[ibis-macro] Re: Replacing BIRD 122 with "Reserved_Model" keyword in [External Model]

  • From: "Walter Katz" <wkatz@xxxxxxxxxx>
  • To: <james.zhou@xxxxxxxxxx>, "'Scott McMorrow'" <scott@xxxxxxxxxxxxx>
  • Date: Wed, 18 Jan 2012 07:35:46 -0500 (EST)

James,

It is not what " IBIS-AMI proposes to do" it is what " IBIS-AMI does". We
can debate all we want on the subtleties of the approximation that Tx and
Rx being LTI, and if anyone has data that shows the LTI approximation
causes engineers to make incorrect design decisions they should present it
not only to IBIS, but PCIeG, IEEE 802.3, Sata, Xaui, and IC Vendor
internal SerDes design tools that all make the LTI assumption.

Walter

-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of James Zhou
Sent: Wednesday, January 18, 2012 2:36 AM
To: Scott McMorrow
Cc: IBIS-ATM; Arpad_Muranyi@xxxxxxxxxx
Subject: [ibis-macro] Re: Replacing BIRD 122 with "Reserved_Model" keyword
in [External Model]

Hi Scott,

Thanks for your detailed reply. Please see my response below.

"By definition a driver is not LTI".  I agree that in reality the Tx/Rx
analog circuits are strictly speaking non-linear. However the question is
about whether the proposed  "model" is non-linear. My reading of Walter's
email is that he is proposing to use LTI models for Tx/Rx analog circuits.
It is debatable whether it is "an over-simplification", but it is one
issue to clarify what is proposed, it is a different issue to debate
whether the proposal is agreeable or not.

Regarding the rest of your comments, my understanding of the IBIS-AMI
specification is that channel impulse responses should  include Tx/Rx
analog models. I think what you have described is correct in concept but
it  is not what IBIS-AMI proposes to do.

Thanks,
James Zhou








From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Tuesday, January 17, 2012 6:16 PM
To: James Zhou
Cc: IBIS-ATM; Arpad_Muranyi@xxxxxxxxxx
Subject: Re: [ibis-macro] Re: Replacing BIRD 122 with "Reserved_Model"
keyword in [External Model]

James

if the driver output impedance is constant it is therefore "static", which
is a synonym.  It is a non-real  fictional entity.  It is a zero order
model for output impedance.  By definition a driver is not LTI.  It is not
part of the interconnect. A driver is used to drive an interconnect, not
be part of the interconnect.  If you want to perform LTI linearization, I
contend that it be done after the driver is used to "ping" the
interconnect.  Otherwise, how will the real condition of differing rising
and falling output impedance of drivers be handled, along with other
non-ideal driver characteristics? IBIS driver models do a better job of
this than a simple output impedance.The model that Walter proposes is an
over-simplification.

Scott



On Tue, Jan 17, 2012 at 9:01 PM, James Zhou
<james.zhou@xxxxxxxxxx<mailto:james.zhou@xxxxxxxxxx>> wrote:
Hi Scott,

Not quite sure what is "static driver output impedance". Walter's original
statement "the impedance is constant over the operating range of the
device" is just another way to say that the Tx driver is LTI.

Thanks,
James Zhou


From: Scott McMorrow
[mailto:scott@xxxxxxxxxxxxx<mailto:scott@xxxxxxxxxxxxx>]
Sent: Tuesday, January 17, 2012 4:51 PM
To: James Zhou
Cc: IBIS-ATM; Arpad_Muranyi@xxxxxxxxxx<mailto:Arpad_Muranyi@xxxxxxxxxx>
Subject: Re: [ibis-macro] Re: Replacing BIRD 122 with "Reserved_Model"
keyword in [External Model]


Consistent,  but not complete.  Small signal linearization does not
require a static driver output impedance.
On Jan 17, 2012 7:43 PM, "James Zhou"
<james.zhou@xxxxxxxxxx<mailto:james.zhou@xxxxxxxxxx>> wrote:
Arpad,

This interpretation of "small signal" is consistent with and equivalent to
the assumption of LTI.

Thanks for the clarification,
James


From:
ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@freelists
.org>] On Behalf Of Muranyi, Arpad
Sent: Tuesday, January 17, 2012 4:27 PM
To: IBIS-ATM
Subject: [ibis-macro] Re: Replacing BIRD 122 with "Reserved_Model" keyword
in [External Model]

James,

I think by "small signal" Walter means what is described in this article:

http://en.wikipedia.org/wiki/Small-signal_model

Thanks,

Arpad
===========================================================

From:
ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@freelists
.org>] On Behalf Of James Zhou
Sent: Tuesday, January 17, 2012 5:25 PM
To: wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>; IBIS-ATM
Subject: [ibis-macro] Re: Replacing BIRD 122 with "Reserved_Model" keyword
in [External Model]

Hi Walter,

Please see my comments and questions below:

(1) "This implies that AMI modeling assumes a small signal interface to
the analog channel."
Can you please clarify the meaning of "a small signal interface"? The only
necessary assumption when representing a channel using impulse response is
that the channel must be LTI.

