Laser temperature control circuit

Abstract

The invention relates to the technical field of laser, and provides a laser temperature control circuit. The laser temperature control circuit comprises a temperature acquisition circuit which comprises a current bridge and a differential amplifier connected with the current bridge, and one bridge arm of the current bridge comprises a thermistor which is arranged outside a laser and is used for measuring temperature; the controller is used for acquiring the detection temperature according to the measurement signal output by the differential amplifier, generating a first error signal according to the detection temperature and a preset given temperature, and performing proportion-integration-differentiation (PID) control on the first error signal to obtain a second error signal; the negative feedback circuit comprises a digital-to-analog converter, the digital-to-analog converter is used for generating a control signal according to the second error signal so as to control the current magnitude and direction of a semiconductor chilling plate, and the semiconductor chilling plate is used for adjusting the external temperature of the laser.

Description

Technical Field

[0001] The present disclosure relates to the field of laser technology, and in particular to a laser temperature control circuit. Background Art

[0002] Magnetometer is a basic instrument for magnetic detection and ground magnetic field observation. Its performance directly determines the accuracy of magnetic field measurement. OPM (Optical-Pumping Magnetometer) refers to a type of magnetometer that uses the optical pumping effect to polarize atoms and destroys the polarization state by applying an external radio frequency field to achieve magnetic field measurement. The polarized atoms can be cesium atoms.

[0003] When designing an optically pumped magnetometer, a single-mode VCSEL (Vertical-Cavity Surface-Emitting Laser) laser with a small beam divergence angle and low power consumption can be used as the magnetometer pump light source. The single-mode characteristics of VCSEL lasers are stable for a long time, polarization is stable, and there will be no mode hopping and power fluctuation. It can achieve stable output of single-mode narrow-linewidth lasers under high temperature conditions. In practical applications, a VCSEL laser with an output power of less than 2W, a spot diameter of 3mm, and an emission wavelength that can resonate with cesium atoms can be selected.

[0004] VCSEL laser frequency is sensitive to temperature, so the temperature of the VCSEL laser needs to be kept highly stable. In related technologies, the temperature control accuracy of VCSEL laser is not high. In order to improve the long-term and short-term stability of the precision measurement system, the temperature adjustment accuracy of the VCSEL laser must be guaranteed. Summary of the invention

[0005] In view of this, an embodiment of the present disclosure provides a laser temperature control circuit to solve the problem of low temperature control accuracy of VCSEL lasers in the prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present disclosure is:

[0007] The embodiment of the present disclosure provides a laser temperature control circuit, which includes: a temperature acquisition circuit, including a current bridge and a differential amplifier connected to the current bridge, wherein one arm of the current bridge includes a thermistor arranged outside the laser for measuring temperature; a controller, used to obtain a detection temperature according to a measurement signal output by the differential amplifier, and to generate a first error signal according to the detection temperature and a preset given temperature, and to perform PID control on the first error signal to obtain a second error signal; a negative feedback circuit, including a digital-to-analog converter, the digital-to-analog converter is used to generate a control signal according to the second error signal to control the current size and direction of a semiconductor refrigeration plate, wherein the semiconductor refrigeration plate is used to adjust the external temperature of the laser.

[0008] In one embodiment, the differential amplifier is an AD7799.

[0009] In one embodiment, the differential amplifier is a Sigma-Delta ADC integrated in the controller.

[0010] In one embodiment, the negative feedback circuit further includes a power amplifier connected to the digital-to-analog converter, and the power amplifier is used to amplify the control signal and input it into the semiconductor cooling chip.

[0011] In one embodiment, the digital-to-analog converter is DAC80502, and / or the power amplifier is MAX9711.

[0012] In one embodiment, the controller controls the digital-to-analog converter to output an analog voltage via an SPI interface.

[0013] In one embodiment, the current bridge includes a first resistor, a second resistor, a third resistor and a fourth resistor with the same resistance value, and the second resistor is a thermistor; the first ends of the first resistor and the third resistor are connected to a power supply, which is used to provide a regulated power supply for the current bridge; the second end of the first resistor is connected to the first end of the second resistor, the second end of the third resistor is connected to the first end of the fourth resistor, and the second ends of the second resistor and the fourth resistor are grounded; wherein the second end of the first resistor and the first end of the second resistor are connected to the positive input terminal of the differential amplifier, and the second end of the third resistor and the first end of the fourth resistor are connected to the negative input terminal of the differential amplifier.

[0014] In one embodiment, the controller performs PID control on the first error signal according to the following formula:

[0015] Δu k =K p (e k -e k-1 )+K i e k +K d (e k -2ek-1 +e k-2 )

[0016] u k =u k-1 +Δu k

[0017] Among them, K p Represents the proportionality coefficient, K i Represents the integral coefficient, K d represents the differential coefficient, e k is the input-output deviation of this time, e k-1 is the last input-output deviation, e k-2 is the previous input-output deviation, u k is the output control quantity for this time, u k-1 is the last output control quantity, Δu k It is the control quantity increment obtained by PID calculation.

[0018] In one embodiment, the thermistor is a negative temperature coefficient thermistor, and the nominal resistance of the thermistor is 10 kΩ.

[0019] In one embodiment, when the second error signal indicates that the detected temperature is less than a given temperature, a forward control signal is generated to control the semiconductor refrigeration chip to have a forward current; when the second error signal indicates that the detected temperature is greater than the given temperature, a reverse control signal is generated to control the semiconductor refrigeration chip to have a reverse current.

[0020] Compared with the prior art, the embodiments of the present disclosure have the following beneficial effects: the controller in the laser temperature control circuit can perform PID control according to the detected temperature and the given temperature, so as to adjust the output increment in the control signal, reduce the impact on the control system actuator, and thereby keep the temperature of the VCSEL laser highly stable, thereby improving the long-term stability and short-term stability of the magnetometer. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 is a schematic diagram of the structure of a laser temperature control circuit provided by an embodiment of the present disclosure;

[0023] Figure 2 is a circuit diagram of a temperature acquisition circuit provided by an embodiment of the present disclosure;

[0024] Figure 3 is a circuit diagram of a negative feedback circuit provided by an embodiment of the present disclosure;

[0025] Figure 4 It is a structural schematic diagram of another laser temperature control circuit provided in an embodiment of the present disclosure. DETAILED DESCRIPTION

[0026] The disclosed embodiments will now be described more fully with reference to the accompanying drawings in which the embodiments are shown. However, the disclosed embodiments may be implemented in many different forms and should not be construed as being limited to the embodiments specifically set forth herein; rather, the purpose of providing these embodiments is to make the disclosure exhaustive and complete and to fully convey the concepts of the embodiments to those skilled in the art so that they can implement the invention. The same reference numerals in the drawings represent the same elements, and therefore their descriptions will be omitted.

[0027] It should be understood that when an element is referred to as being connected to another element or being connected with another element, the element can be directly connected to another element, or there may be intervening elements between them. On the contrary, when an element is referred to as being directly connected to another element, there are no intervening elements.

[0028] Unless otherwise defined, all terms (including technical terms and scientific terms) used herein have the same meaning as those commonly understood by those skilled in the art to which the disclosed embodiments belong. It should also be understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with their meaning in the context of the relevant field, and unless explicitly defined as such in this article, will not be interpreted in an idealized or overly rigid sense.

[0029] The term "device" used in the embodiments may be a software component or a hardware component configured to perform a specific function. The hardware component may include a field programmable gate array (FPGA) or an application specific integrated circuit (ASIC). A software component may refer to data used by an executable code and / or data stored in an addressable storage medium and used by the executable code. Therefore, a software component may be, for example, an object-oriented software component, a class component, and a working component, and may include a process, a function, a property, a procedure, a subroutine, a program code segment, a driver, firmware, microcode, a circuit, data, a database, a data structure, a table, an array, or a variable.

[0030] The words used herein are for the purpose of describing specific embodiments and are not intended to be limiting of the present disclosure. It should be understood that the terms "include", "comprises", "comprising", "having", etc., when used in this specification, indicate the presence of the features, quantities, steps, operations, elements and / or components mentioned, but do not exclude the presence or addition of one or more other features, quantities, steps, operations, elements, components and / or groups thereof.

[0031] The laser temperature control circuit according to the embodiment of the present disclosure will be described in detail below with reference to the accompanying drawings.

[0032] Figure 1 is a schematic diagram of the structure of a laser temperature control circuit provided by an embodiment of the present disclosure; Figure 2 is a circuit diagram of a temperature acquisition circuit provided by an embodiment of the present disclosure; Figure 3 is a circuit diagram of a negative feedback circuit provided in an embodiment of the present disclosure. Figure 4 This is a schematic diagram of the structure of another laser temperature control circuit provided by the embodiment of the present disclosure. Figures 1 to 4 The laser temperature control circuit provided by the embodiments of the present disclosure is described together.

