WO2022048588A1 - 激光麦克风和终端 - Google Patents

激光麦克风和终端 Download PDF

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Publication number
WO2022048588A1
WO2022048588A1 PCT/CN2021/116172 CN2021116172W WO2022048588A1 WO 2022048588 A1 WO2022048588 A1 WO 2022048588A1 CN 2021116172 W CN2021116172 W CN 2021116172W WO 2022048588 A1 WO2022048588 A1 WO 2022048588A1
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WIPO (PCT)
Prior art keywords
laser
current
signal
self
mixing
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PCT/CN2021/116172
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English (en)
French (fr)
Inventor
侯小珂
张世雄
阮盛杰
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华为技术有限公司
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Application filed by 华为技术有限公司 filed Critical 华为技术有限公司
Priority to JP2023514944A priority Critical patent/JP2023540983A/ja
Priority to EP21863652.0A priority patent/EP4199540A4/en
Priority to KR1020237011121A priority patent/KR20230060526A/ko
Publication of WO2022048588A1 publication Critical patent/WO2022048588A1/zh
Priority to US18/177,814 priority patent/US20230209278A1/en

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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R23/00—Transducers other than those covered by groups H04R9/00 - H04R21/00
    • H04R23/008—Transducers other than those covered by groups H04R9/00 - H04R21/00 using optical signals for detecting or generating sound
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01H—MEASUREMENT OF MECHANICAL VIBRATIONS OR ULTRASONIC, SONIC OR INFRASONIC WAVES
    • G01H9/00—Measuring mechanical vibrations or ultrasonic, sonic or infrasonic waves by using radiation-sensitive means, e.g. optical means
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M1/00—Substation equipment, e.g. for use by subscribers
    • H04M1/02—Constructional features of telephone sets
    • H04M1/03—Constructional features of telephone transmitters or receivers, e.g. telephone hand-sets
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2430/00—Signal processing covered by H04R, not provided for in its groups
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R2499/00—Aspects covered by H04R or H04S not otherwise provided for in their subgroups
    • H04R2499/10—General applications
    • H04R2499/11—Transducers incorporated or for use in hand-held devices, e.g. mobile phones, PDA's, camera's

Definitions

  • the present application relates to the technical field of microphones, and in particular, to a laser microphone and a terminal.
  • the use of automatic speech recognition systems in scenarios such as voice control and voice interaction is growing rapidly. At the same time, more and more people record and share video content through the mobile Internet.
  • the microphone used to pick up sound must have good performance to ensure that Great user experience.
  • the signal-to-noise ratio (SNR) of a microphone is a key parameter that affects the quality of the picked-up sound.
  • SNR signal-to-noise ratio
  • the high signal-to-noise ratio helps the microphone pick up distant, weaker target sound sources, while maintaining a lower noise floor when the signal is amplified, improving the quality of long-distance pickup.
  • MEMS Microelectro Mechanical Systems, Micro Electro Mechanical Systems
  • ASIC Application Specific Integrated Circuit, integrated circuit for special application
  • the MEMS capacitor includes two ends of the silicon diaphragm that receives the sound and the silicon back pole.
  • the silicon diaphragm can sense the air vibration generated by the sound wave and vibrate with it. It forms a variable capacitor with the silicon back pole. The change of variable capacitance is processed and converted into electrical signal output.
  • the embodiments of the present application provide a laser microphone with a high signal-to-noise ratio, which can improve the speech recognition rate and wake-up rate, and improve the effect of long-distance sound pickup.
  • a first aspect of the embodiments of the present application provides a laser microphone, including a diaphragm, a laser, a control circuit, a self-mixing signal acquisition device, and a signal processing circuit;
  • the laser is used for emitting light to the vibrating film and receiving a feedback optical signal from the vibrating film, and the feedback optical signal interferes with the laser in the laser resonator to obtain a self-mixing optical signal; the laser
  • the distance between the diaphragm and the diaphragm is L, and the range of L is 30 ⁇ m ⁇ L ⁇ 300 ⁇ m;
  • the control circuit is connected with the laser, and is used for driving and controlling the laser to emit light;
  • the self-mixing signal acquiring device is connected to the laser, and is used for acquiring and outputting a target voltage signal related to the self-mixing optical signal;
  • the signal processing circuit is connected to the self-mixing signal obtaining device, and is used for receiving the target voltage signal output by the self-mixing signal obtaining device, and processing the target voltage signal into an audio voltage signal.
  • the laser microphone provided by the embodiment of the present application adopts a laser self-mixing device to detect the vibration of the diaphragm caused by the voice signal, and the laser self-mixing device has a strong detection capability of weak vibration signals, so the voice recognition sensitivity of the microphone can be improved; Setting it at a suitable distance from the diaphragm can improve the coupling efficiency of the laser output beam reflected by the diaphragm and re-enter the laser resonator cavity, thereby effectively improving the signal-to-noise ratio of the laser microphone and improving the sensitivity of speech recognition.
  • the circuit control modulates the laser drive current to stabilize the laser at the current operating point with the highest sensitivity.
  • the output end of the self-mixing signal obtaining device is connected to the input end of the control circuit, and the control circuit determines the desired voltage according to the target voltage signal output from the self-mixing signal obtaining device. the driving current A j of the laser.
  • the phase fluctuation in the laser resonator will be caused, that is, the self-mixing optical signal fluctuation.
  • a small current disturbance is applied to the laser, and the highest sensitivity of the laser is determined according to the degree of change of the voltage signal output by the self-mixing signal acquisition device caused by the current disturbance, that is, the degree of change of the self-mixing optical signal caused by the current disturbance Therefore, the laser can be kept at the working point with the highest sensitivity to the vibration of the diaphragm, and the signal-to-noise ratio of the microphone can be improved.
  • the control circuit determines the driving current A of the laser according to the target voltage signal output from the self-mixing signal acquisition device j , including:
  • the ⁇ ? is a preset current
  • the alternating current I c is a preset current
  • the frequency of the alternating current I c is greater than the maximum frequency of the sound that the human ear can hear
  • the ⁇ V t is related to the frequency of the alternating current I c ;
  • the t represents the number of current sweeps
  • S13 Determine the scanning current I t corresponding to the largest ⁇ V t among the multiple ⁇ V t obtained in the process of S12 as the driving current A j of the laser obtained by the current driving current modulation.
  • the above-mentioned driving current modulation in the laser working mode can make the laser always stabilize at the current operating point with the highest sensitivity during the whole working process, thereby improving the sound pickup quality of the laser microphone and the long-distance sound pickup effect, as well as improving the laser microphone. pickup stability.
  • the control circuit determines the driving current A j of the laser according to the target voltage signal output from the self-mixing signal acquisition device, including:
  • the I min' is the preset minimum drive current
  • the I max' is the preset maximum drive current
  • the ⁇ ? is the preset current
  • the alternating current I c is the preset current
  • the frequency of the alternating current I c is greater than the maximum frequency of the sound that can be heard by the human ear
  • the t' represents the number of current sweeps
  • S22 Determine the scanning current I t ' corresponding to the largest ⁇ V t' among the multiple ⁇ V t' obtained in the process of S21 as the driving current A j of the laser.
  • the laser starts working mode, by scanning from the preset minimum drive current (usually the laser threshold) to the preset maximum drive current to find the current operating point with the highest laser sensitivity, the pickup quality and long-distance pickup effect of the laser microphone can be improved. .
  • the ⁇ ? The range is 10 ⁇ A ⁇ ? ⁇ 50 ⁇ A. Setting a suitable step size is helpful to find the drive current point value with high sensitivity more accurately.
  • the frequency of the alternating current Ic that is, the frequency of the applied current disturbance is greater than the maximum frequency of the sound that the human ear can hear, so the current disturbance itself will not have a great impact on the stable operation of the laser.
  • the frequency range of the alternating current I c is 20 kHz ⁇ I c ⁇ 50 kHz.
  • the peak-to-peak value of the alternating current I c can be controlled between 10 ⁇ A and 50 ⁇ A.
  • applying the alternating current I c with a smaller current value can also reduce the influence on the stable operation of the laser.
  • the self-mixing signal acquisition device is configured to detect the self-mixing optical signal in the laser resonator, and output a target voltage signal related to the self-mixing optical signal.
  • the self-mixing signal acquisition device includes a photodetector and a transimpedance amplifying circuit
  • the photodetector is connected to the laser, and is used to detect the self-mixing in the laser resonant cavity and converting the self-mixing optical signal into a current signal
  • the transimpedance amplifying circuit is connected with the photodetector, and is used for converting the current signal into the target voltage signal.
  • the self-mixing signal is obtained by using a photodetector and a transimpedance amplifier circuit, and a higher signal-to-noise ratio can be obtained by increasing the driving current of the laser.
  • the photodetector and the laser are monolithically integrated on the same chip, and the photodetector is located on the side of the laser away from the diaphragm, that is, the backside of the laser light-emitting surface.
  • the laser and the photodetector are integrated on the same chip, which can improve the efficiency of the light transmitted from the back of the laser coupling into the photodetector, thereby improving the signal-to-noise ratio, and at the same time, it can also avoid the vibration and drop caused by the discrete arrangement.
  • Optical path deviation thereby maintaining the consistency of the signal throughout the life of the microphone.
  • the self-mixing signal obtaining device includes a buffer circuit connected to the laser, the buffer circuit is used to obtain the terminal voltage of the laser, and the terminal voltage of the laser is related to the self-mixing related to optical signals.
  • the signal processing circuit includes a high-pass filter circuit and a voltage amplification and low-pass filter circuit, the high-pass filter circuit is connected to the self-mixing signal acquisition device, and the voltage amplification and low-pass filter circuit is connected to the The high-pass filter circuit is connected.
  • High-pass filter circuit and voltage amplification and low-pass filter circuit can filter out low-frequency background sound and high-frequency signal.
  • the signal processing circuit further includes a gain control circuit connected to the voltage amplification and low-pass filter circuit, and the gain control circuit is used for outputting signals according to the voltage amplification and low-pass filter circuit.
  • the gain of the voltage amplification and low-pass filter circuit is adjusted.
  • the setting of the gain control circuit can realize the adjustable gain of the voltage amplification and low-pass filter circuit.
  • the light-emitting surface of the laser facing the diaphragm is provided with a beam coupling device, and the beam coupling device includes one or more lenses.
  • the setting of the lens can improve the coupling efficiency of the laser output beam reflected by the diaphragm and re-enter the laser resonator cavity, and has a higher feedback light intensity, that is, a stronger signal, thereby further effectively improving the signal-to-noise ratio of the microphone.
  • the lateral dimension (ie the length and width) of each of the lenses is 20 ⁇ m-200 ⁇ m; the longitudinal dimension (ie the height dimension) of each of the lenses is 20 ⁇ m-200 ⁇ m.
  • the above-mentioned size lens can be processed by laser direct writing or micro-nano printing. Lenses with the above-mentioned size can be integrated on the laser to achieve a more compact assembly and a mass production solution that can be directly fabricated on a wafer. .
  • the specific types of the diaphragms are not limited, and there is no special requirement for electrical conductivity. It is only necessary to consider the vibration characteristics required by the audio frequency, which can be various diaphragms available for existing microphones. Specifically, it may include a MEMS diaphragm, a metal glass diaphragm, a graphene diaphragm, a polymer film or a metal film, and the like.
  • a reflection layer is provided on the side of the diaphragm facing the laser.
  • the reflectivity of the reflective layer is greater than 70%.
  • the reflective layer may be made of gold, aluminum and other materials.
  • the setting of the reflective layer can improve the reflectivity of the outgoing beam of the laser being reflected back into the resonant cavity of the laser when it is emitted to the diaphragm.
  • the diaphragm is generally a composite film structure containing different stress film layers. In this way, the setting of the metal reflective layer can increase the reflectivity In addition, it can also compensate the negative stress of the diaphragm to improve the stability of the diaphragm.
  • the laser is a self-mixing laser, and the specific type is not limited, and may be a vertical cavity surface emitting laser or an edge emitting laser.
  • the output wavelength of the laser can be 750nm-1600nm.
  • the laser microphone further includes a casing, and the diaphragm, the laser, the control circuit, the self-mixing signal acquisition device, and the signal processing circuit are all arranged in the casing, A sound pickup hole is provided on the casing at a position corresponding to the vibrating membrane. The external sound information is picked up through the sound pickup hole.
  • An embodiment of the present application further provides a terminal, where the terminal includes the laser microphone described in the first aspect of the embodiment of the present application.
  • the terminal includes a casing and a circuit board arranged in the casing.
  • the laser microphone is arranged on the circuit board.
  • the terminal casing is provided with a sound-receiving hole corresponding to the position of the laser microphone. The external sound is transmitted to the laser microphone through the sound-receiving hole of the casing.
  • the laser microphone may be set corresponding to the front side of the terminal, may also be set corresponding to the rear side of the terminal, or may be set corresponding to the middle frame on the side of the terminal.
  • the terminal can be a mobile phone (mobile phone), a notebook computer, a tablet computer, a smart TV, a smart speaker, a headset, a video camera, a network camera, a wearable device, a game device, a car audio system or a microphone, a voice navigation device, a spoken voice recognition device , voice-to-text converters and other terminal products in scenarios that require voice command control or need to collect, record, process or analyze speech.
  • the laser microphone provided by the embodiment of the present application based on the laser self-mixing device to detect the vibration of the diaphragm caused by the speech signal, has a strong detection capability of weak vibration signals, and has a higher signal-to-noise ratio than the traditional MEMS microphone.
  • the laser microphone of the embodiment of the present application by setting the laser and the vibrating film at a suitable distance, the coupling efficiency of the laser output beam re-entering the laser resonator after being reflected by the vibrating film is improved, thereby effectively improving the signal-to-noise ratio and improving the voice Identification sensitivity.
  • the laser microphone in the embodiment of the present application modulates the driving current of the laser by constructing a loop control to stabilize the laser at the operating point with the highest sensitivity, which can reduce or eliminate the phase noise caused by current fluctuations, so that the laser microphone can operate and High signal-to-noise ratio is maintained throughout the life cycle.
