Laser control system for coherent population trapping magnetometer

Abstract

The invention discloses a laser control system for a coherent population trapping magnetometer. The laser control system comprises a core control unit, a driving circuit system, a microwave source signal modulation system and an H bridge in bidirectional connection with the core control unit, the driving circuit system comprises a band-gap reference voltage circuit, and the band-gap reference voltage circuit comprises an input end low-power-consumption bias starting circuit and a folding operational amplifier; the core control unit comprises an FPGA (Field Programmable Gate Array) and a temperature control circuit system, and the temperature control circuit system combines an anti-integral saturation algorithm with fuzzy PID (Proportion Integration Differentiation) control and dynamically adjusts PID parameters to realize temperature adjustment; the microwave source signal modulation system comprises an all-digital phase-locked loop, a direct digital synthesizer and a frequency multiplier, and the generation, modulation and amplification of microwave signals are realized through the control of the FPGA. The laser control system is high in microwave source frequency stability and strong in noise suppression capability.

Description

Technical Field

[0001] The present invention relates to the technical field of magnetometers, and particularly to a laser control system for a coherent population trapping magnetometer. Background Art

[0002] A coherent population trapping (CPT) magnetometer measures the magnetic field strength through the quantum effect spectroscopy of laser and alkali metal atoms (such as 87 Rb), and requires a high-stability laser control system. However, in the existing laser control systems, on the one hand, the bandgap reference circuit adopted still relies on the traditional structure, with high power consumption (requiring a startup circuit and a large current bias), significant noise and temperature drift, and it is difficult to meet the requirements of ultra-low power consumption sensors; on the other hand, the temperature control in the existing technology adopts the conventional PID algorithm, with a high overshoot (>1.5%), slow recovery speed, and it cannot adapt to non-linear temperature fluctuations. In addition, the microwave source adopted in the existing laser control systems has a large volume and high phase noise (-80 dBc / Hz @10 kHz), and the modulation ability is limited, making it difficult to support the miniaturization and dynamic modulation requirements of high-precision magnetometers. Summary of the Invention

[0003] The purpose of the present invention is to propose a high-precision laser control system for a coherent population trapping magnetometer with high microwave source frequency stability and strong noise suppression ability.

[0004] The present invention provides a laser control system for a coherent population trapping magnetometer, including a core control unit, a drive circuit system, a microwave source signal modulation system, and an H-bridge bidirectionally connected to the core control unit; The drive circuit system includes a bandgap reference voltage circuit, and the bandgap reference voltage circuit includes an input low-power bias startup circuit and a folded operational amplifier; The core control unit includes an FPGA and a temperature control circuit system, and the temperature control circuit system combines an anti-integral saturation algorithm with fuzzy PID control to dynamically adjust the PID parameters to achieve temperature regulation; The microwave source signal modulation system includes an all-digital phase-locked loop, a direct digital synthesizer, and a frequency multiplier, and realizes the generation, modulation, and amplification of microwave signals through the control of the FPGA.

[0005] The bandgap reference voltage circuit (Bandgap Reference, BGR) of the drive circuit system has been optimized for noise, temperature characteristics, and power, and accurately converts the bandgap reference voltage into a reference current.

[0006] Further, the input low-power bias startup circuit of the laser control system of the present invention consists of a subthreshold bias circuit formed by MOS transistor M1, MOS transistor M2, and MOS transistor M3. MOS transistor M1 is grounded through resistor R1; Subthreshold current , where is the electron mobility in the channel; is the capacitance per unit area of the gate oxide layer; W is the channel width; L is the channel length; is the gate-source voltage; is the drain-source voltage; is the transistor threshold voltage; m is the reciprocal of the gate surface coupling coefficient; V T is the thermal voltage of the semiconductor; ; where k is the Boltzmann constant, T is the temperature, q is the elementary charge; The folded operational amplifier includes MOS transistors M4 to M14, and a compensation capacitor C is provided between the source of MOS transistor M12 and the gate of MOS transistor M15 c ; One end of resistor R5 is connected to Vdd to provide an initial bias voltage for the folded operational amplifier.

[0007] Further, the bandgap reference voltage circuit of the laser control system of the present invention further includes bipolar transistors Q1 and Q2; one end of bipolar transistor Q1 is connected to the drain of MOS transistor M15, and the other end is connected to resistor R2; the source of MOS transistor M15 is connected to resistor R6; The emitter of bipolar transistor Q1 is grounded through resistor R2, The feedback resistor R4 is output after being connected in parallel with capacitor CFF V out ; And it satisfies; ; ; Among them, V ref is the bandgap reference voltage; V out is the output voltage; V PTAT is the voltage proportional to the absolute temperature.

[0008] Further, the anti-integral saturation algorithm of the laser control system of the present invention specifically includes: the temperature measurement module NTC with a negative temperature coefficient inputs to obtain the current temperature T in real timecurrent and calculate the error e(t) and the error change rate ， where t is time; if e(t) > e set , directly output a 100% pulse width modulation (PWM) duty cycle to drive the H-bridge to operate at full power, skip the PID regulation, and reduce the error at the fastest speed; if e(t) ≤ e set , then enter the fuzzy PID control link, and dynamically adjust the control parameters according to the error e(t) and the error change rate de(t) / dt ; where e set is the set temperature target group; the temperature measurement module NTC continuously monitors the current temperature T current , update, and form a closed-loop control; The expression of the anti-integral saturation algorithm is Formula I; Formula I; Formula II; where is the proportionality coefficient corrected by fuzzy PID, is the integral coefficient corrected by fuzzy PID, is the differential coefficient corrected by fuzzy PID, is the initial value of the proportionality coefficient, is the initial value of the integral coefficient, is the initial value of the differential coefficient, is the correction value of the proportionality coefficient, is the correction value of the integral coefficient, is the correction value of the differential coefficient, is the instantaneous value of the error fed back by the system, τ is the integral time constant, is the output of the temperature control circuit system controlled by the PID algorithm.

