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
http://www.teraspeed.com
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