Do we really need a BIRD for this, when it can be done with
[External Model] and IBIS-ISS?
Thanks,
Arpad
=============================================
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx] ;
On Behalf Of BIERNACKI,RADEK (K-Sonoma,ex1)
Sent: Wednesday, June 14, 2017 5:38 PM
To: michael.mirmak@xxxxxxxxx; IBIS-ATM (ibis-macro@xxxxxxxxxxxxx)
<ibis-macro@xxxxxxxxxxxxx>
Subject: [ibis-macro] Re: Terminators, Input models, and BIRD158
Hi Michael,
BIRD 158.x is intended as a choice, not a must, and a mix of Touchstone-based
on-die characterization at one end with a regular IBIS model is even mentioned
in the text of the BIRD. So, in other words, there is nothing contradicting
your desired functionality.
In fact, I have always been somehow reluctant to accept this limitation and can
happily support either the inclusion of the Terminator as a legitimate AMI Rx,
or as you consider adding the Terminator-type keywords to the Input models. If
desired I can help you drafting a BIRD on that.
Best regards,
Radek
From: ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Mirmak, Michael
Sent: Wednesday, June 14, 2017 3:15 PM
To: IBIS-ATM (ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>)
<ibis-macro@xxxxxxxxxxxxx<mailto:ibis-macro@xxxxxxxxxxxxx>>
Subject: [ibis-macro] Terminators, Input models, and BIRD158
IBIS prohibits the Terminator-specific keywords ([Rgnd], [Rpower], [Rac], and
[Cac]) under most other model types, including Model_type Input.
The nominal reason for this is that Terminators are not truly "buffers" and
therefore do not really have input logic thresholds, while Input and related
Model_types do and therefore require Vinh and Vinl.
Bluntly put, this is a rule observed "only in the breach" for quite a few
IBIS-AMI models today. Using a simple pair of keywords to describe a buffer's
impedance is highly convenient, and the original IBIS input logic thresholds
have little applicability to current SerDes buffer designs. The terminator
keywords also have application in single-ended input models.
BIRD158.5 certainly provides a comprehensive solution for complex analog buffer
impedances modeled under IBIS-AMI. However, there will (often?) be cases where
the linearity of a given buffer's impedance, particularly early in the design
cycle, may be assumed and generating a Touchstone file to represent it may be
undesirable. Further, the BIRD158.5 solution is *only* available for IBIS-AMI
models, not standard IBIS models.
Would there be significant opposition to a BIRD relaxing the Input Model_type
keyword rules to permit [Rac], [Cac], [Rgnd] and [Rpower]?
Thanks in advance.
- MM
