[ibis-macro] Re: another silly IBIS-AMI question about deriving the impulse response of a channel
- From: "Walter Katz" <wkatz@xxxxxxxxxx>
- To: <scott@xxxxxxxxxxxxx>, "IBIS-ATM" <ibis-macro@xxxxxxxxxxxxx>
- Date: Thu, 27 May 2010 18:14:07 -0400
Scott,
Your picture is incorrect:
1 --- Network --- 3
|
|
2
It is really
Tx_Pad --- Network --- Rx_Pad --- Input_to_Equalization ---
Output_of_Equalization
There is a high impedance connection between ports Rx_Pad and
Input_to_Equalization.
This should answer your question.
Walter
Walter Katz
303.449-2308
Mobile 720.333-1107
wkatz@xxxxxxxxxx
www.sisoft.com
-----Original Message-----
From: ibis-macro-bounce@xxxxxxxxxxxxx
[mailto:ibis-macro-bounce@xxxxxxxxxxxxx]On Behalf Of Scott McMorrow
Sent: Thursday, May 27, 2010 6:04 PM
To: IBIS-ATM
Subject: [ibis-macro] another silly IBIS-AMI question about deriving the
impulse response of a channel
Since the analog channel is required to be LTI from driver to receiver, I
believe that in order to create a correct impulse response it is necessary
to know what the termination impedance should be. In the case where a
driver or a receiver is terminated at the end of the line, the termination
impedance is obvious. So, for a 100 ohm differential system the
differential impedance used for impulse response extraction is 100 ohms.
Essentially the high-impedance receiver amplifier, or driver current sources
are considered to be lumped at the termination network.
How are people modeling, extracting, and simulating drivers and receivers
where the high-impedance ports are physically isolated from the termination,
where the waveform in the algorithmic domain (driver/receiver) is
substantially different than the waveform in the analog domain at the
termination? I'm confused, since IBIS-AMI does not include the on-die
termination network, except in the rudimentary and unsatisfying form of a
*.ibs model, and that model is a lumped approximation. In my mind, in order
to correctly extract an impulse response of a channel that will give a
correct representation of the waveform at the receiver, one has to either
perform a transient simulation of the full circuit from the driver to the
receiver, or perform frequency domain modeling to impulse response
transformations with known driver/receiver input impedance. Otherwise, the
resulting impulse response is wrong.
For a hypothetical 50 ohm single-ended transmitter or receiver, the simplest
circuit that can correctly model many transmitters and receivers is the
following network:
1 --- Network --- 3
|
|
2
where:
Port 1 = 50 ohm
Port 3 = 50 ohm
Port 2 = some high impedance.
and Port 1 to Port 2 is the path used for computation of the
impulse response
If the Network is lumped into:
1 --- Network --- 2
The resulting impulse response and waveform is different. How are people
solving this problem?
regards,
Scott
--
Scott McMorrow
Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
(401) 284-1827 Business
(401) 284-1840 Fax
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