Fountain clock closed-loop feedback structure and method

Abstract

The invention discloses a fountain clock closed-loop feedback structure and method, and relates to the technical field of time frequency, and the method comprises the steps: a crystal oscillator outputs a frequency signal; a frequency signal is divided into three paths of frequency signals through the power distribution amplifier; taking the first path of frequency signal as a reference frequency of a microwave integrated link to obtain a microwave frequency output by the microwave integrated link; performing frequency discrimination on the microwave frequency signal and the atomic transition probability of the fountain clock to obtain an error signal; the error signal is fed back to a phase micro-jump meter to serve as an input signal of the phase micro-jump meter, and the second path of frequency signal and an output signal of the phase micro-jump meter are subjected to frequency mixing; wherein a frequency signal of the active hydrogen atomic clock is used as a reference signal of the phase micro-jump meter; the frequency-mixed signal is transmitted to a crystal oscillator through a phase-locked loop, and a third-path frequency signal is output as a fountain clock closed-loop feedback signal; according to the method, the short-term stability of the output signal of the fountain clock system is improved while the long-term output of the signal containing the absolute frequency is realized.

Description

Technical Field

[0001] The present invention relates to the field of time-frequency technology, and in particular to a fountain clock closed-loop feedback structure and method. Background Art

[0002] The cesium fountain clock is a cold atomic fountain clock that uses cesium atoms as the frequency discrimination medium. It is the most accurate experimental device for reproducing the definition of seconds. In addition to the cesium fountain clock, the cold atomic fountain clock also includes the rubidium fountain clock. Due to its excellent frequency stability and very high frequency accuracy, the cold atomic fountain clock is used in the timekeeping system of the International Atomic Time. In addition, the cold atomic fountain clock can also be used as a reference clock to calibrate the local time and frequency system and improve the stability and accuracy of the local time and frequency system. The closed-loop feedback system plays a very important role in the cold atomic fountain clock. It can monitor and correct the clock's error in real time, thereby ensuring the accuracy of the atomic clock and outputting a stable standard frequency signal. The closed-loop feedback system is a control system whose purpose is to monitor the output and compare it with the expected value, and then adjust the input according to the difference so that the system output approaches the expected value.

[0003] At present, the commonly used closed-loop schemes for cesium fountain clocks include three methods: digital frequency synthesizer (DDS) feedback locking, local oscillator locking, and phase micro-jump meter feedback locking: (1) The voltage-controlled crystal oscillator with 5MHz and 100MHz output is weakly phase-locked to the hydrogen clock, and then the 9.2GHz signal output by the dielectric resonant oscillator is mixed with the signal near 7.3MHz output by the DDS to generate the transition frequency of the cesium fountain clock 9192631770Hz, which is transmitted to the cesium fountain clock to obtain the error signal. After the error signal is directly fed back to the DDS, the microwave frequency is adjusted through computer control to correct the Ramsey microwave frequency. (2) The dielectric resonant oscillator phase-locked to the reference crystal oscillator generates a 9192.6MHz signal for the atomic transition of the cesium fountain clock, which is transmitted to the cesium fountain clock to obtain a closed-loop feedback signal, which is applied to the analog PI controller through the control voltage, and then applied to the control voltage input of the quartz oscillator; the output of the microwave synthesis chain is locked to the central frequency of the Ramsey fringe, and the frequency modulation width is consistent with half of the half-height full width of the Ramsey fringe, and the working cycle of the cesium fountain clock is the modulation period; (3) The quartz crystal oscillator phase-locked to the hydrogen clock outputs a 5MHz signal to provide a reference for the phase micro-jump meter and the 6.8GHz signal. The 6.8GHz signal passes through the rubidium fountain clock, and the error signal is directly fed back to the phase micro-jump meter. The phase micro-jump meter is continuously updated according to the feedback signal as the fountain clock runs, and its processing can obtain the frequency stability of the rubidium atomic fountain clock.

[0004] However, in the DDS feedback locking mode, DDS plays the role of frequency modulation, and the closed-loop feedback signal of the cesium fountain clock is fed back to the integrated chain, and the frequency of the cesium fountain clock with a single frequency cannot be obtained; in the local oscillator locking mode, the frequency voltage coefficient of the crystal oscillator is relatively large, with a typical value of 0.0375Hz / V, and the adjustment accuracy of the digital-to-analog converter is limited, generally in the μV range, so the feedback accuracy of this mode can only reach 10 -13 ~10 -14 Order of magnitude; the short-term stability of the signal in the phase micro-jump meter feedback locking mode is limited by the stability of the phase micro-jump meter, and the short-term stability of the phase micro-jump meter is generally poor, thereby deteriorating the fountain clock indicators. Summary of the invention

[0005] In view of the poor short-term stability of the phase micro-jump meter in the prior art, which worsens the shortcomings of the fountain clock indicators, the present invention proposes a fountain clock closed-loop feedback structure and method. On the basis of directly feeding back the error signal output by the fountain clock to the phase micro-jump meter, a crystal oscillator with excellent phase noise is locked to the micro-jump meter output through a phase-locked loop, thereby obtaining a low phase noise output driven by the fountain clock, thereby solving the problems existing in the prior art.

