[ibis-macro] Re: Jitter BIRD issues, and Buffer Tstonefile Issues

  • From: "Walter Katz" <wkatz@xxxxxxxxxx>
  • To: <radek_biernacki@xxxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
  • Date: Tue, 06 Dec 2011 14:41:47 -0500 (EST)

Radek,

 

I totally agree.

 

Walter

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of
radek_biernacki@xxxxxxxxxxx
Sent: Tuesday, December 06, 2011 2:36 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Jitter BIRD issues, and Buffer Tstonefile Issues

 

Hi Walter,

 

I believe I mentioned that several times at the time of the extended
discussions on this topic: there is absolutely no need for any unity-gain
amplifier for both the TX and the RX. In general, defining the source
impedance (for TX), and load impedance (for RX) could be left to the user
- the S-parameters do not carry that information. Alternatively, they can
be set in the specification. One possible (and in fact preferable) setting
is the zero source impedance for TX (ideal voltage source) and an infinite
load (open circuit) for the RX. The latter can be spelled out explicitly
in the spec, and any addition of unity-gain amplifies results in exactly
the same excitation and load conditions - thus they are completely
redundant.

 

I believe, the issue of ignoring of S12 or insisting on any specific value
was also discussed long time ago, and it was dismissed.

 

Radek

 

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Friday, December 02, 2011 9:33 AM
To: RAO,FANGYI (A-USA,ex1); ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: Jitter BIRD issues, and Buffer Tstonefile Issues

 

Fangyi,

 

The Rx Touchstone file includes the Rx termination! S21 is the signal
propagated to the AMI algorithmic model, S11 is the signal reflected back
to the channel. S12 is ignored by the EDA tool. One way to accommodate
this in some SPICE simulators is to put a Unit Gain Amplifier (E element)
between the output of the s parameter element and the SPICE "probe" at the
output of the  Touchstone file. (I am assuming that port 1 is at the pad
of the die, and port 2 is at the input to the algorithmic block of the Rx.

 

Does this explanation clearly define the derivation method that the model
developer uses to create the Tstonefile, and the method the EDA tool uses
to generate the Impulse Response of the channel when a Tstonefile is used
by either the Tx and/or Rx?

 

Walter

 

From: fangyi_rao@xxxxxxxxxxx [mailto:fangyi_rao@xxxxxxxxxxx] 
Sent: Friday, December 02, 2011 11:50 AM
To: wkatz@xxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: RE: [ibis-macro] Jitter BIRD issues, and Buffer Tstonefile Issues

 

Walter;

 

Termination is part of the Rx circuit. Only IC vendor knows it. EDA tool
doesn't. If the tool arbitrarily terminates S-parameter block, the circuit
is altered and you get different reflection back to Rx and channel. The
ISS BIRD (116) allows the flexibility for model developers to define any
termination they want because S-parameter block is just one of the circuit
components in the analog model.

 

Fangyi

 

From: Walter Katz [mailto:wkatz@xxxxxxxxxx] 
Sent: Thursday, December 01, 2011 7:05 PM
To: RAO,FANGYI (A-USA,ex1); ibis-macro@xxxxxxxxxxxxx
Subject: RE: [ibis-macro] Jitter BIRD issues, and Buffer Tstonefile Issues

 

Fangyi,

 

Why not let the EDA tool decide how to terminate it, based on the
simulator being used?

 

Walter

 

From: fangyi_rao@xxxxxxxxxxx [mailto:fangyi_rao@xxxxxxxxxxx] 
Sent: Thursday, December 01, 2011 9:04 PM
To: wkatz@xxxxxxxxxx; ibis-macro@xxxxxxxxxxxxx
Subject: RE: [ibis-macro] Jitter BIRD issues, and Buffer Tstonefile Issues

 

Hi, Walter;

 

Regarding touchstone file, the Rx E element is equivalent to terminating
the Rx S-parameter block with open. Since some internal tools used by IC
vendors don't assume the same termination condition, it's better to allow
model developers to specify termination to avoid confusion when
correlating with internal tools.

 

Regards,

Fangyi

 

From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Tuesday, November 29, 2011 2:31 PM
To: IBIS-ATM
Subject: [ibis-macro] Jitter BIRD issues, and Buffer Tstonefile Issues

 

All,

 

The remaining major issue is the handling of Rx_Rj, Rx_DCD, and Rx_Sj.

1.       It has been requested that Rx_Dj be added.

2.       First a discussion on how the Rx clock is handled in the
following two cases

a.       Time Domain

                                                               i.      Rx
AMI_GetWave returns clock ticks in *clock_times.

b.      Statistical

                                                               i.      Rx
AMI_GetWave does not return clock ticks in *clock_times.

                                                             ii.
Using Rx AMI_Init

3.       The current BIRD 123 states that Rx_Rj, Rx_DCD, and Rx_Sj shall
be applied to both Time Domain and Statistical methods.

a.       In Time Domain, Rx_Rj, Rx_DCD, and Rx_Sj can be applied to times
in clock_times, statistically to the clock_times PDF, or statistically to
the persistent eye.

b.      In Statistical, Rx_Rj, Rx_DCD, and Rx_Sj are combined
statistically along with Rx_Clock_PDF, Rx_Clock_Recovery_Rj,
Rx_Clock_Recovery_DCD, and Rx_Clock_Recovery_Sj.

4.       It has been suggested that Rx_Rj, Rx_DCD, and Rx_Sj shall apply
to just Time Domain.

a.       In Time Domain, Rx_Rj, Rx_DCD, and Rx_Sj can be applied to times
in clock_times, statistically to the clock_times PDF, or statistically to
the persistent eye.

b.      In Statistical, only Rx_Clock_PDF, Rx_Clock_Recovery_Rj,
Rx_Clock_Recovery_DCD, and Rx_Clock_Recovery_Sj are applied.

 

Regarding Tstonefile.

1.       Fangyi and I agreed the there is no requirement that S12=S21, and
that S21 can be small or zero.

2.       Fangyi and I agreed that the input to the Tx, and the output of
the Rx S element be isolated with a unit gain amplifier (E element) as in
the following example of a Tx Tstonefile wrapped in an ISS subckt:

a.  .subckt Intrinsic_Tstonefile_Tx DieP PadP DieN PadN file='NA'

b.  * Port order of Touchstone file is DieP PadP DieN PadN

c.  E_H EDieP 0 VCVS DieP 0 1.

d.  E_L EdieM 0 VCVS DieN 0 1.

e.  S1 EDieP PadP EDieN PadN 0 mname=A 

f.  .model A TSTONEFILE=file 

g.  .ends Intrinsic_Tstonefile_Tx

3.       There are now three proposals to implement Tstonefile in .ibs
and/or .ami files.

a.       BIRD 120 proposes the following example, where  (Voh-Vol) = Peak
to Peak voltage swing:

 
i.      (Tstonefile (List "xwc.s4p" "wc.s4p" "nc.s4p" "bc.s4p" "xwc.s4p") 

 
ii.      (Usage Info) (Type String) 

 
iii.      (Description "Extreme Worst, Worst, Nominal, Best, Extreme
Best"))

 
iv.      (Vol  (Value 0.) (Usage Info)(Type Float))

 
v.      (Voh (Range 1 .3 1.2) (Usage Info)(Type Float))

b.      There are a number of BIRDs submitted by Arpad and Ambrish. I have
requested that the above example be implemented using the syntax proposed
in these alternative BIRDs.

 

Walter

 

 

Walter Katz

wkatz@xxxxxxxxxx

Phone 303.449-2308

Mobile 720.333-1107

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