CN111224316A - Semiconductor laser driving system and loop noise suppression method with online adjustable parameters - Google Patents
Semiconductor laser driving system and loop noise suppression method with online adjustable parameters Download PDFInfo
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- CN111224316A CN111224316A CN202010105490.7A CN202010105490A CN111224316A CN 111224316 A CN111224316 A CN 111224316A CN 202010105490 A CN202010105490 A CN 202010105490A CN 111224316 A CN111224316 A CN 111224316A
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Abstract
The invention discloses a semiconductor laser driving system and a loop noise suppression method with online adjustable parameters. The system comprises a semiconductor laser, a singlechip, a communication interface unit, a modulated wave generating unit, a set signal processing unit, an automatic current control unit, a protection unit, a temperature control unit, a power supply conversion unit, a D/A converter and an A/D converter. The automatic current control unit takes a deep negative feedback framework as a core, a loop multipoint noise suppression network with online adjustable parameters is introduced into the system through loop analysis, an upper computer sends a control instruction to an STM32 controller through a communication interface unit, and the parameters of the noise suppression network are changed online according to a set target frequency value, so that multipoint noise suppression in the control loop is realized, and the loop response capability under the target set frequency is effectively ensured while the anti-interference capability is good. The protection function is designed on both software and hardware, and the safe operation of the laser is ensured.
Description
Technical Field
The invention relates to the field of trace gas detection and optical fiber sensing of an absorption spectrum technology, in particular to a semiconductor laser driving system and a loop noise suppression method with online adjustable parameters.
Background
Semiconductor lasers play a significant role in many fields such as communication, medical treatment, information processing, pollution monitoring and the like.
For example, in the technical applications of optical fiber sensing, absorption spectrum trace gas detection and the like, a semiconductor laser is mostly adopted as a light source, the noise size, the frequency stability and the anti-interference capability of an emitted signal of the laser directly affect the precision and the sensitivity of a measurement system, and the stability of a driving circuit is also important besides the correlation with the performance of the semiconductor laser.
Laser applications are characterized by diversity and complexity, and therefore, higher requirements are placed on the driving system and the protection system of the laser. In order to achieve excellent output performance of a semiconductor laser, it is necessary to ensure stability of dc bias and suppress influence of noise of a driving circuit on a modulation signal, and therefore, how to improve stability and interference resistance of a driving system of the semiconductor laser is a technical problem to be solved.
Disclosure of Invention
The invention aims to provide a semiconductor laser driving system and a loop noise suppression method with online adjustable parameters, which are used for reducing the output noise of the laser driving system, improving the stability of the laser driving system in working under a complex environment and realizing the accurate control of the output frequency.
The invention provides a semiconductor laser driving system, which comprises a semiconductor laser, a singlechip, a modulated wave generating unit, a set signal processing unit, an automatic current control unit, a protection unit, a communication interface unit, a temperature control unit, a power supply conversion unit, a reset unit, a clock unit, a D/A converter and an A/D converter, wherein the singlechip is connected with the semiconductor laser; wherein the content of the first and second substances,
the semiconductor laser comprises a laser diode LD1, a semiconductor cooler TEC and a negative temperature coefficient thermistor NTC, wherein the laser diode is used for emitting laser, the semiconductor cooler is used for refrigerating or heating a laser cavity, and the negative temperature coefficient thermistor reflects the temperature into the change of resistance value;
the singlechip is a core controller of the system, completes the overall control of the driving system according to a written instruction, coordinates the work of each part, communicates with an upper computer, sets and outputs related parameters of direct current bias, a modulated wave signal and a noise suppression network through the D/A converter, can realize the selection of two working modes of direct current and modulation, samples current state parameters currently output by the driving system through the current sampling unit and the A/D converter, transmits the current state parameters to the upper computer for monitoring after processing, saves the system parameters when the singlechip is shut down last time in an internal Flash of the singlechip as default values for restarting when the singlechip is started next time, protects the setting in the writing of a program of the singlechip, and prevents the laser from being damaged due to overlarge output of the driving system caused by misoperation;
the modulation wave generating unit can generate sine waves, square waves and triangular waves, and the frequency and amplitude of the modulation waves can be adjusted;
a signal processing unit is arranged, a direct current bias setting signal is converted into a voltage signal through the D/A converter, is connected with a following circuit formed by operational amplifiers, is superposed with a modulation wave setting signal passing through a high-pass filter circuit through an adding circuit, and is converted into a positive value through an inverting circuit to be used as an input end of the automatic current control unit;
the automatic current control unit adopts a deep negative feedback framework to provide low-noise driving modulation current for the laser diode, converts a current signal into a voltage signal and transmits the voltage signal to the singlechip through the follower circuit and the A/D converter, and the amplitude, the frequency and the waveform of the modulation wave are determined by setting signals;
the protection unit comprises a slow start module, an overcurrent protection module and an anti-reverse current module, wherein the slow start module is used for slowly powering on a current branch when a circuit is just powered on and operated to prevent voltage at two ends of the laser diode from suddenly changing, when the circuit fails or the output current value of the current branch exceeds a limit value due to manual misoperation, the overcurrent protection module can automatically disconnect the current branch to start protection, an alarm lamp is turned on, and when reverse current occurs in the current branch, the anti-reverse current module can enable the reverse current to flow to other branches to avoid large negative voltage at two ends of the laser diode, so that the operation safety of the laser is greatly improved;
the communication interface unit is used for carrying out communication between the upper computer and the singlechip and is used for sending control instructions and returning driving current state parameters;
the temperature control unit is used for converting the ambient temperature value of the cavity of the current semiconductor laser into a resistance value through the thermistor with the negative temperature coefficient, converting the resistance value into a voltage value, comparing the voltage value with a temperature set value, and controlling the TEC driver through a hardware PID (proportion integration differentiation) so as to adjust the temperature of the cavity of the semiconductor laser and maintain the temperature at a stable value;
the power supply conversion unit converts the +/-15V direct current input into +/-12V, + 5V, +3.3V, +1.5V power supply groups and supplies power to the analog circuit and the digital circuit in groups;
the resetting unit is used for ensuring that the laser driving system can be reset and starts to operate from a default state;
the clock unit is used for generating 8MHz pulse signals and using the pulse signals as a working clock of the singlechip;
a D/A converter for converting the DC bias setting signal from a digital signal to an analog voltage signal when setting the DC bias current;
the A/D converter is used for converting the current sampling value converted into the voltage signal from the analog voltage signal into a digital signal;
when the laser driving system is powered on, the singlechip firstly accesses the Flash in the singlechip to read a control command word stored when the laser driving system is powered off last time, the singlechip communicates with the D/A converter through the hardware SPI to set the magnitude of the output current direct current bias according to the control command word, communicates with the DDS module through the software SPI to set the waveform and the frequency of the modulation wave, the direct current bias setting signal and the modulation wave setting signal complete voltage following and superposition through the setting signal processing unit to generate a control signal to be provided for the automatic current control unit, so that the stable control of the output current is realized, a deviation value is obtained by an H-bridge circuit in temperature setting and temperature sampling, the deviation value controls the TEC driver through the hardware PID, so that the TEC is driven, and the temperature in a laser cavity is regulated, when the current output current state needs to be changed, a control word is set on the upper computer, and the communication interface unit is communicated with the single chip microcomputer, so that the setting of the driving current is completed.