[0006] A fountain clock closed-loop feedback structure, comprising:

[0007] Crystal oscillator, used to output frequency signal;

[0008] A power distribution amplifier, whose input end is connected to the output end of the crystal oscillator; a first output end of the power distribution amplifier is connected to the input end of the fountain clock system;

[0009] A phase micro-jump meter, whose input port is connected to the output end of the fountain clock system;

[0010] A phase-locked loop, whose input end receives a mixed signal of an output frequency signal of the phase micro-step meter and an output signal of the second output end of the power distribution amplifier; and the output end of the phase-locked loop is connected to the input end of the crystal oscillator.

[0011] Furthermore, the fountain clock system is connected to the power distribution amplifier via a microwave integrated chain.

[0012] Furthermore, the reference port of the phase microstep meter is connected to an active hydrogen atomic clock.

[0013] The present invention also proposes a fountain clock closed-loop feedback method, comprising the following steps:

[0014] The crystal oscillator outputs a frequency signal;

[0015] The frequency signal is outputted as a first frequency signal, a second frequency signal and a third frequency signal through a power distribution amplifier;

[0016] An error signal is obtained according to the first frequency signal and the atomic transition probability in the fountain clock system; the error signal is fed back to the phase micro-jump meter, and the second frequency signal is mixed with the output signal of the phase micro-jump meter; the mixed signal is transmitted to the crystal oscillator through a phase-locked loop to complete the closed-loop feedback of the fountain clock system; the third frequency signal is output as the closed-loop feedback signal of the fountain clock system.

[0017] Furthermore, the method of obtaining an error signal according to the first frequency signal and the atomic transition probability in the fountain clock system specifically includes the following steps:

[0018] The first frequency signal is used as the reference frequency of the microwave integrated link to obtain the microwave frequency output by the microwave integrated link;

[0019] The error signal is obtained by frequency discrimination between the microwave frequency signal and the atomic transition probability in the fountain clock system.

[0020] Furthermore, the output of the active hydrogen atomic clock is used as a reference signal of the phase micro-jump meter.

[0021] The present invention provides a fountain clock closed-loop feedback structure and method, which has the following beneficial effects:

[0022] The present invention directly feeds back the error signal output by the fountain clock to the phase micro-step meter, and locks the crystal oscillator with excellent phase noise to the micro-step meter output through a phase-locked loop, thereby obtaining a low phase noise output driven by the fountain clock; the frequency output driven by the fountain clock can be realized, and the closed-loop feedback resolution is 10 -19 , the output clock signal can effectively retain the excellent short-term stability and phase noise of the crystal oscillator. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of the closed-loop feedback structure of the fountain clock in an embodiment of the present invention. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0025] The present invention proposes a fountain clock closed-loop feedback structure, comprising: a crystal oscillator for outputting a frequency signal; a power distribution amplifier, whose input end is connected to the output end of the crystal oscillator; a microwave synthesis chain, whose input end is electrically connected to the first output end of the power distribution amplifier; a fountain clock system, whose input end is electrically connected to the output end of the microwave synthesis chain; a phase micro-jump meter, whose reference port is connected to an active hydrogen atomic clock; an input port of the phase micro-jump meter is electrically connected to the output end of the fountain clock system; and a phase-locked loop (PLL), whose input end is connected to the phase micro-jump meter and a mixing signal of the second output end of the power distribution amplifier.

[0026] The present invention also proposes a fountain clock closed-loop feedback method, which directly feeds back the error signal output by the cesium fountain clock to the phase micro-step meter, and locks the crystal oscillator with excellent phase noise to the micro-step meter output through a phase-locked loop, thereby obtaining a low phase noise output driven by the fountain clock; the method specifically includes the following steps:

[0027] S1, crystal oscillator output frequency signal.

[0028] S2. The frequency signal is divided into three frequency signals through a power distribution amplifier.

[0029] S3. Use the first frequency signal as the reference frequency of the microwave integrated link to obtain the microwave frequency output by the microwave integrated link; discriminate the microwave frequency signal with the atomic transition probability of the fountain clock system to obtain the error signal. The active hydrogen atomic clock output is used as the reference signal of the phase micro-jump meter.

