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Channel Operating Margin (COM)

This example shows how to use PyAEDT for COM analysis. These standards are supported:

• 50GAUI_1_C2C

• 100GAUI_2_C2C

• 200GAUI_4

• 400GAUI_8

• 100GBASE_KR4

• 100GBASE_KP4

What is COM?

• COM was developed as part of IEEE 802.3bj, 100GBASE Ethernet.

• COM is a figure of merit for an S-parameter representing a high-speed SerDes channel.

• COM is the ratio between eye height and noise.

COM = 20 * log10 (A_signal / A_noise)

Keywords: COM, signal integrity, virtual compliance.

Perform imports

Perform required imports.

import os
import tempfile

from ansys.aedt.core.visualization.post.spisim import SpiSim
from ansys.aedt.core.visualization.post.spisim_com_configuration_files import \
    com_parameters
from pyedb.misc.downloads import download_file

Create temporary directory and download example files

Create a temporary directory where downloaded data or dumped data can be stored. If you’d like to retrieve the project data for subsequent use, the temporary folder name is given by temp_folder.name.

temp_folder = tempfile.TemporaryDirectory(suffix=".ansys")

thru = download_file(
    directory="com_analysis",
    filename="SerDes_Demo_02_Thru.s4p",
    destination=temp_folder.name,
)
fext_2_9 = download_file(
    directory="com_analysis",
    filename="FCI_CC_Long_Link_Pair_2_to_Pair_9_FEXT.s4p",
    destination=temp_folder.name,
)
fext_5_9 = download_file(
    directory="com_analysis",
    filename="FCI_CC_Long_Link_Pair_5_to_Pair_9_FEXT.s4p",
    destination=temp_folder.name,
)
next_11_9 = download_file(
    directory="com_analysis",
    filename="FCI_CC_Long_Link_Pair_11_to_Pair_9_NEXT.s4p",
    destination=temp_folder.name,
)

Run COM analysis

PyAEDT calls SPISim for COM analysis. For supported standardes, see the PyAEDT documentation.

Set port_order="EvenOdd" when the S-parameter has this port order:

1 - 2

3 - 4

Set port_order="Incremental" when the S-parameter has this port order:

1 - 3

2 - 4

spi_sim = SpiSim(thru)
com_results = spi_sim.compute_com(
    standard=1,  # 50GAUI-1-C2C
    port_order="EvenOdd",
    fext_s4p=[fext_5_9, fext_5_9],
    next_s4p=next_11_9,
)

Print COM values

There are two COM values reported by the definition of the standard:

• Case 0: COM value in dB when big package is used.

• Case 1: COM value in dB when small package is used.

print(*com_results)

-0.3574 -1.1228

View COM report

A complete COM report is generated in the temporary folder in HTML format.

print(temp_folder.name)

C:\Users\ansys\AppData\Local\Temp\tmp7sixmsew.ansys

Run COM analysis on custom configuration file

Export template configuration file in JSON format

custom_json = os.path.join(temp_folder.name, "custom.json")
spi_sim.export_com_configure_file(custom_json, standard=1)

Modify the custom JSON file as needed.

Import configuration file and run

com_results = spi_sim.compute_com(
    standard=0,  # Custom
    config_file=custom_json,
    port_order="EvenOdd",
    fext_s4p=[fext_5_9, fext_5_9],
    next_s4p=next_11_9,
)
print(*com_results)

-0.3574 -1.1228

Export SPISim supported configuration file

You can use the exported configuration file in the SPISim GUI.

com_param = com_parameters.COMParametersVer3p4()
com_param.load(custom_json)
custom_cfg = os.path.join(temp_folder.name, "custom.cfg")
com_param.export_spisim_cfg(custom_cfg)

True

PyAEDT also supports the SPISim configuration file.

com_results = spi_sim.compute_com(
    standard=0, config_file=custom_cfg, port_order="EvenOdd"
)  # Custom
print(*com_results)

-0.155 -0.9455

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Download this example

Download this example as a Jupyter Notebook or as a Python script.