(2) "This also implies that the differential impedance of a Tx or Rx is
constant over the operating range of the device."
There are several possible cases of "impedance of a Tx or Rx". It could be
the input or, the output or, the load impedance of Tx analog block.
Please clarify which one is referred to by this statement.   Same
questions exist for Rx.

Thanks,
James Zhou
QLogic Corp.





From:
ibis-macro-bounce@xxxxxxxxxxxxx<mailto:ibis-macro-bounce@xxxxxxxxxxxxx>
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]<mailto:[mailto:ibis-macro-bounce@
freelists.org]> On Behalf Of Walter Katz
Sent: Tuesday, January 17, 2012 1:16 PM
To: IBIS-ATM
Subject: [ibis-macro] Replacing BIRD 122 with "Reserved_Model" keyword in
[External Model]

All,

I would like to extend BIRD 116 to allow the following for AMI [Model]s

[External Model]
Language ISS
Reserved_Model
AMI_Tstonefile_Tx|AMI_Tstonefile_Rx|AMI_Thevenin_Tx|AMI_Thevenin_Rx
[End External Model]

AMI modeling assumes that a channel can be represented by an Impulse
Response. This implies that AMI modeling assumes a small signal interface
to the analog channel. This also implies that the differential impedance
of a Tx or Rx is constant over the operating range of the device. Note
that any legacy IBIS model (IV, Vt curves, Series Pin), that when used in
the real operating range of a SerDes channel (where AMI modeling is
applicable) can be accurately represented by the following Thevenin Tx and
Rx models.



Reserved_Model AMI_Tstonefile_Tx

[External Model]

Language ISS
Reserved_Model AMI_Tstonefile_Tx
[End External Model]



Is equivalent to:



[External Model]

Language ISS

Corner Typ AMI_Tstonefile_Tx.cir AMI_Tstonefile_Tx

Parameters Tstonefile = AMIfile(Tstonefile) | Tstonefile must be an AMI
Model_Specific parameter

Converter_Parameters Vhi = AMIfile(Voh) | Voh must be an AMI
Model_Specific parameter

Converter_Parameters Vlo = AMIfile(Vol) | Vol is 0 if it is not an AMI
Model_Specific parameter

Converter_Parameters Trf = 1.0ps

Ports my_driveP my_driveN A_signal_pos A_signal_neg

D_to_A D_drive my_driveP 0 Vlo Vhi Trf Trf Typ Non-Inverting

D_to_A D_drive my_driveN 0 Vlo Vhi Trf Trf Typ Inverting [End External
Model]


AMI_Tstonefile_Tx.cir.



.SUBCKT AMI_Tstonefile_Tx my_driveP my_driveN A_signal_pos A_signal_neg

+ Tstonefile="NA.s4p"

Sdriver my_driveP my_driveN A_signal_pos A_signal_neg 0 MNAME=Smodel_name

.MODEL Smodel_name S N=4 TSTONEFILE=Tstonefile .ends



Reserved_Model AMI_Tstonefile_Rx





[External Model]

Language ISS
Reserved_Model AMI_Tstonefile_Rx
[End External Model]



Is equivalent to:



[External Model]

Language ISS

Corner Typ AMI_Tstonefile_Rx.cir AMI_Tstonefile_Rx

Parameters Tstonefile = AMIfile(Tstonefile)

Ports A_signal_pos A_signal_neg A_int_pos A_int_neg

A_to_D D_receive A_int_pos A_int_neg -.02 .02 Typ [End External Model]


AMI_Tstonefile_Rx.cir.



.SUBCKT AMI_Tstonefile_Rx A_signal_pos A_signal_neg A_int_pos A_int_neg

+ Tstonefile="NA.s4p"

Sdriver A_signal_pos A_signal_neg A_int_pos A_int_neg 0 MNAME=Smodel_name

.MODEL Smodel_name S N=4 TSTONEFILE=Tstonefile .ends



Reserved_Model AMI_Thevenin_Tx



[External Model]

Language ISS
Reserved_Model AMI_Thevenin_Tx
[End External Model]



Is equivalent to:



[External Model]

Language ISS

Corner Typ AMI_Thevenin_Tx.cir AMI Thevenin_Tx

Parameters Rt = AMIfile(Rt)

Parameters Rs = AMIfile(Rs)

Parameters Cc = AMIfile(Cc)

