JP2010187273A - Rubidium atomic oscillator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To shorten a sweep time. <P>SOLUTION: A rubidium atomic oscillator 100 includes an atomic resonator 1 which generates a resonance signal RS based on a microwave MW, an amplifier 2 which amplifies the resonance signal RS which the atom resonator 1 generates, a low frequency oscillator 10 which outputs a phase modulation signal LW, a frequency control part 4 which outputs a control voltage VC based on the resonance signal RS and the phase modulation signal LW, a voltage controlled oscillator 8 of which the frequency of the oscillation signal OUT is controlled by a controlled voltage VC, a multiply phase modulation part 9 which outputs the microwave MW by multiplying and phase modulating the oscillation signal OUT based on the phase modulation signal LW, a memory part 27, and a control part 26 which causes the memory part 27 to memorize the control voltage VC as a synchronization voltage SV at a predetermined time interval TS when in a lock status that the frequency of the resonance signal RS is locked, and outputs a control signal S2 to the frequency control part 4 based on the control voltage VC and the synchronization voltage SV when in a non-locked status that the frequency of the resonance signal RS is not locked. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a rubidium atomic oscillator, and more particularly to a circuit technique for digitally generating a sweep voltage for pulling in a frequency when an unlocked state occurs.

  In recent years, digital networks such as communication networks and broadcast networks have progressed, and as a result, highly accurate and highly stable oscillators are indispensable as clock sources used to generate clock signals for transmission equipment and reference frequencies for broadcast stations. It has become a thing. As an oscillator that satisfies such a demand, a rubidium atomic oscillator having high oscillation frequency accuracy and stability is often used. In recent years, the demand for miniaturization of atomic oscillators has increased, and there has been a pressing need for miniaturization of the whole including an optical microwave unit (OMU).

The rubidium atomic oscillator requires a sweep circuit for pulling in the frequency when the power is turned on. That is, since the frequency band in which the optical absorption characteristic of atomic resonance occurs is very narrow compared to the variable range of the voltage controlled crystal oscillator (the variable range of the voltage controlled crystal oscillator is about 1 × 10 ⁻⁵ , the optical absorption characteristic of atomic resonance is There about 1 × 10 ^-7 generation frequency band), the conventional, the frequency of the voltage controlled crystal oscillator, the light absorption characteristics of the atomic resonance has been swept circuit is used to draw the frequency generated. Various techniques are used for the purpose of reducing the time (synchronization time) from when the power is turned on until the frequency is locked.

  For example, in Patent Document 1, the sweep speed of the sweep circuit is increased when the frequency of the voltage-controlled crystal oscillator is sufficiently away from the atomic resonance frequency, and the frequency of the voltage-controlled crystal oscillator reaches the vicinity of the atomic resonance frequency. A method for slowing the sweep speed of the sweep circuit is sometimes described. According to this technique, the sweep speed of the sweep circuit is reduced when the frequency of the voltage controlled crystal oscillator is close to the atomic resonance frequency, so that the frequency synchronization state can be detected accurately and quickly. This can speed up the frequency pull-in operation.

  Patent Document 2 discloses a technique for digitizing a sweep circuit and reducing the size of the sweep circuit. All of the conventional sweep circuits sweep a wide frequency range so as to cover the entire range of the oscillation frequency of the voltage controlled crystal oscillator.

Japanese Patent Laid-Open No. 2008-131122 (FIG. 1) JP 2008-131123 A (FIG. 1)