Preferably, the automatic current control unit includes: u13 is put to fortune, and U14 is put to fortune, MOS pipe Q3, sampling resistor R27, loop noise suppression network, set up the signal processing unit connect in U13 forward input end is connected to fortune, sampling resistor R27 converts current signal into voltage signal feedback to fortune is put U13 reverse input end, fortune is put U13 output and is connected loop noise suppression network input end, loop noise suppression network output connect in MOS pipe Q3 grid, MOS pipe Q3 drain-electrode with LD1 negative pole is connected, MOS pipe Q3 source-electrode links to each other with sampling resistor R27 one end, sampling resistor R27 one end connect in the forward input end of the voltage follower that U4 constitutes is put to fortune, the reverse input end of fortune is put U14 connect in fortune is put U14 output, fortune is put U14 output and is connected in A/D converter input.
Preferably, the loop noise suppression network is configured to suppress loop noise at the signal setting end and the output end of the operational amplifier U13 while ensuring a response capability of the driving current at the target setting frequency, where the suppression of the loop noise over ten-fold frequency range of the target frequency can be up to 20dB or more.
Preferably, the loop noise suppression network comprises: one end of the adjustable varistor is connected to the output end of the operational amplifier U13, the other end of the adjustable varistor is connected to the gate of the MOS transistor Q3 and one end of the capacitor C50, the other end of the capacitor C50 is connected to one end of the resistor R26, and the other end of the resistor R26 is connected to ground.
Preferably, the resistor R25 is an adjustable resistor, and the resistance of the adjustable resistor R25 can be adjusted according to the target setting frequency of the modulation wave, so as to adjust the parameters of the noise suppression network.
Preferably, the adjustable resistor R25 is a mechanical potentiometer, and the resistance of the mechanical potentiometer R25 can be adjusted according to the target setting frequency of the modulation wave, so as to adjust the parameters of the noise suppression network.
Preferably, the adjustable resistor R25 is a digital potentiometer, and the resistance of the digital potentiometer R25 can be adjusted online according to the target setting frequency of the modulated wave, so as to adjust the parameters of the noise suppression network online.
A loop noise suppression method with online adjustable parameters is suitable for a semiconductor laser driving system, and comprises the following steps: establishing a simplified small-signal loop model according to the model of a component in a loop, analyzing a control loop, making a loop amplitude-frequency characteristic curve, introducing a loop noise suppression network with online adjustable parameters according to the loop amplitude-frequency characteristic curve, primarily determining the structural composition and the component parameters of the loop noise suppression network, then performing circuit simulation by adopting Tina-TI, further adjusting the structural composition and the component parameters of the loop noise suppression network according to the simulation result, and finally verifying by adopting an experiment, thereby finally determining the structural composition and the component parameters of the loop noise suppression network.
Compared with the prior art, the invention has the advantages that:
(1) the laser driving system realizes the current driving and the temperature control of the laser, and the direct current bias of the driving current, the type of the modulation wave, the frequency of the modulation wave, the amplitude of the modulation wave and the temperature of the cavity of the laser can be adjusted, thereby being convenient for the measurement and the debugging in the optical system.
(2) The laser protection units are designed in the software part and the hardware part, so that the damage to the laser caused by system failure or manual misoperation is prevented, and the safety of the laser operation is ensured.
(3) The invention designs the online adjustable loop multipoint noise suppression network, changes the parameters of the noise suppression network online according to the set target frequency value, realizes the multipoint noise suppression in the control loop, effectively ensures the loop response capability under the target set frequency and has good anti-interference capability.
(4) The invention provides a loop noise suppression method with online adjustable parameters, which establishes a small signal model for a control loop in a driving system, analyzes the loop, introduces a loop noise suppression network with online adjustable parameters by combining simulation and experiment, and provides a basis for designing and expanding a high-stability laser driving system under different index parameter requirements.
According to the semiconductor laser driving system and the loop noise suppression method with the online adjustable parameters, a small signal model is established for a control loop in the driving system, loop analysis is carried out, a loop noise suppression network is introduced by combining Tina-TI simulation and experiments, the parameters of the noise suppression network are changed online according to a set target frequency value, multipoint noise suppression in the control loop is realized, and the loop response capability under the target set frequency is effectively ensured while the good anti-interference capability is realized.
