Laser microphone and terminal

Abstract

The embodiment 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 to emit light to the diaphragm and receive a feedback light signal from the diaphragm, and the feedback light signal interferes with the laser in the laser resonant cavity to obtain a self-mixing light signal; the spacing between the laser and the diaphragm is 30μm-300μm; the control circuit is connected to the laser and is used to drive and control the laser to emit light; the self-mixing signal acquisition device is connected to the laser and is used to obtain a target voltage signal related to the self-mixing light signal; the signal processing circuit is connected to the self-mixing signal acquisition device and is used to receive the target voltage signal output by the self-mixing signal acquisition device and process it into an audio voltage signal. The laser microphone has a high signal-to-noise ratio, can improve the voice recognition rate and wake-up rate, and improve the long-distance sound pickup effect. The embodiment of the present application also provides a terminal including the laser microphone.

Description

Technical Field

[0001] The present application relates to the field of microphone technology, and in particular to a laser microphone and a terminal. Background Art

[0002] The use of automatic speech recognition systems for scenarios such as voice control and voice interaction is rapidly increasing. At the same time, more and more people are recording and sharing video content via mobile internet. Therefore, microphones used to capture sound must have excellent performance to ensure an excellent user experience. A microphone's signal-to-noise ratio (SNR) is a key parameter affecting the quality of captured sound. A high SNR helps the microphone maintain a low noise floor during signal amplification when capturing distant, weak target sound sources, thereby improving long-range sound pickup quality.

[0003] Currently, most devices, such as mobile communication terminals and smart homes, use MEMS (Microelectromechanical Systems) microphones to collect voice signals. These devices consist of a MEMS capacitive sensor, an ASIC (Application Specific Integrated Circuit) conversion circuit, and a sound chamber. A MEMS capacitor consists of a sound-receiving silicon diaphragm and a silicon backplate. The silicon diaphragm senses the air vibrations generated by sound waves and vibrates accordingly, forming a variable capacitor with the silicon backplate. A circuit detects the change in this variable capacitance under an applied bias and converts it into an electrical signal for output. The small distance between the diaphragm and the silicon backplate introduces high squeeze-film damping, which in turn introduces high mechanical noise, limiting the potential for improving the signal-to-noise ratio. Furthermore, the pull-in effect between the silicon backplate and the diaphragm requires a certain distance between them, limiting the potential for improving sensitivity and the acoustic overload point. Traditional MEMS microphones face bottlenecks in further improving their signal-to-noise ratio. Therefore, pursuing microphones with higher signal-to-noise ratios, improving speech recognition and wake-up rates, and enhancing long-distance voice pickup requires exploring new technological approaches. Summary of the Invention

[0004] The embodiment of the present application provides a laser microphone with a high signal-to-noise ratio, which can improve the voice recognition rate and wake-up rate and improve the long-distance sound pickup effect.

[0005] Specifically, a first aspect of an embodiment 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;

[0006] The laser is used to emit light toward the diaphragm and receive a feedback light signal from the diaphragm, wherein the feedback light signal interferes with the laser light in the laser resonant cavity to obtain a self-mixing light signal; the distance between the laser and the diaphragm is L, and the range of L is 30 μm ≤ L ≤ 300 μm;

[0007] The control circuit is connected to the laser and is used to drive and control the laser to emit light;

[0008] The self-mixing signal acquisition device is connected to the laser and is used to acquire and output a target voltage signal related to the self-mixing optical signal;

[0009] The signal processing circuit is connected to the self-mixed signal acquisition device, and is configured to receive the target voltage signal output by the self-mixed signal acquisition device and process the target voltage signal into an audio voltage signal.

[0010] The laser microphone provided in the embodiment of the present application uses a laser self-mixing device to detect the diaphragm vibration caused by the voice signal. The laser self-mixing device has a strong ability to detect weak vibration signals, thereby improving the voice recognition sensitivity of the microphone; and by setting the laser and the diaphragm at an appropriate distance, the coupling efficiency of the laser output light beam after reflection from the diaphragm and re-entering the laser resonant cavity can be improved, thereby effectively improving the signal-to-noise ratio of the laser microphone and enhancing the voice recognition sensitivity.

[0011] Due to factors such as ambient temperature fluctuations and laser aging, the laser current may fluctuate, causing the laser light emission frequency to drift and introducing phase noise. In order to reduce or eliminate this phase noise and improve the signal-to-noise ratio of the laser microphone, the embodiment of the present application further modulates the laser drive current by constructing a loop control to stabilize the laser at the current operating point with the highest sensitivity. Specifically, in the embodiment of the present application, the output end of the self-mixed signal acquisition device is connected to the input end of the control circuit, and the control circuit determines the drive current A of the laser according to the target voltage signal output by the self-mixed signal acquisition device. j .

[0012] Because both laser current fluctuations and diaphragm vibrations cause phase fluctuations within the laser resonant cavity, i.e., fluctuations in the self-mixing optical signal, the embodiments of the present application apply a small current perturbation to the laser and determine the laser's most sensitive operating point based on the degree of change in the voltage signal output by the self-mixing signal acquisition device caused by the current perturbation, i.e., the degree of change in the self-mixing optical signal caused by the current perturbation. This allows the laser to remain at the operating point with the highest sensitivity to diaphragm vibration, thereby improving the microphone's signal-to-noise ratio.

[0013] In the embodiment of the present application, in the laser working mode, when the jth driving current modulation is performed, the control circuit determines the driving current A of the laser according to the target voltage signal output by the self-mixed signal acquisition device. j ,include:

[0014] S11: The control circuit modulates the driving current A obtained by the previous driving current j-1 Determine the scanning current range of this drive current modulation [I min , I max ], wherein said I min =A j-1 -I0, I max =A j-1 +I 0’ ,0.1mA≤I0≤0.5mA, 0.1mA≤I 0’ ≤0.5mA; j represents the number of drive current modulations and is an integer greater than or equal to 2;

[0015] S12: The control circuit is I min is the initial value, ΔI is the step size, and I max The laser is subjected to a scanning current I of the termination value. t , and in each scan, the scanning current I t The superimposed AC current I c , and obtain the peak-to-peak value of the output voltage fluctuation ΔV for each scan t ;

[0016] Wherein, the ΔI is a preset current; the AC current I c is the preset current, the AC current I c The frequency is greater than the maximum frequency of the sound that the human ear can hear; the ΔV t With the alternating current I c The frequency of t represents the number of current sweeps;

[0017] S13: Execute multiple ΔV obtained in the process of S12 t The largest ΔV t The corresponding scanning current I t Determine the driving current A of the laser obtained by this driving current modulation j .

[0018] Performing the above-mentioned drive current modulation in the laser working mode can make the laser always stable at the current working point with the highest sensitivity during the entire working process, thereby improving the sound pickup quality and long-distance sound pickup effect of the laser microphone, and improving the sound pickup stability of the laser microphone.

[0019] In the embodiment of the present application, when the laser starts the working mode, the control circuit determines the driving current A of the laser according to the target voltage signal output by the self-mixed signal acquisition device. j ,include:

[0020] S21: The control circuit is I min’ is the initial value, ΔI is the step size, and I max’ The laser is subjected to a scanning current I of the termination value. t’ , and in each scan, the scanning current I t’ The superimposed AC current I c , and obtain the peak-to-peak value of the output voltage fluctuation ΔV for each scan t′ ;

[0021] Wherein, the I min’ is the preset minimum driving current, the I max’ is the preset maximum driving current; the ΔI is the preset current; the AC current I c is the preset current, the AC current I c The frequency is greater than the maximum frequency of the sound that the human ear can hear; the ΔV t′ With the alternating current I c The frequency of t' represents the number of current scans;

[0022] S22: Execute multiple ΔV obtained in the process of S21 t′ The largest ΔV t′ The corresponding scanning current I t’ Determine the driving current A of the laser j .

