[ibis-macro] Re: Analog Model Isolation Definition
- From: James Zhou <james.zhou@xxxxxxxxxx>
- To: "bob@xxxxxxxxxxxxx" <bob@xxxxxxxxxxxxx>, 'IBIS-ATM' <ibis-macro@xxxxxxxxxxxxx>
- Date: Wed, 21 Mar 2012 10:52:55 -0700
Hi Bob,
Thanks for providing the link of past references. It is helpful for those of us
who were not on the list a couple of years ago.
With reference to: "the complete interface needs to be known and defined ... to
get the proper gain (S21 term).", this is a proven and well-known principle in
circuit and LTI network analysis. The conclusion at yesterday's meeting
sufficiently satisfies this requirement. The conclusion as I interpreted was
that, IBIS Specification only need to say that the Tx analog circuit input must
be driven by ideal voltage sources (i.e. zero source impedance), and Rx analog
circuit output must drive a load with infinite impedance. Once this is
established, the Specification does not need to say anything about what goes
into, or how to model, the "bigger blockbox" in the diagram (provided it
satisfies other IBIS requirements such as LTI and IBIS-ISS compliant, etc.).
With reference to: "In both cases, the transfer function S21 term is changed by
a factor of 2...", these two cases represent total reflection by open or short
circuits (S11=1 or -1). In both cases, S21 must be 0. This result is consistent
with the general formula of S-parameter modeling when S11 can have arbitrary
values (including the cases of S11=1 or -1). The treatment for these specific
cases of open and short circuits can be provided in the Specification as
examples instead of requirements of the Specification.
On the issue of setting S12=0, there have been IBIS discussions or
presentations recommending this. However, it is not necessary to impose this
condition on the analog circuits and it should not be treated as a requirement
of the BIS Specification.
Regards,
James Zhou
QLogic Corp.
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx [mailto:ibis-macro-bounce@xxxxxxxxxxxxx]
On Behalf Of Bob Ross
Sent: Tuesday, March 20, 2012 2:57 PM
To: 'IBIS-ATM'
Subject: [ibis-macro] Analog Model Isolation Definition
All:
Per the discussion today on the block interface definition,
here is a derivation based on BIRD122 for just s2p 2-ports (but should
apply to s4p files with more math). It shows the gain sensitivity to
the explicit S11 term for TX and S22 term for RX from a reference impedance
definition (e.g., TX: S11=0 or 50 ohm to infinite impedance S11 = 1
and RX: S22=0 to zero impedance S11=-1).
In both cases, the transfer function S21 term is changed by a
factor of 2 (assuming no S12 term). This is equivalent
to specifying the isolation interfaces with a unity gain ideal voltage
amplifier.
//www.freelists.org/post/ibis-macro/Eelement-in-analog-model-BIRD,1
Sorry, but some of the prior material may have involved some
lost or private e-mails and also a presentation or e-mail shown to
the ATM committee according to questions and exchanges in
the Dec. 14, 2010 minutes including:
Walter showed an email from Fangyi:
- Fangyi: The equation is at the bottom
- Bob: We have defined S12 as zero
- The real voltage gain is a function of S11
- Todd: Is this because S11 can affect V1 and therefore V2?
- Fangyi: No
- If V1 was fixed V2 would still be affected by S11
- Bob: The defaults should be zero for series impedances and
infinity for impedances to ground.
http://www.vhdl.org/ibis/macromodel_wip/minutes/20101214/mikelabontecisco/Mi
nutes%20for%20the%2012-14-2010%20ibis-atm%20meeting/20101214.txt
The main point is that the complete interface needs to be known and
defined in the Specification (for S-parameters and perhaps
different for a SPICE model) to get the proper gain (S21 term).
Bob
--
Bob Ross
Teraspeed Consulting Group, LCC
http://www.teraspeed.com
bob@xxxxxxxxxxxxxx
Direct : 503-246-8048
Teraspeed Labs: 503-430-1065
Headquarters: 401-284-1827
Teraspeed is a registered service mark of Teraspeed Consulting Group LLC
---------------------------------------------------------------------
IBIS Macro website : http://www.eda.org/pub/ibis/macromodel_wip/
IBIS Macro reflector: //www.freelists.org/list/ibis-macro
To unsubscribe send an email:
To: ibis-macro-request@xxxxxxxxxxxxx
Subject: unsubscribe
This message and any attached documents contain information from QLogic
Corporation or its wholly-owned subsidiaries that may be confidential. If you
are not the intended recipient, you may not read, copy, distribute, or use this
information. If you have received this transmission in error, please notify the
sender immediately by reply e-mail and then delete this message.
---------------------------------------------------------------------
IBIS Macro website : http://www.eda.org/pub/ibis/macromodel_wip/
IBIS Macro reflector: //www.freelists.org/list/ibis-macro
To unsubscribe send an email:
To: ibis-macro-request@xxxxxxxxxxxxx
Subject: unsubscribe
Other related posts:
