Microwave Modulation Method and Device for CPT Atomic Clock Based on Discrete Sine Wave Frequency Modulation

Abstract

The present invention discloses a microwave modulation method and device for a CPT atomic clock based on discrete sine wave frequency modulation, including: determining the frequency of the frequency discrimination signal; determining the charge pump current value according to the frequency of the frequency discrimination signal; determining the center frequency by setting the numerator frequency division coefficient and the denominator frequency division coefficient according to the charge pump current value and combining the frequency of the frequency discrimination signal; determining the VCO frequency band and the tuning range according to the center frequency; determining the target bandwidth and the phase margin according to the VCO frequency band and the tuning range, designing a third-order passive loop filter to filter the VCO output signal to obtain a filtered carrier signal; determining the modulation frequency, determining the maximum frequency deviation, determining the frequency deviation value and adjusting the microwave power gain according to the carrier signal, so as to generate a frequency modulation signal. This method can reduce the spectral broadening of the modulated microwave signal and improve the short-term frequency stability of the CPT atomic clock.

Description

Technical Field

[0001] This application relates to the field of precise time and frequency metrology, and particularly to a microwave modulation method and device for a CPT atomic clock based on discrete sine wave frequency modulation. Background Art

[0002] The coherent population trapping (CPT) atomic clock is a precise time and frequency metrology device based on the coherent population trapping effect. Compared with traditional atomic clocks, the CPT atomic clock has significantly reduced volume and power consumption because it does not require a microwave resonator, while maintaining high-precision performance. It has broad application prospects and market value in fields such as autonomous navigation, time and frequency reference, micro-nano satellites, and unmanned driving.

[0003] According to the working principle of the CPT atomic clock, the optical frequency shift caused by the Stark Effect is one of the important factors affecting the frequency stability of the atomic clock, which involves the influence of each optical frequency component on the energy levels of alkali metal atoms. Although the microwave signal does not directly interact with the atoms, when considering the effects of each sideband comprehensively, the influence of the sideband expansion caused by microwave frequency modulation on the coherent two-color light needs to be considered.

[0004] Currently, the microwave signal in the CPT atomic clock mainly adopts the 2FSK modulation method based on a phase-locked loop (PLL). By adjusting the frequency division factor of the phase-locked loop, frequency hopping is achieved, which has advantages such as precise frequency switching and simple implementation method. However, this method has the following deficiencies in practical applications: (1) Frequency hopping will cause the spectrum of the microwave signal to broaden, which increases the spectral components participating in atomic transitions, reduces the coherence between the microwave signal and atomic transitions, and thus affects the frequency stability; (2) During the modulation process, the center frequency of the microwave signal may shift, and this shift will interfere with the matching between the microwave signal and the atomic resonance frequency, affecting the locking accuracy of the CPT signal; (3) Due to the slow frequency switching speed of the PLL, when rapid adjustment of the microwave signal is required, the dynamic response ability of 2FSK modulation may be insufficient, affecting the real-time performance of the system. Summary of the Invention

[0005] In view of the deficiencies of the existing microwave modulation method for CPT atomic clocks, the present invention proposes a microwave modulation method and device based on discrete sine wave frequency modulation. By adopting direct digital frequency synthesis (DDS) technology, the microcontroller is used to precisely program and control the digital phase-locked loop chip, and the internal discrete FSK function of the phase-locked loop chip is called to achieve continuous switching of multiple carrier frequencies. Combining the physical system and the circuit system, the sine modulation of the microwave frequency of the CPT atomic clock is realized.

[0006] According to the first aspect of the embodiments of the present application, a microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation is provided, including:

[0007] Obtain the input frequency of the phase-locked loop chip, the doubler, the pre-R divider, the frequency multiplier, and the R divider, and determine the frequency of the frequency discrimination signal;

[0008] Determine the charge pump current value according to the frequency of the frequency discrimination signal;

[0009] Determine the center frequency according to the charge pump current value by setting the numerator division coefficient and the denominator division coefficient and combining the frequency of the frequency discrimination signal;

[0010] Determine the VCO frequency band and the tuning range according to the center frequency;

[0011] Determine the target bandwidth and the phase margin according to the VCO frequency band and the tuning range, design a third-order passive loop filter, filter the VCO output signal, and obtain the filtered carrier signal;

[0012] Determine the modulation frequency, determine the maximum frequency deviation, determine the frequency deviation value, and adjust the microwave power gain according to the carrier signal, so as to generate a frequency modulation signal.

