Study On Precise Frequency Correction Technology Of Frequency Standard Source

Because of the temperature effect or components aging and so on,the frequency of the standard frequency source output signal will change with time.Although this change is very small,there will be great errors in high precision situations such as navigation and positioning system,clock synchronization timing and so on.For example,at the navigation and positioning system,the deviation of 10ns will result in a positioning error of approximately 3m,which is intolerable for the application of the target tracking and positioning of missiles.Therefore,in high-precision applications such as navigation and positioning,it is necessary to monitor the frequency of the frequency source output signal.And the frequency could be adjusted and corrected when it is detected that there is a deviation.In order to solve the problem that the frequency of frequency source output signal could change over time,a precise frequency correction technology based on the principle of direct digital measurement is proposed in this paper.And based on this technology,a prototype of frequency corrector that can monitor and adjust the output signal frequency of frequency source is developed.The frequency correction technique is based on the principle of the feedback loop:First,the frequency value of the output signal of the measured frequency source is measured applying the principle of direct digital measurement.The frequency difference between the two could be obtained,comparing the measured frequency with the nominal value of the frequency source or the expected frequency value.And then,the independent adjustment method combining the large-scale adjustment to the fine adjustment is achieved through the dual DAC composite output structure.Secondly,the frequency of the VCXO output signal is corrected using the independent adjustment way.And finally,the frequency value of the VCXO output signal could be locked fleetly near the nominal value or the target frequency value.Direct digital measurement principle is based on the clock cursor effect what the two signals have,and there is a slight frequency difference between the two signals with the same frequency.And it uses the principle of digital border effect and the innovation theory that the stability of the quantification system is significantly better than the quantification resolution itself.The quantification error in counting is suppressed through designing the high-precision virtual gate,and with reducing the measurement error during the frequency measurement.Comparing to the principle design of the single channel ADC,the two-channel ADC system scheme adopted in the frequency corrector solves the problem that the response time is limited by the frequency difference between the two signals,so that the frequency value of the VCXO output signal could be quickly locked.The experimental verification shows that the frequency stability of the frequency corrector designed and implemented in this paper could achieve7.34×10^-12/sin the case of self-calibration.And in the case of frequency correction,its frequency stability could achieve8.42×10^-11/swhen the output frequency is locked at?10M+0.1?Hz.Its frequency stability could achieve2.83×10^-11/swhen the output frequency is locked at10MHz.The design principle of the frequency corrector is innovative and its structure is simple,and its cost is low.At the same time,it doesn't require the complicated frequency transformation.The measurement accuracy could be further improved and breakthrough through the improvement of the experimental conditions and its principle.Moreover,the principle of the direct digital measurement solves effectively the problem of the quantization error affecting the measurement accuracy in the digital measurement and functional expansion.