Pre-amplification circuit and coupled cavity system of calibrator

Abstract

The invention discloses a pre-amplification circuit and a coupled cavity system of a calibrator. The pre-amplification circuit comprises a polarization voltage unit, a direct current bias unit and an amplification unit, the polarization voltage unit, the direct current bias unit and the amplification unit are electrically connected with one another; the polarization voltage unit is electrically connected with polarization voltage and is used for absorbing peak voltage generated by the circuit during hot plugging; the direct current bias unit is electrically connected with the microphone and is used for acquiring a sound signal; and the amplification unit is electrically connected with the power supply and the signal processing circuit. According to the main technical scheme and effects, the polarization voltage unit is designed, so that the scheme supports the polarization voltage up to 200V and supports hot plug.

Description

Technical Field

[0001] The present invention relates to the field of amplification, and in particular to a coupling cavity system for a preamplifier circuit and a calibrator. Background Art

[0002] A preamplifier refers to a circuit or electronic device placed between a sensor and a signal processing circuit. Generally, it is directly connected to a sensor that detects signals and is designed specifically to receive weak voltage signals from a signal source. The noise figure of the entire detection system mainly depends on the noise figure of the preamplifier. The minimum signal that the instrument can detect also mainly depends on the noise of the preamplifier. For many sensors, their internal resistance output impedance is often relatively high. If directly applied to a signal acquisition and amplification circuit, some signals will be lost, resulting in signal distortion during acquisition, or when the sensor output signal is small, the signal will become difficult to acquire. A preamplifier is generally used to convert the high output impedance of the sensor into a low output impedance for subsequent circuit acquisition and processing. For a preamplifier used in the pre-stage of a microphone, due to the large span of the frequency range of the measured sound signal, the preamplifier in the pre-stage is required to have good frequency response performance.

[0003] Currently, there are many defects in the use of current sound sensors as follows:

[0004] When some microphones are in use, they need to be used under a polarization voltage of up to 200V. Most of the existing preamplifier circuits are only applied to low-voltage scenarios and are not designed for high-polarization voltage usage scenarios.

[0005] The preamplifier in the pre-stage applicable to a microphone is required to support a relatively large polarization voltage. To avoid the spike voltage caused by the plugging and unplugging actions under a large polarization voltage, the existing preamplifier circuits generally do not support hot plugging. During the use of an instrument with a modular design, if it involves replacing the sensor or storage, the instrument usually needs to be powered off, otherwise it is easy to cause damage to the pre-circuit, which is extremely inconvenient.

[0006] Most of the existing preamplifiers are used for the research and development of sensors such as MEMS microphones. The main components used are triodes, and the triode belongs to a current-controlled device. Its input impedance is still relatively low compared to sensors with high internal resistance such as microphones. If directly applied to the impedance transformation of a microphone, signal loss and distortion will still occur. Summary of the Invention

[0007] Object of the Invention: The object of the present invention is to solve the defects in the prior art and provide a coupling cavity system for a preamplifier circuit and a calibrator.

[0008] Technical Solution:

[0009] In a first aspect, the present application proposes a pre-amplification circuit, which includes a polarization voltage unit, a DC bias unit, and an amplification unit;

[0010] The polarization voltage unit, the DC bias unit, and the amplification unit are electrically connected to each other;

[0011] The polarization voltage unit is electrically linked to the polarization voltage and is used to absorb the spike voltage generated when the circuit is hot-plugged;

[0012] The DC bias unit is electrically connected to the microphone and is used to obtain the sound signal;

[0013] The amplification unit is electrically connected to the power supply and the signal processing circuit and is used to transmit the amplified sound signal after processing to the signal processing circuit.

[0014] Preferably, the polarization voltage unit includes a first resistor and a first capacitor. One end of the first resistor is grounded through the first capacitor. The end where the first resistor and the first capacitor are electrically connected is electrically connected to the polarization voltage. The other end of the first resistor is electrically connected to the positive electrode of the microphone.