[0023] When the laser is in startup mode, the sound pickup quality and long-distance sound pickup effect of the laser microphone can be improved 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.

[0024] In the embodiment of the present application, the range of ΔI is 10 μA≤ΔI≤50 μA. Setting a suitable step size is conducive to more accurately finding a driving current point value with high sensitivity.

[0025] In the embodiment of the present application, the AC current I c 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 significant impact on the stable operation of the laser. In some embodiments of the present application, the AC current I c The frequency range is 20kHz<I c ≤50kHz. The AC current Ic The peak-to-peak value can be controlled between 10μA and 50μA. Similarly, applying a smaller current value of AC current I c It can also reduce the impact on the stable operation of the laser.

[0026] In one embodiment of the present application, the self-mixing signal acquisition device is used to detect the self-mixing optical signal in the laser resonant cavity and output a target voltage signal related to the self-mixing optical signal.

[0027] In one embodiment of the present application, the self-mixing signal acquisition device includes a photodetector and a mutual impedance amplifier circuit. The photodetector is connected to the laser and is used to detect the self-mixing light signal within the laser resonant cavity and convert it into a current signal. The mutual impedance amplifier circuit is connected to the photodetector and is used to convert the current signal into the target voltage signal. Using the photodetector and mutual impedance amplifier circuit to acquire the self-mixing signal can achieve a higher signal-to-noise ratio by increasing the laser drive current.

[0028] In this embodiment of the present application, the photodetector and the laser are monolithically integrated on the same chip. The photodetector is located on the side of the laser facing away from the diaphragm, that is, behind the laser's light-emitting surface. Integrating the laser and photodetector on the same chip improves the efficiency of coupling light from the back of the laser into the photodetector, thereby improving the signal-to-noise ratio. It also avoids optical path deviation caused by discrete arrangements under conditions such as vibration and drops, thereby maintaining signal consistency throughout the microphone's lifecycle.

[0029] In another embodiment of the present application, the self-mixing signal acquisition device includes a buffer circuit connected to the laser. The buffer circuit is configured to acquire a terminal voltage of the laser, where the terminal voltage of the laser is correlated with the self-mixing optical signal. By acquiring the terminal voltage of the laser to obtain a target voltage signal correlated with the self-mixing optical signal, a suitable signal-to-noise ratio can be achieved at a low laser drive current (i.e., low power consumption).

[0030] In an embodiment of the present application, the signal processing circuit includes a high-pass filter circuit and a voltage amplifier and low-pass filter circuit. The high-pass filter circuit is connected to the self-mixing signal acquisition device, and the voltage amplifier and low-pass filter circuit is connected to the high-pass filter circuit. The high-pass filter circuit and the voltage amplifier and low-pass filter circuit can filter out low-frequency background sounds and high-frequency signals.

[0031] In some embodiments of the present application, the signal processing circuit further includes a gain control circuit connected to the voltage amplifier and low-pass filter circuit, wherein the gain control circuit is configured to adjust the gain of the voltage amplifier and low-pass filter circuit based on an output signal of the voltage amplifier and low-pass filter circuit. The configuration of the gain control circuit enables adjustable gain of the voltage amplifier and low-pass filter circuit.

[0032] In the embodiments of the present application, a beam coupling device is provided on the light-emitting surface of the laser facing the diaphragm, and the beam coupling device includes one or more lenses. The lens arrangement can improve the coupling efficiency of the laser's outgoing beam after reflection from the diaphragm and its re-entry into the laser resonant cavity, resulting in higher feedback light intensity, i.e., a stronger signal, thereby further effectively improving the microphone's signal-to-noise ratio.

[0033] In the embodiments of the present application, the lateral dimensions (i.e., length and width) of each lens are 20μm-200μm; the longitudinal dimensions (i.e., height) of each lens are 20μm-200μm. Lenses of these dimensions can be fabricated through methods such as laser direct writing or micro-nanoprinting. Lenses of these dimensions can be integrated into lasers, achieving more compact assembly and enabling mass production directly on wafers.

[0034] In the embodiments of the present application, the diaphragm is not limited to a specific type, and there are no special requirements for conductivity. The only consideration is the vibration characteristics required for audio. The diaphragm can be any diaphragm used in existing microphones. Specifically, it can include a MEMS diaphragm, a metallic glass diaphragm, a graphene diaphragm, a polymer film, or a metal film.

[0035] In an embodiment of the present application, a reflective layer is provided on the side of the diaphragm facing the laser. The reflectivity of the reflective layer is greater than 70%. Specifically, the reflective layer can be made of gold, aluminum, or other materials. The provision of the reflective layer can increase the reflectivity of the laser's outgoing light beam when it is emitted to the diaphragm and reflected back into the laser resonant cavity. In addition, in order to control the overall stress of the diaphragm within a smaller range and improve the sound pressure displacement sensitivity, the diaphragm is generally a composite membrane structure comprising different stress film layers. In this way, by providing a metal reflective layer, in addition to increasing the reflectivity, the negative stress of the diaphragm can also be compensated, thereby improving the stability of the diaphragm.

[0036] In the embodiments of the present application, the laser is a self-mixing laser, and the specific type is not limited, and it can be a vertical cavity surface emitting laser or an edge emitting laser. The output wavelength of the laser can be 750nm-1600nm.

[0037] In an embodiment of the present application, the laser microphone further includes a housing, wherein the diaphragm, the laser, the control circuit, the self-mixing signal acquisition device, and the signal processing circuit are all disposed within the housing, and a sound pickup hole is disposed on the housing at a position corresponding to the diaphragm. External sound information is picked up through the sound pickup hole.

[0038] The embodiment of the present application also provides a terminal, which includes the laser microphone described in the first aspect of the embodiment of the present application. The terminal includes a housing and a circuit board arranged in the housing, the laser microphone is arranged on the circuit board, and the terminal housing is provided with a sound receiving hole corresponding to the position of the laser microphone, and the external sound is transmitted to the laser microphone through the sound receiving hole of the housing. The laser microphone can be arranged corresponding to the front side of the terminal, or corresponding to the rear side of the terminal, or corresponding to the side middle frame of the terminal. The terminal can be a mobile phone (cell phone), a laptop computer, a tablet computer, a smart TV, a smart speaker, a headset, a camera, a webcam, a wearable device, a gaming device, a car audio system or microphone, a voice navigation device, a spoken speech recognition device, a speech to text converter, and other terminal products in scenarios that require voice command control or require the collection, recording, processing or analysis of speech.

[0039] The laser microphone provided in the embodiment of the present application is based on the diaphragm vibration caused by the detection of voice signals by a laser self-mixing device, and has a strong ability to detect weak vibration signals, and has a higher signal-to-noise ratio than traditional MEMS microphones. The laser microphone in the embodiment of the present application, by setting the laser and the diaphragm at a suitable distance, improves the coupling efficiency of the laser outgoing light beam re-entering the laser resonant cavity after reflection from the diaphragm, thereby effectively improving the signal-to-noise ratio and improving the voice recognition sensitivity. In addition, 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 maintain a high signal-to-noise ratio during operation and throughout its life cycle. The laser microphone in the embodiment of the present application can significantly improve the voice pickup in the whispering mode in quiet scenes, the detection of weak voice signals at a long distance, and the voice pickup quality during long-distance video recording, thereby improving the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 1 is a schematic diagram of the circuit structure of a laser microphone provided in one embodiment of the present application;

[0041] Figure 2 is a schematic diagram of the circuit structure of a laser microphone provided in another embodiment of the present application;

[0042] Figure 3 is a schematic structural diagram of a signal processing circuit 50 in one embodiment of the present application;

[0043] Figure 4 1 is a schematic diagram of the circuit structure of a laser microphone provided in one embodiment of the present application;

[0044] Figure 5 is a schematic diagram of the circuit structure of a laser microphone provided in another embodiment of the present application;

[0045] Figure 6 This is a schematic structural diagram of a top-entry sound structure laser microphone provided in one embodiment of the present application;

[0046] Figure 7 This is a schematic diagram of the structure of a bottom-input laser microphone provided in one embodiment of the present application;

[0047] Figure 8 Schematic diagram of lens arrangement in one embodiment of the present application;

[0048] Figure 9 This is a schematic diagram of the setting position of the laser microphone in the terminal provided in an embodiment of the present application. DETAILED DESCRIPTION

[0049] The embodiments of the present application are described below in conjunction with the drawings in the embodiments of the present application.

