Sub-nanosecond Distributed Synchronisation via the Universal Serial Bus

We present a distributed synchronisation architecture based on the universal serial bus (USB) found on every PC and laptop. This work has extended the capabilities of USB by adding a synchronization layer, capable of synchronizing a distributed USB network. Synchronization is achieved without consuming USB bandwidth or modifying the USB protocol. The synchronous USB device contains a phase-locked local oscillator. Oscillator phase accuracy is <700 ps across the distributed system, regardless of connection topology and clock jitter is better than 150 ps RMS. The synchronous USB device also contains a notion of real time allowing coordinated real-time operation. This local area synthetic instrumentation (SI) architecture offers sub-nanosecond distributed clock accuracy.