[0015] Preferably, the DC bias unit includes a second capacitor, a second resistor, a third resistor, and a fourth resistor;

[0016] One end of the second capacitor is electrically connected to the positive electrode of the microphone. The other end of the second capacitor is electrically connected to the amplification unit and is also electrically connected to the amplification unit through the second resistor. One end of the second resistor is electrically connected to the power supply through the third resistor. The other end of the third resistor is electrically connected to the second resistor, the amplification unit, and the fourth resistor respectively. The other end of the fourth resistor is electrically connected to the negative electrode of the microphone and to the ground respectively.

[0017] Preferably, the amplification unit includes a field effect transistor, a first triode, a second triode, a third capacitor, a fourth capacitor, a fifth resistor, a sixth resistor, and a seventh resistor;

[0018] The gate of the field effect transistor is electrically connected to the DC bias unit. One end of the third capacitor is electrically connected to the DC bias unit. The other end of the third capacitor is electrically connected to the source of the field effect transistor and the fifth resistor. The other end of the fifth resistor is grounded. The other end of the third capacitor is electrically connected to the base of the second triode. The collector of the second triode is grounded. The emitter of the second triode is electrically connected to the signal processing circuit. The drain of the field effect transistor is electrically connected to the emitter of the first diode. The collector of the first diode is electrically connected to the power supply. The base of the first diode is electrically connected to the power supply through the sixth resistor. The seventh resistor and the fourth capacitor are in parallel, and both ends are electrically connected to the sixth resistor and the signal processing circuit respectively.

[0019] In a second aspect, the present application also proposes a coupling cavity system for a calibrator, including a microphone, a fixing device, a connector, and a circuit board of the circuit as described in the above embodiments;

[0020] The microphone, the connector, and the circuit board are all placed on the fixing device;

[0021] The device to be detected can be inserted into the fixing device for fixation to calibrate the device to be detected;

[0022] The microphone is electrically connected through the circuit board, the connector, and an external signal processing circuit.

[0023] Preferably, the fixing device includes an outer wall, an upper cover, and a lower cover;

[0024] One end of the connector is fixed inside the outer wall through a cable. The upper end of the outer wall is connected to the upper cover, the lower end of the outer wall is connected to the lower cover, and the microphone is placed inside the outer wall.

[0025] Preferably, a sound insulation fixing member is provided inside the outer wall. An installation seat is provided at the lower end of the sound insulation fixing member. A cavity is formed inside the sound insulation fixing member to place the device to be detected, and the microphone is detachably placed at the bottom end of the cavity.

[0026] Preferably, a sealing rubber pad that abuts against the outer side of the microphone is provided inside the cavity, and a sealing rubber ring for placing the device to be detected is provided on the inner wall of the cavity.

[0027] Preferably, a plastic isolation member is provided on the lower side of the installation seat. The circuit board is provided on the lower side of the plastic isolation member. The positive electrode of the microphone is electrically connected to the circuit board through a thimble, and the negative electrode of the microphone is electrically connected to the circuit board through the installation seat.

[0028] Preferably, a loudspeaker is embedded in the sound insulation fixing member.

[0029] Advantageous effects:

[0030] Since the polarization voltage generally requires a very large value (up to 200V at most), in the present application, one end of the capacitor C10 is connected to R10 and one end of the Pol_Votage polarization voltage is grounded, so that it forms a low-pass filter with the resistor R10 to absorb the spike voltage generated during hot plugging and unplugging of the circuit, thereby effectively protecting the microphone and the subsequent circuit. Therefore, the design of the polarization voltage unit enables this solution to support a polarization voltage of up to 200V and supports hot plugging;

[0031] Since the equivalent resistance of the constant-current load is 1 GΩ, the output signal is very close to the input signal, and the transmission loss can be ignored, effectively reducing the output impedance of the preamplifier and ensuring that the designed amplification unit can operate normally under a polarization voltage of up to 200V;