[0050] See also Figure 1 and Figure 2 The embodiment of the present application provides a laser microphone 100, comprising a diaphragm 10, a laser 20, a control circuit 30, a self-mixing signal acquisition device 40, and a signal processing circuit 50. The diaphragm 10 is used to receive sound waves generated by external sounds and generate vibrations. The light-emitting surface of the laser 20 is opposite to the diaphragm 10. The laser 20 is used to emit light to the diaphragm 10 and receive a feedback light signal from the diaphragm 10. Based on the laser self-mixing interference effect, the feedback light signal interferes with the laser light in the resonant cavity of the laser 20 to obtain a self-mixing light signal. The output terminal 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 acquisition device 40 is connected to the laser 20 and is used to obtain a target voltage signal related to the self-mixing light signal. The input terminal 50a of the signal processing circuit 50 is connected to the first output port 40b of the self-mixing signal acquisition device 40, and is used to receive the target voltage signal output by the self-mixing signal acquisition device 40 and process the target voltage signal into an audio voltage signal.

[0051] The working mechanism of the laser microphone 100 in the embodiment of the present application is as follows: the sound waves generated by external sounds act on the diaphragm 10, and the diaphragm 10 generates vibration displacement as the sound pressure of the sound waves changes; the control circuit 30 provides a driving current to the laser 20 to drive the laser 20 to emit light, and the laser beam is emitted to the diaphragm 10 and reflected by the diaphragm 10 to obtain a feedback light signal. The feedback light signal carries the vibration information of the diaphragm 10, and its phase relative to the emitted light changes. The feedback light signal is reflected back to the resonant cavity of the laser 20 and undergoes self-mixing interference with the laser in the cavity to obtain a self-mixing light signal; the self-mixing signal acquisition device 40 obtains a target voltage signal of the laser 20 related to the self-mixing light signal, and the signal processing circuit 50 receives the target voltage signal output by the self-mixing signal acquisition device 40, and amplifies, filters, and other processing on the target voltage signal to obtain the final output audio voltage signal.

[0052] In the embodiment of the present application, the distance between the laser 20 and the diaphragm 10 is L, and the range of L is 30μm≤L≤300μm, that is, the distance between the light-emitting surface of the laser 20 close to the diaphragm 10 and the reflective surface of the diaphragm 10 is 30μm-300μm. 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 length of the external reflection cavity formed by the reflective surface of the diaphragm and the light-emitting surface of the laser, thereby changing the phase of the feedback light. By setting the laser and the diaphragm at a suitable distance, that is, maintaining a suitable external cavity length, the embodiment of the present application can improve the coupling efficiency of the laser output light beam re-entering the laser resonant cavity after reflection from the diaphragm, thereby effectively improving the signal-to-noise ratio and improving the voice recognition sensitivity.

[0053] In some embodiments of the present application, the self-mixing signal acquisition device 40 is used 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. Figure 1 As shown, the self-mixing signal acquisition device 40 includes a photodetector 41 and a mutual impedance amplifier circuit 42. The photodetector 41 is connected to the laser 20, and the input end of the mutual impedance 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 resonant cavity and convert the self-mixing optical signal into a current signal. The mutual impedance amplifier circuit 42 is used to convert the current signal output by the photodetector 41 into a voltage signal. In this embodiment, the feedback optical signal obtained by the diaphragm reflection is reflected back to the laser 20 resonant cavity and undergoes self-mixing interference with the light field in the cavity, causing the laser light intensity to change. The light intensity change caused by self-mixing is detected by the photodetector 41, which converts the optical signal into a photocurrent signal. The mutual impedance amplifier circuit 42 converts the photocurrent signal into an amplified target voltage signal. The signal processing circuit 50 then performs signal amplification and filtering, and ultimately outputs the signal as an audio voltage signal.

[0054] In some other embodiments of the present application, the self-mixing signal acquisition device 40 is used to directly acquire the target voltage signal related to the self-mixing optical signal from the laser 20. Specifically, Figure 2 As shown, the self-mixing signal acquisition device 40 includes a buffer circuit 43 connected to the output terminal of the laser 20. Buffer circuit 43 can obtain the terminal voltage of the laser 20. In this application, the terminal voltage of the laser 20 refers to the voltage difference between the two ends of the laser or the voltage at one end of the laser relative to ground. Buffer circuit 43 is a protective circuit that can suppress current increases.

[0055] See also Figure 3 In some embodiments of the present application, the signal processing circuit 50 includes a high-pass filter circuit 51 and a voltage amplifier and low-pass filter circuit 52. The input port 51a of the high-pass filter circuit 51 is connected to the first output port 40b of the self-mixed signal acquisition device 40, and the input port 52a of the voltage amplifier 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 isolate the output signal of the self-mixed signal acquisition device 40 and filter out low-frequency noise. The voltage amplifier and low-pass filter circuit 52 can amplify and low-pass filter the high-frequency AC signal output by the high-pass filter circuit 51 after isolation. In some embodiments of the present application, 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 amplifier and low-pass filter circuit 52, and the output port 53b of the gain control circuit 53 is connected to the input port 52c of the voltage amplifier and low-pass filter circuit 52. The gain control circuit 53 adjusts the gain of the voltage amplifier and low-pass filter circuit 52 based on the output signal of the voltage amplifier and low-pass filter circuit 52. The output port 52b of the voltage amplifier and low-pass filter circuit 52 serves as the output terminal of the signal processing circuit 50 to output the signal.

[0056] Due to factors such as ambient temperature fluctuations and laser aging, the laser current may fluctuate, causing the laser light emission frequency to drift and introducing phase noise. In order to reduce or eliminate the phase noise and improve the microphone signal-to-noise ratio, the embodiment of the present application modulates the laser drive current by constructing a loop control to stabilize the laser at the drive current operating point with the highest sensitivity to the diaphragm vibration. Since both the laser current fluctuation and the diaphragm vibration will cause phase fluctuations in the laser resonant cavity, that is, fluctuations in the self-mixing optical signal. The embodiment of the present application applies a small current disturbance to the laser, and determines the drive current operating point with the highest laser sensitivity based on the degree of change in the output signal of the self-mixing signal acquisition device caused by the current disturbance, that is, the degree of change in the self-mixing optical signal caused by the current disturbance. This allows the laser to also remain at the drive current operating point with the highest sensitivity to the diaphragm vibration, thereby improving the microphone signal-to-noise ratio. In this application, the laser drive current is a DC current.

[0057] The following describes a specific scheme for modulating the laser drive current by constructing a loop control in an embodiment of the present application:

[0058] See also Figure 1 and Figure 2 In the embodiment of the present application, 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 determines the driving current A of the laser 20 according to the output signal of the second output port 40c of the self-mixed signal acquisition device 40. j That is, two signals are output from the mixed signal acquisition 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 signals of the same voltage.