  • the laser microphone according to the embodiment of the present application can significantly improve the voice pickup in the soft-spoken mode in quiet scenes, the detection of weak voice signals at a distance, and the voice pickup quality during long-distance video recording, thereby improving user experience.
  • FIG. 1 is a schematic diagram of a circuit structure of a laser microphone provided by an embodiment of the present application.
  • FIG. 2 is a schematic diagram of a circuit structure of a laser microphone provided by another embodiment of the present application.
  • FIG. 3 is a schematic structural diagram of a signal processing circuit 50 in an embodiment of the present application.
  • FIG. 4 is a schematic diagram of a circuit structure of a laser microphone provided by an embodiment of the present application.
  • FIG. 5 is a schematic diagram of a circuit structure of a laser microphone provided by another embodiment of the present application.
  • FIG. 6 is a schematic structural diagram of a laser microphone with a jacking sound structure provided by an embodiment of the present application.
  • FIG. 7 is a schematic structural diagram of a laser microphone with a bottom-in sound structure provided by an embodiment of the present application.
  • FIG. 8 is a schematic diagram of the arrangement of a lens in an embodiment of the present application.
  • FIG. 9 is a schematic diagram of the arrangement position of a laser microphone in a terminal provided by an embodiment of the present application.
  • an embodiment of the present application provides a laser microphone 100 , including a diaphragm 10 , a laser 20 , a control circuit 30 , a self-mixing signal acquisition device 40 and a signal processing circuit 50 .
  • the vibrating film 10 is used to receive the sound wave generated by the external sound and generate vibration.
  • the light-emitting surface of the laser 20 is opposite to the vibrating film 10.
  • the laser 20 is used to emit light to the vibrating film 10 and receive the feedback light signal from the vibrating film 10.
  • the feedback optical signal interferes with the laser light in the resonant cavity of the laser 20 to obtain a self-mixing optical signal;
  • the output end 30b of the control circuit 30 is connected to the laser 20, and the control circuit 30 is used to drive and control the laser 20 to emit light.
  • the self-mixing signal acquiring device 40 is connected to the laser 20, and the self-mixing signal acquiring device 40 is used for acquiring a target voltage signal related to the self-mixing optical signal.
  • the input end 50a of the signal processing circuit 50 is connected to the first output port 40b of the self-mixed signal obtaining device 40 for receiving the target voltage signal output from the mixed signal obtaining device 40 and processing the target voltage signal into an audio voltage signal.
  • the working mechanism of the laser microphone 100 in the embodiment of the present application is as follows: the sound wave generated by the external sound acts on the diaphragm 10, and the diaphragm 10 generates vibration displacement with the change of the sound pressure of the sound wave; the control circuit 30 provides the laser 20 with a driving current to drive the laser 20.
  • the laser beam is directed to the diaphragm 10 and is reflected by the diaphragm 10 to obtain a feedback optical signal.
  • the feedback optical signal carries the vibration information of the diaphragm 10 and changes the phase relative to the emitted light.
  • the laser in the cavity undergoes self-mixing interference to obtain a self-mixing optical signal;
  • the self-mixing signal acquiring device 40 acquires the target voltage signal related to the laser 20 and the self-mixing optical signal, and the signal processing circuit 50 receives the target output from the self-mixing signal acquiring device 40 voltage signal, and amplify and filter the target voltage signal to obtain the final output audio voltage signal.
  • the distance between the laser 20 and the diaphragm 10 is L, and the range of L is 30 ⁇ m ⁇ L ⁇ 300 ⁇ m, that is, between the light-emitting surface of the laser 20 on the side close to the diaphragm 10 and the reflection surface of the diaphragm 10
  • the distance is 30 ⁇ m-300 ⁇ m.
  • the distance between the light-emitting surface of the laser 20 and the reflective surface of the diaphragm 10 can be regarded as an equivalent external cavity.
  • the vibration displacement of the surface of the diaphragm 10 along the direction of the laser beam changes the external reflection formed by the reflective surface of the diaphragm and the light-emitting surface of the laser. Cavity length, and then change the phase of the feedback light.
  • the coupling efficiency of the laser beam outgoing beam after being reflected by the diaphragm and re-entering the laser resonator can be improved, thereby effectively improving the signal-to-noise ratio.
  • Improve voice recognition sensitivity by setting the laser and the diaphragm at a suitable distance, that is, maintaining a suitable outer cavity length, the coupling efficiency of the laser beam outgoing beam after being reflected by the diaphragm and re-entering the laser resonator can be improved, thereby effectively improving the signal-to-noise ratio.
  • Improve voice recognition sensitivity improves voice recognition sensitivity.
  • the self-mixing signal acquiring device 40 is configured to acquire the self-mixing optical signal in the resonant cavity of the laser 20, and output a target voltage signal related to the self-mixing optical signal.
  • the self-mixing signal acquisition device 40 includes a photodetector 41 and a transimpedance amplifier circuit 42 , the photodetector 41 is connected to the laser 20 , and the input end of the transimpedance amplifier circuit 42 is electrically connected to the photodetector 41 .
  • the photodetector 41 is used to detect the self-mixing optical signal in the laser resonator and convert the self-mixing optical signal into a current signal
  • the transimpedance amplifier circuit 42 is used to convert the current signal output by the photodetector 41 into a voltage signal.
  • the feedback optical signal reflected by the diaphragm is reflected back to the resonant cavity of the laser 20 and self-mixing interference occurs with the optical field in the cavity, causing the laser light intensity to change.
  • the light intensity change caused by self-mixing is determined by the photodetector 41 It is detected that the photodetector 41 converts the optical signal into a photocurrent signal, the transimpedance amplifier circuit 42 converts the photocurrent signal into an amplified target voltage signal, and then the signal processing circuit 50 amplifies and filters the signal, and finally The output is an audio voltage signal.
  • the self-mixing signal acquiring device 40 is used to directly acquire the target voltage signal related to the self-mixing optical signal from the laser 20 .
  • the self-mixing signal acquisition device 40 includes a buffer circuit 43 connected to the output end of the laser 20 .
  • the buffer circuit 43 can acquire the terminal voltage of the laser 20 .
  • the terminal voltage of the laser 20 refers to the voltage difference between the two ends of the laser or the voltage of one end of the laser relative to the ground.
  • the snubber circuit 43 is a protection circuit that suppresses current rise.
  • the signal processing circuit 50 includes a high-pass filter circuit 51 , a voltage amplification and a low-pass filter circuit 52 , an input port 51 a of the high-pass filter circuit 51 and a first output port of the self-mixed signal acquisition device 40 40b is connected, and the input port 52a of the voltage amplification and low-pass filter circuit 52 is connected to the output port 51b of the high-pass filter circuit 51 .
  • the high-pass filter circuit 51 can block the output signal from the mixed-signal acquisition device 40 and filter out low-frequency noise
  • the voltage amplification and low-pass filter circuit 52 can perform DC blocking on the high-frequency AC signal output by the high-pass filter circuit 51.
  • the signal processing circuit 50 may further include a gain control circuit 53, the input port 53a of the gain control circuit 53 is connected to the output port 52b of the voltage amplification and low-pass filter circuit 52, and the output port of the gain control circuit 53 53b is connected to the input port 52c of the voltage amplification and low-pass filter circuit 52 .
  • the gain control circuit 53 adjusts the gain of the voltage amplification and low-pass filter circuit 52 based on the output signal of the voltage amplification and low-pass filter circuit 52 .
  • the output port 52b of the voltage amplification and low-pass filter circuit 52 serves as the output end of the signal processing circuit 50 to output a signal.
  • the laser drive current is modulated to stabilize the laser at the drive current operating point with the highest sensitivity to the vibration of the diaphragm. Due to the current fluctuation of the laser and the vibration of the diaphragm, the phase fluctuation in the laser resonator will be caused, that is, the self-mixing optical signal fluctuation.
  • a small current disturbance is applied to the laser, and the drive with the highest laser sensitivity is determined according to the degree of change of the output signal of the self-mixing signal acquisition device caused by the current disturbance, that is, the degree of change of the self-mixing optical signal caused by the current disturbance Therefore, the laser can also be kept at the driving current operating point with the highest sensitivity to the vibration of the diaphragm, and the signal-to-noise ratio of the microphone can be improved.
  • the laser driving current is a direct current.
  • the second output port 40c of the self-mixed signal acquisition device 40 is connected to the input port 30a of the control circuit 30, and the control circuit 30 obtains the self-mixed signal according to the second output port of the device 40
  • the output signal of 40c determines the drive current A j of the laser 20 . That is, two signals are output from the mixed signal obtaining device 40 , one signal is output to the signal processing circuit 50 , and the other signal is output to the control circuit 30 , and the two signals are the same voltage signal.
  • the control circuit 30 determines the driving current A j of the laser 20 according to the target voltage signal output from the mixed signal obtaining device 40 , including:
  • I min' is the preset minimum drive current
  • I max' is the preset maximum drive current
  • ⁇ ? is the preset current
  • the alternating current I c is the preset current
  • the frequency of the alternating current I c is greater than the maximum frequency of the sound that the human ear can hear
  • ⁇ V t' is related to the frequency of the alternating current I c
  • t' represents the number of current sweeps ;
  • step S21 of this embodiment the control circuit 30 superimposes the alternating current I c on the scanning current I t' of each scan and outputs it to the laser 20, and the self-mixed signal acquiring device 40 outputs the target voltage signal V 1 based on I t' and I c , after the control circuit 30 obtains the target voltage signal V 1 , performs FFT (Fast Fourier Transform, Fast Fourier Transform) on the target voltage signal V 1 , and identifies the peak-to-peak value ⁇ V t of the output voltage fluctuation at the frequency of the alternating current I c ' .
  • FFT Fast Fourier Transform
  • ⁇ V t' is related to the frequency of the AC current I c , which means that according to the frequency of the superimposed AC current I c , the peak-to-peak value ⁇ V t' of the output voltage fluctuation at this frequency is identified in the voltage signal after FFT is performed. For example, if the frequency of the superimposed alternating current I c is 25 kHz, it is necessary to identify the peak-to-peak value ⁇ V t′ of the output voltage fluctuation at the frequency of 25 kHz.
  • the preset minimum driving current I min' and the preset maximum driving current I max' of the laser may be reasonably set according to specific requirements of the laser.
  • the preset minimum driving current I min' may be 0.5 mA
  • the preset maximum driving current I max' may be 3 mA.
  • one scan means that the control circuit superimposes the alternating current I c on the scanning current I t' at a certain point value and applies it to the laser, and obtains the peak-to-peak value ⁇ V of the output voltage fluctuation of the laser when the alternating current I c is superimposed under the action of the scanning current I t' . t' process.
  • Peak-to-peak (pk-pk) ⁇ V t' refers to the difference between the largest positive voltage value and the largest negative voltage value in the waveform.
  • S22 Determine the scanning current I t ' corresponding to the largest ⁇ V t' among the multiple ⁇ V t' obtained in the process of S21 as the driving current A j of the laser.
  • the control circuit stably applies the driving current A j to the laser according to the driving current A j determined in S22 .
  • the starting working mode of the laser refers to the process in which the laser starts the pickup mode from the non-sound pickup mode every time.
  • the laser is defined as a cycle from power-on to power-off, and starting the pickup mode after each power-on is the starting working mode. In one cycle, from standby to starting the pickup mode, it also counts as starting the working mode.
  • the working mode of the laser refers to the pickup mode of the laser, that is, the pickup mode state after the laser starts the working mode.
  • the control circuit 30 determines the driving current A j of the laser 20 according to the target voltage signal output from the mixed signal acquiring device 40 , including:
  • step S11 when j is equal to 2, that is, during the first drive current modulation after the laser starts the working mode, the drive current A j-1 obtained after the previous drive current modulation is executed when the working mode is started S21 and S22.
  • the driving current A j-1 obtained after the previous driving current modulation may be the driving current determined after performing S11 to S13 in the previous laser operating mode.
  • the control circuit Before performing the next driving current modulation, the control circuit always applies the driving current obtained after the previous driving current modulation to the laser. Therefore, the driving current obtained after the previous modulation of the driving current of the laser is usually the current operating driving current of the laser.
  • I 0 and I 0′ may have the same value or different values.
  • the scanning current range [I min , I max ] may also be determined to be within the range of plus or minus 0.4 mA or within the range of 0.5 mA of the current operating current. Specifically, it can be set according to the current fluctuation of the laser.
  • the value of I max should be less than or equal to I max'
  • the value of I min should be greater than or equal to I min' .
  • the ⁇ ? is a preset current
  • the alternating current I c is a preset current
  • the frequency of the alternating current I c is greater than the maximum frequency of the sound that the human ear can hear
  • the ⁇ V t is related to the frequency of the alternating current I c ;
  • the t represents the number of current sweeps
  • step S12 of this embodiment the control circuit 30 superimposes the alternating current I c on the scanning current I t of each scan and outputs it to the laser 20 , and the self-mixed signal acquiring device 40 outputs the target voltage signal V 1 based on I t and I c , and controls After the circuit 30 obtains the target voltage signal V 1 , it performs FFT on the target voltage signal V 1 , and identifies the peak-to-peak value ⁇ V t of the output voltage fluctuation at the frequency of the alternating current I c .
  • ⁇ V t is related to the frequency of the AC current I c , which means that according to the frequency of the superimposed AC current I c , the peak-to-peak value ⁇ V t of the output voltage fluctuation at this frequency is identified in the voltage signal after performing FFT. For example, if the frequency of the superimposed alternating current I c is 25 kHz, it is necessary to identify the peak-to-peak value ⁇ V t of the output voltage fluctuation at the frequency of 25 kHz.
  • one scan means that the control circuit superimposes the alternating current I c on the scanning current I t at a certain point value and applies it to the laser, and obtains the output voltage fluctuation peak-to-peak value ⁇ V t of the laser when the alternating current I c is superimposed under the action of the scanning current I t .
  • S13 Determine the scanning current I t corresponding to the largest ⁇ V t among the multiple ⁇ V t obtained in the process of S12 as the driving current A j of the laser obtained by the current driving current modulation.
