Airport Core Switch PAM4

PAM4 signaling enables high-speed data transmission in airport core switches by encoding two bits per symbol, effectively doubling bandwidth compared to traditional NRZ signaling.

PAM4 Fundamentals

Pulse-Amplitude Modulation 4-Level (PAM4) is a multilevel signaling technique that uses four distinct voltage levels to represent two bits per symbol (00, 01, 10, 11), unlike traditional NRZ (PAM2) which uses two levels for one bit per symbol . This allows PAM4 to double the data rate for a given channel bandwidth, making it ideal for high-speed Ethernet links such as 400GbE, 800GbE, and 1.6T Ethernet, as well as PCIe 6.0 . However, PAM4 is more susceptible to noise, jitter, and intersymbol interference, requiring careful design and forward error correction (FEC) to maintain signal integrity .

Application in Core Switches

Airport core switches, which handle high-throughput traffic between network aggregation points, benefit from PAM4 because it supports higher lane speeds without increasing the physical channel bandwidth. Modern switches use PAM4 SerDes (Serializer/Deserializer) technology to achieve 112G or 224G per lane, enabling 400GbE or 800GbE switch fabrics . For example, Broadcom's BCM87400 PHY supports four lanes of 112-Gb/s PAM4 at 56 Gbaud, providing low-power, high-performance 400GbE connectivity .

Clocking and Signal Integrity

High-speed PAM4 links require ultra-low jitter clocks to maintain signal fidelity. For instance, TI's LMK5B33216 clock generator achieves 42fs RMS jitter, meeting the stringent requirements of 112G and 224G PAM4 SerDes used in data center switches . Proper clocking, pre-emphasis, and equalization are critical to compensate for channel loss and optical impairments, ensuring reliable operation across backplanes, cables, and optical modules .

Advantages and Considerations

• Higher data rates without doubling channel bandwidth
• Enables 400GbE/800GbE switch fabrics in compact form factors
• Requires advanced DSP and FEC to mitigate noise and signal degradation
• Sensitive to jitter and amplitude variations, demanding precise clocking and testing In summary, PAM4 is a key enabler for modern airport core switches, allowing high-speed, high-density Ethernet connectivity while balancing power, signal integrity, and cost. Its adoption in 400GbE and beyond ensures that core network infrastructure can handle the growing data demands of airports and large-scale enterprise networks.