[0009] Furthermore, the fuzzy PID control of the laser control system of the present invention includes a membership function optimized by a genetic algorithm. The membership function optimized by the genetic algorithm includes: S1: Encode the rule base of the fuzzy PID controller using a real number coding method to generate an initial rule base; S2: Evaluate the fitness of the initial rule base using an evaluation function; S3: Then perform selection, crossover, and mutation processes on the encoded rule base to generate an optimized new rule base; S4: Re-evaluate the fitness of the new rule base. If the minimum fitness condition is met, decode and output the optimal fuzzy rule table and update the rule base; S5: Real-time collect the error value of the controlled object, and calculate through fuzzy processing, fuzzy rule mapping, and defuzzification operations to obtain ; S6: Superimpose the , , with K p0 ，K I0 ，K D0 to obtain K p ，K I ，K D ， to achieve dynamic adjustment of PID control parameters.

[0010] Furthermore, the output end of the all-digital phase-locked loop of the laser control system of the present invention is connected to a second-order active loop filter, and then connected to a frequency multiplier through a microstrip line; The all-digital phase-locked loop incorporates a voltage-controlled oscillator VCO and a digital phase detector. The all-digital phase-locked loop configures the register Register using the serial peripheral interface SPI with the core control unit to set INT and FRAC , and the calculation formula is: ; wherein, is the output frequency, is the input reference frequency, INT is the integer division ratio, FRAC is the fractional division ratio, MOD is the modulus of fractional division, used to control the resolution of the fractional bit, INT, FRAC, MOD adjusted according to the chip manual; The output end of the direct digital synthesizer is connected to the all-digital phase-locked loop after being serially connected with a band-pass filter; The output microstrip line of the frequency multiplier is connected to the input end of a microwave amplifier, and the output end of the microwave amplifier is directly connected to a three-port DC bias network Bias-Tee for biasing.

[0011] Furthermore, the microwave source signal modulation system of the laser control system of the present invention further includes a reference frequency source, a microwave amplifier, and a modulation control unit; The reference frequency source includes a high-precision temperature-compensated crystal oscillator, and a 3.3V regulated power supply is used to supply power to the high-precision temperature-compensated crystal oscillator. The output end of the high-precision temperature-compensated crystal oscillator is connected to the reference clock input pin of the direct digital synthesizer through printed circuit board PCB traces.

[0012] Furthermore, the drive circuit system of the laser control system of the present invention further includes a digital-to-analog converter connected to the core control unit, and a low-dropout linear regulator disposed between the digital-to-analog converter and the bandgap reference voltage circuit.

[0013] Furthermore, the frequency doubler of the laser control system of the present invention includes a first-stage frequency doubler and a second-stage frequency doubler; both the first-stage frequency doubler and the second-stage frequency doubler are frequency doublers with a doubling factor of two; band-pass filters capable of filtering the fundamental frequency are provided after both the first-stage frequency doubler and the second-stage frequency doubler.

[0014] Furthermore, the output frequency of the high-precision temperature-compensated crystal oscillator of the laser control system of the present invention is 10 MHz, and the stability is ±0.1 ppm.

[0015] The laser control system for a coherent population trapping magnetometer of the present invention has the following beneficial effects: The bandgap reference voltage circuit adopted by the laser control system for a coherent population trapping magnetometer of the present invention builds a low-power consumption bias start-up circuit at the input end, which reduces the system power consumption and also suppresses the rising speed of the system temperature. The intermediate operational amplifier structure improves the output impedance, thereby increasing the gain. At the same time, it also reduces the Miller effect, improves the frequency response, reduces the temperature drift of the zero point, ensures that the circuit operates at an appropriate operating point, and uses two pairs of differential pairs to better improve the common-mode rejection ratio (CMRR) and enhance the anti-interference ability to noise. And by excluding external interference factors, the reference voltage is only linearly related to temperature.

[0016] The combination of the improved anti-integral saturation algorithm and fuzzy PID control of the present invention solves the overshoot problem of traditional PID in nonlinear systems, and at the same time makes up for the defect of insufficient steady-state accuracy of traditional control, and can greatly improve the temperature control effect of vertical cavity surface emitting lasers (VCSELs), such as solving problems such as rapid recovery after overshoot and stable accuracy.

[0017] Output limiting, integral limiting, rate limiting, and nonlinear limiting logics are introduced into the integral link of traditional PID. When the error exceeds the set threshold, the integral action is suspended to prevent overshoot or oscillation caused by excessive accumulation of the integral term; when the error returns to the normal range, the integral action is gradually restored to ensure steady-state accuracy. By improving the logic of anti-integral saturation, when the temperature fluctuates greatly, full-power heating or cooling is judged and carried out, effectively improving the speed of returning to the set temperature, which can exceed the speed of the traditional PID anti-integral saturation algorithm by about 10%; at the same time, PID is only enabled when the fluctuation is small, and the values of the three PID parameters can be reduced, so that the single adjustment amount is reduced, thereby reducing the overshoot amount, and the overshoot amount can reach ≤1%, and it can still converge stably in the fast temperature change scenario.

