JP4360385B2 - Atomic oscillator - Google Patents

Description

The present invention relates to a phase modulator and a rubidium atomic oscillator, and more particularly to a circuit configuration that improves the linearity of the phase shift amount of the phase modulator and suppresses output level fluctuations.

In recent years, digital networks such as communication networks and broadcasting networks have been developed, and accordingly, a highly accurate and highly stable oscillator is required as a clock source used for generating clock signals for transmission devices and reference frequencies for broadcasting stations. It has become indispensable. As an oscillator that meets such requirements,
Rubidium atomic oscillators with high oscillation frequency accuracy and stability are often used. In order to lock the rubidium atomic resonance frequency, this rubidium atomic oscillator uses a phase modulator that modulates the phase of the microwave with a low frequency in order to detect whether the resonance frequency is shifted or coincident. ing.

FIG. 4 is a circuit diagram showing an example of a conventional phase modulator.
This phase modulator 100 has an inductance L connected to the collector of the transistor TR1.
In parallel, a varactor circuit is connected in parallel, the cathode DC bias voltage of the varactor diode RC1 is fixed by the resistor R4, and the modulation wave 111Hz is superimposed via the C7 on the anode DC bias voltage determined by the resistance voltage division of R9 and RX1. Thus, phase modulation is performed, and the modulation degree is adjusted by adjusting the level of the modulated wave with RV1.

FIG. 5 is a diagram showing the amplitude and phase characteristics of the phase modulator 100. The vertical axis shows the amplitude and phase,
Frequency is shown on the horizontal axis. In this figure, the phase characteristic is indicated by reference numeral 50, and the Pass characteristic is indicated by reference numeral 51.
It shows with. For example, when the cathode voltage of the varactor diode RC1 is changed from 3.5 V to 4.5 V, the phase change width at 10 MHz changes from +8 degrees to −12 degrees (between a and b),
It can be seen that the amplitude fluctuation at that time fluctuates between 480 mV and 440 mV (about 0.8 dB) (between c and d).

Further, as a conventional technique, Patent Document 1 discloses that an input signal and a modulation signal are divided into two parts, each having 2
A phase modulator that combines power after modulation by two phase modulation circuits is disclosed.
Japanese Patent Application Laid-Open No. H8-2222956

However, in the phase modulation signal by the conventional modulator shown in FIG. 4, the influence of the level fluctuation (between c and d) due to deviation from the tuning point of the tank circuit remains as an amplitude modulation component, and this amplitude modulation component is removed. Such a limiter circuit is required in the subsequent stage. Further, there is a problem that adjustment of the circuit is required and adjustment cost is required.

Further, the conventional technique disclosed in Patent Document 1 obtains phase modulation characteristics by canceling amplitude modulation components generated in each phase modulation circuit when power is combined after modulation by two phase modulation circuits. As a result, two phase modulation circuits and a synthesis circuit are required, and the circuit configuration is complicated, resulting in a problem that the circuit scale increases and the component cost increases.

In view of such a problem, the present invention uses a quadrature hybrid to connect a variable reactance element to a phase advance terminal and a phase delay terminal, thereby modulating to a desired phase and minimizing fluctuations in output level. An object is to provide a suppressed phase modulator.

In order to solve such a problem, the present invention provides a microwave resonator that resonates with the resonance frequency of an atom used in an atomic gas of an atomic oscillator, a radiation antenna that radiates a microwave into the microwave resonator, an atom An optical microwave unit having a photosensor for detecting the intensity of light transmitted through the gas, a phase discriminator that receives a signal output from the photosensor, and a voltage output from the phase discriminator. A voltage-controlled oscillator whose oscillation frequency is controlled, a phase modulator, a frequency multiplier that multiplies the output signal of the phase modulator, and a micro wave that is radiated from the radiating antenna that receives the output signal of the frequency multiplier An intermodulation unit for generating a wave, wherein the phase modulator has a quadreach hybrid, and the quadrechet hybrid is a phase advance terminal A phase delay terminal, an output terminal from which the output signal of the phase modulator is output, and an input terminal that receives supply of a signal from the voltage controlled oscillator, and the phase advance terminal includes the voltage controlled oscillator. A signal whose phase is advanced with respect to the phase of the output signal is generated, and a signal whose phase is delayed with respect to the phase of the output signal of the voltage controlled oscillator is generated at the slow phase terminal. In order to modulate the output signal of the oscillator, a first variable reactance element whose reactance value is controlled by voltage is connected to the phase advance terminal, and a second variable reactance element whose reactance value is controlled by voltage is connected to the slow phase It is connected to the terminal.

