A heating system and device for a CPT atomic clock

Abstract

The present invention discloses a heating system for a CPT atomic clock, which includes a third resistor R3, a fourth resistor R4, a thermistor, an operational amplifier, a triode, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8; one end of the third resistor R3 is connected to a power supply chip, and the other end is connected to the collector of the triode. The fourth resistor R4 is connected in parallel with the third resistor R3; the positive input terminal of the operational amplifier is used to input a reference voltage; the output terminal of the operational amplifier is connected to the base of the triode; the first end of the sixth resistor R6 is connected to the emitter of the triode, and the first ends of the eighth resistor R8 and the seventh resistor R7 are both connected to the second end of the sixth resistor R6. The second end of the eighth resistor is connected to the negative input terminal of the operational amplifier, and the second end of the seventh resistor R7 is grounded; one end of the thermistor is connected to a first constant voltage source, and the other end is connected to the negative input terminal of the operational amplifier. The integrated temperature heating circuit adopted enables the VCSEL and the vapor bubble to be heated simultaneously, which is convenient for adjustment and control.

Description

Technical Field

[0001] The present invention relates to the technical field of atomic clocks, and particularly relates to a heating system and device for a CPT atomic clock. Background Art

[0002] In the continuous exploration of microscopic particles by humans, in 1976, Alzetta et al. discovered the phenomenon of Coherent Population Trapping (CPT), which made the miniaturization and microminiaturization of atomic clocks possible. In recent years, with the development of science and technology, more and more industries and fields require accurate and precise clock information, such as transportation, real-time positioning, real-time navigation, real-time communication, and the military field.

[0003] Vertical Cavity Surface Emitting Laser (VCSEL) is a new type of laser, and its main feature is that it emits light perpendicular to the surface. The output wavelength of the laser is affected by the ambient temperature and the operating current. Keeping the temperature constant and changing the laser current, the laser wavelength increases as the current increases. Keeping the laser current constant, as the temperature rises, the output wavelength of the laser increases. In order to obtain the required wavelength, a stable operating temperature must be provided for the laser.

[0004] The vapor bubble is the core component of the physical part of the atomic clock, and its function is to provide a stable and reliable atomic vapor. At room temperature, the alkali metal is in a liquid state in the vapor bubble, and the liquid atoms cannot interact with the laser field. By heating, the alkali metal is vaporized, and the vaporized atoms fill the entire vapor bubble, facilitating the full interaction between the atoms and the light field.

[0005] Researchers at Peking University mentioned in the paper "Experimental Research on Miniaturized Coherent Population Trapping Atomic Clocks" and the existing patent 201811585192.1 "A VCSEL Temperature Point Scanning Method and System for CPT Atomic Clocks" a method of separating the laser from the vapor bubble for temperature control. The laser uses the thyristor current flow integrated on the VCSEL to control the temperature. When the current is positive, heating is started, and when the current is negative, temperature cooling is started. Although this method can control the temperature change of the VCSEL within a very small range, the range of stable temperature control that can be achieved by this method is small, and the laser needs to be isolated from the vapor bubble. During the isolation process, additional heat insulation materials need to be added, which will greatly increase the volume and assembly difficulty of the physical packaging of the atomic clock. In addition, the laser and the vapor bubble require two independent heating circuits, and the increase in components will also bring difficulties to the PCB design and increase the workload of writing control code. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a heating system and device for a CPT atomic clock, and the integrated temperature heating circuit adopted by it enables the simultaneous heating of the VCSEL and the vapor bubble, which is convenient for adjustment and control.