[0033] like Figure 1 As shown, an embodiment of the present disclosure provides a laser temperature control circuit, which includes: a temperature acquisition circuit 101, including a current bridge and a differential amplifier connected to the current bridge, wherein one arm of the current bridge includes a thermistor arranged outside the laser for measuring temperature; a controller 102, used to obtain a detection temperature according to a measurement signal output by the differential amplifier, and to generate a first error signal according to the detection temperature and a preset given temperature, and to perform PID (Proportional Integral Derivative) control on the first error signal to obtain a second error signal; a negative feedback circuit 103, including a digital-to-analog converter, the digital-to-analog converter is used to generate a control signal according to the second error signal to control the current size and direction of the semiconductor refrigeration plate, wherein the semiconductor refrigeration plate is used to adjust the external temperature of the laser.

[0034] In the related art, the VCSEL laser used in magnetometers has high requirements for wavelength and frequency accuracy. The wavelength of the output laser of the VCSEL laser is linearly related to the operating current and is a relatively easy-to-control variable. The temperature of the VCSEL laser will affect the stability and measurement accuracy of the magnetometer.

[0035] The laser temperature control circuit provided by the embodiment of the present disclosure is an ultra-high precision temperature control circuit, which can ensure that the temperature of the VCSEL laser will not change with the external environment and its own heating when working for a long time, thereby avoiding temperature effects such as temperature drift, so that the temperature of the VCSEL laser remains highly stable, thereby improving the long-term stability and short-term stability of the magnetometer. When the VCSEL laser is used in a magnetometer, the accuracy of magnetic field measurement can be improved.

[0036] The controller 102 may use an STM32F3 series microcontroller, which integrates a 32-bit ARM Cortex-M4 core with DSP (Digital Signal Processing) and FPU (Floating Point Unitfpu) instructions, an operating frequency of 72MHz, and advanced analog peripherals, thereby improving flexibility. This series realizes embedded DSC (Digital Signal Controller) design innovation by integrating the Cortex-M4 core, fast 12-bit 5MSPS and precise 16-bit Sigma-Delta ADC (Analog-to-Digital Converter), programmable gain amplifier, fast 50ns comparator, and a multi-function clock control unit with an operating frequency of 144MHz, thereby achieving optimal integration, wherein the programmable gain amplifier has 4-speed gain and an accuracy of 1%. It includes a series of 32-bit products with high performance, real-time functions, digital signal processing, low power consumption and low voltage operation characteristics, while also maintaining the characteristics of high integration and easy development. The unparalleled and complete range of STM32 products are based on industry standard cores and provide a large number of tools and software options, making this series of products an ideal choice for small projects and complete platforms. The technical solution of the disclosed embodiment can use the STM32F373CCT6 of this series as the processor, which has 256KBFlash, 72MHzCPU, MPU (Microprocessor Unit), 16-bit ADC and comparator, which can meet all the peripheral requirements of the design.

[0037] The temperature acquisition circuit uses a current bridge to collect the electrical signal changes caused by the change in the resistance of the thermistor with temperature changes, and provides real-time feedback data as a closed-loop control. The feedback data can be converted to digital using an external high-performance ADC chip and differentially amplified. When the ADC chip is an external chip, the controller can read the digital conversion result output by the ADC chip through the SPI interface and calculate the measured temperature based on the digital conversion result.

[0038] The ADC chip used in the embodiment of the present disclosure may be AD7799. AD7799 is a low-power, low-noise, complete analog front end suitable for high-precision measurement applications. It has a built-in low-noise 24-bit Σ-Δ ADC, which contains 3 differential analog inputs and an integrated on-chip low-noise instrumentation amplifier, so that small signals can be directly input. The root mean square (RMS) noise of AD7799 is 27nV. The on-chip features of AD7799 include a low-end power switch, reference voltage detection, programmable digital output pins, fuse current control, and an internal clock oscillator. The output data rate can be set by software programming and can vary in the range of 4.17Hz to 470Hz.