  • the larger the ⁇ V t the greater the degree of change of the self-mixing optical signal caused by the AC current disturbance of the laser, that is, the higher the sensitivity of the self-mixing optical signal to the laser current disturbance. Since both the laser current disturbance and the vibration of the diaphragm will cause the phase fluctuation in the laser cavity, that is, the self-mixing optical signal fluctuation, the greater the ⁇ V t , the higher the sensitivity of the self-mixing optical signal to the vibration of the diaphragm.
  • one-time driving current modulation means that the control circuit completes scanning the laser driving current from I min to I max , and at the same time superimposes the alternating current I c at each scanning current point It , and obtains the output according to each scanning
  • the process of obtaining the laser driving current determined by the modulation in the peak-to-peak voltage fluctuation, that is, the process of S11 to S13 is performed once.
  • the process from S21 to S22 is executed once, it is also regarded as one drive current modulation.
  • the above-mentioned driving current modulation process from S11 to S13 may be performed once every 2-20 seconds, for example, once every 5 seconds, or once every 10 seconds. It depends on the actual work situation and is not limited in this application. If the laser current is relatively stable, the interval between two current modulations can be longer, and when the laser current is not stable, the interval between two current modulations can be shorter.
  • the driving current modulation process from S21 to S22 can also be used for driving current modulation in the laser working mode, but compared with the driving current modulation process from S11 to S13, the scanning current range is larger, which is not conducive to quickly finding the working mode. The highest sensitivity operating current point.
  • the preset current ⁇ ? The range can be 10 ⁇ A ⁇ ? ⁇ 50 ⁇ A.
  • ⁇ ? The value of can be, but not limited to, 10 ⁇ A, 20 ⁇ A, 25 ⁇ A, 30 ⁇ A, 40 ⁇ A, and 50 ⁇ A.
  • the frequency of the alternating current I c is greater than the maximum frequency of the sound that the human ear can hear. Since the frequency of the sound that the human ear can hear is generally 20 Hz-20 kHz, the frequency of the alternating current I c is greater than 20kHz, specifically, 20kHz ⁇ Ic ⁇ 50kHz . In some embodiments of the present application, the frequency of the alternating current Ic is 25 kHz, 30 kHz, 40 kHz, and 50 kHz.
  • the peak-to-peak value of the alternating current I c may be controlled between 10 ⁇ A and 50 ⁇ A, specifically, but not limited to, 10 ⁇ A, 20 ⁇ A, 30 ⁇ A, 40 ⁇ A, and 50 ⁇ A.
  • the AC current I c has a higher frequency and a smaller peak-to-peak value, which is beneficial to the stable operation of the laser.
  • the sampling frequency at which the control circuit 30 collects the output signal from the output end of the self-mixed signal obtaining device 40 may be between 100 kHz and 500 kHz, specifically, for example, 100 kHz, 200 kHz, 300 kHz, and 500 kHz.
  • the process that the control circuit determines the driving current of the laser through current modulation is as follows:
  • S101 Activate the laser driving current modulation, set the peak-to-peak value of the alternating current I c to 17 ⁇ A, and the modulation frequency to 25 kHz; set the initial value of the scanning current of the laser, that is, the preset minimum driving current I min' is 0.5 mA; set the scanning current of the laser The termination value, that is, the preset maximum drive current I max' is 3mA; the scan step ⁇ I of the laser drive current is set to 25 ⁇ A;
  • S102 Scan the laser driving current from 0.5mA to 3mA, and superimpose 17 ⁇ A AC current on the scan current during each scan; at the same time, the control circuit obtains each scan output from the output end of the self-mixing signal acquisition device at a sampling frequency of 200kHz the target voltage signal obtained, perform FFT on the obtained target voltage signal, and identify the peak-to-peak value ⁇ V t′ of the output voltage fluctuation under the modulation frequency of 25kHz;
  • S103 Find the laser current value at the maximum ⁇ V t' at the modulation frequency of 25 kHz in the process of scanning from 0.5 mA to 3 mA; set the laser driving current at the scanning current value at the maximum ⁇ V t' , and turn off the modulation.
  • the laser finds the optimal operating point of the driving current with the highest sensitivity, and stabilizes the driving current of the laser at this optimal operating point before the next modulation of the driving current.
  • the above-mentioned modulation process is controlled and executed by the control circuit 30 .
  • the control circuit 30 stops collecting the target voltage signal from the self-mixing signal obtaining device 40 .
  • the drive current modulation process in the working mode of the laser microphone, when performing the j-th drive current modulation, it is not necessary to scan from the preset minimum drive current to the preset maximum drive current, and it is only necessary to determine a suitable scanning range based on the current working current,
  • the drive current modulation process can be simplified.
  • the process of performing the j-th drive current modulation may be:
  • the current operating current I 1 of the laser is actually the driving current I j-1 determined by the last modulation, i.e. the j-1th modulation;
  • S202 Scan the laser driving current from 2.0mA to 2.6mA, and superimpose the AC current of 17 ⁇ A on the scan current in each scan; at the same time, the control circuit obtains each scan from the output end of the self-mixing signal acquisition device at a sampling frequency of 200kHz For the output target voltage signal, perform FFT on the obtained target voltage signal, and identify the peak-to-peak value ⁇ V t of the output voltage fluctuation under the modulation frequency of 25kHz;
  • S203 Find the laser current value at the maximum ⁇ V t at the modulation frequency of 25 kHz in the process of scanning from 2.0 mA to 2.6 mA; set the laser driving current to the scanning current value at the maximum ⁇ V t , and turn off the modulation.
  • the embodiment of the present application modulates the driving current of the laser by constructing a loop control, which can adjust the working state of the laser in real time, stabilize the laser at a working point with high sensitivity, reduce or eliminate the low-frequency phase jitter related to the environment, and make the self-mixing laser operate.
  • the feedback interference mechanism is more stable, so that the laser microphone can maintain a high signal-to-noise ratio during operation (ie, in working mode) and throughout its life cycle.
  • the control circuit 30 includes a first controller 31 and a drive circuit 32 connected to the first controller 31 .
  • the driving circuit 32 includes a digital potentiometer 321, a resistor R7, a resistor R8, a capacitor C4, an operational amplifier OP3, a transistor Q1, and a resistor R10.
  • the digital potentiometer 321 includes a variable resistor R6 , the output port 31 a of the first controller 31 is connected to the digital potentiometer 321 , and the input signal of the input terminal 31 b of the first controller 31 is the output signal from the mixed signal obtaining device 40 .
  • the first end of the digital potentiometer 321 is connected to the positive input terminal of the operational amplifier OP3, and the second end of the digital potentiometer 321 is connected to the first end of the resistor R10.
  • the second end of the digital potentiometer 321 and the first end of the resistor R10 are both connected to a positive power supply.
  • the first end of the resistor R7 and the first end of the capacitor C4 are connected between the first end of the digital potentiometer 321 and the positive input end of the operational amplifier OP3, and the second end of the resistor R7 and the first end of the capacitor C4 are connected. Both ends are connected to ground.
  • the second end of the resistor R10 is connected to the emitter of the transistor Q1, the inverting input end of the operational amplifier OP3 is connected between the second end of the resistor R10 and the emitter of the transistor Q1, and the output end of the operational amplifier OP3 is connected to the transistor Q1
  • the base of the resistor R8 is connected to the collector of the transistor Q1 , and the second end of the resistor R8 is connected to the anode of the laser 20 as the output port of the control circuit 30 .
  • the input port 31b of the first controller 31 is used as the input port 30b of the control circuit 30 to be connected to the output port 40c of the self-mixing signal acquisition device 40 .
  • the variable resistor R6 and the resistor R7 are voltage dividing resistors, which can play a voltage dividing function.
  • the resistor R8 and the resistor R10 can play a current limiting role, wherein R10 can control the current passing through the transistor Q1, so as to avoid excessive power consumption caused by the excessive current of the transistor Q1.
  • the capacitor C4 can realize the slow start of the drive circuit 32 .
  • the first controller 31 outputs a control signal based on the acquired output signal of the self-mixed signal acquisition device 40 to control the effective resistance value of the variable resistor R6, which can be controlled by changing the effective resistance value of the variable resistor R6.
  • the drive current output from the drive circuit 32 to the laser 20 is adjusted to realize the adjustable drive current of the laser 20 .
  • the driving circuit 32 is a constant current source circuit, which can provide the laser 20 with a constant DC bias current that hardly changes with temperature, so as to stabilize the operating point.
  • the self-mixing signal acquisition device 40 includes a photodetector 41 and a transimpedance amplifier circuit 42, the photodetector 41 is connected to the laser 20, and the input end of the transimpedance amplifier circuit 42 is connected to the photodetector 41 connections.
  • the output end of the control circuit 30, that is, the second end of the resistor R8, is connected to the anode of the laser 20, the anode of the photodetector 41 is electrically connected to the cathode of the laser 20, and the common electrode of the photodetector 41 and the laser 20 is grounded.
  • the cathode is connected to the input end of the transimpedance amplifying circuit 42 , and the output end of the transimpedance amplifying circuit 42 is connected to the input end of the high-pass filter circuit 51 as the output port 40b (see FIG. 1 ) of the self-mixing signal obtaining device 40 .
  • the transimpedance amplifier circuit 42 includes an operational amplifier OP1, a resistor R1, and a capacitor C1.
  • the output end of the photodetector 41 is connected to the inverting input end of the operational amplifier OP1, and the first end of the resistor R1 is connected to the capacitor C1.
  • the first end of C1 is connected between the output end of the photodetector 41 and the inverting input end of the operational amplifier OP1, and the second end of the resistor R1 and the second end of the capacitor C1 are both connected to the output end of the operational amplifier OP1
  • the output end, the forward input end of the operational amplifier OP1 inputs the current bias of the photodetector, and the output end of the operational amplifier OP1 is connected to the input end of the high-pass filter circuit 51 as the output end of the self-mixing signal obtaining device 40 .
  • Capacitor C1 is a feedback compensation capacitor, which is used to compensate the node capacitance of the photodetector and the input capacitance of the operational amplifier to keep the circuit stable.
  • Resistor R1 is a feedback resistor for converting the current signal into a voltage signal.
  • the self-mixing signal acquisition device 40 includes a buffer circuit 43 connected to the laser 20 .
  • the buffer circuit 43 includes an operational amplifier OP4.
  • the positive input terminal of the operational amplifier OP4 is connected to the anode of the laser 20, the cathode of the laser 20 is connected to ground, and the output terminal of the operational amplifier OP4 is used as the output port 40b (see FIG.
  • the input terminal is connected, and the inverting input terminal of the operational amplifier OP4 is connected between the output terminal of the operational amplifier OP4 and the input terminal of the high-pass filter circuit 51 .
  • the signal processing circuit 50 includes a high-pass filter circuit 51 , a voltage amplification and low-pass filter circuit 52 , and a gain control circuit 53 .
  • the high-pass filter circuit 51 includes a capacitor C2 and a resistor R2.
  • the first end of the capacitor C2 is connected to the output port 40b of the self-mixing signal acquisition device 40 as the input end of the high-pass filter circuit 51, and the second end of the capacitor C2 is connected to the voltage amplification and low-pass as the output end of the high-pass filter circuit 51.
  • Filter circuit 52 The first end of the resistor R2 is connected to the second end of the capacitor C2, and the second end of the resistor R2 is connected to ground.
  • the high-pass filter circuit 51 formed by the capacitor C2 and the resistor R2 can filter out the DC current and low-frequency signals.
  • the voltage amplification and low-pass filter circuit 52 includes an operational amplifier OP2, a capacitor C3, a digital potentiometer 521, a resistor R3 and a resistor R5.
  • the forward input terminal of the operational amplifier OP2 is used as the input terminal of the voltage amplification and low-pass filter circuit 52 to be connected to the output terminal of the high-pass filter circuit 51, and the output terminal of the operational amplifier OP2 is connected to the first end of the resistor R5.
  • the resistor R5 The second end of the signal is used as the output end of the voltage amplification and low-pass filter circuit 52 , that is, the output end of the signal processing circuit 50 outputs the audio voltage signal to the outside.
  • the first end of the resistor R3, the first end of the digital potentiometer 521 and the first end of the capacitor C3 are all connected to the inverting input of the operational amplifier OP2, and the second end of the digital potentiometer 521 and the capacitor C3 are connected.
  • the second ends are both connected between the output end of the operational amplifier OP2 and the first end of the resistor R5, and the second end of the resistor R3 is connected to ground.
  • the digital potentiometer 521 is connected to the gain control circuit 53, and the digital potentiometer 521 includes a variable resistor R4.
  • a low-pass filter circuit can filter out high-frequency signals.
  • the high-pass filter circuit 51 and the voltage amplification and low-pass filter circuit 52 can form a band-pass filter circuit.
  • the lower cut-off frequency of the band-pass is determined by R2 and C2, and the upper cut-off frequency is determined by R4 and C3.
  • the band-pass range can be 20Hz ⁇ 20kHz , to filter out low-frequency background sounds and high-frequency signals.
  • the OP1 and OP2 two-stage amplifying circuit systems are at different DC operating points.
  • the gain control circuit 53 includes a second controller 531.
  • the input end of the second controller 531 is connected to the output end of the signal processing circuit 50 for collecting the voltage signal output by the signal processing circuit 50.
  • the output end of the second controller 531 is connected to the output end of the signal processing circuit 50.
  • the second controller 531 outputs a control signal to control the effective resistance value of the variable resistor R4 of the digital potentiometer 521.
  • the gain of the voltage amplification and low-pass filter circuit 52 can be adjusted.
  • the above-mentioned operational amplifier OP1, operational amplifier OP2, operational amplifier OP3, and operational amplifier OP4 are low-noise operational amplifiers, and a high PSRR (Power Supply Rejection Ratio, power supply ripple rejection ratio) power supply circuit (such as LDO) can be used.
  • PSRR Power Supply Rejection Ratio, power supply ripple rejection ratio
  • the use of low-noise operational amplifiers is beneficial to improve the signal-to-noise ratio.
  • the resistance values of the above resistors should be as small as possible under the condition of satisfying their functions, so as to reduce the thermal noise generated by the resistors.