[0018] Meanwhile, during the PID regulation process, the improved fuzzy PID algorithm is used. The fuzzy PID can dynamically adjust parameters to adapt to non-linearity. The membership function in the fuzzy PID control defines the energy function through the Lyapunov function , under the constraint of the anti-windup mechanism, the control rate satisfies , where e(t) is the error, is the error change rate, and t is the time. It ensures that the system quickly converges to the equilibrium point near the steady state. The steady-state error is controlled within ±0.01K, meeting the wavelength stability requirements of the high-precision vertical cavity surface emitting laser (VCSEL).

[0019] The theoretical steady-state error of the system approaches zero, and the actual accuracy is limited by the resolution of the NTC temperature sensor and circuit noise (equivalent to ±0.005°C).

[0020] The microwave source signal modulation system of the laser control system described in the present invention exhibits significant advantages in terms of frequency stability, phase noise, modulation ability, volume power consumption, and integration level.

[0021] Improve frequency stability and accuracy: The frequency stability of the microwave source is better than ±0.1 ppm, far exceeding ±1 ppm of traditional microwave sources. The temperature-compensated crystal oscillator (TCXO) provides a high-stability reference of ±0.1 ppm. The direct digital synthesizer (DDS) achieves microhertz-level accuracy through a 32-bit control word, and the digital locking mechanism of the all-digital phase-locked loop (DPLL) further eliminates drift. In contrast, traditional microwave sources are limited by analog filters and environmental interference and have poor stability.

[0022] Reduce phase noise: The phase noise is better than -100 dBc / Hz @ 10 kHz offset, better than -80 dBc / Hz of traditional microwave sources. The all-digital phase-locked loop (DPLL) adopts a digital phase detector and an optimized loop filter design, with stronger noise suppression ability; the low-frequency signal generated by the direct digital synthesizer (DDS) is pure, providing a low-noise basis for subsequent frequency multiplication. The analog circuits of traditional microwave sources are prone to introducing additional noise.

[0023] The low phase noise reduces the laser spectral broadening, improves the atomic energy level excitation efficiency, and enhances the sensitivity of the atomic magnetometer.

[0024] Enhance modulation ability: Combined with the FPGA module, it supports modulation modes such as frequency modulation (FM) and phase modulation (PM), with a fast response speed. Analysis: The high-speed control ability of the FPGA, combined with the frequency flexibility of the direct digital synthesizer (DDS) and the phase adjustment function of the all-digital phase-locked loop (DPLL), realizes dynamic modulation; traditional microwave sources only support fixed output, and modulation relies on external devices, with low efficiency and complexity.

[0025] Flexible modulation can be used in lock-in amplification or noise suppression technologies to further improve measurement accuracy and meet diverse experimental requirements.

[0026] Achieve miniaturization and low power consumption: The system size is reduced to 10cm×10cm, and the power consumption is 5 - 10W, far lower than the dozens of watts of traditional microwave sources. Surface-mounted components and on-chip amplifiers reduce the volume, and the integrated design optimizes the power consumption; traditional technologies rely on discrete devices with higher volume and energy consumption.

[0027] Miniaturization makes the microwave source suitable for portable atomic magnetometers, such as field geological exploration or medical device integration.

[0028] Improve system integration and ease of use: The microwave source and modulation unit are integrated, with simple debugging and strong anti-interference ability. The integration of printed circuit board (PCB) eliminates the complex connections between discrete modules, and the parameters can be adjusted through software by the centralized control of FPGA; traditional systems require manual calibration and are vulnerable to interference. It simplifies the development and maintenance processes of atomic magnetometers and enhances the engineering practicability.

[0029] By constructing a vertical-cavity surface-emitting laser (VCSEL) circuit control system and combining the dynamic control of FPGA and temperature feedback, this solution effectively solves the limitations of traditional magnetometers in aspects such as frequency stability, phase noise, modulation flexibility, volume power consumption, and system integration. Its technical effect significantly improves the measurement accuracy and sensitivity of the coherent population trapping effect magnetometer, and at the same time promotes its development in portable and integrated applications. Description of the Drawings

[0030] Figure 1 It is the structural block diagram of the laser control system described in the present invention; Figure 2 It is the structural block diagram of the drive circuit system described in the present invention; Figure 3 It is the circuit diagram of the bandgap reference voltage described in the present invention; Figure 4 It is the logic diagram of the anti-integral saturation algorithm described in the present invention; Figure 5 It is the structural diagram of the fuzzy PID algorithm control described in the present invention; Figure 6 It is the schematic block of the microwave source signal modulation system described in the present invention; Figure 7 It is the fuzzy rule table described in Embodiment 1 of the present invention. Detailed Embodiments

[0031] For a clearer understanding of the technical features, objectives, and effects of the present invention, the specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings. The described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention. For those not specified in the specific embodiments, they are carried out according to conventional conditions or the conditions provided by the manufacturer.

[0032] When the following description refers to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present disclosure. The terms used in the present disclosure are only for the purpose of describing specific embodiments and are not intended to limit the present disclosure.

[0033] A laser control system for a coherent population trapping magnetometer includes a core control unit, a drive circuit system, a microwave source signal modulation system, and an H-bridge bidirectionally connected to the core control unit;

[0034] The drive circuit system includes a bandgap reference voltage circuit, and the bandgap reference voltage circuit includes an input low-power bias startup circuit and a folded operational amplifier; The core control unit includes an FPGA and a temperature control circuit system. The temperature control circuit system combines an anti-integral saturation algorithm with fuzzy PID control to dynamically adjust the PID parameters to achieve temperature regulation; The microwave source signal modulation system includes an all-digital phase-locked loop, a direct digital synthesizer, and a frequency multiplier, and realizes the generation, modulation, and amplification of microwave signals through the control of the FPGA.

