[ibis-macro] Re: redriver in spice simulation

  • From: "Walter Katz" <wkatz@xxxxxxxxxx>
  • To: <Arpad_Muranyi@xxxxxxxxxx>, <ibis-macro@xxxxxxxxxxxxx>
  • Date: Wed, 13 Mar 2013 15:07:37 -0400 (EDT)

Arpad,



From my repeater BIRD:



STATEMENT OF THE ISSUE:



A Differential SerDes Repeater is a four pin model consisting of a 
differential SerDes Rx model and a SerDes differential Tx model. Both the Rx 
and Tx models must also contain AMI models. The Rx model may or may not have 
a clock and data recovery loop (CDR). The Rx model may or may not return 
clock ticks. The output of the Rx model is connected to the input of the Tx 
model.



This BIRD introduces a new IBIS keyword [Repeater Pin] which associates 
Repeater Pins.



The  repeater BIRD specifically ties together a SerDes Rx differential model 
containing an AMI model with a SerDes Tx differential model containing an 
AMI model. So unless someone submits a BIRD to generalize Repeaters to be 
between two pins with legacy IBIS models this whole e-mail thread is a total 
waste of time.



Walter







From: ibis-macro-bounce@xxxxxxxxxxxxx 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Muranyi, Arpad
Sent: Wednesday, March 13, 2013 2:49 PM
To: ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: redriver in spice simulation



Walter,



I would like to encourage everyone to use crisper language in this

conversation to avoid these kinds of confusion.



An “output” is not driven by anything, otherwise you have two outputs

connected which is a contention.  Logic simulators don’t even allow

you to make such connections, it is an error. It seems that you mean

an “an output buffer’s input is driven by something – it’s stimulus”.



Regarding “So there is never a need to do a SPICE simulation from the 
channel Tx to the

channel Rx through the retimer or redriver.”, I don’t want to put words into

the mouth of the person who asked the question, but I don’t think that

the motivation was channel characterization.  One could potentially

use these repeater analog models for normal legacy simulations as well,

and it seems that it would be convenient to define how the Rx output

goes into the Tx input of a repeater analog model.



I tend to agree with the rest of your comments about the need for

defining a few more things in Fangyi’s proposal as I described it

in my previous posting on this thread.



Thanks,



Arpad

========================================================================







From: ibis-macro-bounce@xxxxxxxxxxxxx 
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx] On Behalf Of Walter Katz
Sent: Wednesday, March 13, 2013 1:09 PM
To: Muranyi, Arpad; ibis-macro@xxxxxxxxxxxxx
Subject: [ibis-macro] Re: redriver in spice simulation



Arpad,



Of course an output is driven by something – it’s stimulus. In the case of a 
redriver, the stimulus is a continuous waveform. In the case of a retimer 
the stimulus is a “digital” waveform that transitions between -.5 and +.5. 
There are no constraints on the voltage range of the stimulus input to a 
redriver output.



Note that both a redriver and a retimer are “repeaters”.



As far as SPICE simulation with a redriver or retimer (the retimer flow is 
identical to a redriver flow, except that jitter can be inserted by the EDA 
tool in a retimer), the requirement is that the EDA tool generate an impulse 
response from the initial Tx to the Repeater Rx, and a separate impulse 
response from the repeater Tx to the next Rx. The is two separate SPICE 
simulations (if you choose to do SPICE simulations to generate the two 
impulse responses). So there is never a need to do a SPICE simulation from 
the channel Tx to the channel Rx through the retimer or redriver.



I stated before, and I repeat my concern that the EDA tool does need to know 
how to generate the impulse response from redriver Tx to the channel Rx, and 
the Redriver BIRD is not clear on how to do this. Since the redriver Tx is a 
true analog circuit it can be represented by an s4p (BIRD 158), and if the 
analog circuit is defined using BIRD 158 generating this impulse response is 
trivial and can be done using SPICE or S parameter arithmetic (assuming the 
RX is LTI). Because the redriver Tx is an analog object it cannot be 
represented by a legacy IBIS model or a BIRD 116 External Model (which has a 
D/A converter).



Walter

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