hi, vinod,
ALWAYS, in multiload s param,you will see some peaking in some freq
points(rising with respect to frequency), due to the reflection and resonance
of each branch. You can extend the freq to 10G or 20G level. If there is no
mistake on your simulation setting, you should see the degradation due to loss.
you can go ahead your trancient simulation to see whether the waveform is make
sense.OR you can only add two port in your 2.5D simulator(one receiver one
load, other loads terminated by Cin or the real odt maybe in real system.) to
see what is the behavior.
BTW,what is the rising/faling edge of your signal. For example, if it is below
100ps level, 3GHz is too low for signal s parameter model. Recommended to
extent to 20G. Depended on your slew rate.
Regards.
BILLY CHEN
IDT INTEGRITY
------------------ Original ------------------
From: "vinod ah";<ah.vinod@xxxxxxxxx>;
Date: Nov 19, 2015
To: "SI-LIST"<si-list@xxxxxxxxxxxxx>;
Subject: [SI-LIST] [SI-List]: S parameters for Multi-point Topology
Hi All,
I am extracting S parameters of multi-point topology where a traces starts
from controller and branches out to 4 loads/devices in T-shape i.e. one
trace going to 4 loads.
Trace length from controller to each device is ~5 inches. The branching to
4 loads happens at ~ 4 inches from controller. Trace is microstrip on FR4.
I have assigned ports at the controller and the devices. Port 1 is at
controller, Port 2,3,4,5 is at device. S parameter is extracted from 1MHz
to 3GHz with spacing of 1MHz using 2.5D solver.
I am seeing the extracted S5P model is non-causal and also when i plot S31
or S51, i see the plot rising with respect to frequency instead of a
falling graph i.e. gain is seen, while loss is expected.
When i try to convert this S5P file to Broadband spice model, In rational
model fitting there is no convergence.
Are these problems related to multi-point topology? Is it a standard
practice to extract S parameter for this topology or just go with transient
simulation?
Regards
Vinod A H
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