Drawings
Fig. 1 is a block diagram of a semiconductor laser driving system according to an embodiment of the present invention;
fig. 2 is a minimum system and a communication interface unit of a single chip microcomputer of a semiconductor laser driving system according to an embodiment of the present invention;
fig. 3 is a direct current bias setting unit, a modulated wave generating unit, and a setting signal processing unit of the semiconductor laser driving system according to the embodiment of the present invention;
fig. 4 illustrates an automatic current control unit and a protection unit of a semiconductor laser driving system according to an embodiment of the present invention;
fig. 5 is a temperature control unit of a semiconductor laser driving system according to an embodiment of the present invention;
fig. 6a is a simple small-signal model diagram of a loop of an automatic current control unit before a loop noise suppression network is introduced according to an embodiment of the present invention;
fig. 6b is a schematic diagram of a simple small signal model of an automatic current control unit loop after a mechanical potentiometer is introduced into a loop noise suppression network according to an embodiment of the present invention;
FIG. 6c is a schematic diagram of a simple small signal model of a loop in an automatic current control unit after a digital potentiometer is introduced into a loop noise suppression network according to an embodiment of the present invention;
fig. 7a is an analysis diagram of the amplitude-frequency characteristics of the loop before the automatic current control unit is introduced into the loop noise suppression network according to the embodiment of the present invention;
fig. 7b is an analysis diagram of the loop amplitude-frequency characteristics of the automatic current control unit after the loop noise suppression network is introduced by using the mechanical potentiometer according to the embodiment of the present invention;
fig. 7c is an analysis diagram of the loop amplitude-frequency characteristics of the automatic current control unit after the loop noise suppression network is introduced by using the digital potentiometer according to the embodiment of the present invention;
fig. 8a is a circuit diagram of Tina-TI simulation before the loop noise suppression network is introduced into the automatic current control unit according to the embodiment of the present invention;
fig. 8b is a circuit diagram of an automatic current control unit Tina-TI simulation circuit after a loop noise suppression network is introduced by using a mechanical potentiometer according to an embodiment of the present invention;
FIG. 8c is a circuit diagram of an automatic current control unit Tina-TI simulation circuit according to an embodiment of the present invention after a loop noise suppression network is introduced by using a digital potentiometer;
fig. 9a is a simulation curve of loop amplitude-frequency characteristics of an automatic current control unit before a loop noise suppression network is introduced according to an embodiment of the present invention;
fig. 9b is a loop amplitude-frequency characteristic simulation curve of the automatic current control unit after the loop noise suppression network is introduced by using the mechanical potentiometer according to the embodiment of the present invention;
fig. 9c is a loop amplitude-frequency characteristic simulation curve of an automatic current control unit of a loop noise suppression network introduced by using a digital potentiometer according to an embodiment of the present invention;
fig. 10a is a simulation result of an anti-interference capability test before a loop noise suppression network is introduced into an automatic current control unit loop according to an embodiment of the present invention;
fig. 10b is a simulation result of an anti-interference capability test after a loop noise suppression network is introduced into a loop of an automatic current control unit according to an embodiment of the present invention;
fig. 11 is a loop responsiveness test simulation result after a loop of an automatic current control unit is introduced into a loop noise suppression network according to an embodiment of the present invention;
fig. 12a is a result of experimental testing of anti-interference capability of a loop before and after the loop of an automatic current control unit is introduced into a loop noise suppression network according to an embodiment of the present invention;
fig. 12b is a loop responsivity experimental test result at a target setting frequency before and after the loop of the automatic current control unit is introduced into the loop noise suppression network according to the embodiment of the present invention;
fig. 13 is a frequency control linearity and precision experimental test result of the semiconductor laser driving system according to the embodiment of the present invention;
fig. 14a is a short-term stability test of the output current of the semiconductor laser driving system according to the embodiment of the present invention;
fig. 14b is a long-term stability test of the output current of the semiconductor laser driving system provided by the embodiment of the present invention under the condition of simulating the environmental temperature variation;
fig. 15 is a flowchart of software of a single chip microcomputer of a semiconductor laser driving system according to an embodiment of the present invention.
Detailed description of the preferred embodiments
The invention is further described with reference to the following figures and detailed description.
Fig. 1 is a schematic block diagram of a semiconductor laser driving system in this embodiment, and the present invention provides a semiconductor laser driving system, including: the device comprises a semiconductor laser, a singlechip, a modulated wave generating unit, a setting signal processing unit, an automatic current control unit, a protection unit, a communication interface unit, a temperature control unit, a power supply conversion unit, a reset unit, a clock unit, a D/A converter and an A/D converter;
the semiconductor laser comprises a laser diode LD1, a semiconductor cooler TEC and a negative temperature coefficient thermistor NTC, wherein the laser diode is used for emitting laser, the semiconductor cooler is used for refrigerating or heating a laser cavity, and the negative temperature coefficient thermistor reflects the temperature into the change of resistance value;
the singlechip is a core controller of the system, completes the overall control of the driving system according to a written command, coordinates the work of each part, communicates with an upper computer, sets relevant parameters of output direct current bias, a modulated wave signal and a noise suppression network through the D/A converter, and can realize the selection of two working modes of direct current and modulation. Sampling current state parameters output by a driving system at present through a current sampling unit and the A/D converter, processing the current state parameters and transmitting the current state parameters to an upper computer for monitoring, wherein the system parameters in the last shutdown are stored in an internal Flash of the single chip microcomputer to serve as default values for the next startup and restart;
the modulation wave generating unit can generate sine waves, square waves and triangular waves, and the frequency and amplitude of the modulation waves can be adjusted;
a signal processing unit is arranged, a direct current bias setting signal is converted into a voltage signal through the D/A converter, is connected with a following circuit formed by operational amplifiers, is superposed with a modulation wave setting signal passing through a high-pass filtering module through an adding circuit, and is converted into a positive value through an inverting circuit to be used as an input end of the automatic current control unit;
the automatic current control unit adopts a deep negative feedback framework to provide low-noise driving modulation current for the laser diode, converts a current signal into a voltage signal and transmits the voltage signal to the singlechip through the follower circuit and the A/D converter, and the amplitude, the frequency and the waveform of the modulation wave are determined by setting signals;
the protection unit comprises an over-slow starting module, an over-current protection module and an anti-reverse current module, wherein the slow starting module is used for slowly powering on a current branch when a circuit is just powered on and runs to prevent voltage at two ends of the laser diode from suddenly changing, when the circuit fails or the output current value of the current branch exceeds a limit value due to manual misoperation, the over-current protection module can automatically disconnect the current branch to start protection, and when the current branch has reverse current, the anti-reverse current module can enable the reverse current to flow to other branches to avoid large negative voltage at two ends of the laser diode, so that the operation safety of the laser is greatly improved;
the communication interface unit is used for carrying out communication between the upper computer and the singlechip and is used for sending control instructions and returning driving current state parameters; the temperature control unit is used for converting the ambient temperature value of the cavity of the current semiconductor laser into a resistance value through the thermistor with the negative temperature coefficient, converting the resistance value into a voltage value, comparing the voltage value with a temperature set value, and controlling the TEC driver through a hardware PID (proportion integration differentiation) so as to adjust the temperature of the cavity of the semiconductor laser and maintain the temperature at a stable value;
the power supply conversion unit converts the +/-15V direct current input into +/-12V, + 5V, +3.3V, +1.5V power supply groups and supplies power to the analog circuit and the digital circuit in groups;
the resetting unit is used for ensuring that the laser driving system can be reset and starts to operate from a default state;
the clock unit is used for generating 8MHz pulse signals and using the pulse signals as a working clock of the singlechip;
a D/A converter for converting the DC bias setting signal from a digital signal to an analog voltage signal when setting the DC bias current;
the A/D converter is used for converting the current sampling value converted into the voltage signal from the analog voltage signal into a digital signal;
a software implementation flow diagram of a semiconductor laser driving system in an embodiment of the present invention is shown in fig. 15, and includes a main program diagram, an interrupt subroutine diagram, and an automatic current control unit state parameter setting subroutine diagram; the single chip microcomputer STM32F103RCT 6U 1 is responsible for control and coordination of the whole system, after the semiconductor laser driving system is powered on or reset, the single chip microcomputer U1 firstly completes initialization work of each module, then reads control command words stored in power failure of the last shutdown from internal Flash, and processes the command words to enable the automatic current control unit 42 to recover the working state of the last shutdown. When parameters such as direct current bias, modulation wave waveform and frequency of the driving current need to be changed, a control word is sent to a lower computer from an upper computer through a communication interface unit 22, a serial port interrupt function is triggered, the control word is read from a queue, whether the current state parameter is transmitted to the upper computer and whether the working state of a laser driving system needs to be modified or not is judged according to instruction requirements, if the current driving current state is read only, the driving system reads the current value through an A/D converter, and sends the current value, the modulation wave waveform and the modulation wave frequency to the upper computer to be displayed to a user. And if the current working state of the driving system needs to be modified, storing a new control word, and setting the state of the driving current according to the instruction requirement. And parameters of the noise suppression network are changed according to the setting target of the modulation wave, so that the anti-interference capability of the automatic current control unit is improved while the loop responsivity of the automatic current control unit is ensured. In order to prevent the phenomenon that the laser is damaged due to overlarge output of the driving current caused by the error of an input instruction, protection is added to software, and when the current set by the misoperation of a user is larger than the maximum current borne by the laser, the driving system can automatically limit the driving current within the range of a safety threshold value, so that the safe operation of the laser is ensured.
Fig. 2 is a schematic diagram of a partial circuit of a semiconductor laser driving system according to an embodiment of the present invention, in which a clock unit 21a includes a capacitor C1, a capacitor C2, and an 8MHz crystal oscillator Y1, and the clock unit 21a is connected to a pin 5 and a pin 6 of a single chip microcomputer U1, respectively, to provide a working clock for the single chip microcomputer U1; the reset unit 21b comprises a capacitor C3, a resistor R2 and a key switch S1, when the key switch S1 is pressed, the 7 pin NRST of the singlechip U1 is pulled low, and when the key switch S1 is released, the power supply slowly charges the capacitor C3 through the resistor R2, so that the reset of the system is realized; the communication interface unit 22 comprises a USB-to-serial port chip CH340-G, a capacitor C6, a capacitor C7, a capacitor C8, a capacitor C9, a capacitor C10, a crystal oscillator Y1 and a USB socket U4, wherein a clock circuit consisting of the capacitor C9, the capacitor C10 and a 12MHz crystal oscillator Y2 provides a working clock for the communication interface unit;