[0059] In the embodiment of the present application, when the laser is in the starting working mode, the control circuit 30 determines the driving current A of the laser 20 according to the target voltage signal output from the mixed signal acquisition device 40. j ,include:

[0060] S21: Control circuit with I min’ is the initial value, ΔI is the step size, and I max’ Apply a scanning current I to the laser as the termination value t’ , and in each scan the scanning current I t’ The superimposed AC current I c , and obtain the peak-to-peak value of the output voltage fluctuation ΔV for each scan t′ ;

[0061] Among them, I min’ is the preset minimum drive current, I max’ is the preset maximum drive current; ΔI is the preset current; AC current Ic is the preset current, AC current I c The frequency is greater than the maximum frequency of the sound that the human ear can hear; ΔV t′ With AC current I c The frequency of t' represents the number of current sweeps.

[0062] In step S21 of this embodiment, the control circuit 30 controls the scanning current I t’ The superimposed AC current I c Output to the laser 20, the self-mixed signal acquisition device 40 is based on I t’ and I c Output target voltage signal V1. After the control circuit 30 obtains the target voltage signal V1, it performs FFT (Fast Fourier Transform) on the target voltage signal V1 and identifies the AC current I c The peak-to-peak value of the output voltage fluctuation ΔV at the frequency t′ . Among them, ΔV t′ With AC current I c The frequency of the superimposed AC current I c The frequency of the output voltage fluctuation peak-to-peak value ΔV at this frequency is identified in the voltage signal after performing FFT. t′ For example, the superimposed AC current I c The frequency is 25kHz, then it is necessary to identify the peak-to-peak value of the output voltage fluctuation ΔV at 25kHz. t′ .

[0063] In the embodiment of the present application, the preset minimum driving current I min’ and preset maximum drive current I max’ It can be reasonably set according to the specific needs of the laser. For example, in some embodiments of the present application, the minimum driving current I min’ It can be 0.5mA, the preset maximum drive current I max’ It can be 3mA.

[0064] Among them, one scan refers to the control circuit scanning the current I at a certain point value. t’ The superimposed AC current I c Apply to the laser and obtain the laser scanning current I t’ The superimposed AC current I c When the output voltage fluctuation peak-to-peak value ΔV t′ Peak-to-peak (pk-pk)ΔV t′ It refers to the difference between the maximum positive voltage value and the maximum negative voltage value in the waveform.

[0065] S22: Execute multiple ΔV obtained in the process of S21 t′ The largest ΔV t′ The corresponding scanning current I t’ Determined as the laser driving current A j The control circuit determines the driving current A according to S22. j , apply the driving current A to the laser stably j .

[0066] The laser startup mode refers to each time the laser switches from non-pickup mode to pickup mode. A laser cycle is defined as the time from power-on to power-off. Each time the pickup mode is activated after power-on, it is considered the startup mode. Within a cycle, switching from standby mode to pickup mode is also considered the startup mode. The laser's "operating mode" refers to the state of the laser in pickup mode, i.e., the state of the pickup mode after the laser has been activated.

[0067] In the embodiment of the present application, in the laser working mode, when the jth driving current modulation is performed, the control circuit 30 determines the driving current A of the laser 20 according to the target voltage signal output by the self-mixed signal acquisition device 40. j ,include:

[0068] S11: The control circuit modulates the driving current A obtained by the previous driving current j-1 Determine the scanning current range of this drive current modulation [I min , I max ], wherein said I min =A j-1 -I0, I max =A j-1 +I 0’ ,0.1mA≤I0≤0.5mA, 0.1mA≤I 0’ ≤0.5mA; j represents the number of drive current modulations and is an integer greater than or equal to 2;

[0069] In 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 obtained after the previous drive current modulation is j-1 It is the driving current determined after executing S21 and S22 when starting the working mode. When j is greater than 2, the driving current A obtained after the previous driving current modulation j-1 This can be the drive current determined after the previous execution of S11 to S13 in the laser operating mode. Before the next drive current modulation is performed, the control circuit continues to apply the drive current obtained after the previous drive current modulation to the laser. Therefore, the drive current obtained after the previous drive current modulation of the laser is usually the current operating drive current of the laser.

[0070] In the embodiment of the present application, I0 and I 0’ It can be the same value or different values. In some embodiments of the present application, the scanning current range [I min , I max ] is determined to be within the range of plus or minus 0.3mA of the current working current, that is, I min =A j-1 -0.3mA, I max =A j-1 +0.3mA. In some other embodiments, the scanning current range [I min , I max ] It can also be determined to be within the range of plus or minus 0.4mA or 0.5mA of the current operating current. The specific setting can be based on the current fluctuation of the laser.

[0071] In the embodiment of the present application, I max The value should be less than or equal to I max’ , I min The value is greater than or equal to I min’ .

[0072] Therefore, when the scanning current range [I min , I max ] is determined to be within the range of plus or minus 0.3mA of the current working current, that is, I min =A j-1 -0.3mA, I max =A j-1 +0.3mA. When A j-1 +0.3mA is less than or equal to the preset maximum drive current I max’ , confirm I max =A j-1 +0.3mA; and when A j-1 +0.3mA is greater than the preset maximum drive current I max’ When I max =I max’ Similarly, when A j-1 -0.3mA is greater than or equal to the preset minimum drive current I min’ When I min =A j-1 -0.3mA; and when A j-1 -0.3mA is less than the preset minimum drive current I min’ When I min =I min’ .

[0073] S12: Control circuit with I min is the initial value, ΔI is the step size, and I maxApply a scanning current I to the laser as the termination value t , and in each scan the scanning current I t The superimposed AC current I c , and obtain the peak-to-peak value of the output voltage fluctuation ΔV for each scan t ;

[0074] Wherein, the ΔI is a preset current; the AC current I c is the preset current, the AC current I c The frequency is greater than the maximum frequency of the sound that the human ear can hear; the ΔV t With the alternating current I c The frequency of t represents the number of current sweeps;

[0075] In step S12 of this embodiment, the control circuit 30 controls the scanning current I t The superimposed AC current I c Output to the laser 20, the self-mixed signal acquisition device 40 is based on I t and I c Output target voltage signal V1. After the control circuit 30 obtains the target voltage signal V1, it performs FFT on the target voltage signal V1 and identifies the AC current I c The peak-to-peak value of the output voltage fluctuation ΔV at the frequency t . Among them, ΔV t With AC current I c The frequency of the superimposed AC current I c The frequency of the output voltage fluctuation peak-to-peak value ΔV at this frequency is identified in the voltage signal after performing FFT. t For example, the superimposed AC current I c The frequency is 25kHz, then it is necessary to identify the peak-to-peak value of the output voltage fluctuation ΔV at 25kHz. t .

[0076] Among them, one scan refers to the control circuit scanning the current I at a certain point value. t The superimposed AC current I c Apply to the laser and obtain the laser scanning current I t The superimposed AC current I c When the output voltage fluctuation peak-to-peak value ΔV t process.

[0077] S13: Execute multiple ΔV obtained in the process of S12 t The largest ΔV t The corresponding scanning current I t Determine the driving current A of the laser obtained by this driving current modulation jΔV t The larger the value, the greater the change in the self-mixing optical signal caused by the laser AC current disturbance, 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 diaphragm vibration will cause the phase fluctuation in the laser cavity, that is, the self-mixing optical signal fluctuation, ΔV t The larger the value, the higher the sensitivity of the self-mixing light signal to the diaphragm vibration.

[0078] In the embodiment of the present application, a drive current modulation is to control the laser drive current from I to min Scan to I max , at each scanning current point I t Superimposed AC current I c The process of obtaining the laser drive current determined by this modulation based on the peak-to-peak value of the output voltage fluctuation obtained in each scan is a process of executing S11 to S13 once. Similarly, executing S21 to S22 once is also considered a drive current modulation.

[0079] In the embodiment of the present application, in the laser operating mode, the drive current modulation process of S11 to S13 can be performed once every 2-20 seconds, for example, once every 5 seconds, or once every 10 seconds. The specific time can be determined according to the actual working conditions of the laser and is not limited by this application. If the laser current is relatively stable, the interval between the two current modulations can be longer, while when the laser current is not stable, the interval between the two current modulations can be shorter.