[0032] Capacitor C12, resistor R11, resistor R147, triode Q10, and field-effect transistor Q11 form a cascaded bootstrap circuit, which can reduce the parasitic capacitance of the field-effect transistor Q11 and improve the frequency response of the circuit in the high-frequency band;

[0033] Capacitor C14 is a feedback capacitor that can feedback the signal output from the source of the field-effect transistor Q11 to the DC bias unit, reducing the influence of the equivalent parallel capacitance of the resistors used in the DC bias unit and also improving the frequency response of the circuit in the high-frequency band. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a schematic diagram of the framework provided by the present invention;

[0035] Figure 2 It is a schematic diagram of the circuit provided by the present invention;

[0036] Figure 3 It is a schematic diagram of the structure of the coupling cavity system of the calibrator provided by the present invention.

[0037] REFERENCE NUMERALS:

[0038] 1, microphone; 2, circuit board; 3, thimble; 4, upper cover; 5, outer wall; 6, lower cover; 7, sealing rubber pad; 8, sealing rubber ring; 9, mounting seat; 10, plastic spacer; 11, sound insulation fixing piece; 12, speaker; 13, connector; 14, cable; 15, polarization voltage unit; 16, DC bias unit; 17, amplification unit; 18, signal processing circuit. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To make the technical solution of the present invention clearer, the following further describes the present invention in detail with reference to the specific embodiments in the drawings.

[0040] Embodiment 1

[0041] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein shall have the ordinary meanings understood by those of ordinary skill in the art to which the present invention pertains. The words such as "including" used herein mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0042] Regarding the problems existing in the prior art, such as Figure 1 and Figure 2 shown, a preamplifier circuit includes a polarization voltage unit 15, a DC bias unit 16, and an amplification unit 17;

[0043] The polarization voltage unit 15, the DC bias unit 16, and the amplification unit 17 are electrically connected to each other;

[0044] The polarization voltage unit 15 is electrically linked to the polarization voltage and is used to absorb the spike voltage generated during hot plugging and unplugging of the circuit;

[0045] The DC bias unit 16 is electrically connected to the microphone M10 and is used to obtain the sound signal;

[0046] The amplification unit 17 is electrically connected to the power supply and the signal processing circuit 18 and is used to transmit the amplified sound signal after processing to the signal processing circuit 18.

[0047] Specifically, the sound of the device to be detected is obtained through the microphone 1. The main function of the polarization voltage unit 15 is to provide the required polarization voltage for the microphone 1, and at the same time, it can absorb the spike voltage generated during hot plugging and unplugging. The polarization voltage is usually a high voltage (such as 200V), and voltage spikes may be generated during the hot plugging and unplugging process, which may damage the circuit and components. Through the design of this unit, the circuit can be effectively protected and the stable operation of the microphone 1 can be ensured. The function of the DC bias unit 16 is to provide the required bias voltage for the microphone 1 so that it can work normally and output the sound signal. The design of the bias voltage needs to ensure that it will not generate too high voltage or current on the microphone 1 so as not to affect its performance. The DC bias unit 16 usually isolates the interference between the polarization voltage and the signal output through the electrical connection with the microphone 1 to ensure the stable operation of the microphone 1. The main task of the amplification unit 17 is to amplify the sound signal transmitted from the microphone 1 so that the subsequent signal processing circuit 18 can effectively process the signal;

[0048] The signal processing circuit 18 is not the key point of the design of this application. It is a unit that processes the signal output by the amplification unit 17 and is a mature technology in the prior art.

[0049] In some specific embodiments, the polarization voltage unit 15 includes a first resistor R10 and a first capacitor C10. One end of the first resistor R10 is grounded through the first capacitor C10. The end where the first resistor R10 and the first capacitor C10 are electrically connected is electrically connected to the polarization voltage. The other end of the first resistor R10 is electrically connected to the positive electrode of the microphone M10. Among them, the first resistor R10 uses a 1GΩ resistor.