fig. 3 is a schematic diagram of a partial circuit of a semiconductor laser driving system according to an embodiment of the present invention, where the modulation wave generating unit 31 includes a modulation wave generating circuit 31a, a high-pass filter circuit 31b, and a voltage follower circuit 31c, the modulation wave generating circuit 31a uses a DDS generator U5 as a core, and communicates with a single-chip microcomputer U1 through a software SPI, so as to set a waveform and a frequency for generating a modulation wave, an amplitude of the modulation wave is set through a sliding rheostat R11, an output end of the modulation wave generating circuit 31a is connected to an input end of the high-pass filter circuit 31b, so as to filter a dc component in an output signal of the modulation wave generating circuit, and an output end of the high-pass filter circuit 31b is connected to; the direct current bias voltage setting unit 32 comprises a D/A converter 32a and a voltage follower circuit 32b, the D/A converter 32a communicates with the single chip microcomputer through a hardware SPI (serial peripheral interface) to generate a direct current bias setting signal, the output end of the D/A converter 32a is connected with the input end of the voltage follower circuit 32b, and the voltage follower circuit 31c and the voltage follower circuit 32b both play an isolation role to reduce the influence of a post-stage circuit on a pre-stage circuit; the setting signal processing unit 33 includes an addition circuit 33a and an inverse proportion circuit 33b, the voltage follower circuit 31c and the voltage follower circuit 32b are respectively connected to two input terminals of the addition circuit 33a, two sets of setting signals are superimposed by the addition circuit 33a, an output terminal of the addition circuit 33a is connected to an input terminal of the inverse proportion circuit 33b, so that the voltage setting signal is positive, and the signal is used as an input signal of the automatic current control unit 42, thereby setting a state of outputting a driving current;
fig. 4 is a schematic diagram of a partial circuit of a semiconductor laser driving system according to an embodiment of the present invention, in which the protection unit 41 includes a slow start module 41a, an overcurrent protection module 41b and an anti-reverse current module 41C, the slow start module 41a mainly includes a capacitor C41, a resistor R20 and a MOS transistor Q1, at the moment of powering up, a voltage across the capacitor C41 is close to 0V, so that a gate voltage of the MOS transistor Q1 is close to +12V, at this time, the MOS transistor Q1 is in a turned-off state, as the capacitor C41 is charged, the gate voltage of the MOS transistor Q1 is slowly reduced, the MOS transistor Q7 is slowly turned on, an output driving current of the current branch is slowly increased to a set value, the overcurrent protection module 41b mainly includes a resistor R21, a resistor R24, an operational amplifier U12 and a MOS transistor Q2, when the output current is smaller than a limit value, an output voltage of the operational amplifier U12 is close to 5390V, the MOS, when misoperation or circuit fault occurs and the output current is too large to exceed the limit value, the voltage at the output end of the U12 is close to +12V, the MOS tube Q2 is turned off, the current source branch is turned off, the warning lamp D1 is turned on at the same time, the reverse current prevention module 41c mainly comprises a Schottky diode D2, when reverse current occurs in the current branch, the reverse current can pass through the D2, and too large reverse voltage can not occur at the two ends of the LD 1. The automatic current control unit 42 takes a deep negative feedback architecture as a core, and mainly comprises an operational amplifier U13, an operational amplifier U14, an MOS tube Q3, a sampling resistor R27 and a loop noise suppression network 42a, wherein the sampling resistor R27 converts a current signal into a voltage signal and feeds the voltage signal back to the reverse input end of the operational amplifier U13 so as to compare with a setting signal, a direct current component is provided by a D/A converter, the voltage signal is between 0V and 3.3V, in order to ensure the control precision within 0-110mA, a high-precision sampling resistor with the precision of 30 omega, the precision of 0.1 percent and the temperature drift coefficient of 25 ppm/DEG C is selected, an error signal of the feedback signal and the setting signal is reflected at the output end of the operational amplifier U13, the output end of the operational amplifier U13 is connected with the input end of the loop noise suppression network, the output end of the loop noise suppression network is connected with the grid of the MOS tube Q3, the conduction degree, the drain electrode of the MOS tube Q3 is connected with the cathode of the LD1, the source electrode of the MOS tube Q3 is connected with one end of a sampling resistor R27, one end of the sampling resistor R27 is connected with the positive input end of a voltage follower formed by the operational amplifier U4, the reverse input end of the operational amplifier U14 is connected with the output end of the operational amplifier U14, and the output end of the operational amplifier U14 is connected with the input end of the A/D converter, so that the currently output drive current parameters are transmitted to an upper computer and displayed to a user. The noise suppression network 42a mainly comprises a digital potentiometer R25, a capacitor C50 and a resistor R26, the network ensures the response capability of a loop under a target set frequency, and simultaneously suppresses the loop noise at a signal set end and an output end of an operational amplifier U13, the suppression of the loop noise above ten-fold frequency range of the target frequency can reach more than 20dB, and the anti-interference capability and the stability of the system are greatly improved.
Fig. 5 is a schematic circuit diagram of a temperature control part of a semiconductor laser driving system according to an embodiment of the present invention, which includes a temperature sampling circuit 51, a temperature setting circuit 52, a PID circuit 53 and a TEC driving circuit 54, where the temperature sampling circuit 51 and the temperature setting circuit 52 form an H-bridge circuit, the NTC is one of bridge arms of the H-bridge, a deviation between a set voltage and a sampled voltage signal is used as an input of the PID circuit 53, and a current temperature value and an output of a new PID circuit are combined, a 10-pin CTL1 of U16 is controlled according to the output of the PID circuit to control a current flowing through the NTC, and a target temperature value to be controlled of a semiconductor laser cavity can be set by adjusting a slide rheostat R33. 54a limits the maximum output current value flowing through the TEC and the maximum output voltage value across the TEC, and the limit value can be set by adjusting the values of the resistor R34 and the resistor R35.
The embodiment of the invention also provides a semiconductor laser driving system and a loop noise suppression method with online adjustable parameters, and the design target of the output driving current frequency adjusting range of the embodiment of the invention is 0-50kHz and U is used13Low frequency dominant pole fpLHigh frequency dominant pole fpHAnd open loop output resistance RoFor modeling according to the modeling, the simplified small-signal model diagram of the automatic current control loop is shown in fig. 6a, 61 is a simple small-signal model of the operational amplifier, 62 is a MOS transistor Q3Simple small-signal model of (2), RgIs Q3Current limiting resistor of grid, RgNot only in favor of the division of the following loopAlso, an interface is provided for the introduction of a noise suppression network. RinFor fortune to put U13VCVS is a voltage-controlled voltage source, Cgs、Cgd、CdsAnd RdsAre MOS transistors Q respectively3The gate-source capacitance, the gate-drain capacitance, the drain-source capacitance, and the drain-source on-resistance, Ra、CaForm an operational amplifier U13Low frequency dominant pole fpL，Rb、CbForm U13High frequency dominant pole fpH. This is obtained by the following formula:
the analysis of LOOP # 0 is shown in fig. 7 a. When the output current of the constant current source branch of the unit is dozens of milliamperes, the MOS tube Q3Low frequency mutual conductance gmCan take 1s, so the equivalent capacitance C from the MOS tube grid to the groundgAnd a resistor RgAnd operational amplifier U13Open loop output resistor RoA high frequency zero is generated at 1/β (the LOOP gain of the AC small signal LOOP of the LOOP) (i.e., a high frequency pole is generated at LOOP # 0). when the frequency is less than the pole, 1/β is about 0dB (i.e., log)101dB), when the frequency is higher than the pole, 1/β rises at the speed of +20dB/decade, the position of the high-frequency pole can be obtained according to the Tina-TI simulation, as shown in figure 10a, and the relation is shown as the formula (3), and the capacitance to ground C can also be obtainedgThe value of (c).
