A closed-loop feedback structure and method for a fountain clock

Abstract

This invention discloses a closed-loop feedback structure and method for a fountain clock, relating to the field of time and frequency technology. The method includes: a crystal oscillator outputting a frequency signal; the frequency signal being divided into three frequency signals by a power distribution amplifier; the first frequency signal being used as a reference frequency for a microwave synthesis link to obtain the microwave frequency output by the microwave synthesis link; the microwave frequency signal being frequency-discriminated with the atomic transition probability of the fountain clock to obtain an error signal; the error signal being fed back to a phase transition meter as its input signal; the second frequency signal being mixed with the output signal of the phase transition meter; wherein, the frequency signal of an active hydrogen atomic clock is used as the reference signal for the phase transition meter; the mixed signal is transmitted to the crystal oscillator through a phase-locked loop; and the third frequency signal is used as the closed-loop feedback signal output of the fountain clock. This method achieves long-term output of a signal containing absolute frequency while improving the short-term stability of the fountain clock system's output signal.

Description

Technical Field

[0001] This invention relates to the field of time and frequency technology, specifically to a closed-loop feedback structure and method for a fountain clock. Background Technology

[0002] The cesium fountain clock, a cold atom fountain clock using cesium atoms as the frequency discrimination medium, is the experimental device with the highest accuracy in reproducing the definition of the second. Besides the cesium fountain clock, cold atom fountain clocks also include rubidium fountain clocks, etc. Due to their excellent frequency stability and very high frequency accuracy, cold atom fountain clocks are used in the International Atomic Time (IAT) system. Furthermore, cold atom fountain clocks can also be used as reference clocks to calibrate local time and frequency systems, improving their stability and accuracy. The closed-loop feedback system plays a crucial role in the cold atom fountain clock, enabling real-time monitoring and correction of clock errors, thereby ensuring the accuracy of the atomic clock and outputting a stable standard frequency signal. A closed-loop feedback system is a control system whose purpose is to monitor the output and compare it with the desired value, then adjust the input based on the difference to make the system's output approximate the desired value.

[0003] Currently, the commonly used closed-loop schemes for cesium atomic fountain clocks include three methods: Direct Digital Synthesizer (DDS) feedback locking, local oscillator locking, and phase micro-jump meter feedback locking. (1) A voltage-controlled crystal oscillator with outputs of 5MHz and 100MHz is weakly phase-locked to the hydrogen clock. Then, a 9.2GHz signal output from a dielectric resonant oscillator is mixed with a signal around 7.3MHz output from the DDS to generate the transition frequency 9192631770Hz of the cesium atomic fountain clock, which is transmitted to the cesium fountain clock to obtain an error signal. After the error signal is directly fed back to the DDS, the microwave frequency is adjusted by computer control to correct the Ramsey microwave frequency. (2) A 9192.6MHz signal is generated by the dielectric resonator of the reference crystal oscillator for the atomic transition of the cesium fountain clock. This signal is transmitted to the cesium fountain clock to obtain a closed-loop feedback signal. The control voltage is applied to the analog PI controller and then to the control voltage input of the quartz oscillator. The output of the microwave synthesis chain is locked at the center frequency of the Ramsey fringe, and the modulation width is consistent with half the full width at half maximum (FWHM) of the Ramsey fringe. The modulation period is the working period of the cesium fountain clock. (3) A 5MHz signal is output from the quartz crystal oscillator of the phase-locked hydrogen clock 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 to obtain an error signal that is directly fed back to the phase micro-jump meter. The output signal of the phase micro-jump meter is continuously updated according to the feedback signal as the fountain clock runs. Processing this signal can obtain the frequency stability of the rubidium atomic fountain clock.

[0004] However, in the DDS feedback-locked method, the DDS acts as a frequency modulator, feeding back the closed-loop feedback signal of the cesium fountain clock to the synthesis chain, making it impossible to obtain a cesium fountain clock frequency with a single frequency. In the local oscillator-locked method, due to the relatively large frequency voltage coefficient of the crystal oscillator (typically 0.0375Hz / V) and the limited adjustment accuracy of the digital-to-analog converter (generally on the order of μV), the feedback accuracy of this method only reaches 10. -13 ~10 -14 In the phase micro-jump meter feedback locking method, the short-term stability of the signal 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, thus deteriorating the fountain clock performance. Summary of the Invention

[0005] To address the shortcomings of existing phase micro-step meters in terms of poor short-term stability, which worsens the performance of fountain clocks, this invention proposes a closed-loop feedback structure and method for fountain clocks. By directly feeding the error signal output by the fountain clock to the phase micro-step meter, a crystal oscillator with excellent phase noise is locked to the output of the micro-step meter through a phase-locked loop, thereby obtaining a low phase noise output driven by the fountain clock and solving the problems existing in the prior art.

[0006] A closed-loop feedback structure for a fountain clock includes:

[0007] Crystal oscillators are used to output frequency signals;

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

[0009] The phase micrometer's input port is connected to the output of the fountain clock system;

[0010] A phase-locked loop (PLL) receives a mixed signal at its input terminal from the output frequency signal of the phase micrometer and the output signal from the second output terminal of the power distribution amplifier; the output terminal of the PLL is connected to the input terminal 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 micro-jump meter is connected to an active hydrogen atomic clock.

