What is PAM4?
PAM4 is short of pulse amplitude modulation 4. It is a modulation technology that uses four different signal levels for signal transmission. it with an additional two levels compared with the NRZ (non-return to zero) modulation. This means that, under the same baud rate, the bit rate of PAM4 signals is twice that of NRZ signals, achieving twice the transmission efficiency. Due to its high transmission efficiency and low construction costs, PAM4 has seen significant uptake in next-generation high-speed signal interconnection. It is now widely used in 50G tranceivers, single-lambda 100G optics, and 400G (non-ZR) optical modules to empower various network applications.
The use of four levels enables PAM4 to encode two bits in each optical pulse period instead of one, as NRZ does. PAM4 therefore carries twice the data with a signal of roughly the same bandwidth as NRZ. The tradeoff, however, is that amplitude noise has a greater impact, since with PAM4 it takes a smaller noise spike to cause the receiver to read the wrong value.
Advantages of PAM4:
- Used in 400 gigabit Ethernet
- Can pull twice the signal vs. NRZ
- Operates on four levels vs. two levels
- Throughput of 2 bit per Unit Interval (UI)
