Modern data center switches and telecom systems rely on IEEE 1588 PTP to achieve nanosecond-level time synchronization. The PPS signal from the switch host is fed into the optical module to align the module's time domain with the system-level PTP clock. This ensures all modules remain time-aligned, which is critical for coherent beamforming, phase matching, and data integrity across parallel optical channels. The adoption of ePPS functionality marks a significant evolution of OSFP-XD^[3] — transitioning from a simple data transceiver to a timing-aware intelligent optical module capable of participating in precisely synchronized network architectures.

Per protocol specification, the ePPS signal is multiplexed onto the OSFP LPWn/PRSn pins. As shown in Figure 2, the TMUX131 (2-channel, 1:3) is used to multiplex and select between the LPW and ePPS signals sent from the host to the module, routing them respectively to the MCU and ODSP bidirectionally. With an on-state capacitance of only 1.3pF and a propagation delay of 50ps, TMUX131 ensures highly accurate ePPS signal transmission, including higher slew rate and lower delay.

Design Note

1. ePPS signal transmission demands extremely high timing accuracy and tight rise/fall time requirements. When introducing a multiplexer into the signal path, careful attention must be paid to the parasitic capacitance of the device to ensure sufficient fast edge transitions and maintain system-level ePPS alignment precision.

2. Off Isolation would be another design consideration, in case the high slew rate brings unwanted signals to un-selected channel.

3. TMUX1511^[4] (4-channel, 1:1) and TMUX136^[5] (2-channel, 1:2) offer comparable performance parameters with small form factors, providing additional flexibility for different system design requirements.