  • the first controller 31 and the second controller 531 may be provided separately, or may be the same controller.
  • the laser microphone 100 includes a casing 1 , and the casing 1 includes a base plate 11 , a cover plate 12 and a middle frame 13 arranged oppositely, and the base plate 11 , the cover plate 12 and the middle frame 13 are formed by surrounding
  • the accommodating cavity, the diaphragm 10, the laser 20, the photodetector 41, and the ASIC (Application Specific Integrated Circuit, integrated circuit) chip 2 are all arranged in the accommodating cavity.
  • the diaphragm 10 is fixed on the cover plate 12, the laser 20 is disposed on the substrate 11, the photodetector 41 is disposed on the substrate 11, and is located on the side of the laser 20 away from the diaphragm 10, and the cover plate 12 is provided with a sound pickup
  • the hole 121, the diaphragm 10 is arranged corresponding to the sound pickup hole 121.
  • the laser microphone 100 of the present embodiment emits and returns the beam in the same path, does not require a reference interference arm, has fewer components, and the optical path is self-aligned, which can allow smaller size packaging.
  • the distance between the diaphragm 10 and the light-emitting surface of the laser 20 (that is, the side facing the diaphragm 10 ) is set in the range of 30 ⁇ m-300 ⁇ m, and a suitable distance can improve the light reflected back to the laser by the diaphragm 10 Coupling efficiency with light in the laser cavity.
  • the distance between the diaphragm 10 and the laser 20 may be set in the range of 50 ⁇ m-100 ⁇ m. In other embodiments, the distance between the diaphragm 10 and the laser 20 may be set in the range of 100 ⁇ m-200 ⁇ m.
  • the diaphragm 10 can sense air vibrations generated by external sound waves, generate vibrations, and reflect the light emitted by the laser back into the laser resonator. External sound waves can be transmitted to the diaphragm 10 through the sound pickup holes 121 .
  • the laser microphone of the embodiment of the present application is different from the capacitance detection mechanism of the traditional MEMS microphone, and does not need to set a back plate, so there is no special requirement for the conductive characteristics of the diaphragm.
  • the diaphragm 10 may be a MEMS (micro-electro-mechanical system, micro-electromechanical system) diaphragm, a metal glass diaphragm, a graphene diaphragm, a polymer film or a metal film.
  • a reflection layer may be provided on the side of the diaphragm 10 facing the laser 20 to improve the reflectivity, and the material of the reflection layer may be a metal with high reflectivity such as aluminum and gold.
  • the side of the diaphragm 10 coated with the reflective layer faces the light-emitting surface of the laser 20 and is aligned at the center.
  • a negative-stressed SOI (Silicon-On-Insulator, silicon on insulating substrate) film layer is used in combination with a positive-stressed metal reflective layer, which reduces the stress of the vibrating film and improves the performance of the vibrating film. Sound pressure displacement sensitivity.
  • the embodiment of the present application adopts a back-pole diaphragm, which reduces the damping of the pressure film, improves the sound pressure displacement sensitivity, and reduces the noise.
  • the diaphragm design of the embodiments of the present application allows the detection of weaker sounds and a stronger sound signal response amplitude, which is beneficial to the realization of a high signal-to-noise ratio.
  • the diaphragm 10 is provided with one or more balance holes for balancing the air pressure inside and outside the diaphragm, and the diameter of the balance holes can be 1 ⁇ m-5 ⁇ m (including the end values of 1 ⁇ m and 5 ⁇ m).
  • the diaphragm 10 is a MEMS silicon diaphragm, with a thickness of 300 nm-800 nm and a diameter of 600 ⁇ m-1200 ⁇ m.
  • the surface of the central area of the MEMS silicon diaphragm is coated with a high-reflection metal layer, such as an aluminum layer, a gold layer, etc.
  • the thickness of the metal layer can be 30nm-100nm (including the endpoint values of 30nm and 100nm), and the radius of the metal layer is 20 ⁇ m-50 ⁇ m.
  • the sound pressure displacement sensitivity of the MEMS silicon diaphragm is 0.05 ⁇ m/Pa ⁇ 0.5 ⁇ m/Pa.
  • the thickness of the MEMS silicon diaphragm is 400 nm, the diameter is 900 ⁇ m, the central area of the diaphragm is plated with aluminum, the thickness of the aluminum layer is 90 nm, and the radius is 30 ⁇ m, and two balance holes are set on the diaphragm, each The diameter of the balance hole is 2 ⁇ m, and the sound pressure displacement sensitivity of the MEMS diaphragm is 0.1 ⁇ m/Pa.
  • a silicon substrate based on SOI or polysilicon is used to manufacture the diaphragm, which is beneficial to reduce stress and improve the displacement sensitivity of sound pressure.
  • the setting of the metal reflective layer can balance the stress of the film layer and at the same time improve the light reflectivity of the diaphragm. Through stress control, the linearity of the vibration amplitude of the diaphragm with the change of sound pressure is further improved.
  • the laser microphone 100 may have a top-in sound structure.
  • the diaphragm 10 is located on the cover plate 12
  • the sound pickup hole 121 is provided on the cover plate 12
  • the diaphragm 10 and the cover plate 12 are located between the diaphragm 10 and the cover plate 12 .
  • a front cavity 3 is formed between, and a rear cavity 4 is formed between the diaphragm 10 and the housing.
  • the diaphragm 10 is arranged on the cover plate 12 to form a larger rear cavity 4 .
  • the diaphragm 10, the laser 20 and the sound pickup hole 121 are arranged correspondingly, and may be arranged coaxially.
  • the laser microphone of the jack-in-sound structure is generally fixed on the PCB board in the terminal through the substrate 11 .
  • the photodetector 41 is electrically connected to the chip 2 through the metal trace 5 , and the chip 2 is directly connected to the external metal electrode through the via hole on the substrate 11 . 6 Electrical connections.
  • the laser microphone 100 may also have a bottom-in sound structure. As shown in FIG. The laser 20 and the photodetector 41 are located on the cover plate 12 , a front cavity 3 is formed between the diaphragm 10 and the substrate 11 , and a rear cavity 4 is formed between the diaphragm 10 and the casing. The diaphragm 10 is disposed on the substrate 11 to form a larger rear cavity 4 .
  • the diaphragm 10 In the bottom-in sound structure, the diaphragm 10, the laser 20 and the sound pickup hole 121 are arranged correspondingly, and may be arranged coaxially. There may be one or more sound pickup holes 121 .
  • the laser microphone with bottom-in sound structure is generally fixed on the PCB board in the terminal through the substrate 11 .
  • the photodetector 41 is electrically connected to the chip 2 through the metal trace 5 , and the chip 2 passes through the metal trace 5 and the via hole on the substrate 11 . It is electrically connected to the external metal electrode 6 .
  • Both the laser microphones with the above two structures obtain a back cavity with a larger air volume, which makes it easier for sound waves to push the diaphragm to move, thereby improving the sensitivity and signal-to-noise ratio of the microphone.
  • the packaging substrate 11 , the packaging cover 12 , and the middle frame 13 are all made of PCB material, or the packaging substrate 11 is made of PCB material or Made of ceramic material, the package cover 12 and the middle frame 13 are of an integrated structure and are made of metal or other materials.
  • the self-mixing optical signal acquisition device 40 when the self-mixing optical signal acquisition device 40 includes a photodetector 41 and a transimpedance amplifying circuit 42, the photodetector 41 and the laser 20 can be integrated on an optical chip, and the optical The detector 41 is located on the side of the laser 20 away from the diaphragm 10 , and the transimpedance amplifier circuit 42 can be integrated with the control circuit 30 and the signal processing circuit 50 on an ASIC chip 2 .
  • Integrating the photodetector 41 and the laser 20 on an optical chip can improve the efficiency of coupling the light penetrating from the back of the laser into the photodetector, thereby improving the signal-to-noise ratio, and at the same time, it can avoid discrete arrangement in the case of vibration and drop. The resulting optical path deviation, thereby maintaining the consistency of the signal during the life cycle of the module.
  • the photodetector 41 and the laser 20 may also be arranged separately, the laser 20 may be directly attached to the photodetector 41, and the back of the laser 20, that is, the side away from the diaphragm 10 emits light Direct coupling into the photodetector 41 is also possible.
  • the working wavelength of the photodetector 41 may be 360 nm-1600 nm (including the end values of 360 nm and 1600 nm).
  • the buffer circuit can be integrated with the control circuit 30 and the signal processing circuit 50 on one ASIC chip 2 .
  • the laser 20 is a self-mixing laser, and the specific type is not limited, and may be a vertical cavity surface emitting laser or an edge emitting laser.
  • the emission wavelength of the laser can be 750nm-1600nm.
  • the laser 20 is a single-mode working vertical cavity surface emitting laser (Vertical-Cavity Surface-Emitting Laser, VCSEL), and its emission wavelength is 850 nm.
  • the typical threshold current of the vertical cavity surface emitting laser is 0.7mA, the typical operating current is about 2.5mA, the typical output power is about 0.5mW, and the typical output photocurrent of the corresponding photodetector is 0.5mA.
  • Typical dimensions of a vertical cavity surface emitting laser may be: 120 ⁇ m-200 ⁇ m in length, 120 ⁇ m-200 ⁇ m in width, and 100 ⁇ m-150 ⁇ m in thickness.
  • the laser microphone further includes a beam coupling device, which is located between the laser 20 and the diaphragm 10 .
  • the beam coupling device may include one or more lenses 70 , and the lenses 70 are fabricated on the light-emitting surface of the laser 20 .
  • the lens 70 may be a collimating lens or a condensing lens. The use of a lens to couple the outgoing and reflected light can improve the feedback coupling efficiency, increase the feedback light intensity to the vibration signal carrying the diaphragm, and thus improve the signal-to-noise ratio of the laser microphone. As shown in FIG.
  • the lens 70 is a collimating lens, including a lens cylinder and a lens curved surface, wherein the lens cylinder can be fabricated by lithography or laser direct writing, and the lens curved surface can be made by embossing , inkjet printing, etc.
  • the collimating lens can collimate the outgoing light of the laser to the reflection surface of the diaphragm, and couple the reflected light into the light outgoing hole of the laser. By setting the collimating lens, the light reflected back to the laser can be greatly increased, thereby improving the light intensity of the feedback signal, thereby improving the signal-to-noise ratio of the microphone.
  • the material of the lens is a material with a light transmittance greater than 90% in the working wavelength range of the laser.
  • the lateral dimension (ie, the length and width) of each of the lenses is 20 ⁇ m-200 ⁇ m (including the endpoints of 20 ⁇ m and 200 ⁇ m); the longitudinal dimension (ie, the height dimension) of each of the lenses is 20 ⁇ m-200 ⁇ m (Including endpoint values of 20 ⁇ m and 200 ⁇ m).
  • the above-mentioned all parameter values with a numerical range include two end-point values.
  • the laser microphone of the embodiment of the present application improves the sound pressure displacement sensitivity of the diaphragm based on the design of the backless diaphragm, and at the same time improves the detection capability of weak vibration signals through the laser self-mixing interference effect, thereby improving the vibration response sensitivity and dynamic range. Can pick up slight voice signals.
  • the vibration of the diaphragm is detected by means of laser self-mixing coherence, which has high detection sensitivity.
  • the laser microphone of the embodiment of the present application can significantly improve the voice pickup in the soft-spoken mode in quiet scenes, the detection of weak voice signals at a distance, and the voice pickup quality during long-distance video recording.
  • the signal-to-noise ratio of the laser microphone of the embodiment of the present application is greater than 75dB, for example, 80dB. Compared with the traditional MEMS microphone (signal-to-noise ratio of 65dB), the signal-to-noise ratio is significantly improved.
  • an embodiment of the present application further provides a terminal 200 including the laser microphone 100 described above in the embodiment of the present application.
  • the terminal 200 includes a casing and a circuit board arranged in the casing.
  • the laser microphone is arranged on the circuit board.
  • the terminal casing is provided with a sound-receiving hole 101 corresponding to the position of the laser microphone, and external sound is transmitted to the laser microphone through the sound-receiving hole 101 of the casing.
  • the laser microphone 100 can be set corresponding to the front side of the terminal, and the sound-receiving hole 101 is correspondingly set on the front cover plate 201 of the terminal (refer to the front view of FIG.
  • the hole 101 is arranged on the rear side cover plate 202 of the terminal (refer to the rear view of FIG. 9 ); the laser microphone 100 can also be arranged corresponding to the side frame 203 of the terminal, and the sound-receiving hole 101 is correspondingly arranged on the side middle frame 203 of the terminal Specifically, as shown in the bottom view in FIG. 9 , the sound-receiving hole 101 is arranged on the lower middle frame of the terminal, or may be arranged on the upper, left or right middle frame.
  • the sound-collecting hole of the laser microphone 100 is arranged corresponding to the sound-receiving hole 101 on the terminal shell, and may be arranged coaxially.
  • the middle frame 203 and the rear side cover 202 may be an integrally formed structure, or may be a separate structure.
  • the terminal 200 can be a mobile phone, a notebook computer, a tablet computer, a smart TV, a smart speaker, a headset, a video camera, a network camera, a wearable device, a game device, a car audio system or a microphone, a voice navigation device, a spoken voice recognition device, a voice To text converters and other end products that require voice command control or scenarios that need to capture, record, process or analyze speech.