[0007] To solve the above technical problem, the present invention provides a heating system and device for a CPT atomic clock, including a third resistor R3, a fourth resistor R4, a thermistor, an operational amplifier, a triode, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8;

[0008] One end of the third resistor R3 is connected to a power supply chip, and the other end is connected to the collector of the triode. The fourth resistor R4 is connected in parallel with the third resistor R3; the third resistor R3 and the fourth resistor R4 are heating resistors;

[0009] The positive input terminal of the operational amplifier is used to input a reference voltage; the output terminal of the operational amplifier is connected to the base of the triode; the first end of the sixth resistor R6 is connected to the emitter of the triode, the first ends of the eighth resistor R8 and the seventh resistor R7 are both connected to the second end of the sixth resistor R6, the second end of the eighth resistor is connected to the negative input terminal of the operational amplifier, and the second end of the seventh resistor R7 is grounded;

[0010] One end of the thermistor is connected to a first constant voltage source, and the other end is connected to the negative input terminal of the operational amplifier. The resistance value of the thermistor and the current temperature value are obtained by collecting the voltage across the eighth resistor.

[0011] Preferably, it further includes a microcontroller unit MCU for reading the current temperature value.

[0012] Preferably, it further includes a coarse and fine adjustment unit for adjusting the reference voltage at the positive input terminal of the operational amplifier. The coarse and fine adjustment unit includes a first resistor R1 and a second resistor R2. The resistance value of the first resistor R1 is greater than that of the second resistor R2. The microcontroller unit MCU includes a first digital-to-analog output terminal and a second digital-to-analog output terminal. The first digital-to-analog output terminal is connected to the first end of the first resistor R1, the second digital-to-analog output terminal is connected to the first end of the second resistor R2, and the second ends of the first resistor and the second resistor are both connected to the positive input terminal of the operational amplifier.

[0013] Preferably, the resistance value of the first resistor R1 is n times that of the second resistor R2, and the value of n ranges from 1000 to 4000.

[0014] Preferably, the microcontroller unit MCU includes a first analog-to-digital input terminal and a second analog-to-digital input terminal, and the first analog-to-digital input terminal and the second analog-to-digital input terminal are arranged at both ends of the eighth resistor R8.

[0015] Preferably, a filter capacitor C1 is connected in parallel across the eighth resistor.

[0016] Preferably, a fifth resistor R5 is connected between the output terminal of the operational amplifier and the base of the triode.

[0017] Preferably, the thermistor is a resistor with a negative temperature coefficient.

[0018] Preferably, both the third resistor R3 and the fourth resistor R4 are ITO thin films.

[0019] A heating device for a CPT atomic clock, based on the above-mentioned heating system of the CPT atomic clock, includes a first encapsulation shell, and the third resistor R3, the fourth resistor R4 and the thermistor are located inside the first encapsulation shell.

[0020] Advantages of the present invention:

[0021] 1. The integrated temperature heating circuit adopted by the present invention enables the simultaneous heating of the VCSEL and the vapor bubble. Without using thermal insulation materials and only using one heating circuit, the physical encapsulation volume can be reduced, and the assembly complexity and the PCB design difficulty can be lowered.

[0022] 2. A thermistor is connected in the circuit of the present invention. The resistance value of the thermistor changes with the change of the current temperature value. Thus, it is convenient to obtain the resistance value of the thermistor and the current temperature value by collecting the voltage across the eighth resistor, so as to facilitate the monitoring and regulation of the current temperature.

[0023] 3. The present invention is provided with an operational amplifier and a triode. The positive input terminal of the operational amplifier is used to input a reference voltage. Through the cooperation of the operational amplifier and the triode, the heat generation of the third resistor R3 and the fourth resistor R4 is adjusted, and the stable temperature control range is relatively large. Description of the Drawings

[0024] Figure 1 is a schematic diagram of the principle of the present invention;

[0025] Figure 2 is a schematic diagram of the structure of the heating system of the present invention;

[0026] Figure 3 is a schematic diagram of the current flow direction of the triode part. Detailed Embodiments

[0027] The present invention will be further described below in conjunction with the drawings and specific embodiments, so that those skilled in the art can better understand the present invention and be able to implement it, but the embodiments given are not intended to limit the present invention.