  A microwave resonator that resonates at the resonance frequency of the rubidium atom; a radiation antenna that radiates microwaves into the microwave resonator; and a photosensor that detects the intensity of light transmitted through the rubidium gas. An optical microwave unit; a phase discriminator that receives supply of a signal output from the photosensor; a voltage-controlled oscillator whose oscillation frequency is controlled based on a voltage output from the phase discriminator; and a phase modulator; A frequency multiplier for multiplying the output signal of the phase modulator; and a cross-modulator for generating a microwave radiated from the radiation antenna, to which the output signal of the frequency multiplier is input. The modulator has a quadlet hybrid, and the quadlet hybrid outputs a phase advance terminal, a phase delay terminal, and an output signal of the phase modulator. Output signal and an input terminal that receives supply of a signal from the voltage controlled oscillator, the phase advance terminal generates a signal whose phase is advanced with respect to the phase of the output signal of the voltage controlled oscillator, A signal whose phase is delayed with respect to the phase of the output signal of the voltage controlled oscillator is generated at the slow phase terminal, and the reactance value is controlled by the voltage in order to modulate the output signal of the voltage controlled oscillator. The first variable reactance element is connected to the phase advance terminal, and the second variable reactance element whose reactance value is controlled by voltage is connected to the slow phase terminal.

  Quad Recha Hybrid is a Magic T and Branched used in the microwave band.
-It gives the same operation as a hybrid and has 4 ports. This property is
When a signal is input from the power terminal, power appears at the leading and lagging terminals. At this time, two terminals
The phase is advanced at the leading terminal, delayed at the slow terminal, and a phase difference of 90 degrees between the two terminals. So
As a result, no output appears at the output terminal. In the present invention, this property is utilized to advance the phase advance terminal and the delay time.
A variable reactance element is connected to the phase terminal, and signals with different phases are output to the output terminal
It is. This allows a phase modulator that suppresses fluctuations in output level with a simple circuit configuration.
Can be provided.

  Further, in addition to the above feature, the quadlet hybrid hybrid connects an input terminal of the quadlet hybrid and the phase advance terminal via a first capacitor, and the input terminal and the phase lag terminal are connected to each other by a first capacitor. The phase advance terminal and the output terminal of the quadrature hybrid are connected via a second inductance, and the phase delay terminal and the output terminal are connected via a second capacitor. It has the structure.
  According to the present invention, a small and low-priced rubidium atomic oscillator can be provided by applying a phase modulator that suppresses fluctuations in output level and has a small circuit scale.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .

FIG. 1 is a circuit diagram showing an example of a phase modulator of the present invention. This phase modulator 11 is 10M
An oscillation source 24 that oscillates an oscillation signal VI of Hz, an input terminal a that receives the oscillation signal VI oscillated from the oscillation source 24, a phase advance terminal c that advances in phase with respect to the phase of the oscillation signal VI, and an oscillation signal A quadrature hybrid 30 having a slow terminal b whose phase is delayed with respect to the phase of VI, and an output terminal d that combines and outputs the phase appearing at the fast terminal c and the phase appearing at the slow terminal b; Variable capacitance element (variable reactance element) C connected between the slow phase terminal b and the ground
3 and a variable capacitance element (variable reactance element) C4 connected between the phase advance terminal c and the ground.
And an output terminal d. The quadreach hybrid 30 includes two inductances L1 and L2 wound around the core 31 in the same phase, and an inductance L1.
, A capacitor C1 connected between one terminal 25, 27 of L2, and an inductance L1,
The capacitor C2 is connected between the other terminals 26 and 28 of L2, the terminal 25 is connected to the input terminal a, the terminal 27 is connected to the leading terminal c, and the terminal 26 is connected to the slow terminal b. The terminal 28 is connected to the output terminal d. Then, the oscillation signal VI is input to the input terminal a, and the variable capacitance elements C4 and C3 are connected to the fast terminal c and the slow terminal b, respectively, thereby modulating the phase of the oscillation signal output to the output terminal d. It is.