[0039] In addition, the differential amplifier can be a Sigma-Delta ADC integrated in the controller. Sigma-Delta ADC is a Σ-Δ digital-to-analog converter, which can be referred to as SDADC. It consists of an analog modulator and a downsampling decimation filter. It samples the input signal at a sampling frequency much higher than the Nyquist frequency. The sampled signal is converted into a low-bit, high-bitrate digital signal stream after being processed by the modulator. Sigma-Delta ADC can reduce the design requirements for analog circuits by adopting oversampling, noise shaping, and digital filtering technology, and achieve high precision and low power consumption that other types of ADCs cannot achieve.

[0040] like Figure 2 As shown, the current bridge includes a first resistor R1, a second resistor R2, a third resistor R3 and a fourth resistor R4 with the same resistance, and the second resistor R2 is a thermistor; the first ends of the first resistor R1 and the third resistor R3 are connected to the power supply VCC, which is used to provide a regulated power supply for the current bridge; the second end of the first resistor R1 is connected to the first end of the second resistor R2, the second end of the third resistor R3 is connected to the first end of the fourth resistor R4, and the second ends of the second resistor R2 and the fourth resistor R4 are grounded; wherein, the second end of the first resistor R1 and the first end of the second resistor R2 are connected to the positive input terminal ADCIN+ of the differential amplifier, and the second end of the third resistor R3 and the first end of the fourth resistor R4 are connected to the negative input terminal ADCIN- of the differential amplifier.

[0041] When the current bridge is in a balanced state, no current flows through the two diagonals of the current bridge, and when the current bridge is unbalanced, current flows through. The first resistor R1, the third resistor R3, and the fourth resistor R4 are all fixed resistors, so the resistance value of the second resistor R2 can be calculated by measuring the current.

[0042] In the disclosed embodiment, the thermistor is a negative temperature coefficient thermistor, and the nominal resistance of the thermistor is 10 kΩ.

[0043] Thermistors are divided into two types: NTC (Negative Temperature Coefficient thermistor) and PTC (Positive Temperature Coefficient thermistor). The resistance of NTC thermistors decreases as the temperature increases, while the resistance of PTC thermistors suddenly increases after reaching a certain temperature. At 25°C, the nominal resistance (R25) of NTC thermistors is the most commonly used resistance. In practical applications, the resistance of thermistors will change with temperature. For example, the resistance of NTC thermistors will decrease as the temperature increases, while the resistance of PTC thermistors will suddenly increase at a certain temperature.

[0044] like Figure 2 As shown, the input end of the differential amplifier A1 is connected to the current bridge. Specifically, the positive input end ADCIN+ of the differential amplifier A1 can be connected to the second end of the first resistor R1 and the first end of the second resistor R2, and the negative input end ADCIN- of the differential amplifier can be connected to the second end of the third resistor R3 and the first end of the fourth resistor R4. The differential amplifier is used to amplify the voltage change value of the second resistor R2, such as by x times, where the specific amplification factor indicated by x can be set according to the actual application scenario and is not specifically limited here. The differential amplifier A1 can be a chip AD7799, but is not limited to this.

[0045] The laser temperature control in the embodiment of the present disclosure adopts a PID control algorithm, which is a discrete incremental PID. The following formula (1) is a calculation formula of the discrete incremental PID, and formula (2) is an output formula of the discrete incremental PID. The controller performs PID control on the first error signal according to formula (1) and formula (2):

[0046] Δu k =K p (e k -e k-1 )+K i e k +K d (e k -2e k-1 +e k-2 ) (1)

[0047] u k =u k-1 +Δu k (2)

[0048] Among them, K p Represents the proportionality coefficient, K i Represents the integral coefficient, Kd represents the differential coefficient, e k is the input-output deviation of this time, e k-1 is the last input-output deviation, e k-2 is the previous input-output deviation, u k is the output control quantity for this time, u k-1 is the last output control quantity, Δu k It is the control quantity increment obtained by PID calculation.

[0049] In engineering practice, the most widely used regulator control law is proportional, integral, and differential control, referred to as PID control, also known as PID regulation. The PID controller has a simple structure, good stability, reliable operation, and convenient adjustment, making it one of the main technologies in industrial control. The basic principle of the PID control algorithm is to calculate a control quantity based on the error or deviation of the system. The control quantity consists of three parts: proportional term, integral term, and derivative term.

[0050] The proportional term is proportional to the error and is used to adjust the size of the output signal according to the size of the error. The role of the proportional term is to make the system approach the expected value faster, but it may cause overshoot or oscillation. The integral term is proportional to the accumulated value of the error and is used to eliminate the steady-state error of the system. The role of the integral term is to adjust the output signal according to the accumulation of historical errors of the system so that the system can reach the expected value more accurately. The differential term is proportional to the rate of change of the error and is used to predict the future change trend of the system. The role of the differential term is to adjust the output signal according to the rate of change of the error so that the system can approach the expected value more stably and reduce overshoot and oscillation.