Abstract

本申请实施例提供一种激光麦克风，包括振膜、激光器、控制电路、自混合信号获取装置、信号处理电路；激光器用于向振膜发射光，并接收来自振膜的反馈光信号，反馈光信号与激光器谐振腔内的激光相干涉得到自混合光信号；激光器与振膜之间的间距为30μm-300μm；控制电路与激光器连接，用于驱动控制激光器发光；自混合信号获取装置与激光器连接，用于获取与自混合光信号相关的目标电压信号；信号处理电路与自混合信号获取装置连接，用于接收自混合信号获取装置输出的目标电压信号，并处理成音频电压信号。该激光麦克风具有高信噪比，可以提升语音识别率和唤醒率，改善远距离拾音效果。本申请实施例还提供包括该激光麦克风的终端。

Description

激光麦克风和终端
本申请要求于2020年9月4日提交中国专利局、申请号为202010924113.6、申请名称为“激光麦克风和终端”的中国专利申请的优先权，其全部内容通过引用结合在本申请中。
技术领域
本申请涉及麦克风技术领域，尤其涉及一种激光麦克风和终端。
背景技术
语音控制、语音交互等场景下的自动语音识别系统的使用正在迅速增长，同时，越来越多的人们通过移动互联网录制与分享视频内容，用于拾取声音的麦克风必须具备很好的性能才能确保出色的用户体验。麦克风的信噪比(SNR)是影响拾取声音质量的关键参数。高信噪比有助于麦克风在拾取远距离、信号较弱的目标声源时，在信号放大时保持较低的本底噪音，从而提高远距离拾音质量。
目前在移动通信终端、智能家居等设备中大多采用MEMS(Microelectro Mechanical Systems，微机电系统)麦克风来采集语音信号。其由MEMS电容传感器、ASIC(Application Specific Integrated Circuit，用于供专门应用的集成电路)转换电路、音腔等组成。MEMS电容包括接受声音的硅振膜和硅背极两个端，硅振膜可以感知声波产生的空气振动并随之振动，与硅背极形成一个可变电容，通过电路检测外加偏置下该可变电容的变化，并处理转换成电信号输出。由于振膜与硅背极的间距较小，会引入较高的压膜阻尼，从而引入较高的机械噪声，限制了信噪比的提升空间。另外，硅背极与硅振膜间的吸合效应，使得两者之间必须保持一定的距离，从而使得灵敏度与声学过载点的提升空间受到限制。传统MEMS麦克风面临着信噪比进一步提升的瓶颈，因此，想要获得更高信噪比的麦克风，提高语音识别率和唤醒率，改善远距离拾音效果，需要探索新的技术路线。
发明内容
本申请实施例提供了一种激光麦克风，其具备高信噪比，可以提升语音识别率和唤醒率，改善远距离拾音效果。
具体地，本申请实施例第一方面提供一种激光麦克风，包括振膜、激光器、控制电路、自混合信号获取装置、信号处理电路；
所述激光器用于向所述振膜发射光，并接收来自所述振膜的反馈光信号，所述反馈光信号与所述激光器谐振腔内的激光相干涉得到自混合光信号；所述激光器与所述振膜之间的间距为L，所述L的范围为30μm≤L≤300μm；
所述控制电路与所述激光器连接，用于驱动控制所述激光器发光；
所述自混合信号获取装置与所述激光器连接，用于获取并输出与所述自混合光信号相关的目标电压信号；
所述信号处理电路与所述自混合信号获取装置连接，用于接收所述自混合信号获取装置输出的所述目标电压信号，并将所述目标电压信号处理成音频电压信号。
本申请实施例提供的激光麦克风，采用激光自混合器件检测语音信号引起的振膜振动，激光自混合器件具备较强的微弱振动信号探测能力，因而可以提升麦克风的语音识别灵敏度； 而通过将激光器与振膜设置在适合间距，可以提升激光器出射光束经振膜反射后重新进入激光器谐振腔内的耦合效率，从而有效提高激光麦克风的信噪比，提升语音识别灵敏度。
由于环境温度波动、激光器老化等原因会导致激光器电流产生波动，从而导致激光器发光频率漂移，引入相位噪声，为减少或消除该相位噪声，提高激光麦克风信噪比，本申请实施例进一步通过构建环路控制对激光器驱动电流进行调制，将激光器稳定在灵敏度最高的电流工作点。具体地，本申请实施方式中，所述自混合信号获取装置的输出端与所述控制电路的输入端连接，所述控制电路根据所述自混合信号获取装置输出的所述目标电压信号确定所述激光器的驱动电流A j。
由于激光器的电流波动和振膜振动都会导致激光器谐振腔内相位波动，也即自混合光信号波动。本申请实施例通过对激光器施加较小的电流扰动，并根据该电流扰动导致的自混合信号获取装置输出的电压信号的变化程度，即电流扰动导致自混合光信号的变化程度来确定激光器灵敏度最高的工作点，从而能够使激光器保持在对振膜的振动灵敏度最高的工作点，提高麦克风信噪比。
本申请实施方式中，在所述激光器工作模式下，进行第j次驱动电流调制时，所述控制电路根据所述自混合信号获取装置输出的所述目标电压信号确定所述激光器的驱动电流A j，包括：
S11：所述控制电路根据前一次驱动电流调制后得到的驱动电流A j-1确定本次驱动电流调制的扫描电流范围[I min，I max]，其中，所述I min＝A j-1-I 0，所述I max＝A j-1+I 0’，0.1mA≤I 0≤0.5mA，0.1mA≤I 0’≤0.5mA；所述j表示驱动电流调制次数，且取大于或等于2的整数；
S12：所述控制电路以I min为初始值，以Δ？为步长，以I max为终止值对所述激光器施加扫描电流I t，且在每一次扫描时在所述扫描电流I t上叠加交流电流I c，并获取每一次扫描的输出电压波动峰峰值ΔV t；
其中，所述Δ？为预设电流；所述交流电流I c为预设电流，所述交流电流I c的频率大于人耳能听到的声音的最大频率；所述ΔV t与所述交流电流I c的频率相关；所述t表示电流扫描次数；
S13:将执行S12过程中获取的多个ΔV t中，最大的ΔV t对应的扫描电流I t确定为本次驱动电流调制获得的所述激光器的驱动电流A j。
在激光器工作模式下进行上述驱动电流调制，可以使激光器在整个工作过程中，总是稳定在灵敏度最高的电流工作点，从而提高激光麦克风的拾音质量及远距离拾音效果，以及提高激光麦克风的拾音稳定性。
本申请实施方式中，在所述激光器启动工作模式时，所述控制电路根据所述自混合信号获取装置输出的所述目标电压信号确定所述激光器的驱动电流A j，包括：
S21：所述控制电路以I min’为初始值，以Δ？为步长，以I max’为终止值对所述激光器施加扫描电流I t’，且在每一次扫描时在所述扫描电流I t’上叠加交流电流I c，并获取每一次扫描的输出电压波动峰峰值ΔV t′；
其中，所述I min’为预设最小驱动电流，所述I max’为预设最大驱动电流；所述Δ？为预设电流；所述交流电流I c为预设电流，所述交流电流I c的频率大于人耳能听到的声音的最大频率；所述ΔV t′与所述交流电流I c的频率相关；所述t’代表电流扫描次数；
S22:将执行S21过程中获取的多个ΔV t′中，最大的ΔV t′对应的扫描电流I t’确定为所述激光器的驱动电流A j。
在激光器启动工作模式时，通过从预设最小驱动电流(一般为激光器阈值)扫描至预设 最大驱动电流寻找激光器灵敏度最高的电流工作点，可以提高激光麦克风的拾音质量及远距离拾音效果。
本申请实施方式中，所述Δ？的范围为10μA≤Δ？≤50μA。设置适合的步长有利于较准确地找到灵敏度高的驱动电流点值。
本申请实施方式中，交流电流I c的频率，即施加的电流扰动的频率大于人耳能听到的声音的最大频率，因此电流扰动本身不会对激光器的稳定工作产生较大影响。本申请一些实施方式中，所述交流电流I c的频率范围为20kHz＜I c≤50kHz。所述交流电流I c的峰峰值可以是控制在10μA至50μA之间。同样，施加较小电流值的交流电流I c也能够减小对激光器稳定工作的影响。
本申请一实施方式中，所述自混合信号获取装置用于探测所述激光器谐振腔内的所述自混合光信号，并输出与所述自混合光信号相关的目标电压信号。
本申请一具体实施方式中，所述自混合信号获取装置包括光探测器和互阻抗放大电路，所述光探测器与所述激光器连接，用于探测所述激光器谐振腔内的所述自混合光信号，并将所述自混合光信号转换成电流信号；所述互阻抗放大电路与所述光探测器连接，用于将所述电流信号转换成所述目标电压信号。采用光探测器和互阻抗放大电路获取自混合信号，可以通过增大激光器驱动电流，获得更高的信噪比。
本申请实施方式中，所述光探测器与所述激光器单片集成在同一个芯片上，所述光探测器位于所述激光器背离所述振膜的一侧，即激光器出光面的背面。激光器与光探测器集成在同一个芯片上，可以提升从激光器背面透出的光耦合进光探测器的效率，进而提升信噪比，同时也可避免分立布置在振动与跌落等情形下导致的光路偏差，进而保持信号在麦克风整个生命周期的一致性。
本申请另一实施方式中，所述自混合信号获取装置包括与所述激光器连接的缓冲电路，所述缓冲电路用于获取所述激光器的端电压，所述激光器的端电压与所述自混合光信号相关。通过获取激光器端电压得到与自混合光信号相关的目标电压信号，可以在较小的激光器驱动电流(即较小功耗)下，获得适度的信噪比。
本申请实施方式中，所述信号处理电路包括高通滤波电路和电压放大及低通滤波电路，所述高通滤波电路与所述自混合信号获取装置连接，所述电压放大及低通滤波电路与所述高通滤波电路连接。高通滤波电路和电压放大及低通滤波电路可以滤除低频背景声音和高频信号。
本申请一些实施方式中，所述信号处理电路还包括与所述电压放大及低通滤波电路连接的增益调控电路，所述增益调控电路用于根据所述电压放大及低通滤波电路的输出信号调节所述电压放大及低通滤波电路的增益。增益调控电路的设置可以实现电压放大及低通滤波电路的增益可调。
本申请实施方式中，所述激光器朝向所述振膜一侧的出光面设置有光束耦合装置，所述光束耦合装置包括一个或多个透镜。透镜的设置可以提升激光器出射光束经振膜反射后重新进入激光器谐振腔内的耦合效率，具有更高的反馈光强，也即更强的信号，从而进一步有效提高麦克风的信噪比。
本申请实施方式中，每一所述透镜的横向尺寸(即长宽尺寸)为20μm-200μm；每一所述透镜的纵向尺寸(即高度尺寸)为20μm-200μm。通过激光直写或者微纳打印等方式可以实现如上尺寸透镜的加工，具有上述尺寸的透镜可以集成在激光器上，实现更紧凑的组装，以及可实现在wafer晶圆上直接制作的量产化方案。
本申请实施方式中，所述振膜的具体种类不限，对导电性无特殊要求，只需考虑音频需要的振动特性，可以是现有麦克风可用的各种振膜。具体可包括MEMS振膜、金属玻璃振膜、石墨烯振膜、高分子薄膜或金属类薄膜等。
本申请实施方式中，所述振膜朝向所述激光器的一侧设有反射层。所述反射层的反射率大于70％。具体地，反射层可以是金、铝等材质。反射层的设置可以提高激光器出射光束发射到振膜时被反射回激光器谐振腔内的反射率。另外，为将振膜的整体应力控制在一个较小的范围，提升声压位移灵敏度，振膜一般为包含不同应力膜层的复合膜结构，这样，通过金属反射层的设置，在增加反射率之外，还可补偿振膜的负应力，提升振膜稳定性。
本申请实施方式中，所述激光器为自混合激光器，具体类型不限，可以是垂直腔面发射激光器，也可以是边发射激光器。激光器的输出波长可以是750nm-1600nm。
本申请实施方式中，所述激光麦克风还包括壳体，所述振膜、所述激光器、所述控制电路、所述自混合信号获取装置和所述信号处理电路均设置于所述壳体内，所述壳体上与所述振膜相对应的位置设置有拾音孔。外界声音信息通过拾音孔拾取。
本申请实施例还提供了一种终端，所述终端包括本申请实施例第一方面所述的激光麦克风。终端包括外壳和设置于外壳内的电路板，激光麦克风设置在电路板上，终端外壳上设置有与激光麦克风的位置相对应的收音孔，外界声音通过外壳的收音孔传至激光麦克风。激光麦克风可以是对应于终端前侧设置，也可以是对应于终端后侧设置，还可以是对应于终端侧边中框设置。该终端可以是移动电话(手机)、笔记本电脑、平板电脑、智能电视、智能音箱、耳机、摄像机、网络摄像机、穿戴式装置、游戏装置、车载音频系统或麦克风、语音导航设备、口述语音识别设备、语音到文本转换器等需要语音命令控制或需要采集、记录、处理或分析语音的场景中的终端产品。
本申请实施例提供的激光麦克风，基于激光自混合器件检测语音信号引起的振膜振动，具备较强的微弱振动信号探测能力，相比于传统的MEMS麦克风具有更高的信噪比。本申请实施例的激光麦克风，通过将激光器与振膜设置在适合间距，提升了激光器出射光束经振膜反射后重新进入激光器谐振腔内的耦合效率，从而有效提高了信噪比，提升了语音识别灵敏度。另外，本申请实施例激光麦克风通过构建环路控制对激光器的驱动电流进行调制，将激光器稳定在灵敏度最高的工作点，可以减少或消除电流波动导致的相位噪声，使得激光麦克风可以在工作期间以及整个生命周期内保持较高的信噪比。本申请实施例激光麦克风可显著改善安静场景下的轻声细语模式下的语音拾取、远距离的微弱语音信号的探测以及远距视频录制时的语音拾取质量，提升用户体验。
附图说明
图1是本申请一实施例提供的激光麦克风的电路结构示意图；
图2是本申请另一实施例提供的激光麦克风的电路结构示意图；
图3是本申请一实施例中信号处理电路50的结构示意图；
图4是本申请一实施例提供的激光麦克风的电路结构示意图；
图5是本申请另一实施例提供的激光麦克风的电路结构示意图；
图6是本申请一实施例提供的顶进音结构激光麦克风的结构示意图；
图7是本申请一实施例提供的底进音结构激光麦克风的结构示意图；
图8是本申请一实施例中透镜的设置示意图；
图9是本申请实施例提供的终端中激光麦克风的设置位置示意图。
具体实施方式
下面结合本申请实施例中的附图对本申请实施例进行描述。