Here, the operation of the quad-recha hybrid is publicly known, but an outline will be described. Quadrecha Hybrid (also called 90-degree hybrid) gives the same operation as Magic T and Branched Hybrid used in the microwave band, and has four ports. This property is that when a signal is input from the input terminal a, power appears at the phase advance terminal c and the phase delay terminal b. At this time, the phase of the two terminals is advanced 45 degrees at the leading terminal c, delayed by 45 degrees at the slow terminal b, and a phase difference of 90 degrees between the two terminals. Basically, the phase difference is ± 45 degrees with respect to the input terminal a. No output appears at the output terminal d. In the present invention, utilizing this property, variable capacitance elements C4 and C3 are connected to the phase advance terminal c and the phase delay terminal b, and signals having different phases are output to the output terminal d. Thereby, it is possible to provide a phase modulator that suppresses fluctuations in the output level with a simple circuit configuration.

In the present invention, the phase of the oscillation signal output to the output terminal d is modulated by changing the capacitance by controlling the terminal voltages of the variable capacitance elements C4 and C3. That is, various variable reactance elements can be considered, but a variable capacitance element is optimal in view of ease of control. The variable capacitance element is an element whose capacitance value changes due to a potential difference between terminals, and the capacitance can be changed within a predetermined range by an external control voltage. Thereby, the phase of the signal can be easily modulated by changing the control voltage from the outside. Note that a varactor diode is preferably used as the variable capacitance element.

FIG. 2 is a diagram showing a simulation result of phase modulation characteristics when a varactor diode is connected to the variable capacitance element of the phase modulator of the present invention. The vertical axis (left) is the amount of phase shift (phase change width) (de
g), the vertical axis (right) represents the output level (mV) of the output terminal d, and the horizontal axis represents the control voltage (V) of the varactor diode. A line segment 21 represents the amount of phase shift, and a line segment 22 represents the output level. As can be seen from this figure, the phase shift amount 21 changes substantially linearly when the control voltage is changed from 1V to 6V. The output level 22 at that time is
It can be seen that it is substantially flat around 500 (mV), and there is almost no level fluctuation.
That is, it can be seen that the phase shift amount 21 shows very good linearity between the actual use areas A and B, and the output level 22 at that time hardly fluctuates around 500 (mV). .

FIG. 3 is a block diagram showing a schematic configuration of the rubidium atomic oscillator of the present invention. The rubidium atomic oscillator 50 includes a lamp excitation unit 1 for lighting a rubidium lamp (hereinafter referred to as Rb lamp) 5, an Rb lamp 5 for exciting rubidium atoms in a rubidium gas cell (hereinafter referred to as Rb gas cell) 6, Rb gas cell 6 encapsulating rubidium atoms, microwave resonator 3 adjusted to resonate with the resonance frequency of rubidium atoms in Rb gas cell 6, and radiation antenna 4 for radiating microwaves to microwave resonator 3 , A photosensor 7 for detecting the intensity of light transmitted through the Rb gas cell 6, a phase discriminator 10 for discriminating the phase of the low frequency amplitude modulation signal appearing in Amp 9, and a predetermined frequency based on the voltage of the phase discriminator 10. A voltage-controlled oscillator 13 that oscillates, a phase modulator 11 that modulates the phase of a microwave with a low frequency, and a voltage-controlled oscillator 13 A frequency multiplier 12 that multiplies an oscillation signal into a microwave, and a multi-modulator 14 that modulates the multiplied oscillation signal and generates a frequency signal that is the same as the resonance frequency of the rubidium atom. . A unit composed of the Rb lamp 5, the microwave resonator 3, and the photosensor 7 is referred to as an optical microwave unit 8. Further, the intermodulation unit 14
Is connected to the radiating antenna 4.

