AN 835: PAM4 Signaling Fundamentals

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ID 683852
Date 3/12/2019
Public
Document Table of Contents
Document Table of Contents x
1. Introduction 2. CEI-56G-MR Transmitter 3. CEI-56G-MR-PAM4 Interface Details 4. CEI-56G-MR-PAM4 Receiver 5. PAM4 Link Case Study 6. Medium Reach (MR) PAM4 System Design Study 7. Glossary and Acronyms 8. References 9. Document Revision History for AN 835: PAM4 Signaling Fundamentals
1. Introduction x
1.1. NRZ Fundamentals 1.2. Standards Using PAM4 Coding Scheme 1.3. CEI-56G Interconnect Reaches and Application Distances
1.3. CEI-56G Interconnect Reaches and Application Distances x
1.3.1. VSR (Very Short Reach) Chip-to-Module 1.3.2. MR (Mid-Range Reach) - Chip to Chip Within a PCBA 1.3.3. LR (Long Reach) - Chip to Chip Across a Backplane/Midplane or a Cable
2. CEI-56G-MR Transmitter x
2.1. Naming Conventions 2.2. Eye Height (EH6) and Eye Width (EW6) 2.3. Eye Linearity 2.4. Electrical Characteristics 2.5. PAM4 Jitter Methodology 2.6. TX Pre-Emphasis Method
2.4. Electrical Characteristics x
2.4.1. Transmitter Characteristics 2.4.2. Transmitter Return Loss 2.4.3. Transmitter Linearity (RLM) 2.4.4. Signal-to-Noise-and-Distortion Ratio (SNDR)
3. CEI-56G-MR-PAM4 Interface Details x
3.1. COM Introduction 3.2. Normative Channel Specification COM 3.3. Informative Channel Insertion Loss 3.4. Informative Channel Return Loss
3.1. COM Introduction x
3.1.1. Backplane Measurements
4. CEI-56G-MR-PAM4 Receiver x
4.1. Challenges in Analyzing PAM4 Signals 4.2. PAM4 Receiver Architecture 4.3. Equalization Technique 4.4. CEI-56G-MR-PAM4 Receiver Details
4.2. PAM4 Receiver Architecture x
4.2.1. Analog vs. Digital Receiver 4.2.2. Slicer 4.2.3. Clock and Data Recovery (CDR)
4.4. CEI-56G-MR-PAM4 Receiver Details x
4.4.1. Electrical Characteristics 4.4.2. Receiver Input Return Loss 4.4.3. Receiver Interference Tolerance 4.4.4. Receiver Jitter Tolerance
5. PAM4 Link Case Study x
5.1. OIF_Stressed 5.2. OIF_Compliant
5.1. OIF_Stressed x
5.1.1. Channel Characteristics 5.1.2. OIF_Stressed PAM4 Link Simulation with the Advanced Link Analyzer
5.2. OIF_Compliant x
5.2.1. Channel Characteristics 5.2.2. OIF_Compliant PAM4 Link Simulation with the Advanced Link Analyzer
6. Medium Reach (MR) PAM4 System Design Study x
6.1. System Power 6.2. System Cost 6.3. Board Space 6.4. Conclusion
1. Introduction
2. CEI-56G-MR Transmitter
3. CEI-56G-MR-PAM4 Interface Details
4. CEI-56G-MR-PAM4 Receiver
5. PAM4 Link Case Study
6. Medium Reach (MR) PAM4 System Design Study
7. Glossary and Acronyms
8. References
9. Document Revision History for AN 835: PAM4 Signaling Fundamentals

2.2. Eye Height (EH6) and Eye Width (EW6)

When using NRZ, the eye height and width are measured from the biggest opening of an eye. However, this is not the case for PAM4’s eye height and eye width.

For the PAM4 eye, one needs to locate the Tmid point first. See the following figure for more details. Tmid is the midpoint of the maximum horizontal eye opening for a 10-3 (this methodology is defined in section 16.3.10.2 of the OIF-CEI56G-VSR standard) inner eye contour (red) of the middle eye.

Figure 10. How EW6 and EH6 Are Measured

EH6 represents the eye height at a BER of 10-6 (green). After the Tmid point is found, draw a vertical line that intersects with the three eyes' 10-6 contour ring (green). EH6 is the vertical distance between two intersection points on the 10-6 contour ring in an eye. As shown in the previous figure, EH6 is not necessarily the maximum eye height.

EW6 represents the eye width at a BER of 10-6 (green). Taking the upper eye for example, you find the half point of the eye height, (EH6 upp)/2. Draw a horizontal line that intersects with the 10-6 contour ring (green). The EW6 of the upper eye is the horizontal distance between two intersection points on the 10-6 contour ring in the eye. The lower eye’s EW6 is measured in the same manner. From the figure, notice that the EW6 of each eye is not the widest opening. The asymmetry of the upper and lower eye causes the widest portion of the eye to be off-center. Compared with the widest portion, EW6 is considerably reduced.

This methodology can be used to determine the expected eye mask for a signal for a given BER as per the following figure.

Figure 11. PAM4 Horizontal Eye Mask Sample
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