[0013] According to the second aspect of the embodiments of the present application, there is provided a CPT atomic clock microwave modulation device based on discrete sine wave frequency modulation, characterized in that it includes:

[0014] A first determination module, configured to obtain the input frequency of the phase-locked loop chip, the doubler, the pre-R divider, the frequency multiplier, and the R divider, and determine the frequency of the frequency discrimination signal;

[0015] A second determination module, configured to determine the charge pump current value according to the frequency of the frequency discrimination signal;

[0016] A third determination module, configured to determine the center frequency according to the charge pump current value by setting the numerator division coefficient and the denominator division coefficient and combining the frequency of the frequency discrimination signal;

[0017] A fourth determination module, configured to determine the VCO frequency band and the tuning range according to the center frequency;

[0018] A fifth determination module, configured to determine the target bandwidth and the phase margin according to the VCO frequency band and the tuning range, design a third-order passive loop filter, filter the VCO output signal, and obtain the filtered carrier signal;

[0019] A generation module, configured to determine the modulation frequency, determine the maximum frequency deviation, determine the frequency deviation value, and adjust the microwave power gain according to the carrier signal, so as to generate a frequency modulation signal.

[0020] According to the second aspect of the embodiments of the present application, there is provided an electronic device, including:

[0021] One or more processors;

[0022] A memory for storing one or more programs;

[0023] When the one or more programs are executed by the one or more processors, the one or more processors implement the method as described in the first aspect.

[0024] According to a second aspect of the embodiments of the present application, there is provided a computer-readable storage medium, on which computer instructions are stored, and when the instructions are executed by a processor, the steps of the method as described in the first aspect are implemented.

[0025] The technical solutions provided by the embodiments of the present application may include the following beneficial effects:

[0026] As can be seen from the above embodiments, the present application adopts direct digital frequency synthesis technology and combines the discrete FSK function of a digital phase-locked loop chip to achieve continuous switching of multi-carrier frequencies. Compared with the existing frequency modulation schemes based on analog circuits (such as sine wave modulation and triangular wave modulation), this scheme overcomes the problems of difficult debugging, complex implementation, and large frequency deviation, and significantly improves the short-term frequency stability of the CPT atomic clock. At the same time, on the basis of not increasing the hardware complexity, this scheme can flexibly adjust the modulation depth and frequency using a microprocessor, further improving the performance of the microwave modulation signal. In addition, this scheme can effectively improve the signal-to-noise ratio of the frequency discrimination signal at a specific modulation index, optimize the narrowband frequency modulation signal, greatly compress the CPT signal linewidth, and enhance the reliability and stability of the system.

[0027] It should be understood that the above general description and the following detailed description are only exemplary and explanatory, and cannot limit the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present application and used together with the specification to explain the principles of the present application.

[0029] Figure 1 It is an overall structural diagram of a CPT atomic clock shown according to an exemplary embodiment.

[0030] Figure 2 It is a flowchart of a microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation shown according to an exemplary embodiment.

[0031] Figure 3 It is a relationship diagram between the modulation frequency and the frequency deviation shown according to an exemplary embodiment.

[0032] Figure 4It is a block diagram of a microwave modulation device for a CPT atomic clock based on discrete sine wave frequency modulation shown according to an exemplary embodiment. Detailed implementation manners

[0033] Here, the exemplary embodiments will be described in detail, and examples thereof are shown in the drawings. When the following description refers to the drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The implementation manners described in the following exemplary embodiments do not represent all implementation manners consistent with the present application. On the contrary, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0034] The terms used in the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application. The singular forms "a", "the", and "said" used in the present application and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term "and / or" as used herein refers to and includes any or all possible combinations of one or more of the associated listed items.