introducing a pair of zero poles f on 1/βznAnd fpnAs shown in FIG. 8b, for VOUT/VINCarrying out derivation analysis to obtain the formula (4), VINTo set the voltage, VOUTThe voltage across the sampling resistor is used. As can be seen from this formula, the compound,at the cut-off frequency fcl' front, VOUT/VIN0dB, no A when truncated to frequencyolβ to correct the error, VOUT/VINBegin to follow Aolthe curve starts to descend at the speed of-20 dB/Decode, and then the descending speed of-20 dB/Decode is increased every 1/β zero (namely, the pole on the loop) is passed, which is also beneficial to increasing the attenuation speed of the loop to the high-frequency noise at the input end.
Fixed fznThe position is not changed, and f is adjusted according to the setting frequency of the alternating current component of the setting voltagepnPosition of, i.e. adjustable loop VOUT/VINBandwidth of, suppressing high frequency noise pairs V at the forward input of the loopOUTbecause the value of the high-frequency band 1/β can be increased by introducing the pair of zero poles, the parasitic capacitance of the operational amplifier output end PCB or the high-frequency noise pair V generated by the self factor can be simultaneously restrainedOUTThereby improving the interference capability of the entire loop. Resistance R25A simplified model of the small signal of the automatic current control loop after introducing the adjustable loop noise suppression network 64 using a mechanical potentiometer is shown in fig. 6a, and an artificial loop analysis is shown in fig. 7 b. The simulation is performed by using the Tina SPICE of the Tina-TI acquisition component, the simulation diagram before the loop noise suppression network is introduced is shown in FIG. 8a, and the resistor R25The simulation graph after the loop noise suppression network is introduced by the mechanical potentiometer is shown in fig. 8b, the simulation test is carried out by the traditional loop gain method, and the large capacitance C55Ensure the separation of AC signal source and DC, large inductance L1Causing the ac signal to be turned off at that point and the dc signal to be turned on at that point. Wherein the zero point f is introducedznAnd fpnCalculated by the expressions (5) and (6), respectively.
When R is25+Ro＝10R26Due to this time R25>>RoTherefore, it can be approximately considered as R25＝10R26The pole-zero introduced at this time remains ten times the frequency range. Due to R26>>RoThus when R is25Adjusted to be very small so that R26>>R25When the zero poles introduced almost coincide, the loop V is at this momentOUT/VINHas the largest bandwidth, and f is introduced into a noise suppression networkz0' can be calculated from the formula (7).
To achieve on-line tuning of the loop noise suppression network at the target set frequency, R25A digital potentiometer can be used, and a simplified model of the small signal of the automatic current control loop after the adjustable loop noise suppression network 67 is introduced is shown in FIG. 7C, 671 is the SPICE model of the digital potentiometer X9C103 used in this embodiment, wherein the capacitor C islAnd a capacitor ChAre all 10pF, a capacitor CwAt 25pF, a capacitance ChAnd operational amplifier U13Open loop output resistor Roa zero point f is introduced at 1/βz1' (i.e., a high frequency pole is generated on LOOP # 0) can be estimated by equation (8). Capacitor ClCapacitor CwAnd the equivalent capacitance C of the MOS tube grid electrode to the groundgAnd Rta zero point f is introduced at 1/βz2' (i.e., a high frequency pole is generated on LOOP # 0) can be estimated by equation (9).
fz1' at about 265MHz due to Cg>>(Cl+Cw) thus introducing a zero point f at 1/βz2' with f introduced when the machine is a potentiometerz0The position was almost the same, and the artificial loop analysis was similar to that of the case of using the mechanical potentiometer in fig. 7b, as shown in fig. 7 c. FIG. 9a shows the simulation result of Tina-TI before the introduction of the noise suppression network, FIG. 9b shows the simulation result of Tina-TI after the introduction of the noise suppression network by using the mechanical potentiometer, and FIG. 9c shows the simulation result of Tina-TI after the introduction of the noise suppression network by using the digital potentiometer, from the analysis result and the simulation result, it can be known that V is a V which employs the mechanical potentiometer and the digital potentiometer within the adjustment rangeout/VinThe consistency is achieved, the loop analysis and the simulation result are relatively high in correlation, and the accuracy of the loop analysis is verified.
The DC bias is set to 1.8V, sine waves with frequency of 100kHz and amplitude of 400mV are adopted to respectively test the noise anti-interference capability of the loops before and after the noise suppression network is introduced, the anti-interference capability test result before the noise suppression network is introduced and the anti-interference capability test result after the noise suppression network is introduced are respectively shown in figures 10a and 10b, in figure 10a, V isINAnd VIN' indicates the voltage waveform, V, at the input terminal when analog noise is introduced from the input terminal and the output terminal of the operational amplifier before the noise suppression network is introducedOUTAnd VOUT' Voltage test simulation output waveform when analog noise is introduced from the input terminal and the output terminal of the operational amplifier before introducing the noise suppression network, respectively, in FIG. 10b, VINAnd VIN' shows the voltage waveform of the input terminal, V, when analog noise is introduced from the input terminal and the output terminal of the operational amplifier after the noise suppression network is introducedOUTAnd VOUT' respectively represents the voltage test simulation output waveform when analog noise is introduced from the input end and the output end of the operational amplifier after the noise suppression network is introduced.