  However, in the conventional method, if the sweep speed of the sweep circuit is excessively increased, the detection of the frequency synchronization state becomes unstable. Therefore, there is a limit to increasing the sweep speed as a whole. In the conventional sweep circuit, There is a problem that a sweep time of at least several minutes is required and it is difficult to further shorten the synchronization time.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
An atomic resonator that generates a resonance signal based on a microwave; an amplifier that amplifies the resonance signal generated by the atomic resonator; a low-frequency oscillator that outputs a phase modulation signal; the resonance signal and the phase modulation signal; A frequency control unit that outputs a control voltage based on the control voltage, a voltage-controlled oscillator that controls the frequency of the oscillation signal based on the control voltage, and the microwave that is multiplied and phase-modulated based on the phase modulation signal. The control voltage is stored as a synchronization voltage in the storage unit at a predetermined time interval when the frequency phase of the multiplying phase modulation unit, the storage unit, and the frequency of the resonance signal are locked, and the resonance signal frequency is A control unit that outputs a control signal to the frequency control unit based on the control voltage and the synchronization voltage in an unlocked and unlocked state, and the frequency Control unit, the including the sweep voltage data generating unit that generates based sweep voltage data for retraction of frequency of the resonant signal in the control signal when the unlocked state, rubidium atomic oscillator, characterized in that.

  According to this configuration, since the sweep range of the control voltage of the voltage controlled oscillator is limited to the vicinity of the synchronization voltage, the sweep time can be shortened when the power is turned on, and the time from the start of the power supply to the synchronization is reduced. It can be shortened.

[Application Example 2]
In the rubidium atomic oscillator described above, the sweep voltage data generation unit includes a positive voltage data generation unit that generates positive voltage data synchronized with the phase modulation signal for increasing the control voltage, and a voltage drop for the control voltage. A negative voltage data generation unit that generates negative voltage data that is inverted and synchronized with the phase modulation signal for switching, and the positive voltage data or the negative voltage data is switched based on the control signal and is output as the sweep voltage data. A rubidium atomic oscillator characterized by comprising:

  According to this configuration, since the sweep range of the control voltage of the voltage controlled oscillator is limited to the vicinity of the synchronization voltage, the sweep time can be shortened when the power is turned on, and the time from the start of the power supply to the synchronization is reduced. It can be shortened.

[Application Example 3]
In the rubidium atomic oscillator described above, the control unit is configured to output the positive voltage during a period until the voltage value of the control voltage rises from a first voltage lower than the synchronization voltage to a second voltage higher than the synchronization voltage. The control signal for selecting voltage data is output, and the control signal for selecting the negative voltage data is output during a period until the voltage value of the control voltage drops from the second voltage to the first voltage. A rubidium atomic oscillator characterized by that.

  According to this configuration, since the sweep range of the control voltage of the voltage controlled oscillator is limited to the vicinity of the synchronization voltage, the sweep time can be shortened when the power is turned on, and the time from the start of the power supply to the synchronization is reduced. It can be shortened.

[Application Example 4]
In the rubidium atomic oscillator described above, the frequency controller includes an A / D converter that outputs a digital signal obtained by converting the resonance signal into a digital signal, and whether the locked state or the unlocked state is based on the digital signal. A state determination unit that outputs a determination signal that has been determined, a bandpass filter that outputs filtered data obtained by filtering the frequency component of the phase modulation signal included in the digital signal, and the determination signal when the determination signal is in the locked state. A second switch circuit that outputs filtered data, and outputs the sweep voltage data when the determination signal is in the unlocked state; and outputs an analog signal obtained by converting the output of the second switch circuit to analog D A phase detector that generates a frequency control signal by phase-detecting the analog signal and the phase modulation signal; Including an integrating circuit for generating the control voltage by integrating processing said frequency control signal, rubidium atomic oscillator, characterized in that.

  According to this configuration, since the sweep range of the control voltage of the voltage controlled oscillator is limited to the vicinity of the synchronization voltage, the sweep time can be shortened when the power is turned on, and the time from the start of the power supply to the synchronization is reduced. It can be shortened.

The block diagram which shows the structure of the rubidium atomic oscillator which concerns on 1st Embodiment. The timing diagram which shows operation | movement of the conventional rubidium atomic oscillator. The timing diagram which shows the operation | movement of the rubidium atomic oscillator which concerns on 1st Embodiment. The block diagram which shows the structure of the control part of the rubidium atomic oscillator which concerns on the modification 1. FIG.

  Hereinafter, embodiments of a rubidium atomic oscillator will be described with reference to the drawings.

(First embodiment)
<Configuration of rubidium atomic oscillator>
First, the configuration of the rubidium atomic oscillator according to the first embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of a rubidium atomic oscillator according to the first embodiment.