[0035] It should be understood that although the terms first, second, third, etc. may be used in the present application to describe various information, such information should not be limited to these terms. These terms are only used to distinguish the same type of information from each other. For example, without departing from the scope of the present application, the first information may also be referred to as the second information, and similarly, the second information may also be referred to as the first information. Depending on the context, the word "if" as used herein may be interpreted as "when" or "while" or "in response to determining".

[0036] As Figure 1 shown, the structure of the CPT atomic clock consists of a physical system and a circuit system. Among them, the physical system includes: a laser, a quarter-wave plate, an atomic gas cell, and a magnetic shielding enclosure; the circuit system includes: a photodetector (PD), a band-pass filter, a microprocessor, a voltage-controlled constant current source, a crystal oscillator, a radio frequency generator, a power amplifier, and a Bias-Tee. Among them, the microprocessor, the radio frequency generator, and the power amplifier together constitute the microwave modulation unit of the CPT atomic clock. The radio frequency generator generates a stable microwave signal through its internal charge pump phase-locked loop, and its main components include: a phase frequency detector (PFD), a loop filter, a voltage-controlled oscillator (VCO), an integer N divider, and a Δ-Σ modulator. The microprocessor can control the frequency of the microwave signal output by the radio frequency generator, and the power amplifier can adjust the power of the microwave signal output by the radio frequency generator.

[0037] Figure 2 It is a flowchart of a microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation shown according to an exemplary embodiment, asFigure 2 As shown, this method is applied to a terminal and may include the following steps:

[0038] S1: Obtain the input frequency of the phase-locked loop chip, the doubler, the pre-R divider, the multiplier, and the R divider, and determine the frequency of the frequency discrimination signal;

[0039] Specifically, obtain the input frequency of the phase-locked loop chip , the multiplication factor OSC_2X of the doubler, the division factor PLL_R_PRE of the pre-R divider, the multiplication factor MULT of the multiplier, and the division factor PLL_R of the R divider, to obtain the frequency of the frequency discrimination signal , where:

[0040] .

[0041] According to the requirements of the CPT atomic clock for the microwave frequency, first set the division factor of the integer multiple N divider to generate the initial microwave frequency of the CPT atomic clock for realizing the coarse frequency adjustment range.

[0042] S2: Determine the charge pump current value according to the frequency of the frequency discrimination signal;

[0043] Specifically, the charge pump current is a key factor in the phase-locked loop loop gain. According to the frequency of the frequency discrimination signal evaluate the influence of the charge pump current on the loop performance, and at the same time combine the target loop bandwidth and the phase margin design requirements, adjust the current to achieve the balance between the loop bandwidth and the phase noise performance, and finally determine the charge pump current value to ensure the system maintains stability and noise performance while quickly locking.

[0044] S3: According to the charge pump current value, by setting the numerator division factor and the denominator division factor, and combining the frequency of the frequency discrimination signal, determine the carrier signal with the center frequency;

[0045] Specifically, according to the requirements of the CPT atomic clock for the microwave frequency, set the division factor PLL_N of the integer multiple N divider to generate the initial microwave frequency of the CPT atomic clock;

[0046] To further improve the frequency resolution and adjustment accuracy, use the Sigma-Delta fractional division technology to determine the center frequency by setting the numerator division factor PLL_NUM and the denominator division factor PLL_DEN , where:

[0047] .

[0048] This process combines coarse tuning and fine tuning, which not only ensures the high precision of the center frequency but also meets the strict requirements of the CPT atomic clock for frequency stability and adjustable range.

[0049] S4: Determine the VCO frequency band and tuning range according to the center frequency;

[0050] Specifically, according to the center frequency , select the VCO module and set the starting frequency band. By adjusting the tuning voltage range, ensure that the frequency coverage requirements are met, avoid disorders or difficult switching caused by too narrow a bandwidth, and set the bias current magnitude of the VCO to ensure that the VCO operates in the linear region.

[0051] S5: Determine the target bandwidth and phase margin according to the VCO frequency band and tuning range, design a third-order passive loop filter, and obtain the loop filter parameters;

[0052] Specifically, comprehensively consider the requirements of indicators such as loop bandwidth, lock time, phase noise, and spurious signals, and set the loop filter order and capacitance and resistance parameters.