[0050] Specifically, a 1GΩ resistor can provide a very high input impedance, which is very useful in applications that require a high input impedance (such as the preamplifier of the microphone 1). The microphone 1 usually requires a relatively high input impedance to avoid the loading effect, that is, not to interfere with the signal source. The capacitor C10 forms a filter in combination with R10, and its function is to isolate the DC component and reduce the high-frequency noise in the circuit. The value of the capacitor needs to be reasonably selected according to the operating frequency of the microphone 1 and the requirements of the polarization voltage. Too small a capacitor may cause the high-frequency signal to not be effectively filtered, while too large a capacitor may result in a slower response time;

[0051] One end of the resistor R10 is connected to the Pol_Votage polarization voltage, and the other end is connected to the polarization voltage pin of the microphone M10. The series-connected resistor R10 is used to provide the polarization voltage for the microphone M10. The resistor R10 uses a resistor with a relatively large resistance value (a 1GΩ resistor is used in this solution) to increase the input impedance of the preamplifier circuit and ensure that the voltage value of the polarization voltage reaches the required voltage. Since the application and signal output of the polarization voltage of the microphone M10 are generally the same pin, for the microphone, the access of the resistor R10 also increases the input impedance. Since the polarization voltage generally requires a very large value (up to 200V at most), one end of the capacitor C10 is connected to the end where R10 and the Pol_Votage polarization voltage are connected and grounded, so that it forms a low-pass filter with the resistor R10 to absorb the spike voltage generated during hot plugging of the circuit, thereby protecting the microphone and the subsequent circuit.

[0052] In some specific embodiments, the DC bias unit 16 includes a second capacitor C13, a second resistor R15, a third resistor R13, and a fourth resistor R16;

[0053] One end of the second capacitor C13 is electrically connected to the positive electrode of the microphone M10, and the other end of the second capacitor C13 is electrically connected to the amplification unit 17. The other end of the second capacitor C13 is electrically connected to the amplification unit 17 through the second resistor R15. One end of the second resistor R15 is electrically connected to the power supply through the third resistor R13. The other end of the third resistor R13 is respectively connected to the second resistor R15, the amplification unit 17, and the fourth resistor R16. The other end of the fourth resistor R16 is respectively connected to the negative electrode of the microphone M10 and grounded.

[0054] Specifically, the DC bias unit 16 is composed of a capacitor C13, a resistor R13, a resistor R15, and a resistor R16. One end of the capacitor C13 is connected to the signal output pin of the microphone M10, and the other end is connected to the gate of the field effect transistor Q11 of the subsequent amplification unit 17. Since the precision field effect transistor cannot withstand the polarization voltage as high as 200V required by the microphone, the capacitor C10 is set to remove the DC component of the polarization voltage of the microphone M10. Since this solution is designed to be used in a single power supply environment, there is only a positive voltage and no negative voltage. Therefore, one end of the resistor R13 is connected to the VCC, and one end is connected to the resistor R16. The other end of the resistor R16 is grounded. The resistor R13 and the resistor R16 form a series voltage dividing circuit. After series voltage division, it is connected to the gate of the field effect transistor Q11 through the resistor R15 to provide a bias voltage for the field effect transistor Q11, so that the voltage amplitude of the output signal is within the working range of the field effect transistor Q11. In order to increase the input impedance of the entire amplification circuit to the microphone, the resistors R13, R15, and R16 are all designed to use resistors with larger resistance values. Among them, the resistor R15 still uses a 1GΩ resistor. In order not to affect the voltage value of the series voltage division of the resistor R13 and the resistor R16, the resistance values of the resistor R13 and the resistor R16 are appropriately reduced, and both use 10MΩ resistors.

