[ibis-macro] Re: Replacing BIRD 122 with "Reserved_Model" keyword in [External Model]
- From: "Muranyi, Arpad" <Arpad_Muranyi@xxxxxxxxxx>
- To: IBIS-ATM <ibis-macro@xxxxxxxxxxxxx>
- Date: Wed, 18 Jan 2012 02:46:25 +0000
Scott,
While your points are all valid, I think we need to be careful
in this discussion about our wording and be clear about whether
we are talking about the existing IBIS-AMI specification, real
life, or circuit theory, or what have you.
On pg. 139 of the IBIS 5.0 specification I see these words:
| This proposal breaks SERDES device modeling into two parts - electrical
| and algorithmic. The combination of the transmitter's analog back-end, the
| serial channel and the receiver's analog front-end are assumed to be linear
| and time invariant.
According to this, the IBIBS-AMI specification is clear that
the assumption is that the analog portions of Tx and Rx are
part of the channel, and are assumed to be LTI.
We might question the validity of this assumption, but it
seems that Walter's discussion today was working within
this frame. Our comments on Walter's proposal should stay
within these boundaries, or if that is not sufficient any
more, we need to revisit this assumption. But that should
be treated as a separate discussion, and not as comments on
Walter's proposal that was discussed today.
Thanks,
Arpad
=============================================================
From: Scott McMorrow [mailto:scott@xxxxxxxxxxxxx]
Sent: Tuesday, January 17, 2012 8:16 PM
To: James Zhou
Cc: IBIS-ATM; Muranyi, Arpad
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@xxxxxxxxxxxxx>]
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@xxxxxxxxxxxxx>]
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@xxxxxxxxxxxxx]>
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
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