  As shown in FIG. 1, a rubidium atomic oscillator 100 includes an atomic resonator (OMU) 1, an amplifier (Amp) 2, a low-frequency oscillator 10, a frequency controller 4, and a voltage-controlled oscillator. (VCXO: Voltage Controlled Xtal Oscillator) 8, multiplying phase modulator 9, EEPROM (Electrically Erasable and Programmable Read Only Memory) 27, A / D converter (Analog Digital Converter) 25, timer 15 And the control unit 26.

  The OMU 1 is generally composed of a rubidium (Rb) lamp, an Rb gas cell, and a photodetector, and irradiates the Rb gas cell resonated with the microwave MW with the resonance light of the Rb lamp and is output from the Rb gas cell. Is detected by a photodetector and a resonance signal RS is output. Amp2 amplifies the resonance signal RS and outputs an amplified signal AS. The frequency control unit 4 outputs a control voltage VC based on the amplified signal AS and the phase modulation signal LW output from the low frequency oscillator 10. In the VCXO 8, the frequency of the oscillation signal OUT is controlled based on the control voltage VC. The multiplication phase modulation unit 9 multiplies and phase modulates the oscillation signal OUT based on the phase modulation signal LW and outputs a microwave MW. The A / D converter 25 converts the control voltage VC into a digital signal VD and outputs the digital signal VD to the controller 26.

  The control unit 26 synchronizes the synchronization voltage SV to the EEPROM 27 at a time interval TS that is a predetermined time interval at which the timer 15 outputs a digital signal VD obtained by converting the control voltage VC to digital when the frequency of the resonance signal RS is locked. And the control signal S2 is output to the frequency controller 4 based on the digital signal VD and the synchronization voltage SV when the frequency of the resonance signal RS is not locked.

  The frequency control unit 4 includes a sweep voltage data generation unit 12, an A / D conversion unit 3, a state determination unit 11, a band pass filter 13, a switch circuit 14 that is a second switch circuit, and a D / A conversion. The unit 5 includes a phase detector 6 and an integrating circuit 7.

  The sweep voltage data generation unit 12 generates the sweep voltage data SD for pulling in the frequency of the resonance signal RS in the unlocked state based on the control signal S2. The A / D converter 3 converts the amplified signal AS into a digital signal DS. The state determination unit 11 outputs a determination signal S1 that determines whether the state is locked or unlocked based on the digital signal DS. For example, the determination signal S1 is set to the H level in the locked state and to the L level in the unlocked state. The band pass filter 13 outputs filtered data BD obtained by filtering the frequency component of the phase modulation signal LW included in the digital signal DS.

  The switch circuit 14 outputs the filtered data BD (a terminal and c terminal are connected) when the determination signal S1 is in the locked state (H level), and the sweep voltage when the determination signal S1 is in the unlocked state (L level). Data SD is output (b terminal and c terminal are connected). The D / A converter 5 outputs an analog signal AD obtained by converting the output of the switch circuit 14 to analog. The phase detector 6 detects the phase of the analog signal AD and the phase modulation signal LW and generates a frequency control signal FS. The integrating circuit 7 integrates the frequency control signal FS to generate a control voltage VC.

  The sweep voltage data generation unit 12 includes a positive voltage data generation unit 19, a negative voltage data generation unit 20, and a switch circuit 21 that is a first switch circuit.

  The positive voltage data generation unit 19 generates positive voltage data PD synchronized with the phase modulation signal LW for increasing the control voltage VC. The negative voltage data generation unit 20 generates negative voltage data MD that is inverted and synchronized with the phase modulation signal LW for decreasing the control voltage VC. The switch circuit 21 switches the positive voltage data PD (a terminal) or the negative voltage data MD (b terminal) on the basis of the control signal S2, and outputs it as the sweep voltage data SD (from the c terminal). For example, if the positive voltage data PD is output as the sweep voltage data SD when the control signal S2 is at the H level, the a terminal and the c terminal of the switch circuit 21 are connected, and the negative value is obtained when the control signal S2 is at the L level. If the voltage data MD is output as the sweep voltage data SD, the b terminal and the c terminal of the switch circuit 21 are connected.

