200G/400G Transceivers - High Speed test challenges - Kees Propstra - Multilane
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200G/400G Transceivers - High Speed test challenges Kees Propstra
Outline ▪ Transceiver evolution ▪ Transceiver overview ▪ Introduction test solutions ▪ 100G to 200G/400G transition ▪ Measurement challenges ▪ Solutions
Transceiver evolution
400G OSFP
QSFP-DD
100G QSFP28
40G
QSFP+
10G
SFP+
1G SFP graph for illustrative purposes only
2000 2005 2010 2015 2020
What is next?
Credit: Intel
Mid-Board Optics Co-packaged ASIC & Photonics
QSFP28 Module Module
Optical Embedded optical module
ASIC Re-timer Module ASIC ASIC w/ photonics Fiber
Fiber
PCBA PCBA PCBA
Courtesy: Luxtera
Transceiver overview Block diagram for 100G-SR4 PMD Block diagram for 100G-CWDM4 PMD Credit: IEEE 802.3bm-2015 Credit: CWDM4_MSA_Technical_Spec
Introduction test solutions
▪ BERT - Bit Error Rate Tester
▪ DSO – Digital Sampling Oscilloscope
▪ TDR – Time Domain Reflectometry
Tx
DUT
Rx
TDR BERT DSO
Signal migration from 100G to 200/400G
25G NRZ vs. 50/100G PAM4
NRZ
▪ Mask margin is key figure of
merit
PAM4
▪ 4 levels, 3 eyes, 12 transitions
▪ Simple mask margin probably
not a good predictor of link 53GBaud PAM4
performance
▪ Effect of fiber link
▪ Receiver equalization
25G NRZ
Why PAM4?
Transmission channels are
lossy
▪ 10 dB at 13 GHz typical
Modulator bandwidths are
limited
▪ 40 GHz available today
PAM4 Modulation
▪ Same data throughput at
half the frequency
▪ Double data rate at the
same frequency
▪ 2 bits/symbol, data rate = 2
x symbol rate
one symbol
Measurement Challenges - Optical
TDECQ - is the new TX metric
Transmitter Dispersion Eye Closure (Quaternary)
▪ TDECQ is the “new” mask margin test
of PAM4, it is a predictor of a system
performance of a PAM4 transmitter
▪ TDECQ Calculates the dB ratio of how
much noise can be added to the
transmitter signal while meeting the
target symbol error ratio
Worst case fiber environment Reference receiver
▪ TDECQ measurements should mimic
what’s expected for a real receiver
▪ There is good correlation between R is noise margin at a fixed symbol error rate
TDECQ and link performance
▪ Higher R is better
▪ Lower TDECQ is betterTDECQ Measurement Accuracy 0
-5
Transfer [dB]
-10
-15 scope BW
Ideal BT4
-20
It is critical that measurement accuracy is ensured -25
and that multiple test vendors provide identical -30
results 0 1E+10 2E+10 3E+10 4E+10 5E+10
Frequency [GHz]
▪ Measurement equipment correction SIRC
▪ System Impulse Response Correction – compensate the
measurement channel to meet the IEEE defined filter
characteristic
▪ Scope Noise Compensation – TDECQ measurement has a R is noise margin
measurement system noise compensation factor s = O to E and oscilloscope noise
▪ Correlation
▪ Multi-vendor test correlation
▪ IEEE provided standard waveform
(mazzini_3cd_01a_0518)
▪ Correlation typical 0.2 dB
TEK 1.95 dB ML 1.91 dBMeasurement Challenges - Electrical
Typical Test Configuration
Connector DUT
▪ No
measurements Instrument
possible on the
signal after the
channel 0
without de- -2
embedding! -4
dB(S(1,3))
-6
▪ Effect of the -8
channel must -10
be de- -12
embedded. -14
0 5 10 15 20 25 30 35 40
This can either Freq, GHz
be done using a Pristine signal Channel Distorted signal
VNA or a DSOCompensating for Channel Losses
Method 1: DSO De-embedding
▪ Using s-parameters generated in a VNA or a simulation tool
▪ Using s-parameters measured by the DSO
Method 2: FFE taps generated by DSO and used to configure the PPG signal shaper so it
compensates for channel losses (Tx equalization)
Method 3: Error-Detector of the BERT uses an equalizer (FFE, DFE, CTLE) to de-embed
channel losses (Rx equalization)
DUT DSO
Connector
PPG
EDExample of De-embedding using a Scope
Connector
DUT
DSO
DSO measures
and de-embeds
DUT signal
the channel in
after
frequency
Compensating
domain
for the trace
lossesFFE Equalization at 53 GBd using a DSO/PPG
DUT DSO
Connector
PPG
ED
Distorted signal from channel DSO calculates FFE taps FFE taps from DSO loaded
In PPGSolutions
Time
Domain
Analysis
dBm
Frequency
Domain
AnalysisSolutions
ML4035 ML4015D
Cable test, impedance Optical DSO
4 CH 35 GHz 25/40 GHz
SM/MM
ML4039E ML1016D-CR
BERT 4CH Optical Clock
56 GBd, 112 Gbps Recovery
26/53 GBd PAM4
ML4039D/79D ML4015D
BERT 4/8CH Electrical DSO
28 GBd, 56 Gbps 32/50 GHzTHANK YOU
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