[0080] It is understandable that 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 current point with the highest sensitivity in the working mode.

[0081] In the embodiment of the present application, the preset current ΔI may be in the range of 10μA ≤ ΔI ≤ 50μA. Specifically, the value of ΔI may be, but is not limited to, 10μA, 20μA, 25μA, 30μA, 40μA, and 50μA. Setting an appropriate step size ΔI during the current scan process facilitates more accurately finding a high-sensitivity drive current point value.

[0082] In the embodiment of the present application, the AC current I c The frequency 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 20Hz-20kHz, the AC current I c The frequency is greater than 20kHz, specifically 20kHz<I c ≤50kHz. In some embodiments of the present application, the AC current Ic The frequency of is 25kHz, 30kHz, 40kHz, 50kHz. In the embodiment of the present application, the AC current I c The peak-to-peak value of the AC current can be controlled between 10μA and 50μA, specifically but not limited to 10μA, 20μA, 30μA, 40μA, and 50μA. c Having a higher frequency and a smaller peak-to-peak value is beneficial to the stable operation of the laser.

[0083] In the embodiment of the present application, the sampling frequency of the output signal collected by the control circuit 30 from the output terminal of the self-mixed signal acquisition device 40 may be between 100 kHz and 500 kHz, for example, 100 kHz, 200 kHz, 300 kHz, or 500 kHz.

[0084] In a specific embodiment of the present application, when the laser microphone starts working mode, the process of the control circuit determining the laser driving current through current modulation is as follows:

[0085] S101: Activate laser drive current modulation and set the AC current I c The peak-to-peak value is 17μA, and the modulation frequency is 25kHz; set the initial value of the laser scanning current, that is, preset the minimum driving current I min’ 0.5mA; Set the laser scanning current termination value, that is, preset the maximum drive current I max’ is 3mA; set the scanning step size ΔI of the laser driving current to 25μA;

[0086] S102: Sweep the laser drive current from 0.5mA to 3mA, superimposing an AC current of 17μA on the scan current during each scan; simultaneously, the control circuit obtains the target voltage signal outputted from the output of the self-mixed signal acquisition device at a sampling frequency of 200kHz for each scan, performs FFT on the obtained target voltage signal, and identifies the peak-to-peak value of the output voltage fluctuation ΔV at a modulation frequency of 25kHz. t′ ;

[0087] Among them, during the first scan, the current output by the control circuit to the laser includes a scanning current of 0.5mA and an AC current of 17μA; during the second scan, the current output by the control circuit to the laser includes a scanning current of 0.5mA+ΔI=0.525mA and an AC current of 17μA; during the third scan, the current output by the control circuit to the laser includes a scanning current of 0.525mA+ΔI=0.55mA and an AC current of 17μA; and so on, until the scan reaches 3mA.

[0088] S103: Find the ΔV at 25kHz modulation frequency during the process of scanning from 0.5mA to 3mA t′The laser current value at the maximum; and the laser drive current is set at ΔV t′ The sweep current value at maximum, with modulation turned off.

[0089] After the modulation process of S101-S103, the laser finds the optimal operating point of the drive current with maximum sensitivity and stabilizes the laser drive current at this optimal operating point before the next drive current modulation. In the embodiment of the present application, the above modulation process is controlled and executed by the control circuit 30. When the modulation is turned off, the control circuit 30 stops collecting the target voltage signal from the self-mixed signal acquisition device 40.

[0090] In this application, when performing the jth drive current modulation in the laser microphone working mode, it is not necessary to scan from the preset minimum drive current to the preset maximum drive current. It is only necessary to determine the appropriate scanning range based on the current working current, which can simplify the drive current modulation process.

[0091] In a specific embodiment of the present application, in the laser microphone working mode, the process of performing the j-th driving current modulation may be:

[0092] S201: Activate laser drive current modulation and set AC current I c The peak-to-peak value is 17μA, and the modulation frequency is 25kHz. According to the current working current of the laser I1=2.3mA, the initial value of the scanning current I is determined. min =2.3mA-0.3mA=2.0mA and scanning current termination value I max =2.3mA+0.3mA=2.6mA, set the scanning step size ΔI of the laser drive current to 25μA;

[0093] Among them, the current working current I1 of the laser is actually the driving current I determined by the last modulation, i.e. the j-1th modulation. j-1 ;

[0094] It should be noted that if the current working current of the laser is I1=2.75mA, then I1+0.3mA>3mA. At this time, the end value of the scanning current is determined to be I max =3mA.

[0095] S202: Sweep the laser drive current from 2.0mA to 2.6mA, superimposing an AC current of 17μA on the scan current during each scan; simultaneously, the control circuit obtains the target voltage signal output from the output end of the self-mixed signal acquisition device at a sampling frequency of 200kHz for each scan, performs FFT on the obtained target voltage signal, and identifies the peak-to-peak value of the output voltage fluctuation ΔV at a modulation frequency of 25kHz. t ;

[0096] Among them, during the first scan, the current output by the control circuit to the laser includes a scanning current of 2.0mA and an AC current of 17μA; during the second scan, the current output by the control circuit to the laser includes a scanning current of 2.0mA+ΔI=2.025mA and an AC current of 17μA; during the third scan, the current output by the control circuit to the laser includes a scanning current of 2.025mA+ΔI=2.05mA and an AC current of 17μA; and so on, until the scan reaches 26mA.

[0097] S203: Find the ΔV at 25kHz modulation frequency during the process of scanning from 2.0mA to 2.6mA. t The laser current value at the maximum; and the laser drive current is set at ΔV t The sweep current value at maximum, with modulation turned off.

[0098] The embodiment of the present application modulates the laser driving current by constructing a loop control, which can adjust the laser working state in real time, stabilize the laser at a higher sensitivity working point, reduce or eliminate low-frequency phase jitter related to the environment, and make the feedback interference mechanism of the self-mixing laser more stable, so that the laser microphone can maintain a high signal-to-noise ratio during operation (i.e., in working mode) and throughout its entire life cycle.

[0099] See also Figure 4 and Figure 5 In the embodiment of the present application, the control circuit 30 includes a first controller 31 and a drive circuit 32 connected to the first controller 31. The drive 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 31a of the first controller 31 is connected to the digital potentiometer 321. The input signal of the input terminal 31b of the first controller 31 is the output signal from the mixed signal acquisition 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 terminal of the operational amplifier OP3, and the second end of the resistor R7 and the second end of the capacitor C4 are both 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, the output end of the operational amplifier OP3 is connected to the base of the transistor Q1, the first end 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. Figure 1 and Figure 2 The input port 31b of the first controller 31 serves as the input port 30b of the control circuit 30 and is connected to the output port 40c of the self-mixed signal acquisition device 40. In the control circuit 30, variable resistor R6 and resistor R7 serve as voltage divider resistors, which can perform a voltage dividing function. Resistors R8 and R10 can function as current limiters, with R10 controlling the current through transistor Q1 to prevent excessive current flow through transistor Q1 and excessive power consumption. Capacitor C4 enables a slow start of the drive circuit 32. In the embodiment of the present application, the first controller 31 outputs a control signal to control the effective resistance of variable resistor R6 based on the output signal obtained from the self-mixed signal acquisition device 40. By changing the effective resistance of variable resistor R6, the drive current output by the drive circuit 32 to the laser 20 can be controlled and adjusted, thereby achieving adjustable drive current for the laser 20. The drive circuit 32 is a constant current source circuit that can provide a constant DC bias current to the laser 20 that is virtually invariant to temperature, thereby stabilizing the operating point.

