AN 835: PAM4 Signaling Fundamentals

ID 683852
Date 3/12/2019
Public
Document Table of Contents

2.1. Naming Conventions

PAM4 uses four voltage levels to represent four combinations of 2 bits logic: 11, 10, 01, and 00. Every two bits are mapped to one symbol. The mapping method can be linear coding or gray coding (see the following table for more details). All PAM4 standards support gray coding.

Table 4.  Linear and Gray Coding
Linear Coding Gray Coding
11 10
10 11
01 01
00 00

Instead of one eye in the NRZ coding scheme, there are three eyes in PAM4 because of the four voltage levels. The naming conventions represent these four voltage levels: -3, -1, 1, 3 or -1, -1/3, 1/3, 1 or 0, 1, 2, 3.

Figure 9. Three PAM4 Signal Levels Naming Conventions