[0030] S4, feeding back the error signal to the phase micro-step meter, and mixing the second frequency signal with the output signal of the phase micro-step meter.

[0031] S5. The mixed signal is transmitted to the crystal oscillator through a phase-locked loop to complete the closed-loop feedback of the fountain clock system; wherein the third frequency signal is output as the closed-loop feedback signal of the fountain clock system.

[0032] Based on the above inventive concept, the present invention proposes an embodiment, comprising the following steps:

[0033] S1, the 5MHz frequency signal output by the crystal oscillator is divided into three paths after power division, marked as A, B, and C respectively.

[0034] S2. The first path is used as the reference frequency of the homemade microwave integrated link. The error signal obtained after the 9.192631770GHz microwave frequency output by the homemade microwave integrated link is discriminated with the atomic transition probability in the cesium atomic fountain clock is fed back to the phase micro-leap meter, among which the 5MHz signal output by the hydrogen clock is used as the reference of the phase micro-leap meter.

[0035] S3, the second 5MHz signal is mixed with the 5MHz signal output by the phase micro-step meter, and then transmitted to the crystal oscillator through the phase-locked loop PLL.

[0036] S4, the third channel is used as the signal output of the closed-loop feedback of the cesium fountain clock system.

[0037] A method for improving the short-term stability of a cesium fountain clock outputting a long-term signal containing an absolute frequency: the error signal output by the atomic clock is directly fed back to the phase micro-jump meter, and the crystal oscillator is locked to the phase micro-jump meter through a phase-locked loop, so that the medium- and long-term stability of the crystal oscillator output is consistent with the medium- and long-term stability of the phase micro-jump meter. This solution retains the short-term stability and phase noise of the crystal oscillator itself, and has the high-resolution characteristics of the phase micro-jump meter. Since the crystal oscillator has the characteristic of good short-term stability, this method not only realizes the long-term output of a signal containing an absolute frequency, but also improves the short-term stability of the system output signal.

[0038] The present invention combines the advantages of three methods, namely, DDS feedback locking, local oscillator locking and phase micro-jump meter feedback locking. Firstly, in the second step, the error signal output by the cesium fountain clock is directly fed back to the phase micro-jump meter. The phase micro-jump meter has the characteristic of high resolution, so the feedback loop has the advantage of high feedback accuracy. Then, in the third step, the output signal of the crystal oscillator is used as the signal containing the absolute frequency output by the system. Since the short-term stability of the crystal oscillator is good, the method realizes the long-term output of the signal containing the absolute frequency while improving the short-term stability of the system output signal.

[0039] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A fountain clock closed-loop feedback structure, characterized in that: include: Crystal oscillator, used to output frequency signal; A power distribution amplifier, whose input end is connected to the output end of the crystal oscillator; a first output end of the power distribution amplifier is connected to the input end of the fountain clock system; A phase micro-jump meter, whose input port is connected to the output end of the fountain clock system; A phase-locked loop, whose input end receives a mixed signal of an output frequency signal of the phase micro-step meter and an output signal of the second output end of the power distribution amplifier; and the output end of the phase-locked loop is connected to the input end of the crystal oscillator.

2. The fountain clock closed-loop feedback structure according to claim 1, characterized in that: The fountain clock system is connected to the power distribution amplifier via a microwave integrated chain.

3. The fountain clock closed-loop feedback structure according to claim 1, characterized in that: The reference port of the phase microstep meter is connected to an active hydrogen atomic clock.

4. A fountain clock closed-loop feedback method, characterized in that: The following steps are involved: The crystal oscillator outputs a frequency signal; The frequency signal is outputted as a first frequency signal, a second frequency signal and a third frequency signal through a power distribution amplifier; An error signal is obtained according to the first frequency signal and the atomic transition probability in the fountain clock system; the error signal is fed back to the phase micro-jump meter, and the second frequency signal is mixed with the output signal of the phase micro-jump meter; The mixed signal is transmitted to the crystal oscillator through a phase-locked loop to complete the closed-loop feedback of the fountain clock system; the third frequency signal is output as the closed-loop feedback signal of the fountain clock system.

5. The closed-loop feedback method of the closed-loop feedback structure of a fountain clock according to claim 4, characterized in that: The error signal is obtained according to the first frequency signal and the atomic transition probability in the fountain clock system; The specific steps include: The first frequency signal is used as the reference frequency of the microwave integrated link to obtain the microwave frequency output by the microwave integrated link; The error signal is obtained by frequency discrimination between the microwave frequency signal and the atomic transition probability in the fountain clock system.

6. The closed-loop feedback method of the closed-loop feedback structure of a fountain clock according to claim 4, characterized in that: The output of the active hydrogen atomic clock is used as a reference signal of the phase microstep meter.

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