[0100] See also Figure 4 In some embodiments of the present application, the self-mixing signal acquisition device 40 includes a photodetector 41 and a mutual impedance amplifier circuit 42. The photodetector 41 is connected to the laser 20, and the input end of the mutual impedance amplifier circuit 42 is connected to the photodetector 41. The output end of the control circuit 30, i.e., 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. The common electrode of the photodetector 41 and the laser 20 is grounded. The cathode of the photodetector 41 is connected to the input end of the mutual impedance amplifier circuit 42. The output end of the mutual impedance amplifier circuit 42 serves as the output port 40b of the self-mixing signal acquisition device 40 (see Figure 1 ) is connected to the input end of the high-pass filter circuit 51.

[0101] In one embodiment of the present application, the mutual impedance amplifier circuit 42 includes an operational amplifier OP1, a resistor R1, and a capacitor C1. The output of the photodetector 41 is connected to the inverting input of the operational amplifier OP1. The first end of the resistor R1 and the first end of the capacitor C1 are both connected between the output of the photodetector 41 and the inverting input of the operational amplifier OP1. The second end of the resistor R1 and the second end of the capacitor C1 are both connected to the output of the operational amplifier OP1. The positive input of the operational amplifier OP1 inputs the photodetector current bias. The output of the operational amplifier OP1 serves as the output of the self-mixed signal acquisition device 40 and is connected to the input of the high-pass filter circuit 51. Capacitor C1 is a feedback compensation capacitor used to compensate for the photodetector node capacitance and the operational amplifier input capacitance to maintain circuit stability. Resistor R1 is a feedback resistor used to convert the current signal into a voltage signal.

[0102] See also Figure 5In some other embodiments of the present application, 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 grounded, and the output terminal of the operational amplifier OP4 serves as the output port 40b of the self-mixing signal acquisition device 40 (see Figure 1 ) is connected to the input end of the high-pass filter circuit 51, and the inverting input end of the operational amplifier OP4 is connected between the output end of the operational amplifier OP4 and the input end of the high-pass filter circuit 51.

[0103] See also Figure 4 and Figure 5 In the embodiment of the present application, the signal processing circuit 50 includes a high-pass filtering circuit 51 , a voltage amplification and low-pass filtering circuit 52 , and a gain control circuit 53 .

[0104] The high-pass filter circuit 51 includes a capacitor C2 and a resistor R2. The first end of capacitor C2 serves as the input of the high-pass filter circuit 51 and is connected to the output port 40b of the self-mixed signal acquisition device 40. The second end of capacitor C2 serves as the output of the high-pass filter circuit 51 and is connected to the voltage amplifier and low-pass filter circuit 52. The first end of resistor R2 is connected to the second end of capacitor C2, and the second end of resistor R2 is grounded. The high-pass filter circuit 51 formed by capacitor C2 and resistor R2 can filter out direct current and low-frequency signals. The voltage amplifier 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 positive input of the operational amplifier OP2 serves as the input of the voltage amplifier and low-pass filter circuit 52 and is connected to the output of the high-pass filter circuit 51. The output of the operational amplifier OP2 is connected to the first end of resistor R5. The second end of resistor R5 serves as the output of the voltage amplifier and low-pass filter circuit 52, i.e., the output of the signal processing circuit 50, which outputs the audio voltage signal. The first end of resistor R3, the first end of digital potentiometer 521, and the first end of capacitor C3 are all connected to the inverting input terminal of operational amplifier OP2. The second end of digital potentiometer 521 and the second end of capacitor C3 are all connected between the output terminal of operational amplifier OP2 and the first end of resistor R5. The second end of resistor R3 is grounded. Digital potentiometer 521 is connected to gain control circuit 53 and includes a variable resistor R4. The low-pass filter circuit can filter out high-frequency signals.

[0105] High-pass filter circuit 51 and voltage amplifier and low-pass filter circuit 52 form a bandpass filter circuit. The lower cutoff frequency of the bandpass is determined by R2 and C2, and the upper cutoff frequency is determined by R4 and C3. The bandpass range can be 20Hz to 20kHz, filtering out low-frequency background sounds and high-frequency signals. The OP1 and OP2 two-stage amplifier circuit systems operate at different DC operating points.

[0106] 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, and is used to collect the voltage signal output by the signal processing circuit 50. The output end of the second controller 531 is connected to the digital potentiometer 521. The second controller 531 outputs a control signal to control the effective resistance value of the variable resistor R4 of the digital potentiometer 521. By changing the effective resistance value of R4, the gain of the voltage amplification and low-pass filtering circuit 52 is adjustable. The circuit working state can be optimized in real time according to the output signal. The gain of the amplifier circuit is A=1+R4 / R3.

[0107] In the embodiment of the present application, 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 circuit (such as LDO) can be used for power supply. The use of a low-noise operational amplifier is beneficial to improving the signal-to-noise ratio. The resistance of each of the above-mentioned resistors is as small as possible while meeting the functional conditions to reduce the thermal noise generated by the resistors. In the embodiment of the present application, the first controller 31 and the second controller 531 can be set separately, or they can be the same controller.

[0108] See also Figure 6 In one embodiment of the present application, a laser microphone 100 includes a housing 1. The housing 1 includes a substrate 11, a cover 12, and a middle frame 13 that are arranged relative to each other. The substrate 11, cover 12, and middle frame 13 form a housing cavity. The diaphragm 10, laser 20, light detector 41, and ASIC (Application Specific Integrated Circuit) chip 2 are all disposed within the housing cavity. The diaphragm 10 is fixed to the cover 12, the laser 20 is disposed on the substrate 11, and the light detector 41 is disposed on the substrate 11 and is located on the side of the laser 20 facing away from the diaphragm 10. A sound pickup hole 121 is provided on the cover 12, and the diaphragm 10 and the sound pickup hole 121 are disposed correspondingly. In the laser microphone 100 of this embodiment, the emission and feedback beams follow the same path, eliminating the need for a reference interferometer arm, resulting in fewer components and self-alignment of the optical path, allowing for a smaller package size.

[0109] In the embodiment of the present application, the spacing between the diaphragm 10 and the light-emitting surface of the laser 20 (i.e., the side facing the diaphragm 10) is set in the range of 30μm-300μm. The appropriate spacing can improve the coupling efficiency between the light reflected back to the laser by the diaphragm 10 and the light in the laser cavity. Specifically, in some embodiments, the spacing between the diaphragm 10 and the laser 20 can be set in the range of 50μm-100μm. In other embodiments, the spacing between the diaphragm 10 and the laser 20 can be set in the range of 100μm-200μm.

[0110] In the embodiment of the present application, the diaphragm 10 can sense the air vibrations generated by external sound waves and generate vibrations, reflecting the light emitted by the laser back into the laser resonant cavity. External sound waves can be transmitted to the diaphragm 10 through the pickup hole 121. The laser microphone in the embodiment of the present application differs from the capacitance detection mechanism of traditional MEMS microphones and does not require a back plate, so there are no special requirements for the conductive properties of the diaphragm. The diaphragm 10 can be a MEMS (micro-electro-mechanical system) diaphragm, a metallic glass diaphragm, a graphene diaphragm, a polymer film, or a metal film. A reflective layer can be provided on the side of the diaphragm 10 facing the laser 20 to increase reflectivity. The reflective layer can be made of a high-reflectivity metal such as aluminum or gold. The side of the diaphragm 10 coated with the reflective layer faces the light-emitting surface of the laser 20 and is centrally aligned. The embodiment of the present application combines a negatively stressed SOI (Silicon-On-Insulator) membrane layer with a positively stressed metal reflective layer to reduce diaphragm stress and thereby improve the diaphragm's sound pressure displacement sensitivity. The embodiment of the present application uses a back-pole-less diaphragm, which reduces squeeze-film damping, improves sound pressure displacement sensitivity, and reduces noise. The diaphragm design of the embodiment of the present application allows for detection of weaker sounds and stronger sound signal response amplitude, which is conducive to achieving a high signal-to-noise ratio.