[0053] Here, according to the VCO frequency band and tuning range, determine the target bandwidth , phase margin , according to the target bandwidth , phase margin , design a third-order passive loop filter. The transfer function of the third-order loop filter is as follows:

[0054]

[0055] Among them, , , , . Among them , reflect the true poles of the third-order loop filter;

[0056] The open-loop gain of the phase-locked loop is:

[0057]

[0058] Among them, is the phase detector gain coefficient, is the VCO voltage-controlled gain coefficient, is the division ratio; Substitute into the open-loop gain to obtain the phase margin at the open-loop gain:

[0059]

[0060] When When it is possible, the loop bandwidth at the maximum phase margin can be obtained:

[0061]

[0062] Introduce the pole ratio , ;

[0063] The total capacitance is:

[0064]

[0065] Solve the above equations simultaneously to obtain , , and values, and then obtain the specific numerical values of the capacitance and resistance parameters of the third-order loop filter.

[0066] Then, use this third-order loop filter to filter the VCO output signal to obtain the filtered carrier signal.

[0067] S6: Determine the modulation frequency, determine the maximum frequency deviation, determine the frequency deviation value, and adjust the microwave power gain according to the carrier signal, so as to generate a frequency modulation signal; this step includes the following sub-steps:

[0068] S61: Adopt a microwave modulation frequency less than 5 times the CPT linewidth, considering the modulation frequency as ;

[0069] Specifically, in the application of the CPT atomic clock, without reducing the contrast of the CPT resonance signal, in order to reduce the linewidth of the CPT resonance spectrum and improve the slope of the frequency discrimination signal, the microwave modulation frequency should be reasonably selected. Under different experimental conditions, the linewidth of the CPT signal ranges from dozens of Hz to dozens of kHz. In order to obtain a continuous and steady CPT signal without distortion, when the microwave source frequency modulates each instantaneous frequency, it should be ensured that the relaxation of the atomic system and the action of the radiation field reach dynamic equilibrium at this moment. If the modulation frequency is too fast, the relaxation action is too late to establish dynamic equilibrium, and the CPT signal will be distorted. Usually, the frequency modulation frequency is taken to be less than 5 times the CPT linewidth to ensure that the CPT signal will not be significantly broadened due to the modulation frequency.

[0070] S62: Determine the maximum frequency deviation as ;

[0071] Specifically, the maximum frequency deviation of microwave modulation affects the modulation depth, and the modulation depth affects the demodulation result of the CPT signal by phase-sensitive detection. When the modulation depth is small, the response signal in the optical signal is weak, and it is difficult to demodulate the CPT signal. Appropriately increasing the modulation depth can rapidly improve the signal-to-noise ratio of the demodulated signal and increase the slope of the frequency discrimination signal. To obtain a CPT frequency discrimination signal with a high signal-to-noise ratio and a high frequency discrimination slope, the maximum frequency deviation is determined to be .

[0072] S63: According to the modulation frequency and the maximum frequency deviation, each modulation period is divided into M sampling points, and each 360° corresponds to sampling points, so as to obtain the frequency deviation of each sampling point, and determine the frequency deviation values corresponding to all sampling points within one period based on the frequency deviation;

[0073] Specifically, according to the theory, the frequency deviation within each modulation period will show a sinusoidal change. This change requires accurately recording the signal characteristics during the frequency modulation process to ensure that the generated signal is consistent with the expectation. To achieve this goal, it is necessary to sample the modulation signal. The choice of the number of sampling points directly affects the accurate restoration of the signal and the system performance. The more sampling points, the more accurately the frequency deviation and phase information of the signal can be characterized, but it will also increase the calculation and storage pressure of the microprocessor, especially when the PLL chip register is updated frequently. On the contrary, too few sampling points may lead to incomplete signal reconstruction, resulting in distortion of the demodulation value of the frequency deviation during the modulation process, thus affecting the stability and accuracy of the system. Assume that each modulation period is divided into M sampling points, and each 360° corresponds to sampling points. The frequency deviation of each sampling point can be calculated by the following formula:

[0074]

[0075] where is the frequency deviation, M is the number of sampling points, n is the serial number of the current sampling point.