  The state determination unit 11 includes a bandpass filter 16, a level detection unit 17, and a determination unit 18. The band pass filter 16 outputs filtered data B2 obtained by filtering the frequency component of the phase modulation signal LW included in the digital signal DS. The level detection unit 17 outputs a level detection signal LV from the filtered data B2. The determination unit 18 determines whether or not the level detection signal LV exceeds a predetermined value (whether or not the resonance signal RS is in a locked state), and outputs a determination signal S1.

<Operation of rubidium atomic oscillator>
Next, the operation of the rubidium atomic oscillator according to the first embodiment will be described with reference to FIGS. FIG. 2 is a timing diagram showing the operation of a conventional rubidium atomic oscillator. FIG. 3 is a timing chart showing the operation of the rubidium atomic oscillator according to the first embodiment.

As shown in FIG. 2, in the conventional rubidium atomic oscillator, the control signal S <b> 2 is switched based on the time interval TS output from the timer 15. That is, the control signal S2 is switched to the H level during the period from the time t0 to the time t1 after the time interval TS, and the control signal S2 is switched to the L level during the period from the time t1 to the time t2 after the time interval TS. . The positive voltage data generator 19 outputs the positive voltage data PD in synchronization with the phase modulation signal LW between the voltages V2 and V1, and the negative voltage data generator 20 phase modulates the negative voltage data MD between the voltages V2 and V3. When output in synchronization with the signal LW, the sweep voltage data SD becomes the positive voltage data PD during the period from the time t0 to the time t1, and becomes the negative voltage data MD during the period from the time t1 to the time t2. Along with the sweep voltage data SD, the control voltage VC rises and falls between the voltages Vb to Va.
Here, although the sweep voltage data SD is digital data, it is displayed as an analog voltage in FIG. 2 for convenience of explanation.

  In the rubidium atomic oscillator 100 according to the first embodiment, the control unit 26 switches the control signal S <b> 2 based on the digital signal VD obtained by converting the control voltage VC into digital and the synchronous voltage SV stored in the EEPROM 27. When the lower limit voltage that is the first voltage lower than the synchronization voltage SV is SV−ΔV and the upper limit voltage that is the second voltage higher than the synchronization voltage SV is SV + ΔV, the control unit 26 determines that the digital signal VD is the lower limit voltage SV. The control signal S2 is set to the H level during the period when the voltage rises from -ΔV to the upper limit voltage SV + ΔV, and the control signal S2 is set to the L level during the period when the digital signal VD falls from the upper limit voltage SV + ΔV to the lower limit voltage SV-ΔV.

  As shown in FIG. 3, the control signal S2 is at the H level during the period from the time point t0 to the time point t1 when the digital signal VD reaches the upper limit voltage SV + ΔV, and from the time point t1 to the time point t2 when the digital signal VD reaches the lower limit voltage SV−ΔV. During the period, the control signal S2 is switched to the L level. The time intervals between time points t0 to t1 and t1 to t2 in FIG. 3 are shorter than the time interval TS output by the timer 15.

  According to the present embodiment described above, the following effects can be obtained.

  In this embodiment, the sweep range of the control voltage VC of the VCXO 8 is limited to the vicinity of the synchronous voltage SV, so that the sweep time can be shortened at the time of power-on and the time from power-on to synchronization is shortened. can do.

  Although the embodiment of the rubidium atomic oscillator has been described above, the present invention is not limited to such an embodiment, and can be implemented in various forms without departing from the spirit of the invention. Hereinafter, a modification will be described.

  (Modification 1) Modification 1 of the rubidium atomic oscillator will be described. FIG. 4 is a block diagram illustrating a configuration of a control unit of the rubidium atomic oscillator according to the first modification. As shown in FIG. 4, the control unit 26 may determine whether the locked state or the unlocked state is based on the alarm signal VX from the power supply monitoring circuit 50 that monitors the fluctuation of the power supply voltage VDD. When the power supply voltage VDD starts to decrease from the ON state to the OFF state (0 V), the power supply monitoring circuit 50 outputs an alarm signal VX to the control unit 26. From this time point, the control unit 26 writes the digital signal VD as the synchronization voltage SV in the EEPROM 27. Next, when the power supply voltage VDD rises from the OFF state to the ON state, the control unit 26 can output the control signal S2 based on the synchronous voltage SV stored in the EEPROM 27, so that the sweep time can be shortened.