[0111] In an embodiment of the present application, one or more balancing holes are provided on the diaphragm 10 to balance the air pressure inside and outside the diaphragm. The diameter of the balancing hole can be 1μm-5μm (including endpoint values ​​of 1μm and 5μm). In some embodiments of the present application, the diaphragm 10 is a MEMS silicon diaphragm with a thickness of 300nm-800nm ​​and a diameter of 600μm-1200μm. The central area of ​​the MEMS silicon diaphragm is coated with a highly reflective metal layer, such as an aluminum layer, a gold layer, etc. The thickness of the metal layer can be 30nm-100nm (including endpoint values ​​of 30nm and 100nm), and the radius of the metal layer is 20μm-50μm. The sound pressure displacement sensitivity of the MEMS silicon diaphragm is 0.05μm / Pa to 0.5μm / Pa. For example, in a specific embodiment of the present application, the MEMS silicon diaphragm has a thickness of 400nm and a diameter of 900μm. The central area of ​​the diaphragm is aluminum-plated, the aluminum layer has a thickness of 90nm and a radius of 30μm, and two balancing holes are provided on the diaphragm. The diameter of each balancing hole is 2μm, and the sound pressure displacement sensitivity of the MEMS diaphragm is 0.1μm / Pa. The embodiment of the present application adopts a silicon substrate based on SOI or polycrystalline silicon to manufacture the diaphragm, which is conducive to reducing stress and improving sound pressure displacement sensitivity. The provision of a metal reflective layer can balance the stress of the membrane layer and improve the light reflectivity of the diaphragm. Through stress control, the linearity of the diaphragm vibration amplitude with the change of sound pressure is further improved.

[0112] In the embodiment of the present application, the laser microphone 100 may be a top-entry sound structure, such as Figure 6 As shown, the diaphragm 10 is located on the cover plate 12, the pickup hole 121 is provided on the cover plate 12, a front cavity 3 is formed between the diaphragm 10 and the cover plate 12, and a rear cavity 4 is formed between the diaphragm 10 and the cover plate 12. The diaphragm 10 is provided on the cover plate 12 to form a larger rear cavity 4. In the top-feed sound structure, the diaphragm 10, the laser 20 and the pickup hole 121 are provided correspondingly, and specifically can be provided coaxially. The laser microphone of the top-feed sound structure is generally fixed to the PCB board in the terminal through the substrate 11, the light detector 41 is electrically connected to the chip 2 through the metal trace 5, and the chip 2 is directly electrically connected to the external metal electrode 6 through the via hole on the substrate 11.

[0113] In the embodiment of the present application, the laser microphone 100 may also be a bottom-input sound structure, such as Figure 7As shown, the diaphragm 10 is located on the substrate 11, and the pickup hole 121 is arranged on the substrate 11 and corresponds to the diaphragm 10. The laser 20 and the light detector 41 are located on the cover 12, and 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 shell. The diaphragm 10 is arranged on the substrate 11 to form a larger rear cavity 4. In the bottom sound-input structure, the diaphragm 10, the laser 20 and the pickup hole 121 are arranged correspondingly, and can be specifically coaxially arranged. There can be one or more pickup holes 121. The laser microphone with a bottom sound-input structure is generally fixed to the PCB board in the terminal through the substrate 11. The light detector 41 is electrically connected to the chip 2 through the metal trace 5, and the chip 2 is electrically connected to the external metal electrode 6 through the metal trace 5 and the via on the substrate 11.

[0114] Both laser microphones with the above two structures have a back cavity with a larger air volume, making it easier for sound waves to drive the diaphragm to move, thereby improving the sensitivity and signal-to-noise ratio of the microphone.

[0115] In the embodiment of the present application, in order to reliably package the diaphragm 10, the laser 20, the light detector 41 and the ASIC chip 2, 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 ceramic material, and the packaging cover 12 and the middle frame 13 are an integrated structure and are made of metal or other materials.

[0116] Combine Figure 6 and Figure 7 In the embodiment of the present application, when the self-mixing optical signal acquisition device 40 includes a light detector 41 and a mutual impedance amplifier circuit 42, the light detector 41 and the laser 20 can be integrated on an optical chip, and the light detector 41 is located on the side of the laser 20 away from the diaphragm 10, and the mutual impedance amplifier circuit 42 can be integrated with the control circuit 30 and the signal processing circuit 50 on an ASIC chip 2. Integrating the light detector 41 and the laser 20 on an optical chip can improve the efficiency of coupling the light transmitted from the back of the laser into the light detector, thereby improving the signal-to-noise ratio, and at the same time avoid the optical path deviation caused by the discrete arrangement in situations such as vibration and falling, thereby maintaining the consistency of the signal during the life cycle of the module. Of course, in some other embodiments of the present application, the light detector 41 and the laser 20 can also be arranged separately, and the laser 20 can be directly attached to the light detector 41, and the light from the back of the laser 20, that is, the side away from the diaphragm 10, can also be directly coupled into the light detector 41. In the embodiment of the present application, the operating wavelength of the light detector 41 may be 360 ​​nm-1600 nm (including endpoint values ​​360 nm and 1600 nm).

[0117] In some other embodiments of the present application, when the self-mixed signal acquisition device 40 includes a buffer circuit, the buffer circuit can be integrated with the control circuit 30 and the signal processing circuit 50 on an ASIC chip 2 .

[0118] In the embodiment of the present application, the laser 20 is a self-mixing laser, and the specific type is not limited. It can be a vertical cavity surface emitting laser or an edge emitting laser. The emission wavelength of the laser can be 750nm-1600nm. In some embodiments of the present application, the laser 20 is a vertical cavity surface emitting laser (VCSEL) operating in single mode, and its emission wavelength is 850nm. 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. The typical dimensions of the vertical cavity surface emitting laser can be: length of 120μm-200μm, width of 120μm-200μm, and thickness of 100μm-150μm.

[0119] See also Figure 8 In some embodiments of the present application, 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 lens 70 is made on the light-emitting surface of the laser 20. In the embodiment of the present application, the lens 70 may be a collimating lens or a converging lens. Using a lens to couple the emitted and reflected light can improve the feedback coupling efficiency, increase the feedback light intensity carrying the diaphragm vibration signal, and thereby improve the signal-to-noise ratio of the laser microphone. Figure 8 As shown, in some embodiments of the present application, the lens 70 is a collimating lens, including a lens cylinder and a lens surface, wherein the lens cylinder can be produced by methods such as photolithography or laser direct writing, and the lens surface can be produced by methods such as embossing and inkjet printing. The collimating lens can collimate the laser output light onto the reflective surface of the diaphragm and couple the reflected light into the laser's light output hole. By setting a collimating lens, the light reflected back to the laser can be greatly increased, thereby increasing the feedback signal light intensity and further improving the signal-to-noise ratio of the microphone. The material of the lens is a material with a transmittance greater than 90% within the operating wavelength range of the laser. In the embodiment of the present application, the lateral dimension (i.e., length and width) of each of the lenses is 20μm-200μm (including the endpoint values ​​of 20μm and 200μm); the longitudinal dimension (i.e., height) of each of the lenses is 20μm-200μm (including the endpoint values ​​of 20μm and 200μm).

[0120] In the implementation manner of the present application, all parameter values ​​mentioned above involving numerical ranges include two endpoint values.

[0121] The laser microphone of the embodiment of the present application improves the sound pressure displacement sensitivity of the diaphragm based on the back-pole-free diaphragm design, 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, and can pick up slight voice signals. This embodiment detects the vibration of the diaphragm by means of laser self-mixing coherence, and has a high detection sensitivity. The laser microphone of the embodiment of the present application can significantly improve the voice pickup in the whisper 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, which is a significant improvement compared to the traditional MEMS microphone (signal-to-noise ratio of 65dB).

