Low-Jitter Systems Synchronization for Doppler Measurements

In some Doppler laboratory measurement, more instruments need to work together. In some cases, a signal generator produces the excitation bursts, while echoes from fluid are sampled by a separate card. In another significant case, the thousands of elements of a 2D array probe are partitioned among different echographs or sections of a complex system. Synchronization of instruments that do not share a common clock is an issue. A Pulse Repetition Interval (PRI) sync signal can be distributed to the equipment, but the jitter produced when the signal is sampled by the individual clock of each instrument results in unbearable noise in the Doppler analysis. In this work, a method that reduces this jitter to less than 100ps rms is presented. The proposed method was implemented in a FPGA of a custom Doppler board. Experiments performed by investigating a 0.5 m/s flow in an 8 mm pipe show that the proposed method can synchronize a Doppler system to an asynchronous trigger without degradation of the measured Doppler spectrum.