[0051] PID control algorithm is widely used in various automatic control systems, such as temperature control, speed control, position control, etc. It is simple, stable, and highly adjustable, and is widely used in the field of industrial automation. The technical solution of the embodiment of the present disclosure uses incremental PID control to adjust the output increment, which can reduce the impact on the control system actuator.

[0052] like Figure 3As shown, the digital-to-analog converter can be DAC80502DRXR of the DAC80502 series, and its output DAC1 is connected to the signal source for controlling heating. The negative feedback circuit also includes a power amplifier connected to the digital-to-analog converter, which is used to amplify the control signal and input the semiconductor cooling chip. The power amplifier is implemented by the power amplification function of the audio amplifier MAX9711. MAX9711 is a stereo / mono 3W BTL (Bridge-Tied Load) audio power amplifier. The device complies with the PC99 / 01 standard, uses a single power supply of 4.5V to 5.5V, and has the industry's top level of 100dB PSRR (Power Supply Rejection Ratio), which allows the device to work in a noisy power supply environment without the need for an additional high-cost power supply. The ultra-low total harmonic distortion plus noise of 0.005% can ensure low-noise and low-distortion amplification of the audio signal, and the proprietary click / pop suppression circuit can eliminate transient noise when the power is turned on and off. Its energy-saving features include: low offset voltage of 2mV to minimize DC current through the speaker, low supply current of 7mA, and 0.5pA current in shutdown mode. The mute function can quickly turn the output on or off. The device has thermal overload protection and operates over the -40℃ to +85℃ extended temperature range.

[0053] The MAX9711 is powered by a single 5V power supply and has an internally generated, power-independent, ground-referenced 2.5V common-mode bias voltage. By inputting different voltage values, the MAX9711 will output positive and negative voltages between the positive and negative output terminals to drive the semiconductor refrigeration chip for cooling or heating.

[0054] like Figure 3 As shown, the controller controls the digital-to-analog converter DAC80502DRXR to output an analog voltage through an SPI (Serial Peripheral Interface) interface. The analog voltage is amplified by an audio amplifier MAX9711 and then input to a semiconductor refrigeration chip for cooling or heating.

[0055] Specifically, the DAC80502DRXR output pin VOUTB outputs a control signal, and the pin SPI2C is grounded, which means that the pin selects the SPI mode between the two transmission modes of the serial interface, SPI and I2C (Inter-Integrated Circuit). Pin SDIN / SDA is the signal input port in the SPI mode. The second error signal output by the controller is input to the DAC80502DRXR via the pin SDIN / SDA for digital-to-analog conversion to obtain a control signal. The control signal is input via the pin IN of the MAX9711, and is output to the power port of the semiconductor cooling chip by the positive output terminal OUT+ and the negative output terminal OUT- of the MAX9711.

[0056] When the second error signal indicates that the detected temperature is lower than the given temperature, a forward control signal is generated to control the semiconductor refrigeration chip to have a forward current; when the second error signal indicates that the detected temperature is higher than the given temperature, a reverse control signal is generated to control the semiconductor refrigeration chip to have a reverse current.

[0057] Semiconductor cooling chips, also known as TEC (Thermo Electric Cooler), are made using the Peltier effect of semiconductor materials. The so-called Peltier effect refers to the phenomenon that when a direct current passes through a couple composed of two semiconductor materials, one end absorbs heat and the other end releases heat. Thermoelectric cooling chips use the Peltier effect of semiconductor materials. When direct current passes through a couple composed of two different semiconductor materials in series, heat can be absorbed and released at both ends of the couple, respectively, to achieve the purpose of cooling. It is a refrigeration technology that produces negative thermal resistance, which is characterized by no moving parts and relatively high reliability.

[0058] When the semiconductor refrigerator has a forward current, the side of the semiconductor refrigerator close to the laser absorbs heat, thereby cooling the laser. When the semiconductor refrigerator has a reverse current, the hot and cold ends of the semiconductor refrigerator can be swapped, and the side of the semiconductor refrigerator close to the laser releases heat, thereby heating the laser.