[0035] In other embodiments, the input low-power bias startup circuit consists of MOS transistors M1, M2, and M3 to form a subthreshold bias circuit, and MOS transistor M1 is grounded through resistor R1; Subthreshold current , where is the electron mobility in the channel; is the capacitance per unit area of the gate oxide layer; W is the channel width; L is the channel length; is the gate-source voltage; is the drain-source voltage; is the transistor threshold voltage; m is the reciprocal of the gate surface coupling coefficient; V T is the thermal voltage of the semiconductor; ; wherek is the Boltzmann constant, T is the temperature, q is the elementary charge; The folded operational amplifier includes MOS transistors M4 to M14, and a compensation capacitor C is provided between the source of MOS transistor M12 and the gate of MOS transistor M15 c ; One end of resistor R5 is connected to Vdd to provide an initial bias voltage for the folded operational amplifier.

[0036] In other embodiments, the bandgap reference voltage circuit further includes a bipolar transistor Q1 and a bipolar transistor Q2; one end of bipolar transistor Q1 is connected to the drain of MOS transistor M15, and the other end is connected to resistor R2; the source of MOS transistor M15 is connected to resistor R6; The emitter of bipolar transistor Q1 is grounded through resistor R2, The feedback resistor R4 is output after being shunted by capacitor CFF V out ; and satisfies ; ; wherein, V ref is the bandgap reference voltage; V out is the output voltage; V PTAT is the voltage proportional to the absolute temperature.

[0037] In other embodiments, the anti-integral saturation algorithm specifically includes: the temperature measurement module NTC with a negative temperature coefficient inputs to obtain the current temperature T current , and calculates the error e(t) and the error change rate ， t is time; if e(t) > e set , directly output a pulse width modulation PWM duty cycle of 100% to drive the H-bridge to operate at full power, skipping the PID adjustment to reduce the error at the fastest speed; if e(t) ≤ e set , then enter the fuzzy PID control link, and dynamically adjust the control parameters according to the error e(t) and the error change rate de (t) / dt ; where e set is the set temperature target group; the temperature measurement module NTC continuously monitors the current temperature T current , updates, and forms a closed-loop control; The expression of the anti-integral saturation algorithm is Formula I; Formula I; Formula II; where is the proportionality coefficient corrected by fuzzy PID, is the integral coefficient corrected by fuzzy PID, is the differential coefficient corrected by fuzzy PID, is the initial value of the proportionality coefficient, is the initial value of the integral coefficient, is the initial value of the differential coefficient, is the correction value of the proportionality coefficient, is the correction value of the integral coefficient, is the correction value of the differential coefficient, is the instantaneous error value fed back by the system, τ is the integral time constant, is the output of the temperature control circuit system controlled by the PID algorithm.

[0038] In other embodiments, the fuzzy PID control includes a membership function optimized by a genetic algorithm, and the membership function optimized by the genetic algorithm includes: S1: Coding the rule base of the fuzzy PID controller using a real number coding method to generate an initial rule base; S2: Evaluating the fitness of the initial rule base using an evaluation function; S3: Then performing selection, crossover, and mutation processes on the already coded rule base to generate a new optimized rule base; S4: Re-evaluating the fitness of the new rule base. If the minimum fitness condition is met, decode and output the optimal fuzzy rule table and update the rule base; S5: Real-time collect the error value of the controlled object, and through fuzzy processing, fuzzy rule mapping, and defuzzification operations, calculate to obtain ; S6: Add the , , with K p0 ，K I0 ，K D0 to obtain K p ，K I ，K D ， to achieve dynamic adjustment of the PID control parameters.

[0039] In other embodiments, the output end of the all-digital phase-locked loop is connected to a second-order active loop filter, and then connected to a frequency multiplier through a microstrip line; The all-digital phase-locked loop incorporates a voltage-controlled oscillator (VCO) and a digital phase detector. The all-digital phase-locked loop configures the register of the core control unit through the Serial Peripheral Interface (SPI) to set the integer division ratio INT and the fractional division ratio FRAC . The calculation formula is: ; where is the output frequency, is the input reference frequency, INT is the integer division ratio, FRAC is the fractional division ratio, MOD is the modulus of the fractional division, used to control the resolution of the fractional bit, INT, FRAC, MOD which is adjusted according to the chip manual; The output of the direct digital synthesizer is connected to the all-digital phase-locked loop after being connected in series with a band-pass filter; The output microstrip line of the frequency multiplier is connected to the input end of the microwave amplifier, and the output end of the microwave amplifier is directly connected to a three-port DC bias network (Bias-Tee) for biasing.

[0040] In other embodiments, the microwave source signal modulation system further includes a reference frequency source, a microwave amplifier, and a modulation control unit; The reference frequency source includes a high-precision temperature-compensated crystal oscillator, which is powered by a 3.3V regulated power supply. The output end of the high-precision temperature-compensated crystal oscillator is connected to the reference clock input pin of the direct digital synthesizer through printed circuit board (PCB) traces.

[0041] In other embodiments, the drive circuit system further includes a digital-to-analog converter connected to the core control unit, and a low-dropout linear regulator disposed between the digital-to-analog converter and the bandgap reference voltage circuit.