The sine wave with 5kHz and 400mV amplitude is adopted to carry out the responsiveness test of the loop after the noise suppression network is introduced, the test result is shown in figure 11, and the result shows that the output responds to the input signalDegree of fineness is good, wherein VIN、VOUT、VG、VOAThe voltage of the input signal, the voltage of the output signal, the voltage of the operational amplifier output end and the voltage waveform of the MOSFET grid electrode are respectively. In summary, after the loop is introduced into the noise suppression network, the loop has a suitable working bandwidth, and has a strong suppression effect on the noise at the positive phase input end and the loop midpoint. The network can carry out parameter self-adjustment according to the target set frequency, and can realize better suppression on loop noise while ensuring higher responsiveness on the input signal of the target frequency in an adjustment range.
And when the target frequency of the modulation wave is set to be 5kHz, loop noise suppression and responsivity test are carried out, and a waveform test is carried out by adopting an oscilloscope. Taking sine wave as an example, firstly, sine wave analog high-frequency noise with the frequency of 100kHz and the amplitude of 400mV is adopted to be respectively superposed on the loop input end and the operational amplifier output end, and then V is observedOUTTest the interference rejection of the loops before and after the introduction of the noise suppression network, as shown in fig. 12a, VOUTAnd VOUT"respectively represents the output waveform V when analog noise is introduced from the input end and the output end of the operational amplifier before the noise suppression network is introducedOUT' and VOUT"' is the output waveform when analog noise is introduced from the input and the output of the operational amplifier after the noise suppression network is introduced. Test results show that the analog noise can generate larger interference on output before the noise suppression network is introduced, the ACC loop has good suppression effect on the noise after the noise suppression network is introduced, and when the target frequency is set to be 5kHz, the suppression on the high-frequency noise of 100kHz reaches more than 20 dB.
The sine wave with the target frequency of 5kHz is used as input to generate a modulation wave with the target frequency, the responsiveness of a control loop of the automatic current control unit is tested, the test result is shown in figure 12b, the test result shows that the loop of the automatic current control unit has good responsiveness under the target set frequency, and the test result has good consistency with a first-order manual analysis result and a Tina-TI simulation result.
The frequency control accuracy of the modulated wave was measured, and an oscilloscope was used as a measuring instrument to read the frequency, and the measurement results are shown in fig. 13. A least squares linear fit is made to the set frequency and the output frequency by:
Y＝B+A·X (10)
where Y here represents the measured frequency and X represents the set frequency. Wherein, A is 1.00002, B is-3.253 × 10-4The correction decision coefficient was 0.9999. The maximum deviation of the measured value and the set value is 0.001Hz, and the test result shows that the driving circuit has higher frequency control precision and better linearity.
The short-term stability test of laser driving is carried out at the ambient temperature, the voltage at two ends of the sampling resistor is measured once every two minutes, then the voltage is converted into a current value, the short-term stability reaches 0.0056%, then the long-term stability test is carried out at different temperatures, and a constant temperature box is adopted to simulate the change of the ambient temperature. The current stability tests are respectively carried out at the temperature of 30 ℃, 55 ℃ and 65 ℃, the mean value of the measured current is 60.002222mA in the environment of 30 ℃, the mean value of the measured current is 60.001111mA in the environment of 55 ℃, the mean value of the measured current is 59.999556mA in the environment of 65 ℃, the mean value of the measured current is 60.0009628 in 63 hours under the condition of simulating the change of the environmental temperature, and the long-term stability reaches 0.011 percent. The short-term current stability test results are shown in fig. 14a, and the long-term current stability test results are shown in fig. 14 b. The test result shows that the short-term stability and the long-term stability of the output current are high, and the driving performance is good.
It will be understood that the above embodiments are merely exemplary embodiments taken to illustrate the principles of the present invention, which is not limited thereto. It will be apparent to those skilled in the art that various modifications and improvements can be made without departing from the spirit and substance of the invention, and these modifications and improvements are also considered to be within the scope of the invention.