参见图1和图2，本申请实施例提供一种激光麦克风100，包括振膜10、激光器20、控制电路30、自混合信号获取装置40和信号处理电路50。振膜10用于接收外界声音产生的声波并产生振动，激光器20的出光面一侧与振膜10相对，激光器20用于向振膜10发射光，并接收来自振膜10的反馈光信号，基于激光自混合干涉效应，该反馈光信号与激光器20谐振腔内的激光相干涉得到自混合光信号；控制电路30的输出端30b与激光器20连接，控制电路30用于驱动控制激光器20发光。自混合信号获取装置40与激光器20连接，自混合信号获取装置40用于获取与自混合光信号相关的目标电压信号。信号处理电路50的输入端50a与自混合信号获取装置40的第一输出端口40b连接，用于接收自混合信号获取装置40输出的目标电压信号，并将目标电压信号处理成音频电压信号。
本申请实施例激光麦克风100的工作机理为：外界声音产生的声波作用在振膜10上，振膜10随着声波的声压变化产生振动位移；控制电路30给激光器20提供驱动电流驱动激光器20发射光，激光光束射向振膜10并被振膜10反射得到反馈光信号，该反馈光信号携带振膜10的振动信息，相对发射光相位改变，反馈光信号反射回激光器20谐振腔并与腔内的激光发生自混合干涉，得到自混合光信号；自混合信号获取装置40获取激光器20与该自混合光信号相关的目标电压信号，信号处理电路50接收自混合信号获取装置40输出的目标电压信号，并将目标电压信号进行放大、过滤等处理，得到最终输出的音频电压信号。
本申请实施方式中，激光器20与振膜10之间的间距为L，L的范围为30μm≤L≤300μm，即激光器20靠近振膜10一侧的出光面与振膜10的反射面之间的距离为30μm-300μm。激光器20出光面与振膜10反射面之间的距离可视作等效外腔，振膜10表面沿着激光光束方向发生的振动位移，改变振膜反射面与激光器出光面所形成的外部反射腔长，进而改变反馈光的相位。本申请实施例通过将激光器与振膜设置在适合间距，即保持适合的外腔长，可以提升激光器出射光束经振膜反射后重新进入激光器谐振腔内的耦合效率，从而有效提高信噪比，提升语音识别灵敏度。
本申请一些实施方式中，自混合信号获取装置40用于获取激光器20谐振腔内的自混合光信号，并输出与自混合光信号相关的目标电压信号。具体地，如图1所示，自混合信号获取装置40包括光探测器41和互阻抗放大电路42，光探测器41与激光器20连接，互阻抗放大电路42的输入端与光探测器41电连接，光探测器41用于检测激光器谐振腔内的自混合光信号并将自混合光信号转化为电流信号，互阻抗放大电路42用于将光探测器41输出的电流信号转换成电压信号。该实施方式中，由振膜反射得到的反馈光信号反射回激光器20谐振腔并与腔内的光场发生自混合干涉，引起激光器光强度变化，自混合导致的光强度变化由光探测器41检测出，光探测器41将光信号转换为光电流信号，互阻抗放大电路42将光电流信号转化为放大的目标电压信号，再由信号处理电路50进行信号的放大和滤波等处理，并最终输出为音频电压信号。
本申请另一些实施方式中，自混合信号获取装置40用于从激光器20直接获取与自混合光信号相关的目标电压信号。具体地，如图2所示，自混合信号获取装置40包括与激光器20的输出端连接的缓冲电路43。缓冲电路43可以获取激光器20的端电压。本申请中，激光器20的端电压是指激光器两端的电压差或者激光器一端相对地的电压。缓冲电路43是一种保护电路，可以抑制电流上升。
参见图3，本申请一些实施方式中，信号处理电路50包括高通滤波电路51、电压放大及 低通滤波电路52，高通滤波电路51的输入端口51a与自混合信号获取装置40的第一输出端口40b连接，电压放大及低通滤波电路52的输入端口52a与高通滤波电路51的输出端口51b连接。其中，高通滤波电路51可以隔直自混合信号获取装置40的输出信号，并滤除低频噪声，电压放大和低通滤波电路52可以对高通滤波电路51输出的隔直后的高频交流信号进行放大和低通滤波处理。在本申请一些实施方式中，信号处理电路50还可以包括增益调控电路53，增益调控电路53的输入端口53a与电压放大及低通滤波电路52的输出端口52b连接，增益调控电路53的输出端口53b与电压放大及低通滤波电路52的输入端口52c连接。增益调控电路53基于电压放大和低通滤波电路52的输出信号，调节电压放大和低通滤波电路52的增益。电压放大及低通滤波电路52的输出端口52b作为信号处理电路50的输出端输出信号。
由于环境温度波动、激光器老化等原因会导致激光器电流产生波动，从而导致激光器发光频率漂移，引入相位噪声，为减少或消除该相位噪声，提高麦克风信噪比，本申请实施例通过构建环路控制对激光器驱动电流进行调制，将激光器稳定在对振膜振动灵敏度最高的驱动电流工作点。由于激光器的电流波动和振膜振动都会导致激光器谐振腔内相位波动，也即自混合光信号波动。本申请实施例通过对激光器施加较小的电流扰动，根据该电流扰动导致的自混合信号获取装置的输出信号的变化程度，即电流扰动导致自混合光信号的变化程度来确定激光器灵敏度最高的驱动电流工作点，从而能够使激光器同样保持在对振膜的振动灵敏度最高的驱动电流工作点，提高麦克风信噪比。本申请中，激光器驱动电流为直流电流。
下面对本申请实施例通过构建环路控制对激光器驱动电流进行调制的具体方案进行说明：
参见图1和图2，本申请实施方式中，自混合信号获取装置40的第二输出端口40c与控制电路30的输入端口30a连接，控制电路30根据自混合信号获取装置40的第二输出端口40c的输出信号确定激光器20的驱动电流A j。即自混合信号获取装置40输出两路信号，一路信号输出至信号处理电路50，另一路信号输出至控制电路30，两路信号为相同电压信号。
本申请实施方式中，在激光器启动工作模式时，控制电路30根据自混合信号获取装置40输出的目标电压信号确定激光器20的驱动电流A j，包括：
S21：控制电路以I min’为初始值，以Δ？为步长，以I max’为终止值对激光器施加扫描电流I t’，且在每一次扫描时在扫描电流I t’上叠加交流电流I c，并获取每一次扫描的输出电压波动峰峰值ΔV t′；
其中，I min’为预设最小驱动电流，I max’为预设最大驱动电流；Δ？为预设电流；交流电流I c为预设电流，交流电流I c的频率大于人耳能听到的声音的最大频率；ΔV t′与交流电流I c的频率相关；t’代表电流扫描次数；
本实施例步骤S21中，控制电路30在每一次扫描的扫描电流I t’上叠加交流电流I c输出给激光器20，自混合信号获取装置40基于I t’和I c输出目标电压信号V 1，控制电路30获得目标电压信号V 1后，对该目标电压信号V 1执行FFT(Fast Fourier Transform,快速傅里叶变换)，并识别交流电流I c的频率下的输出电压波动峰峰值ΔV t′。其中，ΔV t′与交流电流I c的频率相关，是指根据叠加的交流电流I c的频率，在执行FFT后的电压信号中识别该频率下的输出电压波动峰峰值ΔV t′。例如，叠加的交流电流I c的频率为25kHz，则需要识别25kHz频率下的输出电压波动峰峰值ΔV t′。
本申请实施方式中，激光器的预设最小驱动电流I min’和预设最大驱动电流I max’可根据激光器的具体需求进行合理设定。例如，本申请一些实施方式中，预设最小驱动电流I min’可以是0.5mA，预设最大驱动电流I max’可以是3mA。
其中，一次扫描是指控制电路在某一点值扫描电流I t’上叠加交流电流I c施加给激光器，并获取激光器在扫描电流I t’作用下叠加交流电流I c时输出电压波动峰峰值ΔV t′的过程。峰峰值(peak-to-peak，pk-pk)ΔV t′是指波形图中最大的正电压值和最大的负电压值之间的差。
S22:将执行S21过程中获取的多个ΔV t′中，最大的ΔV t′对应的扫描电流I t’确定为激光器的驱动电流A j。控制电路根据S22确定的驱动电流A j，向激光器稳定施加该驱动电流A j。
其中，激光器启动工作模式是指激光器每一次由非拾音模式启动拾音模式的过程。定义激光器从上电到下电为一个周期，每次上电之后启动拾音模式都是启动工作模式。在一个周期内，从待机到启动拾音模式，也算启动工作模式。而在激光器的工作模式下是指在激光器拾音模式下，即激光器启动工作模式后的拾音模式状态下。
本申请实施方式中，在激光器工作模式下，进行第j次驱动电流调制时，控制电路30根据自混合信号获取装置40输出的目标电压信号确定激光器20的驱动电流A j，包括：
S11：所述控制电路根据前一次驱动电流调制后得到的驱动电流A j-1确定本次驱动电流调制的扫描电流范围[I min，I max]，其中，所述I min＝A j-1-I 0，所述I max＝A j-1+I 0’，0.1mA≤I 0≤0.5mA，0.1mA≤I 0’≤0.5mA；所述j表示驱动电流调制次数，且取大于或等于2的整数；
步骤S11中，当j等于2时，即在激光器启动工作模式后的第一次驱动电流调制时，前一次驱动电流调制后得到的驱动电流A j-1是在启动工作模式时执行S21和S22后确定的驱动电流。而当j大于2时，前一次驱动电流调制后得到的驱动电流A j-1可以是在激光器工作模式下前一次执行S11至S13后确定的驱动电流。在进行下一次驱动电流调制之前，控制电路一直向激光器施加前一次驱动电流调制后得到的驱动电流。因此，激光器前一次驱动电流调制后得到的驱动电流通常为激光器当前工作驱动电流。
本申请实施方式中，I 0与I 0’可以是相同取值，也可以是不同取值。本申请一些实施方式中，扫描电流范围[I min，I max]确定为当前工作电流的正负0.3mA范围内，即I min＝A j-1-0.3mA，I max＝A j-1+0.3mA。在其他一些实施方式中，扫描电流范围[I min，I max]也可以是确定为当前工作电流的正负0.4mA范围内或0.5mA范围内。具体可根据激光器的电流波动情况设定。
本申请实施方式中，I max的取值应小于或等于I max’，I min的取值大于或等于I min’。
因此，当预将扫描电流范围[I min，I max]确定为当前工作电流的正负0.3mA范围内，即I min＝A j-1-0.3mA，I max＝A j-1+0.3mA时。当A j-1+0.3mA小于或等于预设最大驱动电流I max’，确定I max＝A j-1+0.3mA；而当A j-1+0.3mA大于预设最大驱动电流I max’时，则确定I max＝I max’。同样当A j-1-0.3mA大于或等于预设最小驱动电流I min’时，确定I min＝A j-1-0.3mA；而当A j-1-0.3mA小于预设最小驱动电流I min’时，确定I min＝I min’。
S12：控制电路以I min为初始值，以Δ？为步长，以I max为终止值对激光器施加扫描电流I t，且在每一次扫描时在扫描电流I t上叠加交流电流I c，并获取每一次扫描的输出电压波动峰峰值ΔV t；
其中，所述Δ？为预设电流；所述交流电流I c为预设电流，所述交流电流I c的频率大于人耳能听到的声音的最大频率；所述ΔV t与所述交流电流I c的频率相关；所述t表示电流扫描次数；
本实施例步骤S12中，控制电路30在每一次扫描的扫描电流I t上叠加交流电流I c输出给激光器20，自混合信号获取装置40基于I t和I c输出目标电压信号V 1，控制电路30获得目标电压信号V 1后，对该目标电压信号V 1执行FFT，并识别交流电流I c的频率下的输出电压波动峰峰值ΔV t。其中，ΔV t与交流电流I c的频率相关，是指根据叠加的交流电流I c的频率，在执行FFT后的电压信号中识别该频率下的输出电压波动峰峰值ΔV t。例如，叠加的交流电流 I c的频率为25kHz，则需要识别25kHz频率下的输出电压波动峰峰值ΔV t。
其中，一次扫描是指控制电路在某一点值扫描电流I t上叠加交流电流I c施加给激光器，并获取激光器在扫描电流I t作用下叠加交流电流I c时输出电压波动峰峰值ΔV t的过程。
S13:将执行S12过程中获取的多个ΔV t中，最大的ΔV t对应的扫描电流I t确定为本次驱动电流调制获得的所述激光器的驱动电流A j。ΔV t越大表示激光器交流电流扰动导致自混合光信号的改变程度越大，也即自混合光信号对激光器电流扰动的灵敏度越高。而由于激光器电流扰动和振膜振动都会导致激光器腔内相位波动，也即自混合光信号波动，因此ΔV t越大则自混合光信号对振膜振动的灵敏度也越高。
本申请实施方式中，一次驱动电流调制是指控制电路完成将激光器驱动电流由I min扫描至I max，同时在每一扫描电流点I t叠加交流电流I c，并根据每一次扫描获得的输出电压波动峰峰值获得本次调制确定的激光器驱动电流的过程，即执行完一次S11至S13的过程。同样，执行完一次S21至S22的过程也算是一次驱动电流调制。
本申请实施方式中，在激光器工作模式下，上述S11至S13的驱动电流调制过程可以是每2-20秒执行一次，例如每5秒执行一次，或者每10秒执行一次，具体可根据激光器的实际工作情况而定，本申请不作限定。若激光器电流较稳定，两次电流调制间隔时间可以长一些，而激光器电流不太稳定时，两次电流调制间隔时间可以短一些。
可以理解地，S21至S22的驱动电流调制过程也可以用于激光器工作模式下的驱动电流调制，但相比S11至S13的驱动电流调制过程，扫描电流范围更大，不利于快速找到工作模式下的灵敏度最高的工作电流点。
本申请实施方式中，预设电流Δ？的范围可以是10μA≤Δ？≤50μA。具体地，Δ？的取值可以但不限于是10μA、20μA、25μA、30μA、40μA、50μA。电流扫描过程中设置适合的步长Δ？有利于较准确地找到灵敏度高的驱动电流点值。