[0042] In other embodiments, the frequency multiplier includes a first-stage frequency multiplier and a second-stage frequency multiplier; both the first-stage frequency multiplier and the second-stage frequency multiplier are frequency multipliers with a doubling factor; band-pass filters capable of filtering the fundamental frequency are provided after both the first-stage frequency multiplier and the second-stage frequency multiplier.

[0043] In other embodiments, the output frequency of the high-precision temperature-compensated crystal oscillator is 10 MHz, and the stability is ±0.1 ppm.

[0044] In other embodiments, the folded operational amplifier includes two pairs of differential pairs, which improve the output impedance and common-mode rejection ratio (CMRR) through cascode transistors, and uses cascaded compensation capacitors to improve the frequency response. The output impedance is increased to the megohm level through cascode transistors, and the gain-bandwidth product (GBW) satisfies whereg m5 is the input-stage transconductance, and Cc is the compensation capacitor.

[0045] In other embodiments, in the printed circuit board (PCB) design, a decoupling capacitor is added around the temperature-compensated crystal oscillator (TCXO) to filter out power supply noise and ensure signal purity.

[0046] In other embodiments, the membership function in the fuzzy PID control defines the energy function through the Lyapunov function , and under the constraint of the anti-windup mechanism, the control rate satisfies , where e(t) is the error, is the error change rate, and t is the time. Ensure that the system quickly converges to the equilibrium point near the steady state.

[0047] Embodiment 1: A laser control system for a coherent population trapping magnetometer, as Figure 1 shown, includes a core control unit, a drive circuit system, a microwave source signal modulation system, and an H-bridge bidirectionally connected to the core control unit.

[0048] The drive circuit system includes a bandgap reference voltage circuit, and the bandgap reference voltage circuit includes an input low-power bias startup circuit and a folded operational amplifier; the drive circuit system further includes a digital-to-analog converter connected to the core control unit and a low-dropout linear regulator disposed between the digital-to-analog converter and the bandgap reference voltage circuit. Figure 2 As shown, the drive circuit system is mainly controlled by an FPGA to input a digital signal, which is converted into an analog signal by a digital-to-analog converter (DAC), and a stable electrical signal with low noise is obtained by processing with a low-dropout linear regulator, and finally a bandgap reference voltage is output to provide drive for the vertical cavity surface emitting laser (VCSEL).

[0049] In this Embodiment 1, as Figure 3 shown, the input low-power bias startup circuit is composed of MOS transistors M1, M2, and M3 to form a subthreshold bias circuit, and MOS transistor M1 is grounded through resistor R1; The subthreshold current , where is the electron mobility in the channel; is the capacitance per unit area of the gate oxide layer; W is the channel width; L is the channel length; is the gate-source voltage; is the drain-source voltage; is the transistor threshold voltage; mis the reciprocal of the gate surface coupling coefficient; V T is the thermal voltage of the semiconductor; ; where k is the Boltzmann constant, T is the temperature, q is the elementary charge; The folded operational amplifier includes MOS transistors M4 to M14, and a compensation capacitor C is provided between the source of MOS transistor M12 and the gate of MOS transistor M15 c ; One end of resistor R5 is connected to Vdd to provide an initial bias voltage for the folded operational amplifier. Vdd is the chip operating voltage.

[0050] The bandgap reference voltage circuit further includes bipolar transistor Q1 and bipolar transistor Q2; one end of bipolar transistor Q1 is connected to the drain of MOS transistor M15, and the other end is connected to resistor R2; the source of MOS transistor M15 is connected to resistor R6; The emitter of bipolar transistor Q1 is grounded through resistor R2, The feedback resistor R4 is output after being shunted with capacitor CFF V out ; and satisfies ; According to Kirchhoff's current law, it can be obtained that: ; wherein, V ref is the bandgap reference voltage; V out is the output voltage; V PTAT is the voltage proportional to the absolute temperature.

[0051] The folded operational amplifier contains two pairs of differential pairs, improves the output impedance and common-mode rejection ratio (CMRR) through cascode transistors, and uses cascaded compensation capacitors to improve the frequency response. The output impedance is boosted to the megohm level through cascode transistors, and the gain-bandwidth product (GBW) satisfies where g m5 is the input-stage transconductance, and Cc is the compensation capacitor.

[0052] The core control unit includes an FPGA and a temperature control circuit system. The temperature control circuit system combines an anti-integral saturation algorithm with fuzzy PID control to dynamically adjust the PID parameters to achieve temperature regulation.

[0053] Such as Figure 4As shown, the anti-integral saturation algorithm specifically includes: the temperature measurement module NTC with a negative temperature coefficient obtains the current temperature T in real time current , and calculates the error e(t) and the error change rate ， where t is time; if e(t) > e set , directly output a pulse width modulation PWM duty cycle of 100%, drive the H-bridge to operate at full power, skip the PID adjustment, and reduce the error at the fastest speed; if e(t) ≤ e set , then enter the fuzzy PID control link, and dynamically adjust the control parameters according to the error e(t) and the error change rate de(t) / dt ; where e set is the set temperature target group; the temperature measurement module NTC continuously monitors the current temperature T current , updates, and forms a closed-loop control; The expression of the anti-integral saturation algorithm is Formula I; Formula I; Formula II; where is the proportionality coefficient corrected by fuzzy PID, is the integral coefficient corrected by fuzzy PID, is the differential coefficient corrected by fuzzy PID, is the initial value of the proportionality coefficient, is the initial value of the integral coefficient, is the initial value of the differential coefficient, is the correction value of the proportionality coefficient, is the correction value of the integral coefficient, is the correction value of the differential coefficient, is the instantaneous value of the error fed back by the system, τ is the integral time constant, is the output of the temperature control circuit system controlled by the PID algorithm.

