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C2M TP1a/TP4 Methodology
Junqing (Phil) Sun, Yasuo Hidaka
Credo Semiconductor
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Introduction
โข C2M module/host inputs have been qualified at TP1a/TP4 with a referencereceiver and test fixtures. With data rate increased to 100Gbps per lane, C2Mchannels are more challenging and reference receivers are more complicated[sun_3ck_01_0519]. This contribution is to discuss challenges to definereference receivers, reference channels, and test fixtures.
1. 100G C2M reference receiver is likely to have adaptive filters. Tuning methodologyneeds to be defined. There are two approaches that may be reused in existing IEEE802.3 standard - Annex 93A for COM and TDECQ approach.
2. Module output is qualified at TP4 near- and far-end. Module TX FIR is set with a TP4far-end reference channel. 100G C2M channel insertion loss is 16dB, and reflectionhas big impact on performance. How to define far-end reference channels formodule TX FIR adjustment and module output signal qualification?
IEEE P802.3ck Task Force 2
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IEEE P802.3ck Task Force 3
Reference Receiver Tuning Methodology
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Ref RX Methodology I โ Leverage Annex 93A and 120E
โข Pulse fitting to extract pulse response. โข Leverage Annex 93A for optimal phase and DFE tap weight. โข Apply phase and DFE weight on measured waveforms. Noise and distortion are
all kept. Reuse Annex 120E for test point measurement. โข Pros: simple algorithm. Reliable and fast. Similarity with COM tool.โข Existing Annex 93A is well documented for receivers that have only DFE taps.
IEEE P802.3ck Task Force 4
-0.6-0.4-0.2
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CH15 CH19 CH15 CH19 CH15 CH19 CH15 CH19
15mm 30mm 15mm 30mm
RLM1.0 RLM0.95
DFE tap weights
COM SIMS
Good correlation is observed for DFE coefficients by waveform simulation and COM tool. This helps to use COM tool for system study.
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Ref RX Methodology II โ TDECQ Approach + Annex 120E
โข TDECQ approach. Reuse Annex 120E for test point measurements.โข The standard does not specify how to optimize FFE. VEC/VEO/EW is calculated
for each step/combination of FFE coefficients. Best setting is picked based oneye statistics.
โข Pros: it has been implemented for TDECQ in existing scopes.โข Cons: optimized based on eye statistics. Reliability and tuning speed may be a
challenge.โข Theoretically this approach can be applied on both FFE- and DFE-based
receivers. But involving DFE taps will require additional phase optimization.Existing TDECQ method is for a receiver with only FFE taps.
IEEE P802.3ck Task Force 5
โข Sufficient samples are needed to construct reliable VEC/EH/EW etc.
โข As it is statistics based, multiple settings may result in similar measured results.
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TP4 Reference Channel Model and MCB
IEEE P802.3ck Task Force 6
- A first cut to try ideal reference channel and test fixture models with focus on module TX FIR setting.
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TP4 - MCB model
โข Same Insertion Loss as ๐ผ๐ฟ๐ถ๐ด๐๐น ๐ in diminico_3ck_01_0519.pdf slide 4โข ๐ผ๐ฟ๐ถ๐ด๐๐น ๐ = 1.073 ร โ0.00125 + 0.12 ๐ + 0.0575๐
โข 2.30 dB at 26.56GHz
โข S-parameter:โข Phase is to match 2.30dB PCB modelโข 45.6mm PCB model has 2.30dB at 26.56GHz using Table 92-12 parameters
shown in config_example_ieee8023_93a=3ck_KR_mellitz_06_12_2019โข ๐พ0 = 0, ๐1 = 5.990 ร 10โ4, ๐2 = 1.022 ร 10โ4, ๐ = 6.200 ร 10โ3
โข Use the exact ๐ผ๐ฟ๐ถ๐ด๐๐น ๐ equation with same delay as PCB model
IEEE P802.3ck Task Force 7
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Module Output Far-End Reference Channel model
โข Host IL (11.5dB) โ MCB IL (2.3dB) = PCB model IL budget (9.2dB)โข 182.6mm PCB model has 9.20dB at 26.56GHz using Table 92-12 parameters
shown in config_example_ieee8023_93a=3ck_KR_mellitz_06_12_2019โข ๐พ0 = 0, ๐1 = 5.990 ร 10โ4, ๐2 = 1.022 ร 10โ4, ๐ = 6.200 ร 10โ3
IEEE P802.3ck Task Force 8
ConnectorS4P model
MCB๐ผ๐ฟ๐ถ๐ด๐๐น ๐
PCB model w/new parameters
Module PCBS4P model
2.30dB9.20dB
TP4 (Near-end Eye)Far-end Eye
11.50dB
TX
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Module Output Near-End
IEEE P802.3ck Task Force 9
โข Ch 21-24 are module trace of channel 17-20 in sun_3ck_01_0519cascaded with MCB.
โข Reference receivers are C2 (3-tap FFE) and D2 (1-tap DFE on post 2). โข Inductor termination model for module.
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Module Output Far-End with Reference Channel
IEEE P802.3ck Task Force 10
โข Ch 25-28 are module trace of channel 17-20 in sun_3ck_01_0519cascaded with MCB and 9.2 dB far-end reference channel.
โข Far-end signal has lower VEO but better VEC.
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Module TX FIR Settings
IEEE P802.3ck Task Force 11
โข TX FIR optimized at TP4 far-end with reference RX C2 are applied to all channels to check TX FIR sensitivity. โข One case is with TX for channel 25 (with MCB and 9.2 dB reference channel).โข The other case is with reference channel increased to 13.2 dB to cover host package loss.
โข 13.2dB reference channel helps performance of 7 and 8 by more than 1 dB.โข XTK of these C2M channels contributed to ck project is not accurate for module-to-host
simulation. It has limited impact to this study.
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Conclusion
โข Annex 93A or TDECQ methodology may be reused for reference receivertuning. Existing Annex 93A is well documented for โDFE-onlyโ receivers, whileTDECQ methodology is used for a โFFE-onlyโ receiver.
โข More than one reference channels may be needed to cover different hosttraces.
IEEE P802.3ck Task Force 12