[0059] In the embodiments of the present disclosure, Figure 4 As shown in the figure, the laser temperature control circuit first obtains the measurement signal from the current bridge, amplifies it through the differential amplifier AD7799, and then performs PID control by the controller STM32F373. Finally, the current direction of the semiconductor cooling plate is controlled by the digital-to-analog converter DAC80502 and the power amplifier MAX9711 to control the laser temperature. Among them, the maximum temperature difference of the laser TEC cooler is >70℃, the nominal resistance of the thermistor is 10K ohms, the B value is 3950K+ / -1%@25 degrees Celsius, the temperature control range is -35℃~+135℃, and the resolution of the temperature acquisition circuit is 0.001℃.

[0060] According to the laser temperature control circuit provided by the embodiment of the present disclosure, the controller in the laser temperature control circuit can perform PID control according to the detected temperature and the given temperature, so that the output increment in the control signal can be adjusted to reduce the impact on the control system actuator, thereby keeping the temperature of the VCSEL laser highly stable and improving the long-term stability and short-term stability of the magnetometer.

[0061] The above description is only a preferred embodiment of the present disclosure and is not intended to limit the present disclosure. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A laser temperature control circuit, characterized in that: The laser temperature control circuit comprises: A temperature acquisition circuit, comprising a current bridge and a differential amplifier connected to the current bridge, wherein one arm of the current bridge comprises a thermistor disposed outside the laser for measuring temperature; A controller, configured to obtain a detected temperature according to a measurement signal output by the differential amplifier, generate a first error signal according to the detected temperature and a preset given temperature, and perform proportional-integral-differential (PID) control on the first error signal to obtain a second error signal; The negative feedback circuit includes a digital-to-analog converter, which is used to generate a control signal according to a second error signal to control the current size and direction of the semiconductor refrigeration chip, wherein the semiconductor refrigeration chip is used to adjust the external temperature of the laser.

2. The laser temperature control circuit according to claim 1, characterized in that: The differential amplifier is AD7799.

3. The laser temperature control circuit according to claim 1, characterized in that: The differential amplifier is a Sigma-Delta ADC integrated in the controller.

4. The laser temperature control circuit according to claim 1, characterized in that: The negative feedback circuit also includes a power amplifier connected to the digital-to-analog converter, and the power amplifier is used to amplify the control signal and input the control signal into the semiconductor refrigeration chip.

5. The laser temperature control circuit according to claim 4, characterized in that: The digital-to-analog converter is DAC80502, and / or the power amplifier is MAX9711.

6. The laser temperature control circuit according to claim 1, characterized in that: The controller controls the digital-to-analog converter to output an analog voltage via a serial peripheral device interface (SPI).

7. The laser temperature control circuit according to claim 1, characterized in that: The current bridge includes a first resistor, a second resistor, a third resistor and a fourth resistor with the same resistance value, the second resistor is the thermistor; the first ends of the first resistor and the third resistor are connected to a power supply, used to provide a regulated power supply for the current bridge; the second end of the first resistor is connected to the first end of the second resistor, the second end of the third resistor is connected to the first end of the fourth resistor, and the second ends of the second resistor and the fourth resistor are grounded; wherein the second end of the first resistor and the first end of the second resistor are connected to the positive input terminal of the differential amplifier, and the second end of the third resistor and the first end of the fourth resistor are connected to the negative input terminal of the differential amplifier.

8. The laser temperature control circuit according to claim 1, characterized in that: The controller performs PID control on the first error signal according to the following formula: Δu k =K p (e k -e k-1 )+K i e k +K d (e k -2e k-1 +e k-2 ) u k =u k-1 +Δu k Among them, K p Represents the proportionality coefficient, K i Represents the integral coefficient, K d represents the differential coefficient, e k is the input-output deviation of this time, e k-1 is the last input-output deviation, e k-2 is the previous input-output deviation, u k is the output control quantity for this time, u k-1 is the last output control quantity, Δu k It is the control quantity increment obtained by PID calculation.

9. The laser temperature control circuit according to claim 7, characterized in that: The thermistor is a negative temperature coefficient thermistor, and the nominal resistance of the thermistor is 10 kΩ.

10. The laser temperature control circuit according to claim 1, characterized in that: When the second error signal indicates that the detected temperature is lower than the given temperature, a forward control signal is generated to control the semiconductor refrigeration chip to have a forward current; when the second error signal indicates that the detected temperature is higher than the given temperature, a reverse control signal is generated to control the semiconductor refrigeration chip to have a reverse current.

Images