Next, since the operation of the rubidium atomic oscillator of the present invention is known, the description thereof is omitted here, but the phase modulator 11 which is the main component of the present invention is a phase modulation composed of each component of FIG. It is a vessel. That is, in order to lock the rubidium atomic resonance frequency, the rubidium atomic oscillator 50 has a phase modulator 11 that modulates the phase of the microwave with a low frequency in order to detect whether the resonance frequency is shifted or coincident. Is required. In the rubidium atomic oscillator 50 of the present invention, the phase modulator of the present invention is used for the phase modulator 11. As a result, it is possible to modulate to a desired phase and minimize the fluctuation of the output level.

It is a circuit diagram which shows an example of the phase modulator of this invention. It is a figure of the simulation result of the phase modulation characteristic at the time of connecting a varactor diode to the phase modulator of this invention. It is a block diagram which shows schematic structure of the rubidium atomic oscillator of this invention. It is a circuit diagram which shows an example of the conventional phase modulator. It is a figure which shows an example of the amplitude of a conventional phase modulator, and a phase characteristic.

Explanation of symbols

11 Phase modulator, 24 Oscillation source, 30 Quadrature hybrid, a input terminal, b slow phase terminal, c fast phase terminal, d output terminal, R1, R2, R3, R4 resistance, C1
, C2 capacitor, C3, C4 variable capacitance element

Claims (3)

  A microwave resonator that resonates at the resonance frequency of an atom used in an atomic gas of an atomic oscillator, a radiation antenna that radiates microwaves into the microwave resonator, and a photo that detects the intensity of light transmitted through the atomic gas An optical microwave unit having a sensor;
A phase discriminator for receiving a signal output from the photosensor;
A voltage-controlled oscillator whose oscillation frequency is controlled based on the voltage output by the phase discriminator;
A phase modulator;
A frequency multiplier for multiplying the output signal of the phase modulator;
An output signal of the frequency multiplication unit is input, and a cross modulation unit for generating a microwave radiated from the radiation antenna, and
The phase modulator has a quadrature hybrid;
The quadrech hybrid includes a phase advance terminal, a phase delay terminal, an output terminal from which an output signal of the phase modulator is output, and an input terminal that receives a signal supplied from the voltage controlled oscillator,
A signal whose phase is advanced with respect to the phase of the output signal of the voltage controlled oscillator is generated at the phase advance terminal, and a phase is delayed with respect to the phase of the output signal of the voltage controlled oscillator at the slow phase terminal. Signal is generated,
A first variable reactance element whose reactance value is controlled by a voltage to modulate an output signal of the voltage controlled oscillator is connected to the phase advance terminal, and a second variable reactance element whose reactance value is controlled by a voltage is connected An atomic oscillator connected to the slow phase terminal.   An optical microwave comprising a microwave resonator that resonates at a resonance frequency of rubidium atoms, a radiation antenna that radiates microwaves into the microwave resonator, and a photosensor that detects the intensity of light transmitted through the rubidium gas. Wave unit,
A phase discriminator for receiving a signal output from the photosensor;
A voltage-controlled oscillator whose oscillation frequency is controlled based on the voltage output by the phase discriminator;
A phase modulator;
A frequency multiplier for multiplying the output signal of the phase modulator;
An output signal of the frequency multiplication unit is input, and a cross modulation unit for generating a microwave radiated from the radiation antenna, and
The phase modulator has a quadrature hybrid;
The quadrech hybrid includes a phase advance terminal, a phase delay terminal, an output terminal from which an output signal of the phase modulator is output, and an input terminal that receives a signal supplied from the voltage controlled oscillator,
A signal whose phase is advanced with respect to the phase of the output signal of the voltage controlled oscillator is generated at the phase advance terminal, and a phase is delayed with respect to the phase of the output signal of the voltage controlled oscillator at the slow phase terminal. Signal is generated,
A first variable reactance element whose reactance value is controlled by a voltage to modulate an output signal of the voltage controlled oscillator is connected to the phase advance terminal, and a second variable reactance element whose reactance value is controlled by a voltage is connected An atomic oscillator connected to the slow phase terminal.   The quadlet hybrid is connected to the input terminal of the quadlet hybrid and the phase advance terminal via a first capacitor, and the input terminal and the phase delay terminal are connected via a first inductance, The phase advance terminal and the output terminal of the quadlet hybrid are connected via a second inductance, and the phase delay terminal and the output terminal are connected via a second capacitor. The atomic oscillator according to claim 1 or 2.

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