[0054] As Figure 5 shown, the fuzzy PID control link specifically includes: Fuzzification: Map the error e and the error change rate de / dt to fuzzy language variables. According to the law of the laser temperature change, determine the domain of discourse of the error e and the error change rate de / dt, and divide the domain of discourse into eight fuzzy sets on average, namely negative large (NB), negative medium (NM), negative small (NS), negative zero (NO), positive zero (PO), positive small (PS), positive medium (PM), and positive large (PB). Among them, negative large and positive large use the activation function Sigmoid membership function, and other fuzzy sets use the triangular membership function, that is, the error e and the error change rate de / dt can be fuzzified.

[0055] Rule Base: Generate control decisions based on preset rules. When the error is large and the error change rate is very large, increase the proportional coefficient K P , increase the integral coefficient K I , increase the differential coefficient K D ; When the error is small and the error change rate is very large, decrease the proportional coefficient K P , increase the integral coefficient K I , decrease the differential coefficient K D ; When the error is large and the error change rate is very small, increase the proportional coefficient K P , increase the integral coefficient K I , increase the differential coefficient K D ; When the error is small and the error change rate is very small, decrease the proportional coefficient K P , increase the integral coefficient K I , decrease the differential coefficient K D ; Specifically, it is like the fuzzy rule table Figure 7 shown

[0056] Defuzzification: According to the fuzzy output value obtained from the fuzzy rules, seven output fuzzy sets are correspondingly output. The membership functions all adopt trigonometric functions. The center-of-gravity method is used to convert the fuzzy output value into three clear values under the combined action of multiple output sets, which are the correction values of the proportional integral and differential coefficients obtained in three different universes of discourse

[0057] Output: Convert it into an accurate pulse width modulation PWM duty cycle adjustment amount according to formula I. The range of the output value is limited to [-1000, 1000], where 1000 corresponds to a forward cooling duty cycle of 100%, -1000 corresponds to a negative heating duty cycle of 1000, the conversion of positive and negative currents is realized through the H-bridge, and the dynamically adjusted pulse width modulation PWM signal drives the vertical cavity surface emitting laser VCSEL through the H-bridge to accurately control the temperature

[0058] The fuzzy PID control adopts a Mamdani-type fuzzy controller, whose core adopts an approximate reasoning method. The results of multiple fuzzy sets are superimposed to obtain the corresponding output fuzzy set, and the center-of-gravity method is used to convert it into a clear value to replace this fuzzy set; Define the input as the error e(t) and the error change rate de(t) / dt ;; The output of the fuzzy PID control is ΔK p , ΔK I , ΔKD 。

[0059] The fuzzy PID control realizes the output function through the multiplier and accumulator embedded in the core control unit, and realizes multiplication and addition operations with a multiplier and an adder respectively.

[0060] The fuzzy PID control includes a membership function optimized by a genetic algorithm, and the membership function optimized by the genetic algorithm includes: S1: Coding the rule base of the fuzzy PID controller using a real number coding method to generate an initial rule base; S2: Evaluating the fitness of the initial rule base using an evaluation function; S3: Then performing selection, crossover, and mutation processes on the already coded rule base to generate an optimized new rule base; S4: Re-evaluating the fitness of the new rule base. If the minimum fitness condition is met, decode and output the optimal fuzzy rule table and update the rule base; S5: Real-time collect the error value of the controlled object, and through fuzzy processing, fuzzy rule mapping, and defuzzification operations, calculate and obtain ; S6: Add the , , with K p0 ，K I0 ，K D0 to obtain K p ，K I ，K D ， to realize the dynamic adjustment of PID control parameters.

[0061] The fuzzy PID control optimizes the rule base through experimental data or a genetic algorithm, combines similar rules, and constructs a partitioned control rule set for rapid heating in the low-temperature zone and fine adjustment in the high-temperature zone.

[0062] As Figure 6 shown, the microwave source signal modulation system includes an all-digital phase-locked loop, a direct digital synthesizer, and a frequency multiplier, and realizes the generation, modulation, and amplification of microwave signals through the control of the FPGA.

[0063] The output end of the direct digital synthesizer is connected to the all-digital phase-locked loop after being serially connected with a band-pass filter; The output microstrip line of the frequency multiplier is connected to the input end of the microwave amplifier, and the output end of the microwave amplifier is directly connected to a three-port DC bias network Bias-Tee for biasing.

[0064] In this Embodiment 1, the microwave source signal modulation system further includes a reference frequency source, a microwave amplifier, and a modulation control unit; The reference frequency source is responsible for providing a stable reference frequency for the direct digital frequency synthesizer DDS module. It includes a high-precision temperature-compensated crystal oscillator. The temperature-compensated crystal oscillator TCXO is soldered to the reserved position on the printed circuit board PCB, and a 3.3V regulated power supply is used to supply power to the high-precision temperature-compensated crystal oscillator. The output end of the high-precision temperature-compensated crystal oscillator is connected to the reference clock input pin of the direct digital synthesizer through the printed circuit board PCB trace. The output frequency of the high-precision temperature-compensated crystal oscillator is 10 MHz, and the stability is ±0.1 ppm.

[0065] In the printed circuit board PCB design, decoupling capacitors are added around the temperature-compensated crystal oscillator TCXO to filter out power supply noise and ensure pure signals.