本申请实施方式中，交流电流I c的频率大于人耳能听到的声音的最大频率，由于人耳能听到的声音的频率一般在20Hz-20kHz，因此，交流电流I c的频率则大于20kHz，具体可以是20kHz＜I c≤50kHz。本申请一些实施方式中，交流电流I c的频率为25kHz、30kHz、40kHz、50kHz。本申请实施方式中，交流电流I c的峰峰值可以是控制在10μA至50μA之间，具体可以但不限于是10μA、20μA、30μA、40μA、50μA。交流电流I c具有较高频率和较小峰峰值有利于激光器的稳定工作。
本申请实施方式中，控制电路30从自混合信号获取装置40的输出端采集输出信号的采样频率可以是在100kHz至500kHz之间，具体例如为100kHz、200kHz、300kHz 500kHz。
本申请一具体实施例中，在激光麦克风启动工作模式时，控制电路通过电流调制确定激光器驱动电流的过程为：
S101：激活激光器驱动电流调制，设置交流电流I c的峰峰值为17μA，调制频率为25kHz；设置激光器的扫描电流初始值，即预设最小驱动电流I min’为0.5mA；设置激光器的扫描电流终止值，即预设最大驱动电流I max’为3mA；设置激光器驱动电流的扫描步长ΔI为25μA；
S102：将激光器驱动电流从0.5mA扫描至3mA，在每一次扫描时在扫描电流上叠加17μA的交流电流；同时控制电路以200kHz的采样频率从自混合信号获取装置的输出端获得每一次扫描输出的目标电压信号，对所获得的目标电压信号执行FFT，并识别在25kHz调制频率下的输出电压波动峰峰值ΔV t′；
其中，第一次扫描时，控制电路向激光器输出的电流包括扫描电流0.5mA和交流电流17μA；第二次扫描时，控制电路向激光器输出的电流包括扫描电流0.5mA+ΔI＝0.525mA和交 流电流17μA；第三次扫描时，控制电路向激光器输出的电流包括扫描电流0.525mA+ΔI＝0.55mA和交流电流17μA；依次类推，直至扫描至3mA。
S103；寻找从0.5mA扫描至3mA过程中，在25kHz调制频率下ΔV t′最大时的激光器电流值；并将激光器驱动电流设置在ΔV t′最大时的扫描电流值，关闭调制。
经过如上S101-S103的调制过程，激光器找到灵敏度最大的驱动电流最佳工作点，并在下一次驱动电流调制之前将激光器驱动电流稳定在该最佳工作点。本申请实施方式中，上述调制过程由控制电路30控制执行完成。调制关闭时，控制电路30停止从自混合信号获取装置40采集目标电压信号。
本申请中，在激光麦克风工作模式下，进行第j次驱动电流调制时，可以不用从预设最小驱动电流扫描至预设最大驱动电流，只需要基于当前工作电流确定适合的扫描范围即可，可以简化驱动电流调制过程。
本申请一具体实施例中，在激光麦克风工作模式下，进行第j次驱动电流调制的过程可以是：
S201：激活激光器驱动电流调制，设置交流电流I c的峰峰值为17μA，调制频率为25kHz；根据激光器当前工作电流I 1＝2.3mA，确定扫描电流初始值I min＝2.3mA-0.3mA＝2.0mA和扫描电流终止值I max＝2.3mA+0.3mA＝2.6mA，设置激光器驱动电流的扫描步长ΔI为25μA；
其中，激光器当前工作电流I 1实际为上一次即第j-1次调制确定的驱动电流I j-1；
需要说明的是，若激光器当前工作电流I 1＝2.75mA，则I 1+0.3mA>3mA，此时，确定扫描电流终止值I max＝3mA。
S202：将激光器驱动电流从2.0mA扫描至2.6mA，在每一次扫描时在扫描电流上叠加17μA的交流电流；同时控制电路以200kHz的采样频率从自混合信号获取装置的输出端获得每一次扫描输出的目标电压信号，对所获得的目标电压信号执行FFT，并识别在25kHz调制频率下的输出电压波动峰峰值ΔV t；
其中，第一次扫描时，控制电路向激光器输出的电流包括扫描电流2.0mA和交流电流17μA；第二次扫描时，控制电路向激光器输出的电流包括扫描电流2.0mA+ΔI＝2.025mA和交流电流17μA；第三次扫描时，控制电路向激光器输出的电流包括扫描电流2.025mA+ΔI＝2.05mA和交流电流17μA；依次类推，直至扫描至26mA。
S203；寻找从2.0mA扫描至2.6mA过程中，在25kHz调制频率下ΔV t最大时的激光器电流值；并将激光器驱动电流设置在ΔV t最大时的扫描电流值，关闭调制。
本申请实施例通过构建环路控制对激光器驱动电流进行调制，可以实时调节激光器工作状态，将激光器稳定在灵敏度较高的工作点，减少或消除与环境相关的低频相位抖动，使得自混合激光器的回馈干涉机制更加稳定，使得激光麦克风可以在工作期间(即工作模式下)以及整个生命周期内保持较高的信噪比。
参见图4和图5，本申请实施方式中，控制电路30包括第一控制器31、与第一控制器31连接的驱动电路32。驱动电路32包括数字电位器321、电阻R7、电阻R8、电容C4、运算放大器OP3、三极管Q1、电阻R10。数字电位器321包括一可变电阻R6，第一控制器31的输出端口31a与数字电位器321连接，第一控制器31的输入端31b的输入信号为自混合信号获取装置40的输出信号。数字电位器321的第一端部连接到运算放大器OP3的正向输入端，数字电位器321的第二端部连接到电阻R10的第一端部。数字电位器321的第二端部与电阻R10的第一端部均连接正电源。电阻R7的第一端部和电容C4的第一端部连接在数字电位器321的第一端部与运算放大器OP3的正向输入端之间，电阻R7的第二端部和电容C4 的第二端部均接地连接。电阻R10的第二端部连接到三极管Q1的发射极，运算放大器OP3的反向输入端连接到电阻R10第二端部与三极管Q1的发射极之间，运算放大器OP3的输出端连接到三极管Q1的基极，电阻R8的第一端部与三极管Q1的集电极连接，电阻R8的第二端部作为控制电路30的输出端口与激光器20的阳极连接。结合图1和图2，第一控制器31的输入端口31b作为控制电路30的输入端口30b与自混合信号获取装置40的输出端口40c连接。控制电路30中，可变电阻R6与电阻R7为分压电阻，可起到分压作用。电阻R8和电阻R10可起到限流作用，其中R10可以控制通过三极管Q1的电流，避免三极管Q1电流过大导致功耗过高。电容C4可以实现驱动电路32缓启动。本申请实施方式中，第一控制器31基于获取到的自混合信号获取装置40的输出信号，输出控制信号控制可变电阻R6的有效阻值，通过改变可变电阻R6的有效阻值可以控制调节驱动电路32向激光器20输出的驱动电流大小，实现激光器20驱动电流可调。驱动电路32为恒流源电路，可以为激光器20提供几乎不随温度变化的恒定的直流偏置电流，以稳定工作点。
参见图4，本申请一些实施方式中，自混合信号获取装置40包括光探测器41和互阻抗放大电路42，光探测器41与激光器20连接，互阻抗放大电路42的输入端与光探测器41连接。控制电路30的输出端即电阻R8的第二端部连接激光器20的阳极，光探测器41的阳极与激光器20的阴极电连接，光探测器41与激光器20共电极接地，光探测器41的阴极与互阻抗放大电路42的输入端连接，互阻抗放大电路42的输出端作为自混合信号获取装置40的输出端口40b(参见图1)与高通滤波电路51的输入端连接。
本申请一实施方式中，互阻抗放大电路42包括运算放大器OP1、电阻R1、电容C1，光探测器41的输出端连接到运算放大器OP1的反向输入端，电阻R1的第一端部和电容C1的第一端部均连接在光探测器41的输出端与运算放大器OP1的反向输入端之间，电阻R1的第二端部和电容C1的第二端部均连接到运算放大器OP1的输出端，运算放大器OP1的正向输入端输入光探测器电流偏置，运算放大器OP1的输出端作为自混合信号获取装置40的输出端与高通滤波电路51的输入端连接。电容C1为反馈补偿电容，用于补偿光探测器节点电容和运算放大器输入电容，以保持电路稳定。电阻R1为反馈电阻，用于使电流信号转变为电压信号。
参见图5，本申请另一些实施方式中，自混合信号获取装置40包括与激光器20连接的缓冲电路43。缓冲电路43包括运算放大器OP4。运算放大器OP4的正向输入端连接到激光器20的阳极，激光器20的阴极接地连接，运算放大器OP4的输出端作为自混合信号获取装置40的输出端口40b(参见图1)与高通滤波电路51的输入端连接，运算放大器OP4的反向输入端连接在运算放大器OP4的输出端与高通滤波电路51的输入端之间。
参见图4和图5，本申请实施方式中，信号处理电路50包括高通滤波电路51、电压放大及低通滤波电路52和增益调控电路53。
其中，高通滤波电路51包括电容C2和电阻R2。电容C2的第一端部作为高通滤波电路51的输入端与自混合信号获取装置40的输出端口40b连接，电容C2的第二端部作为高通滤波电路51的输出端连接到电压放大及低通滤波电路52。电阻R2的第一端部连接到电容C2的第二端部，电阻R2的第二端部接地连接。电容C2和电阻R2构成的高通滤波电路51可以滤掉直流电流和低频信号。电压放大及低通滤波电路52包括运算放大器OP2、电容C3、数字电位器521、电阻R3和电阻R5。其中，运算放大器OP2的正向输入端作为电压放大及低通滤波电路52的输入端与高通滤波电路51的输出端连接，运算放大器OP2的输出端与电阻R5的第一端部连接，电阻R5的第二端部作为电压放大及低通滤波电路52的输出端，也即信 号处理电路50的输出端向外输出音频电压信号。电阻R3的第一端部、数字电位器521的第一端部和电容C3的第一端部均连接到运算放大器OP2的反向输入端，数字电位器521的第二端部和电容C3的第二端部均连接到运算放大器OP2的输出端与电阻R5的第一端部之间，电阻R3的第二端部接地连接。数字电位器521与增益调控电路53连接，数字电位器521包括一可变电阻R4。低通滤波电路可以滤除高频信号。
高通滤波电路51和电压放大及低通滤波电路52可以构成一个带通滤波电路，带通的下截止频率由R2、C2决定，上截止频率由R4、C3决定，带通范围可以是20Hz～20kHz，以滤除低频背景声音和高频信号。OP1和OP2两级放大电路系统在不同的直流工作点。
增益调控电路53包括第二控制器531，第二控制器531的输入端连接到信号处理电路50的输出端，用于采集信号处理电路50输出的电压信号，第二控制器531的输出端连接到数字电位器521，第二控制器531输出控制信号控制数字电位器521的可变电阻R4的有效阻值，通过改变R4的有效阻值大小，实现电压放大及低通滤波电路52增益可调，根据输出信号可实时优化电路工作状态，该放大电路增益A＝1+R4/R3。
本申请实施方式中，上述运算放大器OP1、运算放大器OP2、运算放大器OP3、运算放大器OP4为低噪声运算放大器，可采用高PSRR(Power Supply Rejection Ratio,电源纹波抑制比)供电电路(如LDO)进行供电，采用低噪声运算放大器有利于提高信噪比。上述各电阻在满足功能的条件下阻值尽量小，以减小电阻产生的热噪声。本申请实施方式中，第一控制器31和第二控制器531可以分别设置，也可以是同一控制器。
参见图6，本申请一实施方式中，激光麦克风100包括壳体1，壳体1包括相对设置的基板11、盖板12和中框13，基板11、盖板12和中框13围设形成容置腔，振膜10、激光器20、光探测器41、ASIC(Application Specific Integrated Circuit，集成电路)芯片2均设置于该容置腔内。其中，振膜10固定在盖板12上，激光器20设置于基板11上，光探测器41设置于基板11上，并位于激光器20背离振膜10的一侧，盖板12上设置有拾音孔121，振膜10与拾音孔121对应设置。本实施例的激光麦克风100，发射与回馈光束同路，无需参考干涉臂，组件更少，光路自对准，可允许更小尺寸封装。
本申请实施方式中，振膜10与激光器20出光面(即朝向振膜10的一侧)之间的间距设置在30μm-300μm范围内，适合的间距能够提高经振膜10反射回激光器的光与激光器腔内光的耦合效率。具体地，在一些实施方式中，振膜10与激光器20之间的间距可以是设置在50μm-100μm范围内。在另一些实施方式中，振膜10与激光器20之间的间距可以是设置在100μm-200μm范围内。
本申请实施方式中，振膜10可以感知外界声波产生的空气振动并产生振动，并将激光器发射的光反射回至激光器谐振腔内。外界声波可通过拾音孔121传到振膜10。本申请实施例激光麦克风不同于传统MEMS麦克风的电容检测机制，不需要设置背极板，因此对振膜的导电特性没有特殊要求。振膜10可以是MEMS(micro-electro-mechanical system，微型机电系统)振膜、金属玻璃振膜、石墨烯振膜、高分子薄膜或金属类薄膜。振膜10朝向激光器20的一侧可设置反射层，以提高反射率，反射层的材质可以是铝、金等高反射率金属。振膜10镀有反射层的一面朝向激光器20的出光面，并中心对准。本申请实施例采用带有负应力的SOI(Silicon-On-Insulator，绝缘衬底上的硅)膜层与带有正应力的金属反射层结合，降低了振膜应力，进而提升了振膜的声压位移灵敏度。本申请实施例采用无背极振膜，减小了压膜阻尼，提高了声压位移灵敏度，降低了噪声。本申请实施例的振膜设计，允许更微弱声音的检测和更强的声音信号响应幅度，有利于高信噪比的实现。