[0028] Refer to Figure 1As shown in the figure, the present invention discloses a heating system for a CPT atomic clock, including a third resistor R3, a fourth resistor R4, a thermistor R T , an operational amplifier U1, a triode BJT, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8.

[0029] One end of the third resistor R3 is connected to the power supply chip, and the other end is connected to the collector of the triode BJT. The fourth resistor R4 is connected in parallel with the third resistor R3. The third resistor R3 and the fourth resistor R4 are heating resistors. The third resistor R3 is used to heat the vertical cavity surface emitting laser, and the fourth resistor R4 is used to heat the vapor bubble. In this way, heating of the vertical cavity surface emitting laser and the vapor bubble can be achieved simultaneously, and only one heating circuit is used, which can reduce the physical packaging volume, the assembly complexity, and the PCB design difficulty.

[0030] The positive input terminal of the operational amplifier U1 is used to input the reference voltage. The output terminal of the operational amplifier U1 is connected to the base of the triode BJT. The first end of the sixth resistor R6 is connected to the emitter of the triode BJT. The first ends of the eighth resistor R8 and the seventh resistor R7 are both connected to the second end of the sixth resistor R6. The second end of the eighth resistor is connected to the negative input terminal of the operational amplifier U1, and the second end of the seventh resistor R7 is grounded.

[0031] One end of the thermistor RT is connected to the first constant voltage source, and the other end is connected to the negative input terminal of the operational amplifier U1. By collecting the voltage across the eighth resistor, the resistance value and the current temperature value of the thermistor RT can be obtained as follows: Collect the voltage value across the eighth resistor R8 to obtain the voltage V R8 across the eighth resistor R8. Since the input resistance of the negative terminal of the operational amplifier U1 is infinite and can be approximated as an open circuit, the current flowing through RT is equal to the current flowing through R8. It can be obtained that I R8 = V R8 / R8. The voltage across the thermistor R T is V RT = 2.5V - V ADC1 . V ADC1 is the voltage value collected at the upper end of R8. According to the formula I = V / R, the resistance value of the thermistor R T is R NTC = V RT / I R8 . Since the resistance-temperature change curve of the thermistor R T is known, the temperature value corresponding to the current resistance value of the thermistor R T can be obtained. The thermistor R T is a resistor with a negative temperature coefficient. In this way, the ambient temperature can be monitored at any time.

[0032] The present invention further includes a microcontroller unit (MCU) for reading the current temperature value. The microcontroller unit (MCU) is a prior art and will not be described in detail herein.

[0033] The present invention further includes a coarse and fine tuning unit for adjusting the reference voltage of the positive input terminal of the operational amplifier U1. The coarse and fine tuning unit includes a first resistor R1 and a second resistor R2. The resistance value of the first resistor R1 is greater than that of the second resistor R2. The microcontroller unit (MCU) includes a first digital-to-analog output terminal and a second digital-to-analog output terminal. The first digital-to-analog output terminal is connected to the first end of the first resistor R1, and the second digital-to-analog output terminal is connected to the first end of the second resistor R2. The second ends of the first resistor and the second resistor are both connected to the positive input terminal of the operational amplifier U1. The MCU reads the current temperature value, judges the difference from the preset target heating temperature and makes a PID adjustment, changes the voltage value of the positive input terminal of the operational amplifier U1, and thus continues heating. Since the first resistor R1 is connected to the first digital-to-analog output terminal DAC_OUT1 and the second resistor R2 is connected to the second digital-to-analog output terminal DAC_OUT2. By using the current superposition theorem, the reference voltage of the positive terminal of the operational amplifier U1 is set through the two-way output of the DAC, and the coarse and fine tuning of the reference voltage is performed by the magnitudes of the currents flowing through the resistors R1 and R2. The DAC_OUT1 port performs voltage coarse tuning, and the DAC_OUT2 port performs voltage fine tuning. As a preferred solution, the resistance value of the first resistor R1 is n times that of the second resistor R2, and the value of n is 1000 - 4000. In this way, after the coarse tuning operation is performed through the first digital-to-analog output terminal DAC_OUT1 first, and then the fine tuning operation is performed through the second digital-to-analog output terminal DAC_OUT2, the reference voltage value of the positive terminal of the operational amplifier U1 can be set more precisely.

