The advantages of PAM 4 over NRZ are as follows :

• Higher Throughput: PAM4 has a throughput of 2 bits per Unit Interval (UI), whereas NRZ has a throughput of 1 bit per UI. This means that PAM4 can transmit more data in the same amount of time, making it more efficient for high-speed applications.
• Increased Signal Efficiency: PAM4 uses four signal levels to represent 2 bits of logic information, whereas NRZ uses two signal levels to represent 1 bit of logic information. This means that PAM4 can transmit more data using the same amount of bandwidth.
• Reduced Signal Loss: PAM4 has a lower baud rate than NRZ, which means that it experiences less signal loss due to channel attenuation. This makes it more suitable for long-distance transmission.
• Improved Spectral Efficiency: PAM4 has a higher spectral efficiency than NRZ, which means that it can transmit more data in the same amount of bandwidth.
• Widely Used: PAM4 is widely used in high-speed applications such as 400G Ethernet, 50G, single-wavelength 100G, and 400G (non-ZR) optical modules.
• Low Costs: PAM4 has lower costs compared to NRZ, which makes it a more attractive option for high-speed applications.
• High Transmission Efficiency: PAM4 has a high transmission efficiency, which means that it can transmit data quickly and efficiently.