[0066] The output end of the all-digital phase-locked loop is connected to a second-order active loop filter, and then connected to the frequency multiplier through a microstrip line; The all-digital phase-locked loop incorporates a voltage-controlled oscillator VCO and a digital phase detector. The all-digital phase-locked loop configures the register Register through the serial peripheral interface SPI using the core control unit to set the integer division ratio INT and the fractional division ratio FRAC , and the calculation formula is: ; In this Embodiment 1, is the output frequency, is the input reference frequency, INT is the integer division ratio, FRAC is the fractional division ratio, MOD is the modulus of the fractional division, used to control the resolution of the fractional part, INT, FRAC, MOD Adjusted according to the chip manual to control the chip to output a 1.70875 GHz signal.

[0067] In this Embodiment 1, the chip manual uses the ADF4351 chip of Analog Devices, Inc. The registers of the ADF4351 are written through the FPGA in sequence (the following are in hexadecimal): Register 5: 0x00580005; Register 4: 0x00800042 (enable divider ÷2 and output); Register 3: 0x00000003 (default configuration); Register 2: 0x0000401F (R = 1, charge pump current 5 mA); Register 1: 0x00008004 (MOD = 4, 8 / 9 frequency divider); Register 0: 0x00155003 (INT = 341, FRAC = 3); By configuring the integer division ratio of the ADF4351 (set INT to INT = 341), the fractional division ratio (set FRAC to FRAC = 3, set MOD to MOD = 4), and the RF frequency divider (÷2), the 10 MHz reference signal can be multiplied to 1.70875 GHz. In practical applications, the loop filter and output matching need to be adjusted according to the hardware environment.

[0068] The all-digital phase-locked loop The all-digital phase-locked loop DPLL multiplies the 100 MHz signal to 1.70875 GHz. Using an all-digital phase-locked loop DPLL chip with a built-in VCO and digital phase detector, connect the 100 MHz signal of the direct digital frequency synthesizer DDS module to the reference input pin of the all-digital phase-locked loop DPLL chip. By setting the division ratio, output a 1.70875 GHz signal. Connect an output to a second-order active loop filter to suppress noise, and then connect it to the subsequent frequency multiplier through a microstrip line.

[0069] The frequency multiplier includes a first-stage frequency multiplier and a second-stage frequency multiplier; both the first-stage frequency multiplier and the second-stage frequency multiplier are frequency multipliers with a doubling factor; a band-pass filter capable of filtering the fundamental frequency is provided after both the first-stage frequency multiplier and the second-stage frequency multiplier. In this Embodiment 1, two cascaded frequency multipliers are used to quadruple the frequency of the 1.70875 GHz signal, and the frequency after multiplication is the required 6.835 GHz signal. Two frequency multipliers with a doubling factor are cascaded. After the first stage, the 1.7 GHz fundamental frequency is filtered by a band-pass filter, and the frequency centered at 3.4 GHz is retained. After the second stage, the 3.4 GHz fundamental frequency is filtered by a band-pass filter, and the frequency centered at 6.8 GHz is retained.

[0070] The microwave amplifier amplifies the microwave signal and inputs it into a three-port DC bias network Bias-Tee to modulate the laser. Select a microwave amplifier chip with a gain of about 15 dB to boost the power of the 6.835 GHz signal to the required range. Connect the output of the all-digital phase-locked loop DPLL to the input terminal of the amplifier chip through a 50-ohm microstrip line, and directly connect the output terminal to the three-port DC bias network Bias-Tee, with a supply voltage of 5V.

[0071] Write Verilog code using an FPGA development board to generate a modulation signal, and control a direct digital synthesizer (DDS) chip and an all-digital phase-locked loop (DPLL) chip through a serial peripheral interface (SPI) to achieve microwave frequency modulation and phase modulation.

[0072] In addition, in this Embodiment 1, components are packaged in SMD. Place the temperature-compensated crystal oscillator (TCXO) near the power supply, the direct digital synthesizer (DDS) and the all-digital phase-locked loop (DPLL) close to the center, the amplifier close to the output, and the FPGA in the control area; high-frequency signals travel on 50-ohm microstrip lines, and the power layer and the ground layer are separated to reduce interference. After soldering the components, cover the high-frequency module with a metal shield and connect it to the ground layer to reduce electromagnetic interference. The output is connected to a three-port DC bias network (Bias-Tee) through a radio frequency interface.

[0073] In summary, a miniaturized microwave source controlled by an FPGA can be realized, which can output a microwave signal with a frequency of 6.835 GHz and adjustable frequency and phase.

[0074] The embodiments described above are some, but not all, of the embodiments of the present invention. The detailed description of the embodiments of the present invention is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts fall within the scope of protection of the present invention.

Claims

1. A laser control system for a coherent population trapping magnetometer, characterized in that: It includes a core control unit, a driving circuit system, a microwave source signal modulation system, and an H-bridge bidirectionally connected to the core control unit; The driving circuit system includes a bandgap reference voltage circuit, and the bandgap reference voltage circuit includes an input low power consumption bias start-up circuit and a folding operational amplifier; The core control unit includes an FPGA and a temperature control circuit system, wherein the temperature control circuit system adopts an anti-integral saturation algorithm combined with fuzzy PID control to dynamically adjust PID parameters to achieve temperature regulation; The microwave source signal modulation system comprises a full digital phase-locked loop, a direct digital synthesizer and a frequency multiplier, and realizes the generation, modulation and amplification of microwave signals through the FPGA control.