[0055] In some specific embodiments, the amplification unit 17 includes a field effect transistor Q11, a first triode, a second triode Q14, a third capacitor C14, a fourth capacitor C12, a fifth resistor R17, a sixth resistor R11, and a seventh resistor R14;

[0056] The gate of the field effect transistor Q11 is electrically connected to the DC bias unit 16. One end of the third capacitor C14 is electrically connected to the DC bias unit 16. The other end of the third capacitor C14 is electrically connected to the source of the field effect transistor Q11 and the fifth resistor R17. The other end of the fifth resistor R17 is grounded. The other end of the third capacitor C14 is electrically connected to the base of the second triode Q14. The collector of the second triode Q14 is grounded. The emitter of the second triode Q14 is electrically connected to the signal processing circuit 18. The drain of the field effect transistor Q11 is electrically connected to the emitter of the first diode Q10. The collector of the first diode Q10 is electrically connected to the power supply. The base of the first diode Q10 is electrically connected to the power supply through the sixth resistor R11. The seventh resistor R14 and the fourth capacitor C12 are in parallel, and both ends are electrically connected to the sixth resistor R11 and the signal processing circuit 18 respectively.

[0057] Specifically, the amplification unit consists of the capacitor C12, the capacitor C14, the resistor R11, the resistor R14, the resistor R17, the triode Q10, the triode Q14 and the field effect transistor Q11. The gate of the field effect transistor Q11 serves as the input end of the amplification unit and is connected to the capacitor C13 of the DC bias unit. The source of the field effect transistor Q11 is connected to the resistor R17. The other end connected to the resistor R17 is grounded. The base of the triode Q14 is connected to the source of the field effect transistor Q11. The collector of the triode Q14 is grounded. The emitter of the triode Q14 serves as the output end of the amplifier. One end of C14 is connected to the source of the field effect transistor Q11, and one end is connected to the resistor R15 of the DC bias unit. The emitter of the triode Q10 is connected to the drain of the field effect transistor Q11. The collector of the triode Q10 is connected to the VCC. The base of the triode Q10 is connected to the capacitor C12, the resistor R11 and the resistor R14. The other end of the capacitor C12 is connected to the output end of the amplifier. The other end of the resistor R11 is connected to the VCC. The other end of the resistor R14 is connected to the output end of the amplifier;

[0058] The resistor R17 and the triode Q14 form a constant current circuit as the constant current load of the source output of the field effect transistor Q11. The resistor R17 can be regarded as its load impedance. In this scheme, a 100 kΩ resistor is used. The signal amplitude output from the source of the field effect transistor Q11 is related to its load. The larger the resistance value of the load, the closer its amplitude is to the input signal. However, at the same time, because the size of the noise is positively correlated with the resistance value of the resistor, the introduced noise is also larger. Since the equivalent resistance of the constant current load is 1 GΩ, the output signal is very close to the input signal, and the transmission loss can be ignored, effectively reducing the output impedance of the preamplifier;

[0059] The capacitor C12, resistor R11, resistor R147, triode Q10 and field effect transistor Q11 form a cascaded bootstrap circuit. This design can reduce the parasitic capacitance of the field effect transistor Q11 and improve the frequency response of the circuit in the high-frequency band.

[0060] The capacitor C14 is a feedback capacitor, which can feedback the signal output from the source electrode of the field effect transistor Q11 to the DC bias unit, reduce the influence of the equivalent parallel capacitance of the resistor used in the DC bias unit, and also improve the frequency response of the circuit in the high-frequency band.

[0061] In some specific embodiments, a coupling cavity system of a calibrator is also proposed. Referring to the attached Figure 3 , it includes a microphone 1, a fixing device, a connector 13 and a circuit board 2 of the circuit as described in the above embodiments;

[0062] The microphone 1, the connector 13 and the circuit board 2 are all placed on the fixing device;

[0063] The device to be detected can be inserted into the fixing device for fixation to calibrate the device to be detected;

[0064] The microphone 1 is electrically connected through the circuit board 2, the connector 13 and an external signal processing circuit 18.

[0065] Specifically, the device that needs to perform sound detection from the outside is inserted into the fixing device, so as to facilitate obtaining the corresponding sound through the microphone 1, and the signal is processed by the circuit and transmitted to the external signal processing circuit 18 through the connector 13.