[0034] When the temperature rises such that the voltage of the negative input terminal of the operational amplifier U1 rises to the reference voltage of the positive input terminal, the voltage of the output terminal of the operational amplifier U1 decreases, the conduction ability of the triode decreases, and the heating power consumption decreases. Under the state of temperature stability, the heating power can be fine-tuned by setting the reference voltage of the positive input terminal of the operational amplifier U1, so that the temperature fluctuates slightly above and below the target temperature.

[0035] In the present invention, the circuit also has an anti-overheating function. The voltage division of the thermistor R T and the eighth resistor R8 is directly connected to the negative terminal of the operational amplifier U1. If the heating is too fast, when the thermistor R T is an NTC, the resistance value of R T decreases rapidly, then the voltage of the negative terminal of the operational amplifier U1 may suddenly be greater than the reference voltage of the positive terminal. At this time, the operational amplifier U1 will output a low level, causing the triode BJT to immediately be in the cut-off state and stop heating, so that the heating of the vertical cavity surface emitting laser and the vapor bubble will not be damaged unnecessarily due to too fast or too high temperature changes.

[0036] In the present invention, the microcontroller unit MCU includes a first analog-to-digital input terminal and a second analog-to-digital input terminal, and the first analog-to-digital input terminal and the second analog-to-digital input terminal are arranged at both ends of the eighth resistor R8. The first analog-to-digital input terminal ADC1 and the second analog-to-digital input terminal ADC2 can detect the voltage at both ends of the eighth resistor R8. Thus, the microcontroller unit MCU can obtain the detected temperature value of the temperature-sensitive resistor RT.

[0037] A filter capacitor C1 is connected in parallel across the eighth resistor.

[0038] A fifth resistor R5 is connected between the output terminal of the operational amplifier U1 and the base of the triode BJT. At the initial power-on state of the circuit, the reference voltage, that is, the positive input terminal of the operational amplifier U1, is set to a suitable minimum value, such as 1V, which is an empirical value obtained through debugging according to the actual situation. At this time, the temperature is relatively low, and when the thermistor R T is an NTC, the value of RT is relatively large, and the voltage at the negative input terminal of the operational amplifier U1 is small after the voltage division of RT. Considering the transient process, the operational amplifier U1 acts as a comparator. When the voltage at the negative input terminal is less than the voltage at the positive input terminal, the output of the operational amplifier is at a high level. After passing through the current-limiting and voltage-dividing fifth resistor R5, the emitter junction of the triode BJT is forward-biased, and the collector junction is reverse-biased. The triode BJT is in the amplification state. At this time, the third resistor R3 and the fourth resistor R4 will heat at the maximum power. If you want to change this maximum heating power, you only need to change the resistance value of the fifth resistor R5 to reduce the base current. Refer to Figure 2 As shown, because the collector current i3 of the BJT = β * i1, where i1 is the base current of the BJT and i3 is the collector current of the BJT, for the BJT in the amplification state, the current relationship approximately satisfies the formula i3 = β * i1. Therefore, the magnitude of the base current i1 can be adjusted by changing the magnitude of the resistance value of R5.

[0039] Both the third resistor R3 and the fourth resistor R4 are ITO thin films, which have a thin thickness, a small size, and a large amount of heat generation.

[0040] The present invention also discloses a heating device for a CPT atomic clock. Based on the above-mentioned heating system for a CPT atomic clock, it includes a first encapsulation shell, and the third resistor R3, the fourth resistor R4, and the thermistor R T are located inside the first encapsulation shell. Physical encapsulation is achieved through the first encapsulation shell to encapsulate the third resistor R3, the fourth resistor R4, and the thermistor R T together. Thus, the thermistor R T can be used to detect the temperature inside the first encapsulation shell.