2. The laser control system according to claim 1, characterized in that: The input end low power consumption bias start circuit is composed of MOS tube M1, MOS tube M2, and MOS tube M3 to form a sub-threshold bias circuit, and the MOS tube M1 is grounded through a resistor R1; Subthreshold current ,in is the electron mobility in the channel; is the capacitance per unit area of ​​the gate oxide layer; W is the channel width; L is the channel length; is the gate-source voltage; is the drain-source voltage; is the transistor threshold voltage; m is the inverse of the gate surface coupling coefficient; V T is the thermal voltage of the semiconductor; ;in k is the Boltzmann constant, T is the temperature, q is the elementary charge; The folding operational amplifier includes MOS tubes M4 to M14, and a compensation capacitor C is provided between the source of the MOS tube M12 and the gate of the MOS tube M15. c ; One end of the resistor R5 is connected to Vdd to provide an initial bias voltage for the folding operational amplifier.

3. The laser control system according to claim 1, characterized in that: The bandgap reference voltage circuit also includes a bipolar transistor Q1 and a bipolar transistor Q2; one end of the bipolar transistor Q1 is connected to the drain of the MOS tube M15, and the other end is connected to the resistor R2; the source of the MOS tube M15 is connected to the resistor R6; The emitter of the bipolar transistor Q1 is connected to ground via a resistor R2. Feedback resistor R4 is connected in parallel with capacitor CFF to output V out ; And meet ; ； in, V ref is the bandgap reference voltage; V out is the output voltage; V PTAT It is a voltage that is proportional to the absolute temperature.

4. The laser control system according to claim 1, characterized in that: The anti-integral saturation algorithm specifically includes: inputting a temperature measurement module NTC with a negative temperature coefficient to obtain the current temperature T in real time current , and calculate the error e(t) and the error change rate , t is time; if e(t)>e set , directly output pulse width modulation PWM duty cycle 100%, drive the H bridge to run at full power, skip PID adjustment, and reduce the error as quickly as possible; if e(t)≤e set , then enter the fuzzy PID control link, according to the error e(t) and the error change rate Dynamically adjust control parameters; where e set The temperature measurement module NTC continuously monitors the current temperature T current , update, and form a closed-loop control; The expression of the anti-integral saturation algorithm is Formula 1; Formula I; Formula II; in is the proportional coefficient corrected by fuzzy PID, is the integral coefficient after fuzzy PID correction, is the differential coefficient after fuzzy PID correction, is the initial value of the proportional coefficient, is the initial value of the integral coefficient, is the initial value of the differential coefficient, is the proportional coefficient correction value, is the integral coefficient correction value, is the correction value of the differential coefficient, is the instantaneous value of the error fed back by the system, τ is the integration time constant, go through PID Algorithm-controlled temperature control circuit system output.

5. The laser control system according to claim 1, characterized in that: The fuzzy PID control includes a membership function optimized by a genetic algorithm, and the membership function optimized by the genetic algorithm includes: S1: Encode the rule base of the fuzzy PID controller using a real number encoding method to generate an initial rule base; S2: Use the evaluation function to evaluate the fitness of the initial rule base; S3: Then the encoded rule base is subjected to selection, crossover and mutation processes to generate an optimized new rule base; S4: re-evaluate the fitness of the new rule base. If the fitness minimum condition is met, decode and output the optimal fuzzy rule table and update the rule base. S5: Real-time acquisition of the error value of the controlled object, through fuzzification processing, fuzzy rule mapping and defuzzification operation, calculation and obtain ; S6: , , and K p0 ，K I0 ，K D0 Superposition, get K p ，K I ，K D ， Realize dynamic adjustment of PID control parameters.

6. The laser control system according to claim 1, characterized in that: The output end of the all-digital phase-locked loop is connected to a second-order active loop filter and then connected to a frequency multiplier via a microstrip line; The all-digital phase-locked loop has a built-in voltage-controlled oscillator VCO and a digital phase detector. The all-digital phase-locked loop uses a core control unit to configure a register Register through a serial peripheral interface SPI to set INT and FRAC , the calculation formula is: ； in, is the output frequency, is the input reference frequency, INT is an integer division ratio, FRAC is the fractional division ratio, MOD is the modulus of the fractional frequency division, which is used to control the resolution of the decimal place. INT, FRAC, MOD Adjust according to the chip manual; The frequency multiplier output microstrip line is connected to the input end of the microwave amplifier, and the output end of the microwave amplifier is directly connected to a three-port direct current bias network Bias-Tee for biasing.

7. The laser control system according to claim 1, characterized in that: The microwave source signal modulation system also includes a reference frequency source, a microwave amplifier and a modulation control unit; The reference frequency source includes a high-precision temperature-compensated crystal oscillator, which is powered by a 3.3V regulated power supply. The output end of the high-precision temperature-compensated crystal oscillator is connected to the reference clock input pin of the direct digital synthesizer through a printed circuit board PCB trace.

8. The laser control system according to claim 1, characterized in that: The driving circuit system further comprises a digital-to-analog converter connected to the core control unit, and a low voltage difference linear regulator arranged between the digital-to-analog converter and the bandgap reference voltage circuit.

9. The laser control system according to claim 1, characterized in that: The frequency multiplier comprises a primary frequency multiplier and a secondary frequency multiplier; both the primary frequency multiplier and the secondary frequency multiplier are frequency multipliers with double frequency; and a bandpass filter capable of filtering the baseband is arranged behind the primary frequency multiplier and the secondary frequency multiplier.

10. The laser control system according to claim 7, characterized in that: The output frequency of the high-precision temperature-compensated crystal oscillator is 10 MHz, and the stability is ±0.1 ppm.

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