Subject: Re: [IBIS-Users] Differences between '*_fixture' & '*_ref' parameters
From: Fred Balistreri (fred@apsimtech.com)
Date: Thu Mar 27 2003 - 13:32:49 PST
Not to add to the confusion but Stephen's reply is not totally correct.
R_fixture, V_fixture, and C_fixture are the load conditions under
which the device is tested for generation of the v/t curves.
It is recommended that C_fixture be omitted if at all possible
during the v/t testing. R_fixture in particular is not a parasitic
resistance it is the total resistance connected between the
output pin under test and V_fixture, in other words the load
resistor.
Stephen is correct about the _ref parameters. It is important to
note that the _ref parameters specified in IBIS are NOT used to
generate the IBIS data. The _ref parameters are supposed to be
the IC manufacturer's recommended load conditions for measuring
timing.
The _dut parameters are analogous to the _pkg parameters. They
represent the parasitics of the package. These can be avoided
when generating the model from SPICE. However when IBIS is
generated from measured real devices there may be _dut parameters
that are un-avoidable due to package, ic socket or other such
parasitics. In that case the _dut parameters should be included
in the IBIS data since the data was taken with those parameters
present.
Hope this clears things up a bit.
Best Regards,
"Peters, Stephen" wrote:
>
> Hello Lior:
>
> The _fixture subparameters are intended to document the fixture parasitic
> in the case where the [Rising Waveform]/[Falling Waveform] data comes an
> actual bench measurement. In general, the rising and falling waveform data
> should be taken from simulations into a pure resistive load and the _fixture
> subparameters are not used.
>
> On the other hand, the _ref subparameters document the 'standard test
> load' -- the loading conditions under which the devices propagation or
> clock-to-output delay is measured. This information is required if one want
> to understand how to derate a devices propagation delay due to various
> output loading conditions.
>
> Hope this helps.
>
> Regards,
> Stephen Peters
> Intel Corp.
>
> -----Original Message-----
> From: Lior Aviv [mailto:RM18440@email.sps.mot.com]
> Sent: Wednesday, March 26, 2003 10:02 PM
> To: ibis-users@eda.org
> Cc: Yoked Erlich
> Subject: [IBIS-Users] Differences between '*_fixture' & '*_ref' parameters
>
> Hi,
>
> While creating an ibis model, I encountered a misunderstanding regarding the
> differences between the '*_ref' parameters and the '*_fixture' parameters.
>
> It seems like both are being used for loads.
>
> In addition, I have noticed that the '*_fixture' parameters are being used
> only at the 'rising/falling waveform' simulations.
>
> Does anybody know what the differences are ?
>
> Thanks in advance,
>
> Lior Aviv
> Motorola Semiconductor Israel.
>
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-- Fred Balistreri fred@apsimtech.comhttp://www.apsimtech.com |------------------------------------------------------------------ |For help or to subscribe/unsubscribe, email majordomo@eda.org |with just the appropriate command message(s) in the body: | | help | subscribe ibis <optional e-mail address, if different> | subscribe ibis-users <optional e-mail address, if different> | unsubscribe ibis <optional e-mail address, if different> | unsubscribe ibis-users <optional e-mail address, if different> | |or email a written request to ibis-request@eda.org. | |IBIS reflector archives exist under: | | http://www.eda.org/pub/ibis/email_archive/ Recent | http://www.eda.org/pub/ibis/users_archive/ Recent | http://www.eda.org/pub/ibis/email/ E-mail since 1993
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