[0041] In addition, the present invention can also be provided with a second encapsulation shell, and the second encapsulation shell encapsulates the peripheral circuit composed of the operational amplifier U1 and the triode BJT.

[0042] Figure 1It is a schematic diagram of the principle of the present invention, including an MCU, a multi-channel output DAC, and a power management chip with an enable control bit "EN". When EN is at a high level, the power chip works; when EN is at a low level, the power chip stops working. By controlling the on / off of the EN pin of the power chip with the MCU, the power chip can output a PWM wave. The amplitude of the PWM wave is 3.3V, and the PWM wave provides current to R3 and R4.

[0043] The above-described embodiments are only preferred embodiments given to fully illustrate the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or transformations made by those skilled in the art on the basis of the present invention are all within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A heating system for a CPT atomic clock, characterized in that, It includes a third resistor R3, a fourth resistor R4, a thermistor, an operational amplifier, a triode, a sixth resistor R6, a seventh resistor R7, and an eighth resistor R8; One end of the third resistor R3 is connected to a power chip, and the other end is connected to the collector of the triode. The fourth resistor R4 is connected in parallel with the third resistor R3; the third resistor R3 and the fourth resistor R4 are heating resistors; The positive input terminal of the operational amplifier is used to input a reference voltage; the output terminal of the operational amplifier is connected to the base of the triode; the first end of the sixth resistor R6 is connected to the emitter of the triode, the first ends of the eighth resistor R8 and the seventh resistor R7 are both connected to the second end of the sixth resistor R6, the second end of the eighth resistor is connected to the negative input terminal of the operational amplifier, and the second end of the seventh resistor R7 is grounded; One end of the thermistor is connected to a first constant voltage source, and the other end is connected to the negative input terminal of the operational amplifier. The resistance value of the thermistor and the current temperature value are obtained by collecting the voltage across the eighth resistor; It further includes a micro control unit MCU for reading the current temperature value; It further includes a coarse and fine tuning unit for adjusting the reference voltage at the positive input terminal of the operational amplifier. The coarse and fine tuning unit includes a first resistor R1 and a second resistor R2. The resistance value of the first resistor R1 is greater than that of the second resistor R2. The micro control unit MCU includes a first digital-to-analog output terminal and a second digital-to-analog output terminal. The first digital-to-analog output terminal is connected to the first end of the first resistor R1, the second digital-to-analog output terminal is connected to the first end of the second resistor R2, and the second ends of the first resistor and the second resistor are both connected to the positive input terminal of the operational amplifier; The micro control unit MCU includes a first analog-to-digital input terminal and a second analog-to-digital input terminal, and the first analog-to-digital input terminal and the second analog-to-digital input terminal are arranged at both ends of the eighth resistor R8.

2. The heating system of the CPT atomic clock according to claim 1, characterized in that The resistance value of the first resistor R1 is n times that of the second resistor R2, and the value of n ranges from 1000 to 4000.

3. The heating system of the CPT atomic clock according to claim 1, characterized in that, A filter capacitor C1 is connected in parallel across the eighth resistor.

4. The heating system of the CPT atomic clock according to claim 1, characterized in that A fifth resistor R5 is connected between the output terminal of the operational amplifier and the base of the triode.

5. The heating system of the CPT atomic clock according to claim 1, characterized in that, The thermistor is a resistor with a negative temperature coefficient.

6. The heating system of the CPT atomic clock according to claim 1, wherein Both the third resistor R3 and the fourth resistor R4 are ITO films.

7. A heating device for a CPT atomic clock, based on the heating system of the CPT atomic clock according to any one of claims 1-6, characterized in that, It includes a first encapsulation shell, and the third resistor R3, the fourth resistor R4, and the thermistor are located inside the first encapsulation shell.

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