[IBIS-Users] Re: Question about Vref

Hello Ramiro Lecona:

The Vref value is set to the value that the Rref is connected
(if it exists) for timing test load calibration, per the circuit
specified in the data sheet.

Older devices often used 500
ohms connected to ground. With higher speed technologies,
50 ohms might be connected to Vcc/2 per intended operation.
For Opne_drain devices, Vref might be some higher voltage
such as Vdd. For ECL and PECL, the Vref value is often
2 V below the supply voltage.

So the Vref value is set to the value used for timing
test load measurements and does vary according to data
sheet informaiton.

Bob

RODRIGUEZ LECONA RAMIRO wrote:

>
> Hi, I am modeling some buffer and I have the question that follows:
> Some vendors specify Vref subparameter as 0V, other as VDD and other
> as VDD/2. What's the difference? Why do they use different values to
> determine the propagation delay?
> Thanks.
>
> Ramiro Lecona
>

-- 
Bob Ross
Teraspeed Consulting Group LLC     Teraspeed Labs
121 North River Drive              13610 SW Harness Lane
Narragansett, RI 02882             Beaverton, OR 97008
503-750-6481                       503-430-1065
http://www.teraspeed.com           503-246-8048 Direct
bob@teraspeed.com
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