  DESCRIPTION OF SYMBOLS 1 ... OMU, 2 ... Amp, 3 ... A / D conversion part, 4 ... Frequency control part, 5 ... D / A conversion part, 6 ... Phase detector, 7 ... Integration circuit, 8 ... VCXO, 9 ... Multiplication phase modulation , 10 ... low frequency oscillator, 11 ... state determination unit, 12 ... sweep voltage data generation unit, 13 ... band pass filter, 14 ... switch circuit, 15 ... timer, 16 ... band pass filter, 17 ... level detection unit, 18 DESCRIPTION OF SYMBOLS ... Determination part, 19 ... Positive voltage data generation part, 20 ... Negative voltage data generation part, 21 ... Switch circuit, 25 ... A / D conversion part, 26 ... Control part, 27 ... Memory | storage part, 50 ... Power supply monitoring circuit, 100 … Rubidium atomic oscillator.

Claims (4)

An atomic resonator that generates a resonance signal based on a microwave;
An amplifier for amplifying the resonance signal generated by the atomic resonator;
A low-frequency oscillator that outputs a phase-modulated signal;
A frequency controller that outputs a control voltage based on the resonance signal and the phase modulation signal;
A voltage controlled oscillator in which the frequency of the oscillation signal is controlled based on the control voltage;
A multiplying phase modulation unit for multiplying and phase modulating the oscillation signal based on the phase modulation signal and outputting the microwave;
A storage unit;
The control voltage is stored as a synchronization voltage in the storage unit at a predetermined time interval when the resonance signal frequency is locked, and the control voltage is stored when the resonance signal frequency is not locked. And a control unit that outputs a control signal to the frequency control unit based on the synchronization voltage,
Including
The frequency control unit includes a sweep voltage data generation unit that generates sweep voltage data for pulling in a frequency of the resonance signal based on the control signal in the unlocked state.
A rubidium atomic oscillator characterized by that. The rubidium atomic oscillator according to claim 1,
The sweep voltage data generator is
A positive voltage data generation unit that generates positive voltage data synchronized with the phase modulation signal for increasing the control voltage;
A negative voltage data generation unit that generates negative voltage data that is inverted and synchronized with the phase modulation signal for lowering the control voltage;
A first switch circuit that switches the positive voltage data or the negative voltage data based on the control signal and outputs the data as the sweep voltage data;
including,
A rubidium atomic oscillator characterized by that. The rubidium atomic oscillator according to claim 1 or 2,
The controller is
Outputting the control signal for selecting the positive voltage data in a period until the voltage value of the control voltage rises from a first voltage lower than the synchronous voltage to a second voltage higher than the synchronous voltage;
Outputting the control signal for selecting the negative voltage data during a period until the voltage value of the control voltage drops from the second voltage to the first voltage;
A rubidium atomic oscillator characterized by that. The rubidium atomic oscillator according to any one of claims 1 to 3,
The frequency control unit
An A / D converter that outputs a digital signal obtained by converting the resonance signal into a digital signal;
A state determination unit that outputs a determination signal that determines whether the locked state or the unlocked state based on the digital signal;
A band pass filter that outputs filtered data obtained by filtering the frequency component of the phase modulation signal included in the digital signal;
A second switch circuit that outputs the filtered data when the determination signal is in the locked state, and outputs the sweep voltage data when the determination signal is in the unlocked state;
A D / A converter for outputting an analog signal obtained by converting the output of the second switch circuit into an analog;
A phase detector for detecting a phase of the analog signal and the phase modulation signal to generate a frequency control signal;
An integration circuit that integrates the frequency control signal to generate the control voltage;
including,
A rubidium atomic oscillator characterized by that.

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