WSEAS Transactions on Circuits and Systems
Print ISSN: 1109-2734, E-ISSN: 2224-266X
Volume 14, 2015
Frequency Correction Method of OCXO and its Application in the Data Acquisition of Electrical Prospecting
Authors: Shao-Heng Chun, Ru-Jun Chen, Bi-Wen Xiang
Abstract: The GPS (Global Position System) timing is vulnerable to the external environment which makes the synchronous timing become unlocked easily. Based on FPGA (Field Programmable Gate Array), this paper aims to design a high precision synchronous timing by GPS disciplined oven controlled crystal oscillator (OCXO). The application of building a delay line inside FPGA to measure the time interval with resolution as 71ps and 10ps, ensuring the high accuracy of timing. The average filter is employed to suppress the random noise brought by PPS (Pulses per Second) which is used as a standard signal to correct the frequency of the OCXO, which is demonstrated to be very effective. The synchronous timing is realized simultaneously with the discipline of OCXO, which guarantees the high initial precision between LPS (Local Pulses per Second) and PPS whenever the GPS becomes unlocked. After frequency correction is completed, the timing error reaches 410 ns, 1.6 us, 2.0 us and 33.0 us after the GPS receiver is unlocked by 150 min, 6 h, 12 h, and 24 h respectively, which is more accurate than a commercial product V5-2000. Long-term measurement of timing error demonstrates that the method proposed by us can combine the advantages of GPS timing and OCXO timing, thus to solve the problem existed in the GPS timing. It not only meets the precision requirements of synchronous timing in all the distributed acquisition systems for electrical prospecting, but also can be applied in other industrial fields need high precision timing. The design is realized in one FPGA chip, which greatly reduces the quantities of peripheral elements and simplifies the complexity of the peripheral circuit, thus reduces the cost and power.
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Pages: 68-81
WSEAS Transactions on Circuits and Systems, ISSN / E-ISSN: 1109-2734 / 2224-266X, Volume 14, 2015, Art. #8