CEI-56G - Testing Considerations
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This document discusses testing considerations for 56G PAM-4 signaling, which introduces new impairments compared to previous NRZ signaling. It outlines how the CEI-56G Implementation Agreements are defining new transmitter output and receiver input stress tests to ensure data link integrity. Examples of new tests mentioned include linearity tests on receiver inputs. It also provides an overview of upgraded measurement tools needed for characterizing and testing PAM-4, such as oscilloscopes, pattern generators, and error detectors.
CEI-56G - Testing Considerations
- 1. CEI-56G – Signal Integrity to the Forefront: Testing Considerations Steve Sekel OIF Physical & Link Layer Interoperability Working Group Chair, Keysight Technologies March 22, 2016
- 2. Page New testing needs for 56G links © Optical Internetworking Forum 2016 Evolutionary versus Revolutionary 2 3/22/2016 • 56G NRZ – evolutionary shift from 28G NRZ • Tighter jitter budgets, better loss management, totally closed eyes • Multi-Level signaling changes all the rules – in place for 50+ years! • Packing 4 levels into amplitude swing of 2 – lose 9.6 dB SNR • Better management of noise and return loss • Finite rise time creates inherent DDJ • How to implement clock recovery? • Closed eyes with lower SNR • FEC often required 0 – 3 crossing0 – 1 crossing
- 3. Page New impairments that challenge PAM-4 receivers © Optical Internetworking Forum 2016 3 3/22/2016 • Non-linearity - Amplitude compression in lower eyes • FEC is more susceptible to burst errors than evenly distributed errors • Traditional BERTs do not measure burst counts It’s not just timing jitter anymore!
- 4. Page Ensuring PAM-4 link integrity • As PAM-4 receivers are susceptible to more than just timing jitter.... • The CEI-56G-xx-PAM Implementation Agreements are responding to assure data link integrity • New measurements ARE being defined for Tx Outputs • New stress tests ARE being defined for Rx Input testing © Optical Internetworking Forum 2016 4 3/22/2016
- 5. Page Example: Linearity included in Input Stress Tests • Included in CEI-56G-xx-PAM4 Implementation Agreements • Compliance is static pass/fail test, combined with jitter or interference stress. • Test with stressed PAM-4 eye, with inner levels offset to spec limit • Linearity expressed as “Eye Linearity” (spec limit 0.67) • Set rail voltages with AWG, or individual output amplitudes with 2 channel BERT © Optical Internetworking Forum 2016 5 3/22/2016 0.67 AMax A Max
- 6. Page Upgrading measurement tools for PAM-4 • A “well equipped lab” for characterizing and testing compliance of NRZ will require some new tools for PAM-4 • Good news - All IAs using PAM-4 have similar test requirements • Same tool set works for all © Optical Internetworking Forum 2016 6 3/22/2016
- 7. Page Output (Tx) Measurement Tools • Many test instruments for Output (Tx) measurements can be upgraded from NRZ to PAM-4 • Sampling and Real Time Oscilloscopes can add new PAM-4 measurements with optional software packages • Direct measurements for eye parameters, skew, linearity, noise, etc. • PAM-4 capable clock recovery © Optical Internetworking Forum 2016 Oscilloscope remains the primary tool 7 3/22/2016
- 8. Page Tools for Input (Rx) measurement – a different story • Some NRZ BERTs can be upgraded to PAM-4 with added hardware • Analog combining or PAM – DACs • Use 2 NRZ channels to create single PAM-4 pattern generator channel • Expensive – pattern aligned channels needed to create 1 PAM-4 signal © Optical Internetworking Forum 2016 8 3/22/2016
- 9. Page Native PAM-4 capable BERTs © Optical Internetworking Forum 2016 Just starting to appear on the market 9 3/22/2016
- 10. Page BERT – do you need an error detector? • High speed Arbitrary Waveform Analyzers (AWG) can generate PAM-4 directly • Flexible to create any impairment type • When considering, check for: • Adequate memory depth for long patterns • Ability to make changes on the fly (needed for Jitter Tolerance testing) © Optical Internetworking Forum 2016 Many transceiver ICs have internal error counters 10 3/22/2016
- 11. Page Test solutions vendors • Test equipment and compliance test board vendors are active members contributing to CEI-56 Implementation Agreements • Use their application support teams to help you with your testing needs © Optical Internetworking Forum 2016 Here to help with your CEI-56G testing needs 11 3/22/2016