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

[0014] Crystal oscillator output frequency signal;

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

[0016] An error signal is obtained based on the first frequency signal and the atomic transition probability within the fountain clock system. This error signal is then fed back to the phase micro-jump meter. The second frequency signal is mixed with the output signal of the phase micro-jump meter. The mixed signal is then transmitted to the crystal oscillator via a phase-locked loop, completing the closed-loop feedback of the fountain clock system. The third frequency signal serves as the output signal for the closed-loop feedback of the fountain clock system.

[0017] Furthermore, the step of obtaining an error signal based on the first frequency signal and the atomic transition probabilities within 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 serves as a reference signal for the phase micro-jump meter.

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

[0022] This invention, based on directly feeding the error signal output by the fountain clock to the phase micro-step meter, locks a crystal oscillator with excellent phase noise to the micro-step meter output via a phase-locked loop, thereby obtaining a low phase noise output driven by the fountain clock; it can realize the frequency output driven by the fountain clock, with a closed-loop feedback resolution of 10. -19 The output clock signal can effectively preserve the excellent short-term stability and phase noise of the crystal oscillator. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the closed-loop feedback structure of the fountain clock in an embodiment of the present invention. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

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

[0026] This invention also proposes a closed-loop feedback method for a fountain clock. Based on the direct feedback of the error signal output by the cesium fountain clock to a phase micrometer, a crystal oscillator with excellent phase noise is locked to the output of the micrometer via 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 split into three frequency signals by a power distribution amplifier.

[0029] S3. Using the first frequency signal as the reference frequency of the microwave synthesis link, the microwave frequency output by the microwave synthesis link is obtained; the error signal is obtained by frequency discrimination between the microwave frequency signal and the atomic transition probability of the fountain clock system. The output of the active hydrogen atomic clock is used as the reference signal for the phase micro-jump meter.

[0030] S4. Feed the error signal back to the phase micrometer, and mix the second frequency signal with the output signal of the phase micrometer.

[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; the third frequency signal is used as the signal output for the closed-loop feedback of the fountain clock system.

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

[0033] S1. The 5MHz frequency signal output by the crystal oscillator is divided into three paths by a power divider, and labeled as A, B, and C respectively.

[0034] S2. The first path serves as the reference frequency for the self-made microwave integrated link. The error signal obtained after frequency discrimination between the 9.192631770GHz microwave frequency output by the self-made microwave integrated link and the atomic transition probability in the cesium atomic fountain clock is fed back to the phase micro-jump meter. The 5MHz signal output by the hydrogen clock serves as the reference for the phase micro-jump meter.

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

[0036] S4, the third path, serves as the signal output for the closed-loop feedback of the cesium fountain clock system.

[0037] A method to improve the short-term stability of a cesium fountain clock's output signal while simultaneously providing a long-term signal containing absolute frequency is as follows: The error signal from the atomic clock is directly fed back to a phase micrometer. The crystal oscillator is locked to the phase micrometer via a phase-locked loop, thus ensuring consistency between the medium-to-long-term stability of the crystal oscillator output and that of the phase micrometer. This scheme preserves the short-term stability and phase noise of the crystal oscillator while leveraging the high resolution of the phase micrometer. Because the crystal oscillator exhibits good short-term stability, this method not only achieves long-term output of a signal containing absolute frequency but also improves the short-term stability of the system's output signal.

[0038] This invention combines the advantages of three methods: DDS feedback locking, local oscillator locking, and phase micrometer feedback locking. First, in the second step, the error signal output by the cesium fountain clock is directly fed back to the phase micrometer. The phase micrometer has high resolution, so this 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 system output signal containing absolute frequency. Since the crystal oscillator has good short-term stability, this method can achieve long-term output of a signal containing absolute frequency while improving the short-term stability of the system output signal.

[0039] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A closed-loop feedback method for a fountain clock, applied to a closed-loop feedback structure of a fountain clock, characterized in that, The closed-loop feedback structure of the fountain clock includes: Crystal oscillators are used to output frequency signals; A power distribution amplifier, the input of which is connected to the output of the crystal oscillator; the first output of the power distribution amplifier is connected to the input of the fountain clock system. The phase micrometer's input port is connected to the output of the fountain clock system; A phase-locked loop (PLL) receives at its input a mixed signal of the output frequency signal of the phase micrometer and the output signal of the second output of the power distribution amplifier; the output of the PLL is connected to the input of the crystal oscillator. The closed-loop feedback method for the fountain clock includes the following steps: Crystal oscillator output frequency signal; The frequency signal is output as a first frequency signal, a second frequency signal, and a third frequency signal after passing through a power distribution amplifier; An error signal is obtained based on the first frequency signal and the atomic transition probability within the fountain clock system. This error signal is then fed back to the phase micro-jump meter. The second frequency signal is mixed with the output signal of the phase micro-jump meter. The mixed signal is then transmitted to the crystal oscillator via a phase-locked loop, completing the closed-loop feedback of the fountain clock system. The third frequency signal serves as the output signal for the closed-loop feedback of the fountain clock system.

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

3. The closed-loop feedback method for a fountain clock according to claim 1, characterized in that, The reference port of the phase micro-jump meter is connected to an active hydrogen atomic clock.

4. The closed-loop feedback method for a fountain clock according to claim 2, characterized in that, The error signal is obtained based on the first frequency signal and the atomic transition probability within the fountain clock system; Specifically, the following steps are included: 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.

5. The closed-loop feedback method for a fountain clock according to claim 3, characterized in that, The output of the active hydrogen atomic clock serves as the reference signal for the phase micro-jump meter.

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