[0076] Through the above formula, the frequency deviation values corresponding to all sampling points within one period can be generated, as shown in Figure 3 .

[0077] S64: According to the frequency deviation values, convert each frequency deviation value into an array of parameter values corresponding to the RF generator register at different moments; the single-chip microcomputer periodically queries the frequency deviation values in the array through the timer and writes the frequency deviation value into the RF generator register to generate a discrete sinusoidal frequency modulation signal that meets the requirements;

[0078] S65: Based on the generated discrete sinusoidal frequency-modulated signal, considering the output power range and the signal power attenuation caused by PCB circuit board wiring, set the power amplifier gain to ensure that the output carrier intensity meets the requirements of the CPT atomic clock;

[0079] Specifically, in the application of the CPT atomic clock, when using half-wave modulation, it is necessary to set an appropriate modulation index to maximize the optical intensity of the ±1st order sidebands, and at the same time use symmetric sidebands to achieve CPT resonance, which also helps to reduce the optical frequency shift. Usually, adjusting the output power of the microwave signal to optimize the modulation index is the most convenient and effective way. Considering the output power range and the signal power attenuation caused by PCB circuit board wiring, set the power amplifier gain to ensure that the output microwave intensity meets the requirements of laser frequency locking.

[0080] As can be seen from the above embodiments, the present application adopts the direct digital frequency synthesis technology and combines the discrete FSK function of the digital phase-locked loop chip to achieve continuous switching of multiple carrier frequencies. Compared with the existing frequency modulation schemes based on analog circuits (such as sine wave modulation and triangular wave modulation), this scheme overcomes the problems of difficult debugging, complex implementation, and large frequency deviation, and at the same time significantly improves the short-term frequency stability of the CPT atomic clock. At the same time, on the basis of not increasing the hardware complexity, this scheme can flexibly adjust the modulation depth and frequency using a microprocessor, further improving the performance of the microwave modulation signal. In addition, this scheme can effectively improve the signal-to-noise ratio of the frequency discrimination signal at a specific modulation index, optimize the narrowband frequency modulation signal, greatly compress the CPT signal linewidth, and enhance the reliability and stability of the system.

[0081] Corresponding to the foregoing embodiments of the microwave modulation method of the CPT atomic clock based on discrete sinusoidal frequency modulation, the present application also provides an embodiment of a microwave modulation device of the CPT atomic clock based on discrete sinusoidal frequency modulation.

[0082] Figure 4 is a block diagram of a microwave modulation device of a CPT atomic clock based on discrete sinusoidal frequency modulation shown according to an exemplary embodiment. Referring to Figure 4 , the device includes:

[0083] The first determination module 1 is used to obtain the input frequency of the phase-locked loop chip, the frequency doubler, the pre-R frequency divider, the frequency multiplier, and the R frequency divider, and determine the frequency discrimination signal frequency;

[0084] The second determination module 2 is used to determine the charge pump current value according to the frequency discrimination signal frequency;

[0085] The third determination module 3 is used to determine the center frequency according to the charge pump current value by setting the numerator frequency division coefficient and the denominator frequency division coefficient and combining the frequency discrimination signal frequency;

[0086] The fourth determination module 4 is configured to determine the VCO frequency band and the tuning range according to the center frequency;

[0087] The fifth determination module 5 is configured to determine the target bandwidth and the phase margin according to the VCO frequency band and the tuning range, design a third-order passive loop filter, filter the VCO output signal, and obtain a filtered carrier signal;

[0088] The generation module 6 is configured to determine the modulation frequency, determine the maximum frequency deviation, determine the frequency deviation value, and adjust the microwave power gain according to the carrier signal, so as to generate a frequency modulation signal.

[0089] Regarding the device in the above embodiments, the specific manners in which each module performs operations have been described in detail in the embodiments related to the method, and will not be elaborated herein.