[0066] In some specific embodiments, the fixing device includes an outer wall 5, an upper cover 4 and a lower cover 6;

[0067] One end of the connector 13 is fixed inside the outer wall 5 through a cable 14. The upper end of the outer wall 5 is connected to the upper cover 4, the lower end of the outer wall 5 is connected to the lower cover 6, and the microphone 1 is placed inside the outer wall 5.

[0068] Specifically, it is convenient to open the outer wall 5 through the upper cover 4 and the lower cover 6. The upper cover 4, the outer wall 5 and the lower cover 6 form the outer shell of the entire coupling cavity.

[0069] In some specific embodiments, a sound insulation fixing member 11 is provided inside the outer wall 5. An installation seat 9 is provided at the lower end of the sound insulation fixing member 11. A cavity is formed inside the sound insulation fixing member 11 to place the device to be detected, and the microphone 1 is detachably placed at the bottom end of the cavity.

[0070] Specifically, it is convenient to insert the device to be detected into the cavity and align it with the microphone 1. The installation seat 9 of the microphone 1 is made of metal material.

[0071] In some specific embodiments, a sealing rubber pad 7 is provided in the cavity and abuts against the outer side of the microphone 1, and a sealing rubber ring 8 for placing the device to be detected is provided on the inner wall of the cavity.

[0072] Specifically, the microphone 1 is fixed more tightly and stably. The sealing rubber pad 7 is put on the microphone 1 to ensure that the internal cavity does not leak air from the microphone 1 end. Inserting the device to be detected into the sealing rubber ring 8 is more stable. The installation of the sealing rubber ring 8 is used to ensure that the internal cavity does not leak air from the cavity of the calibrated instrument end.

[0073] In some specific embodiments, a plastic spacer 10 is provided on the lower side of the mounting base 9. The circuit board 2 is arranged on the lower side of the plastic spacer 10. The positive electrode of the microphone 1 is electrically connected to the circuit board 2 through the thimble 3, and the negative electrode of the microphone 1 is electrically connected to the circuit board 2 through the mounting base 9.

[0074] Specifically, it is convenient to electrically connect the microphone 1 and the circuit board 2. The negative electrode of the microphone 1, that is, the outer shell, is connected to the mounting base 9 of the microphone 1. The negative electrode of the circuit board 2 is connected to the mounting base 9 of the microphone 1 through the fixing screw. The plastic spacer 10 is used as an isolation between the two to ensure that the circuit board 2 can work normally in a humid environment. The circuit board 2 is connected to the connector 13 through the cable 14.

[0075] In some specific embodiments, a speaker 12 is embedded in the sound insulation fixing member 11.

[0076] Specifically, the sound insulation fixing member 11 has an opening on the side. The mounting base 9 of the microphone 1 is installed in the sound insulation fixing member 11. Installing the speaker 12 facilitates calibrating the microphone 1 through the speaker 12 and is connected to the connector 13 through the cable 14.

[0077] In some specific embodiments, the external dimensions of the entire calibrator coupling cavity are 39mm×39mm×47.5mm, and it is designed as an easy-to-plug-and-unplug structure, which is convenient for encapsulation and replacement.

[0078] As described above, the above is only the specific implementation manner of the embodiments of the present invention, but the protection scope of the embodiments of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the embodiments of the present invention should be covered by the protection scope of the embodiments of the present invention. Therefore, the protection scope of the embodiments of the present invention should be subject to the protection scope of the claims.

Claims

1. A preamplifier circuit, characterized in that: It includes a polarization voltage unit, a DC bias unit and an amplification unit; The polarization voltage unit, the DC bias unit and the amplification unit are electrically connected to each other; The polarization voltage unit is electrically connected to the polarization voltage and is used to absorb the peak voltage generated by the circuit during hot plugging; The DC bias unit is electrically connected to the microphone and is used to obtain a sound signal; The amplifying unit is electrically connected to the power supply and the signal processing circuit, and is used to transmit the processed amplified sound signal to the signal processing circuit.

