Development Of Master Clock Module For LXI Based On GPS

Advances in network technology and bus technology have greatly promoted thedevelopment of automated test systems. Web-based LXI bus technology since releasedthe first version of the specification in2005has been a popular research theme of manycompanies and research institutions. Currently, there have been various LXI instrumentsof different functions, as technology evolves, the application range of LXI instrumentswill be wider and wider. Among the three function classes of LXI instruments, class Aand class B instruments need the support of IEEE1588precision clock synchronizationprotocol. In consideration of the cost, the master clock of LXI system is generallydriven by the ordinary crystal oscillator, because the accuracy of ordinary crystaloscillator output frequency is not high, susceptible to the influence of ambienttemperature and has bad long-term stability, thus leading to large deviations between themaster clock and the physical time. The existence of this deviation led to a large errorbetween the master clock and the slave clock, the development of master clock moduleof high precision and good stability is required in order to improve the synchronizationaccuracy of IEEE1588.This thesis studied and designed a GPS-based LXI master clock module, whichused the time information of high precision and high stability released by GPS to fix thereal-time clock module of LXI instruments, and improved the synchronization accuracyof precision clock synchronization protocol.In order to obtain the time information globally released by GPS, this thesisdesigned a low-cost GPS receiver. The GPS receiver is a typical embedded system, itshardware include microprocessor, correlator channel, RF front-end and memory; itssoftware include embedded operating system, device drivers and application program oftime solver. The core of GPS receiver is the pseudo-code tracking loop and carriertracking loop, this thesis designed a second-order phase-locked loop assisted by a first-order locked loop to achieve the capture and tracking of the carrier and pseudo-code.After tracking and locking the carrier and pseudo-code, the GPS receiver extracts thenavigation message to calculate the UTC time, and outputs the second pulse of a highdegree of synchronization with UTC. LXI instruments receive the time information andsecond pulse of GPS outputs, amend the real-time clock module of LXI instruments bysecond pulse as the trigger signal, and make the amended LXI instruments to be themaster clock of LXI system.Finally tested the high-frequency channel of the GPS receiver, and used the masterclock module designed by this thesis for synchronization experiments, experimental results showed that the use of this module can achieve higher synchronization accuracy.