本申请实施方式中，振膜10上设置有一个或多个平衡孔，用于使振膜内外的气压平衡，平衡孔的直径可以是1μm-5μm(包括端点值1μm、5μm)。本申请一些实施方式中，振膜10为MEMS硅振膜，厚度为300nm-800nm，直径为600μm-1200μm。MEMS硅振膜的中央区域表面镀有高反射金属层，例如铝层、金层等，金属层的厚度可以是30nm-100nm(包括端点值30nm、100nm)，金属层的半径为20μm-50μm。MEMS硅振膜的声压位移灵敏度为0.05μm/Pa～0.5μm/Pa。例如，本申请一具体实施例中，MEMS硅振膜厚度为400nm，直径为900μm，振膜中央区域镀铝，铝层厚度为90nm，半径为30μm，振膜上设置两个平衡孔，每个平衡孔的直径为2μm，MEMS振膜的声压位移灵敏度为0.1μm/Pa。本申请实施例采用基于SOI或者多晶硅的硅衬底制造振膜，有利于降低应力，提高声压位移灵敏度。金属反射层的设置可以平衡膜层应力，同时提升振膜的光反射率。通过应力控制，进一步改善振膜振动幅度随声压变化的线性度。
本申请实施方式中，激光麦克风100可以为顶进音结构，如图6所示，振膜10位于盖板12上，拾音孔121设置在盖板12上，振膜10与盖板12之间形成前腔3，振膜10与壳体形成后腔4。振膜10设置在盖板12上，可形成较大的后腔4。在顶进音结构中，振膜10、激光器20与拾音孔121对应设置，具体可以是同轴设置。顶进音结构的激光麦克风，一般通过基板11固定在终端内的PCB板上，光探测器41通过金属走线5与芯片2电连接，芯片2通过基板11上的过孔直接与外部金属电极6电连接。
本申请实施方式中，激光麦克风100也可以为底进音结构，如图7所示，振膜10位于基板11上，拾音孔121设置在基板11上，并与振膜10对应设置。激光器20和光探测器41位于盖板12上，振膜10与基板11之间形成前腔3，振膜10与壳体形成后腔4。振膜10设置在基板11上，可形成较大的后腔4。在底进音结构中，振膜10、激光器20与拾音孔121对应设置，具体可以是同轴设置。拾音孔121可以是一个或多个。底进音结构的激光麦克风，一般通过基板11固定在终端内的PCB板上，光探测器41通过金属走线5与芯片2电连接，芯片2通过金属走线5及基板11上的过孔与外部金属电极6电连接。
如上两种结构的激光麦克风均获得了具有更大空气容积的后腔，使得声波更容易推动振膜运动，从而提高麦克风的灵敏度和信噪比。
本申请实施方式中，为了可靠封装振膜10、激光器20、光探测器41及ASIC芯片2，封装基板11、封装盖板12、中框13均采用PCB材质，或者封装基板11采用PCB材质或陶瓷材质，封装盖板12和中框13为一体结构并采用金属等材质。
结合图6和图7，本申请实施方式中，当自混合光信号获取装置40包括光探测器41和互阻抗放大电路42时，光探测器41与激光器20可集成在一个光芯片上，光探测器41位于激光器20远离振膜10的一侧，互阻抗放大电路42可与控制电路30、信号处理电路50集成在一个ASIC芯片2上。将光探测器41与激光器20集成在一个光芯片上，可以提升从激光器背面透出的光耦合进光探测器的效率，进而提升信噪比，同时可避免分立布置在振动与跌落等情形下导致的光路偏差，进而保持信号在模组生命周期的一致性。当然，在本申请其他一些实施方式中，光探测器41与激光器20也可以是分立布置，激光器20可以直接贴合在光探测器41上，激光器20的背面，即远离振膜10一侧出光也可以直接耦合进光探测器41。本申请实施方式中，光探测器41的工作波长可以是360nm-1600nm(包括端点值360nm、1600nm)。
本申请另一些实施方式中，当自混合信号获取装置40包括缓冲电路时，缓冲电路可与控制电路30、信号处理电路50集成在一个ASIC芯片2上。
本申请实施方式中，激光器20为自混合激光器，具体类型不限，可以是垂直腔面发射激光器，也可以是边发射激光器。激光器的发光波长可以是750nm-1600nm。本申请一些实施方式中，激光器20为单模工作的垂直腔面发射激光器(Vertical-Cavity Surface-Emitting Laser，VCSEL)，其发光波长为850nm。垂直腔面发射激光器的典型阈值电流为0.7mA，典型工作电流为约2.5mA，典型输出功率约为0.5mW，相应光探测器的典型输出光电流为0.5mA。垂直腔面发射激光器的典型尺寸可以是：长度为120μm-200μm，宽度为120μm-200μm，厚度为100μm-150μm。
参见图8，本申请一些实施例中，激光麦克风还包括光束耦合装置，位于激光器20与振膜10之间。光束耦合装置可包括一个或多个透镜70，透镜70制作在激光器20出光面上。本申请实施方式中，透镜70可以为准直透镜，也可以为会聚透镜。采用透镜对出射和反射的光进行耦合，可提升回馈耦合效率，提升对携带振膜振动信号的回馈光强，进而提升激光麦克风的信噪比。如图8所示，本申请一些实施方式中，透镜70为准直透镜，包括透镜柱体和透镜曲面，其中透镜柱体可以通过光刻或激光直写等方式制作，透镜曲面可以通过压印、喷墨打印等方式制作。准直透镜可将激光器出射光准直到振膜的反射面上，并将反射光耦合输入到激光器的出光孔。通过设置准直透镜，可以大幅度增加反射回到激光器的光，从而提升反馈信号光强度，进而提升麦克风的信噪比。透镜的材质为在激光器工作波长范围内的透光率大于90％的材料。本申请实施方式中，每一所述透镜的横向尺寸(即长宽尺寸)为20μm-200μm(包括端点值20μm、200μm)；每一所述透镜的纵向尺寸(即高度尺寸)为20μm-200μm(包括端点值20μm、200μm)。
本申请实施方式中，上述涉及到具有数值范围的所有参数值，均包括两个端点值。
本申请实施例的激光麦克风，基于无背极振膜设计提升了振膜的声压位移灵敏度，同时通过激光自混合干涉效应提升了微弱振动信号探测能力，进而提升了振动响应灵敏度与动态范围，可拾取轻微的语音信号。本实施例通过激光自混合相干的方式检测振膜的振动，具有较高的检测灵敏度。本申请实施例的激光麦克风可显著改善安静场景下的轻声细语模式下的语音拾取、远距离的微弱语音信号的探测以及远距视频录制时的语音拾取质量。本申请实施例的激光麦克风的信噪比大于75dB，具体例如80dB，相比传统的MEMS麦克风(信噪比65dB)，信噪比有了明显提升。
参见图9，本申请实施例还提供一种终端200，包括本申请实施例上述的激光麦克风100。终端200包括外壳和设置于外壳内的电路板，激光麦克风设置在电路板上，终端外壳上设置有与激光麦克风的位置相对应的收音孔101，外界声音通过外壳的收音孔101传至激光麦克风。激光麦克风100可以是对应于终端前侧设置，相应地收音孔101设置于终端前侧盖板201上(参见图9正视图)；激光麦克风100也可以是对应于终端后侧设置，相应地收音孔101设置于终端后侧盖板202上(参见图9后视图)；激光麦克风100还可以是对应于终端侧边中框203设置，相应地收音孔101设置于终端的侧边中框203上，具体可以是如图9中的仰视图所示，收音孔101设置于终端的下侧中框上，也可以是设置在上侧、左侧或右侧中框上。激光麦克风100的拾音孔与终端外壳上的收音孔101对应设置，具体可以是同轴设置。中框203与后侧盖板202可以是一体成型结构，也可以是分体结构。该终端200可以是移动电话、笔记本电脑、平板电脑、智能电视、智能音箱、耳机、摄像机、网络摄像机、穿戴式装置、游戏装置、车载音频系统或麦克风、语音导航设备、口述语音识别设备、语音到文本转换器等需要语音命令控制或需要采集、记录、处理或分析语音的场景的终端产品。

Claims (19)

  1. 一种激光麦克风，其特征在于，包括振膜、激光器、控制电路、自混合信号获取装置、信号处理电路；
    所述激光器用于向所述振膜发射光，并接收来自所述振膜的反馈光信号，所述反馈光信号与所述激光器谐振腔内的激光相干涉得到自混合光信号；所述激光器与所述振膜之间的间距为L，所述L的范围为30μm≤L≤300μm；
    所述控制电路与所述激光器连接，用于驱动控制所述激光器发光；
    所述自混合信号获取装置与所述激光器连接，用于获取并输出与所述自混合光信号相关的目标电压信号；
    所述信号处理电路与所述自混合信号获取装置连接，用于接收所述自混合信号获取装置输出的所述目标电压信号，并将所述目标电压信号处理成音频电压信号。
  2. 如权利要求1所述的激光麦克风，其特征在于，所述自混合信号获取装置的输出端与所述控制电路的输入端连接，所述控制电路根据所述自混合信号获取装置输出的所述目标电压信号确定所述激光器的驱动电流A j。
  3. 如权利要求2所述的激光麦克风，其特征在于，在所述激光器工作模式下，进行第j次驱动电流调制时，所述控制电路根据所述自混合信号获取装置输出的所述目标电压信号确定所述激光器的驱动电流A j，包括：
    S11：所述控制电路根据前一次驱动电流调制后得到的驱动电流A j-1确定本次驱动电流调制的扫描电流范围[I min，I max]，其中，所述I min＝A j-1-I 0，所述I max＝A j-1+I 0’，0.1mA≤I 0≤0.5mA，0.1mA≤I 0’≤0.5mA；所述j表示驱动电流调制次数，且取大于或等于2的整数；
    S12：所述控制电路以I min为初始值，以ΔI为步长，以I max为终止值对所述激光器施加扫描电流I t，且在每一次扫描时在所述扫描电流I t上叠加交流电流I c，并获取每一次扫描的输出电压波动峰峰值ΔV t；
    其中，所述ΔI为预设电流；所述交流电流I c为预设电流，所述交流电流I c的频率大于人耳能听到的声音的最大频率；所述ΔV t与所述交流电流I c的频率相关；所述t表示电流扫描次数；
    S13:将执行S12过程中获取的多个ΔV t中，最大的ΔV t对应的扫描电流I t确定为本次驱动电流调制获得的所述激光器的驱动电流A j。
  4. 如权利要求2或3所述的激光麦克风，其特征在于，在所述激光器启动工作模式时，所述控制电路根据所述自混合信号获取装置输出的所述目标电压信号确定所述激光器的驱动电流A j，包括：
    S21：所述控制电路以I min’为初始值，以ΔI为步长，以I max’为终止值对所述激光器施加扫描电流I t’，且在每一次扫描时在所述扫描电流I t’上叠加交流电流I c，并获取每一次扫描的输出电压波动峰峰值ΔV t′；
    其中，所述I min’为预设最小驱动电流，所述I max’为预设最大驱动电流；所述ΔI为预设电流；所述交流电流I c为预设电流，所述交流电流I c的频率大于人耳能听到的声音的最大频率；所述ΔV t′与所述交流电流I c的频率相关；所述t’代表电流扫描次数；
    S22:将执行S21过程中获取的多个ΔV t′中，最大的ΔV t′对应的扫描电流I t’确定为所述激光器的驱动电流A j。
  5. 如权利要求3或4所述的激光麦克风，其特征在于，所述ΔI的范围为10μA≤ΔI≤50μA。
  6. 如权利要求3或4所述的激光麦克风，其特征在于，所述交流电流I c的频率范围为 20kHz＜I c≤50kHz。
  7. 如权利要求1-6任一项所述的激光麦克风，其特征在于，所述自混合信号获取装置用于探测所述激光器谐振腔内的所述自混合光信号，并输出与所述自混合光信号相关的目标电压信号。
  8. 如权利要求7所述的激光麦克风，其特征在于，所述自混合信号获取装置包括光探测器和互阻抗放大电路，所述光探测器与所述激光器连接，用于探测所述激光器谐振腔内的所述自混合光信号，并将所述自混合光信号转换成电流信号；所述互阻抗放大电路与所述光探测器连接，用于将所述电流信号转换成所述目标电压信号。
  9. 如权利要求8所述的激光麦克风，其特征在于，所述光探测器与所述激光器单片集成在一个芯片上，所述光探测器位于所述激光器背离所述振膜的一侧。
  10. 如权利要求1-6任一项所述的激光麦克风，其特征在于，所述自混合信号获取装置包括与所述激光器连接的缓冲电路，所述缓冲电路用于获取所述激光器的端电压，所述激光器的端电压与所述自混合光信号相关。
  11. 如权利要求1-10任一项所述的激光麦克风，其特征在于，所述信号处理电路包括高通滤波电路和电压放大及低通滤波电路，所述高通滤波电路与所述自混合信号获取装置连接，所述电压放大及低通滤波电路与所述高通滤波电路连接。
  12. 如权利要求11所述的激光麦克风，其特征在于，所述信号处理电路还包括与所述电压放大及低通滤波电路连接的增益调控电路，所述增益调控电路用于根据所述电压放大及低通滤波电路的输出信号调节所述电压放大及低通滤波电路的增益。
  13. 如权利要求1-12任一项所述的激光麦克风，其特征在于，所述激光器朝向所述振膜一侧的出光面设置有光束耦合装置，所述光束耦合装置包括一个或多个透镜。
  14. 如权利要求13所述的激光麦克风，其特征在于，每一所述透镜的横向尺寸为20μm-200μm；每一所述透镜的纵向尺寸为20μm-200μm。
  15. 如权利要求1-14任一项所述的激光麦克风，其特征在于，所述振膜包括MEMS振膜、金属玻璃振膜、石墨烯振膜、高分子薄膜或金属类薄膜。
  16. 如权利要求15所述的激光麦克风，其特征在于，所述振膜朝向所述激光器的一侧设有反射层。
  17. 如权利要求1-16任一项所述的激光麦克风，其特征在于，所述激光器为垂直腔面发射激光器或边发射激光器。
  18. 如权利要求1-17任一项所述的激光麦克风，其特征在于，所述激光麦克风还包括壳体，所述振膜、所述激光器、所述控制电路、所述自混合信号获取装置和所述信号处理电路均设置于所述壳体内，所述壳体上与所述振膜相对应的位置设置有拾音孔。
  19. 一种终端，其特征在于，所述终端包括如权利要求1-18任一项所述的激光麦克风。
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