[0090] For the device embodiments, since they basically correspond to the method embodiments, the relevant parts can refer to the partial descriptions of the method embodiments. The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place, or may be distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of the present application. Those of ordinary skill in the art can understand and implement it without creative efforts.

[0091] Correspondingly, the present application further provides an electronic device, including: one or more processors; a memory for storing one or more programs; when the one or more programs are executed by the one or more processors, the one or more processors implement the CPT atomic clock microwave modulation method based on discrete sine wave frequency modulation as described above.

[0092] Correspondingly, the present application further provides a computer-readable storage medium, on which computer instructions are stored, and when the instructions are executed by a processor, the CPT atomic clock microwave modulation method based on discrete sine wave frequency modulation as described above is implemented.

[0093] Those skilled in the art will readily think of other implementation manners of the present application after considering the specification and practicing the content disclosed herein. The present application is intended to cover any variations, uses, or adaptations of the present application, which follow the general principles of the present application and include the common general knowledge or conventional technical means in the technical field not disclosed in the present application. The specification and embodiments are only regarded as exemplary, and the true scope and spirit of the present application are pointed out by the claims.

[0094] It should be understood that the present application is not limited to the exact structures described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation, characterized in that, Including: Obtain the input frequency of the phase-locked loop chip, the doubler, the pre-R divider, the frequency multiplier, and the R divider, and determine the frequency of the frequency discrimination signal; Determine the charge pump current value according to the frequency of the frequency discrimination signal; According to the charge pump current value, by setting the numerator division coefficient and the denominator division coefficient, and combining with the frequency of the frequency discrimination signal, determine the center frequency; Determine the VCO frequency band and tuning range according to the center frequency; According to the VCO frequency band and tuning range, determine the target bandwidth and phase margin, design a third-order passive loop filter, filter the VCO output signal, and obtain the filtered carrier signal; According to the carrier signal, determine the modulation frequency, determine the maximum frequency deviation, determine the frequency deviation value, and adjust the microwave power gain, so as to generate a frequency modulation signal; Among them, obtaining the input frequency of the phase-locked loop chip, the doubler, the pre-R divider, the frequency multiplier, and the R divider, and determining the frequency of the frequency discrimination signal includes: Obtain the input frequency of the phase-locked loop chip , the frequency multiplication factor OSC_2X of the doubler, the frequency division factor PLL_R_PRE of the pre-stage R frequency divider, the frequency multiplication factor MULT of the doubler, and the frequency division factor PLL_R of the R frequency divider to obtain the frequency discrimination signal frequency , where: 。 2. The microwave modulation method of a CPT atomic clock based on discrete sine wave frequency modulation according to claim 1, wherein Determining the charge pump current value according to the frequency of the frequency discrimination signal includes: According to the frequency of the discriminator signal evaluate the influence of the charge pump current on the loop performance, and at the same time combine the target loop bandwidth and phase margin design requirements, adjust the current to achieve the balance between the loop bandwidth and the phase noise performance, and finally determine the charge pump current value.

3. A microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation according to claim 1, characterized in that, According to the charge pump current value, by setting the numerator division coefficient and the denominator division coefficient, and combining with the frequency of the frequency discrimination signal, determining the center frequency includes: According to the requirements of the CPT atomic clock for the microwave frequency, set the division coefficient PLL_N of the integer multiple N divider to generate the initial microwave frequency of the CPT atomic clock; Using Sigma-Delta fractional frequency division technology, the center frequency is determined by setting the numerator frequency division coefficient PLL_NUM and the denominator frequency division coefficient PLL_DEN , where: 。 4. A microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation according to claim 1, characterized in that Determining the VCO frequency band and tuning range according to the center frequency includes: According to the center frequency, select the VCO module and set the starting frequency band. Through the adjustment of the tuning voltage range, ensure the frequency coverage requirement, avoid the difficulty of offset or switching caused by too narrow bandwidth, and set the bias current magnitude of the VCO to ensure that the VCO operates in the linear region.

