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Keysight M809256PB OIF CEI-56G Rx Test Automation Application User Guide
3
Preparing to take Measurements
Overview on Channel Operating Margin (COM)
COM is a figure of merit (FOM) determined from a minimum reference PHY
architecture and channel’s S-parameters. It allows designers to explore
physical design budget (choices) between loss, reflection ISI, crosstalk,
and device specifications.
COM is the Signal to Noise Ratio (SNR) of available signal amplitude (As)
to statistical noise amplitude (An) in dB. It can be calculated using the
equation:
COM = 20 * log
10
(As/N)
where, N = Peak BER Noise and As = Peak signal
Both N and As are calculated based on the transmitter and channel
characteristics assuming a reference receiver with optimized equalization.
A channel set contains a victim channel response called THRU, some
number of far-end crosstalk aggressor responses (FEXT), which do not
have the same transmitter as the victim lane and some number of
near-end aggressor responses (NEXT), which do have the same
transmitter as the victim lane.
Figure 25
Channel Model for COM
For OIF CEI-56G Medium Reach and Long Reach Interfaces, COM shall be
greater than or equal to 3.0 dB for each test. This minimum value allocates
margin for practical limitations on the receiver implementation, the largest
step size allowed for transmitter equalizer coefficients.