Parameters Vt = AMIfile(Vt)

Parameters Cac = AMIfile(Cac)

Parameters Rac = AMIfile(Rac)

Parameters Rd = AMIfile(Rd)

Parameters Cd = AMIfile(Cd)

Parameters Trf = AMIfile(Trf)
| Only  AMI Model_Specific parameters Rt Rs Cc Vt Cac Rac Rd Cd defined 
| in the .ami file shall be passed as parameters to the subckt AMI 
| Thevenin_Tx instance

Converter_Parameters Vhi = AMIfile(Voh) | Voh must be an AMI
Model_Specific parameter

Converter_Parameters Vlo = AMIfile(Vol) | Vol is 0 if it is not an AMI
Model_Specific parameter

Converter_Parameters Trf = AMIfile(Trf) | Trf is 1p if it is not an AMI
Model_Specific parameter

Ports my_driveP my_driveN A_signal_pos A_signal_neg

D_to_A D_drive my_driveP 0 Vlo Vhi Trf Trf Typ Non-Inverting

D_to_A D_drive my_driveN 0 Vlo Vhi Trf Trf Typ Inverting [End External
Model]


AMI_Thevenin_Tx.cir



.SUBCKT AMI_Thevenin_Tx my_driveP my_driveN A_signal_pos A_signal_neg
+ Rt=1Meg Rs=1Meg Cc=0. Vt=0. Cac=0. Rac=1Meg Rd=1Meg Cd=0.
E_H E_my_driveP 0 VCVS my_driveP 0 1.
E_L E_my_driveN 0 VCVS my_driveN 0 1.
R_Rs_H E_my_driveP A_signal_pos R='Rs'
R_Rs_L E_my_driveN A_signal_neg R='Rs'
R_Rd A_signal_pos A_signal_neg R='Rd'
C_Rd A_signal_pos A_signal_neg C='Cd'
R_Rt_H A_signal_pos Vt R='Rt'
R_Rt_H A_signal_neg Vt R='Rt'
V_Vt Vt 0 DC='Vt'
C_Cc_H A_signal_pos 0 C='Cc'
C_CC_L A_signal_neg 0 C='Cc'
R_ac A_signal_pos Nac R='Rac'
C_ac A_signal_neg Nac C='Cac'
.ends




Reserved_Model AMI_Thevenin_Rx





[External Model]

Language ISS
Reserved_Model AMI_Thevenin_Rx
[End External Model]



Is equivalent to:





[External Model]

Language ISS

Corner Typ AMI_Thevenin_Rx.cir AMI_Thevenin_Rx

Parameters Rt = AMIfile(Rt)

Parameters Cc = AMIfile(Cc)

Parameters Vt = AMIfile(Vt)

Parameters Cac = AMIfile(Cac)

Parameters Rac = AMIfile(Rac)

Parameters Rd = AMIfile(Rd)

Parameters Cd = AMIfile(Cd)
|Only  AMI Model_Specific parameters Rt Cc Vt Cac Rac Rd Cd defined in 
|the .ami file shall be passed as parameters to the subckt AMI 
|Thevenin_Tx instance

Ports A_signal_pos A_signal_neg A_int_pos A_int_neg

A_to_D D_receive A_int_pos A_int_neg -.02 .02 Typ [End External Model]

[External Model]



AMI_Thevenin_Rx.cir.


.subckt AMI_Thevenin_Rx A_signal_pos A_signal_neg A_int_pos A_int_neg
+ Rt=1Meg Cc=0. Vt=0. Cac=0. Rac=1Meg Rd=1Meg Cd=0.
E_H A_int_pos 0 VCVS A_signal_pos 0 1.
E_L A_int_neg 0 VCVS A_signal_neg 0 1.
R_Rd A_signal_pos A_signal_neg R='Rd'
C_Rd A_signal_pos A_signal_neg C='Cd'
R_Rt_H A_signal_pos Vt R='Rt'
R_Rt_H A_signal_neg Vt R='Rt'
V_Vt Vt 0 DC='Vt'
C_Cc_H A_signal_pos 0 C='Cc'
C_CC_L A_signal_neg 0 C='Cc'
R_ac A_signal_pos Nac R='Rac'
C_ac A_signal_neg Nac C='Cac'
.ends

Walter Katz
wkatz@xxxxxxxxxx<mailto:wkatz@xxxxxxxxxx>
Phone 303.449-2308
Mobile 720.333-1107


________________________________
This message and any attached documents contain information from QLogic
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________________________________
This message and any attached documents contain information from QLogic
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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.

________________________________
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.



--


Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax


http://www.teraspeed.com<http://www.teraspeed.com/>

TeraspeedR is the registered service mark of Teraspeed Consulting Group
LLC


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