5. A microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation according to claim 1, characterized in that, According to the VCO frequency band and tuning range, determine the target bandwidth and phase margin, design a third-order passive loop filter, filter the VCO output signal, and obtain the filtered carrier signal, including: Determine the target bandwidth according to the VCO frequency band and tuning range , phase margin , according to the target bandwidth , phase margin , design a third-order passive loop filter, and the transfer function of the third-order loop filter is as follows: ； Among them, , , T 3 = , , where and reflect the true poles of the third-order loop filter; The open-loop gain of the phase-locked loop is: Among them, is the phase detector gain coefficient, is the VCO voltage-controlled gain coefficient, is the frequency division number; substituting into the open-loop gain, the phase margin under the open-loop gain can be obtained: When the loop bandwidth at the maximum phase margin can be obtained: Introduced pole ratio , ; The total capacitance is: By solving the above equations simultaneously, find , , and values, and then obtain the specific values of the capacitance and resistance parameters of the third-order loop filter; Use this third-order loop filter to filter the VCO output signal to obtain the filtered carrier signal.

6. A microwave modulation method for a CPT atomic clock based on discrete sine wave frequency modulation according to claim 1, characterized in that According to the carrier signal, determine the modulation frequency, determine the maximum frequency deviation, determine the frequency deviation value, and adjust the microwave power gain, so as to generate a frequency modulation signal, including: S61: Use a microwave modulation frequency less than 5 times the CPT linewidth, considering the modulation frequency as ; S62: Determine, based on the modulation frequency, that the maximum frequency deviation is ; S63: Divide each modulation period into M sampling points according to the modulation frequency and the maximum frequency deviation, with each 360° corresponding to a certain number of sampling points, so as to obtain the frequency deviation of each sampling point, and determine the frequency deviation values corresponding to all sampling points within one period based on the frequency deviation; S64: According to the frequency deviation value, convert each frequency deviation value into an array of parameter values corresponding to the radio frequency generator register at different times; the single-chip microcomputer queries the frequency deviation value in the array through the timer and writes the frequency deviation value into the radio frequency generator register to generate a discrete sinusoidal frequency modulation signal that meets the requirements; S65: According to the generated discrete sinusoidal frequency modulation signal, combined with the output power range, considering the signal power attenuation caused by the PCB circuit board wiring, set the power amplifier gain to ensure that the output carrier intensity meets the requirements of the CPT atomic clock.

7. A microwave modulation device for a CPT atomic clock based on discrete sine wave frequency modulation, characterized in that, Including: The first determination module is used to obtain the input frequency of the phase-locked loop chip, the doubler, the pre-R divider, the frequency multiplier, and the R divider, and determine the frequency of the frequency discrimination signal; The second determination module is used to determine the charge pump current value according to the frequency of the frequency discrimination signal; A third determination module, configured to determine a center frequency according to the charge pump current value by setting a numerator frequency division coefficient and a denominator frequency division coefficient and combining the discriminator signal frequency; A fourth determination module, configured to determine a VCO frequency band and a tuning range according to the center frequency; A fifth determination module, configured to determine a target bandwidth and a phase margin according to the VCO frequency band and the tuning range, design a third-order passive loop filter, filter the VCO output signal, and obtain a filtered carrier signal; A generation module, configured to determine a modulation frequency, determine a maximum frequency deviation, determine a frequency deviation value, and adjust a microwave power gain according to the carrier signal, so as to generate a frequency modulation signal; Wherein, obtaining the input frequency of the phase-locked loop chip, a doubler, a pre-stage R frequency divider, a frequency multiplier, and an R frequency divider, and determining the discriminator signal frequency includes: Obtain the input frequency of the phase-locked loop chip , the frequency multiplication factor OSC_2X of the doubler, the frequency division factor PLL_R_PRE of the pre-stage R frequency divider, the frequency multiplication factor MULT of the doubler, and the frequency division factor PLL_R of the R frequency divider to obtain the frequency discrimination signal frequency , where: 。 8. An electronic device, characterized in that, including: One or more processors; A memory, configured to store one or more programs; When the one or more programs are executed by the one or more processors, the one or more processors implement the method according to any one of claims 1-6.

9. A computer-readable storage medium having computer instructions stored thereon, characterized in that, When the instruction is executed by the processor, the steps of the method according to any one of claims 1-6 are implemented.

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