Claims (8)
1. A semiconductor laser driving system characterized in that: the method comprises the following steps:
the semiconductor laser comprises a laser diode LD1, a semiconductor cooler TEC and a negative temperature coefficient thermistor NTC, wherein the laser diode is used for emitting laser, the semiconductor cooler is used for refrigerating or heating a laser cavity, and the negative temperature coefficient thermistor reflects the temperature into the change of resistance value;
the single chip microcomputer is a core controller of the system, the overall control of the driving system is completed according to a written instruction, the work of each part is coordinated, the single chip microcomputer is communicated with an upper computer, relevant parameters of output direct current bias, a modulated wave signal and a noise suppression network are set through the D/A converter, the selection of two working modes of direct current and modulation can be realized, current state parameters output by the driving system at present are sampled through the current sampling unit and the A/D converter, the current state parameters are transmitted to the upper computer for monitoring after processing, and the system parameters during the last shutdown can be stored in an internal Flash of the single chip microcomputer to serve as default values for the next startup and restart;
the modulation wave generating unit can generate sine waves, square waves and triangular waves, and the frequency and amplitude of the modulation waves can be adjusted;
a signal processing unit is arranged, a direct current bias setting signal is converted into a voltage signal through the D/A converter, is connected with a following circuit formed by operational amplifiers, is superposed with a modulation wave setting signal passing through a high-pass filter circuit through an adding circuit, and is converted into a positive value through an inverting circuit to be used as an input end of the automatic current control unit;
the automatic current control unit adopts a deep negative feedback framework to provide low-noise driving modulation current for the laser diode, converts a current signal into a voltage signal and transmits the voltage signal to the singlechip through the follower circuit and the A/D converter, and the amplitude, the frequency and the waveform of the modulation wave are determined by setting signals;
the protection unit comprises an over-slow starting module, an over-current protection module and an anti-reverse current module, wherein the slow starting module is used for slowly powering on a current branch when a circuit is just powered on and runs to prevent voltage at two ends of the laser diode from suddenly changing, when the circuit fails or the output current value of the current branch exceeds a limit value due to manual misoperation, the over-current protection module can automatically disconnect the current branch to start protection, and meanwhile, an alarm lamp is turned on;
the communication interface unit is used for carrying out communication between the upper computer and the singlechip and is used for sending control instructions and returning driving current state parameters;
the temperature control unit is used for converting the ambient temperature value of the cavity of the current semiconductor laser into a resistance value through the thermistor with the negative temperature coefficient, converting the resistance value into a voltage value, comparing the voltage value with a temperature set value, and controlling the TEC driver through a hardware PID (proportion integration differentiation) so as to adjust the temperature of the cavity of the semiconductor laser and maintain the temperature at a stable value;
the power supply conversion unit converts the +/-15V direct current input into +/-12V, + 5V, +3.3V, +1.5V power supply groups and supplies power to the analog circuit and the digital circuit in groups;
the resetting unit is used for ensuring that the laser driving system can be reset and starts to operate from a default state;
the clock unit is used for generating 8MHz pulse signals and using the pulse signals as a working clock of the singlechip;
a D/A converter for converting the DC bias setting signal from a digital signal to an analog voltage signal when setting the DC bias current;
the A/D converter is used for converting the current sampling value converted into the voltage signal from the analog voltage signal into a digital signal;
when the laser driving system is powered on, the singlechip firstly accesses the Flash in the singlechip to read a control command word stored when the laser driving system is powered off last time, the singlechip communicates with the D/A converter through the hardware SPI to set the magnitude of the output current direct current bias according to the control command word, communicates with the DDS module through the software SPI to set the waveform and the frequency of the modulation wave, the direct current bias setting signal and the modulation wave setting signal complete voltage following and superposition through the setting signal processing unit to generate a control signal to be provided for the automatic current control unit so as to realize stable control of the output current, a deviation value is obtained by an H-bridge circuit in temperature setting and temperature sampling, the deviation value controls the TEC driver through the hardware PID so as to drive the TEC, and the temperature in the cavity of the laser is regulated, when the current output current state needs to be changed, a control word is set on the upper computer, and the communication interface unit is communicated with the single chip microcomputer, so that the setting of the driving current is completed.
2. A semiconductor laser driving system according to claim 1, wherein: the automatic current control unit includes: u13 is put to fortune, and U14 is put to fortune, MOS pipe Q3, sampling resistor R27, loop noise suppression network, set up the signal processing unit connect in U13 forward input end is connected to fortune, sampling resistor R27 converts current signal into voltage signal feedback to fortune is put U13 reverse input end, fortune is put U13 output and is connected loop noise suppression network input end, loop noise suppression network output connect in MOS pipe Q3 grid, MOS pipe Q3 drain-electrode with LD1 negative pole is connected, MOS pipe Q3 source-electrode links to each other with sampling resistor R27 one end, sampling resistor R27 one end connect in the forward input end of the voltage follower that U14 constitutes is put to fortune, the reverse input end of fortune is put U14 connect in fortune is put U14 output, fortune is put U14 output and is connected in A/D converter input.
3. A semiconductor laser driving system according to claim 2, wherein: the loop noise suppression network is used for suppressing loop noise at a signal setting end and an output end of the operational amplifier U13 while ensuring the response capability of a driving current under a target setting frequency, and the suppression of the loop noise above a ten-fold frequency range of the target frequency can be up to more than 20 dB.
4. A semiconductor laser driving system according to claim 3, wherein: the loop noise suppression network includes: one end of the adjustable varistor is connected to the output end of the operational amplifier U13, the other end of the adjustable varistor is connected to the gate of the MOS transistor Q3 and one end of the capacitor C50, the other end of the capacitor C50 is connected to one end of the resistor R26, and the other end of the resistor R26 is connected to ground.
5. A semiconductor laser driving system according to claim 4, wherein: the resistor R25 is an adjustable resistor, and the resistance value of the adjustable resistor R25 can be adjusted according to the target setting frequency of the modulation wave, so that the parameters of the loop noise suppression network are adjusted.
6. A semiconductor laser driving system according to claim 5, wherein: the adjustable resistor R25 is a mechanical potentiometer, and the resistance value of the mechanical potentiometer R25 can be adjusted according to the target setting frequency of the modulation wave, so that the parameters of the loop noise suppression network are adjusted.
7. A semiconductor laser driving system according to claim 5, wherein: the adjustable resistor R25 is a digital potentiometer, and the resistance value of the digital potentiometer R25 can be adjusted on line according to the target setting frequency of the modulation wave, so that the parameters of the loop noise suppression network can be adjusted on line.
8. A loop noise suppression method with online adjustable parameters is suitable for a semiconductor laser driving system and is characterized in that: the loop noise suppression method with the online adjustable parameters comprises the following steps: establishing a simplified small-signal loop model according to the model of a component in a loop, analyzing a control loop, making a loop amplitude-frequency characteristic curve, introducing a loop noise suppression network with online adjustable parameters according to the loop amplitude-frequency characteristic curve, primarily determining the structural composition and the component parameters of the loop noise suppression network, then performing circuit simulation by adopting Tina-TI, further adjusting the structural composition and the component parameters of the loop noise suppression network according to the simulation result, and finally verifying by adopting an experiment, thereby finally determining the structural composition and the component parameters of the loop noise suppression network.
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