2. The preamplifier circuit according to claim 1, characterized in that: The polarization voltage unit includes a first resistor and a first capacitor, one end of the first resistor is grounded through the first capacitor, one end of the first resistor and the first capacitor electrically connected is electrically connected to the polarization voltage, and the other end of the first resistor is electrically connected to the positive pole of the microphone, wherein the first resistor uses a 1GΩ specification resistor.

3. The preamplifier circuit according to claim 1, characterized in that: The DC bias unit includes a second capacitor, a second resistor, a third resistor, and a fourth resistor; One end of the second capacitor is electrically connected to the positive electrode of the microphone, the other end of the second capacitor is electrically connected to the amplification unit, the other end of the second capacitor is electrically connected to the amplification unit through the second resistor, one end of the second resistor is electrically connected to the power supply through the third resistor, the other end of the third resistor is electrically connected to the second resistor, the amplification unit, and the fourth resistor respectively, and the other end of the fourth resistor is electrically connected to the negative electrode of the microphone and the ground respectively.

4. The preamplifier circuit according to claim 1, characterized in that: The amplifying unit includes a field effect transistor, a first triode, a second triode, a third capacitor, a fourth capacitor, a fifth resistor, a sixth resistor, and a seventh resistor; The gate of the field effect tube is electrically connected to the DC bias unit, a section of the third capacitor is electrically connected to the DC bias unit, the other end of the third capacitor is electrically connected to the source of the field effect tube and the fifth resistor, the other end of the fifth resistor is grounded, the other end of the third capacitor is electrically connected to the base of the second triode, the collector of the second triode is grounded, the emitter of the second triode is electrically connected to the signal processing circuit, the drain of the field effect tube is electrically connected to the emitter of the first diode, the collector of the first diode is electrically connected to the power supply, the base of the first diode is electrically connected to the power supply through the sixth resistor, the seventh resistor and the fourth capacitor are connected in parallel, and the two ends are electrically connected to the sixth resistor and the signal processing circuit respectively.

5. A coupling cavity system of a calibrator, comprising a microphone, a fixing device, a connector and a circuit board of the circuit according to any one of claims 1 to 4; The microphone, connector and circuit board are all placed on the fixing device; The device to be tested can be inserted into the fixture and fixed therein so as to calibrate the device to be tested; The microphone is electrically connected to an external signal processing circuit via a circuit board, a connector.

6. The coupling cavity system of the calibrator according to claim 5, characterized in that: The fixing device comprises an outer wall, an upper cover and a lower cover; One end of the connector is fixed to the inner side of the outer wall through a cable, the upper end of the outer wall is connected to the upper cover, the lower end of the outer wall is connected to the lower cover, and the microphone is placed inside the outer wall.

7. The coupling cavity system of the calibrator according to claim 6, characterized in that: A soundproofing fixture is provided on the inner side of the outer wall, a mounting seat is provided at the lower end of the soundproofing fixture, a cavity is formed inside the soundproofing fixture to place the equipment to be detected, and the microphone is detachably placed at the bottom end of the cavity.

8. The coupling cavity system of the calibrator according to claim 7, characterized in that: A sealing rubber pad abutting against the outer side of the microphone is arranged in the cavity, and a sealing rubber ring for placing the device to be detected is arranged on the inner wall of the cavity.

9. The coupling cavity system of the calibrator according to claim 7, characterized in that: A plastic spacer is provided on the lower side of the mounting seat, the circuit board is provided on the lower side of the plastic spacer, the positive electrode of the microphone is electrically connected to the circuit board through a pin, and the negative electrode of the microphone is electrically connected to the circuit board through the mounting seat.

10. The coupling cavity system of the calibrator according to claim 7, characterized in that: A loudspeaker is embedded in the sound insulation fixing piece.

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