[0122] See also Figure 9 The embodiment of the present application further provides a terminal 200, comprising the laser microphone 100 described above in the embodiment of the present application. The terminal 200 comprises a housing and a circuit board disposed within the housing, the laser microphone being disposed on the circuit board, and a sound receiving hole 101 corresponding to the position of the laser microphone being disposed on the terminal housing. External sound is transmitted to the laser microphone through the sound receiving hole 101 of the housing. The laser microphone 100 may be disposed corresponding to the front side of the terminal, and the corresponding sound receiving hole 101 may be disposed on the front cover 201 of the terminal (see FIG. 1 ). Figure 9 Front view); The laser microphone 100 may also be provided corresponding to the rear side of the terminal, and the corresponding sound receiving hole 101 is provided on the rear cover plate 202 of the terminal (see Figure 9 Rear view); The laser microphone 100 can also be set corresponding to the side middle frame 203 of the terminal, and the corresponding sound receiving hole 101 is set on the side middle frame 203 of the terminal, which can be specifically as follows Figure 9 As shown in the bottom view in the figure, the sound receiving hole 101 is provided on the lower middle frame of the terminal, and can also be provided on the upper, left or right middle frame. The sound pickup hole of the laser microphone 100 is provided corresponding to the sound receiving hole 101 on the terminal housing, and can specifically be coaxial. The middle frame 203 and the rear cover plate 202 can be an integrally molded structure or a separate structure. The terminal 200 can be a mobile phone, a laptop computer, a tablet computer, a smart TV, a smart speaker, a headset, a camera, a webcam, a wearable device, a gaming device, an in-car audio system or microphone, a voice navigation device, a spoken speech recognition device, a speech-to-text converter, and other terminal products that require voice command control or scenarios that require the collection, recording, processing or analysis of speech.

Claims

1. A laser microphone, characterized in that: It includes a diaphragm, a laser, a control circuit, a self-mixing signal acquisition device, and a signal processing circuit; The laser is used to emit light toward the diaphragm and receive a feedback light signal from the diaphragm, wherein the feedback light signal interferes with the laser light in the laser resonant cavity to obtain a self-mixing light signal; the distance between the laser and the diaphragm is L, and the range of L is 30 μm ≤ L ≤ 300 μm; The control circuit is connected to the laser and is used to drive and control the laser to emit light; The self-mixing signal acquisition device is connected to the laser and is used to acquire and output a target voltage signal related to the self-mixing optical signal; the output end of the self-mixing signal acquisition device is connected to the input end of the control circuit, and the control circuit determines the driving current A of the laser according to the target voltage signal output by the self-mixing signal acquisition device. j ; In the laser working mode, when the jth driving current modulation is performed, the control circuit determines the driving current A of the laser according to the target voltage signal output by the self-mixed signal acquisition device. j ,include: S11: The control circuit modulates the driving current A obtained by the previous driving current j-1 Determine the scanning current range of this drive current modulation [I min , I max ], wherein said I min =A j-1 -I0, I max =A j-1 +I 0’ , 0.1mA≤I0≤0.5mA, 0.1mA≤I0'≤0.5mA; j represents the number of drive current modulations and is an integer greater than or equal to 2; S12: The control circuit is I min is the initial value, ΔI is the step size, and I max The laser is subjected to a scanning current I of the termination value. t , and in each scan, the scanning current I t The superimposed AC current I c , and obtain the peak-to-peak value of the output voltage fluctuation ΔV for each scan t ; Wherein, the ΔI is a preset current; the AC current I c is the preset current, the AC current I c The frequency is greater than the maximum frequency of the sound that the human ear can hear; the ΔV t With the alternating current I c The frequency of t represents the number of current sweeps; S13: Execute multiple ΔV obtained in the process of S12 t The largest ΔV t The corresponding scanning current I t Determine the driving current A of the laser obtained by this driving current modulation j ; The signal processing circuit is connected to the self-mixed signal acquisition device, and is configured to receive the target voltage signal output by the self-mixed signal acquisition device and process the target voltage signal into an audio voltage signal.

2. The laser microphone according to claim 1, wherein When the laser is in the startup mode, the control circuit determines the driving current A of the laser according to the target voltage signal output by the self-mixed signal acquisition device. j ,include: S21: The control circuit is I min ' is the initial value, ΔI is the step size, and I max ' is the termination value and a scanning current I is applied to the laser t’ , and in each scan, the scanning current I t’ The superimposed AC current I c , and obtain the peak-to-peak value of the output voltage fluctuation ΔV for each scan t′ ; Wherein, the I min’ is the preset minimum driving current, the I max’ is the preset maximum driving current; the ΔI is the preset current; the AC current I c is the preset current, the AC current I c The frequency is greater than the maximum frequency of the sound that the human ear can hear; the ΔV t′ With the alternating current I c The frequency of t' represents the number of current scans; S22: Execute multiple ΔV obtained in the process of S21 t′ The largest ΔV t′ The corresponding scanning current I t’ Determine the driving current A of the laser j .

3. The laser microphone according to claim 1 or 2, characterized in that: The range of ΔI is 10 μA≤ΔI≤50 μA.

4. The laser microphone according to any one of claims 1 to 3, wherein: The alternating current I c The frequency range is 20kHz<I c ≤50kHz.

5. The laser microphone according to any one of claims 1 to 4, characterized in that: The self-mixing signal acquisition device is used to detect the self-mixing optical signal in the laser resonant cavity and output a target voltage signal related to the self-mixing optical signal.

6. The laser microphone according to claim 5, wherein: The self-mixing signal acquisition device includes a light detector and a mutual impedance amplifier circuit. The light detector is connected to the laser and is used to detect the self-mixing light signal in the laser resonant cavity and convert the self-mixing light signal into a current signal; the mutual impedance amplifier circuit is connected to the light detector and is used to convert the current signal into the target voltage signal.

7. The laser microphone according to claim 6, wherein: The light detector and the laser are monolithically integrated on a chip, and the light detector is located on a side of the laser away from the diaphragm.

8. The laser microphone according to any one of claims 1 to 4, characterized in that: The self-mixing signal acquisition device includes a buffer circuit connected to the laser, and 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 optical signal.

9. The laser microphone according to any one of claims 1 to 8, characterized in that: The signal processing circuit includes a high-pass filtering circuit and a voltage amplifying and low-pass filtering circuit. The high-pass filtering circuit is connected to the self-mixing signal acquiring device, and the voltage amplifying and low-pass filtering circuit is connected to the high-pass filtering circuit.

10. The laser microphone according to claim 9, wherein: The signal processing circuit further includes a gain control circuit connected to the voltage amplification and low-pass filtering circuit, wherein the gain control circuit is used to adjust the gain of the voltage amplification and low-pass filtering circuit according to the output signal of the voltage amplification and low-pass filtering circuit.

11. The laser microphone according to any one of claims 1 to 10, characterized in that: A beam coupling device is provided on the light-emitting surface of the laser facing the diaphragm, and the beam coupling device includes one or more lenses.

12. The laser microphone according to claim 11, wherein The lateral size of each lens is 20 μm-200 μm; the longitudinal size of each lens is 20 μm-200 μm.

13. The laser microphone according to any one of claims 1 to 12, wherein: The diaphragm includes a MEMS diaphragm, a metallic glass diaphragm, a graphene diaphragm, a polymer film or a metal film.

14. The laser microphone according to claim 13, wherein: A reflective layer is provided on a side of the diaphragm facing the laser.

15. The laser microphone according to any one of claims 1 to 14, characterized in that: The laser is a vertical cavity surface emitting laser or an edge emitting laser.

16. The laser microphone according to any one of claims 1 to 15, characterized in that: The laser microphone further includes a housing, wherein the diaphragm, the laser, the control circuit, the self-mixing signal acquisition device and the signal processing circuit are all arranged in the housing, and a sound pickup hole is provided on the housing at a position corresponding to the diaphragm.

17. A terminal, characterized in that: The terminal includes the laser microphone according to any one of claims 1-16.

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