bob@teraspeed.com

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