Microphone circuit for eliminating near speaking effect and loud sound distortion

Abstract

The utility model provides a microphone circuit for eliminating near speaking effect and loud sound distortion, comprising a condenser microphone which is coupled with a DC bias power supply used for providing bias voltage, the anode output and the cathode output of the condenser microphone are respectively coupled with a load resistor R2, and audio signal voltage is taken out from two ends of the load resistor R2; the drain electrode of the low-resistance field effect transistor T1 is coupled with the positive electrode output of the microphone through a resistor R1, and the source electrode of the low-resistance field effect transistor T1 is coupled with the negative electrode output of the microphone; the input end of the overload shunt circuit is coupled with the positive electrode output of the microphone and the negative electrode output of the microphone, the output end of the overload shunt circuit is coupled with the grid electrode of the low-resistance field effect transistor T1, and the overload shunt circuit is used for controlling the on-off of the low-resistance field effect transistor T1 based on the output voltage of the microphone; when the output voltage of the microphone exceeds a preset threshold value due to the rising of a near speaking effect or strong noise, the overload shunt circuit outputs voltage / current to open the low-resistance field effect transistor T1, and the loop impedance of the microphone output circuit is smaller than the internal resistance of the direct current bias power supply, so that the bias voltage drops, the gain of the microphone drops, and the distortion is reduced.

Description

Technical Field

[0001] The utility model relates to the technical field of audio circuits, in particular to a microphone circuit for eliminating proximity effect and loud noise distortion. Background Art

[0002] The proximity effect (also known as the near zone effect or near-field effect) is a phenomenon in which a microphone's low frequencies are boosted due to close-range sound pickup. When a microphone is used too close, the proximity effect can cause distortion in large signals. Current approaches typically involve acoustic adjustments such as adding sound-absorbing foam or filters in front of the microphone's diaphragm to reduce the proximity effect. However, this approach can also lead to new problems such as reduced microphone sensitivity or poor frequency response, resulting in poor sound quality, and does not fundamentally address the issue. Furthermore, excessive gain can also cause distortion when the microphone receives louder sounds. Summary of the Invention

[0003] Based on the above background, the present invention provides a microphone circuit that eliminates proximity effect and loudness distortion, and specifically adopts the following technical solutions:

[0004] A microphone circuit for eliminating proximity effect and loudspeaker distortion, comprising:

[0005] A condenser microphone is coupled to a DC bias power supply for providing a bias voltage, wherein the positive output and the negative output are respectively coupled to a load resistor R2, and the audio signal voltage is taken out across the load resistor R2;

[0006] A low-resistance field-effect transistor T1, whose drain is coupled to the positive output of the microphone via a resistor R1, and whose source is coupled to the negative output of the microphone;

[0007] an overload shunt circuit, having an input end coupled to the positive output of the microphone and the negative output of the microphone, and an output end coupled to the gate of the low-resistance field-effect transistor T1, for controlling the switching of the low-resistance field-effect transistor T1 based on the output voltage of the microphone;

[0008] When the microphone is operating normally, the low-resistance field-effect transistor T1 is turned off, and the impedance characteristic of the microphone output circuit is close to the internal resistance of the DC bias power supply at a preset frequency;

[0009] When the output voltage of the microphone rises above a preset threshold due to proximity effect or strong noise, the overload shunt circuit outputs voltage / current to turn on the low-resistance field-effect transistor T1. The loop impedance of the microphone output circuit is less than the internal resistance of the DC bias power supply, causing the bias voltage to drop, thereby reducing the gain of the microphone and reducing distortion.

[0010] Furthermore, the overload shunt circuit includes a capacitor C1 and a resistor R3 connected in series, wherein one end of the capacitor C1 is coupled to the positive output of the microphone, and the other end is coupled to the gate of the low-resistance field-effect transistor T1 and one end of the resistor R3, and the other end of the resistor R3 is coupled to the negative output of the microphone.

[0011] Furthermore, the output impedance of the condenser microphone is 800Ω to 3000Ω, the output voltage is 1-20mV@1KHz@1Pa, and the signal sensitivity is -30dB@1KHz@1Pa to -6030dB@1KHz@1Pa.

[0012] Furthermore, the DC bias power supply is provided by a built-in power supply of a computer, tablet or mobile phone, and the bias voltage is 1.8V@1mA.

[0013] Furthermore, the low-resistance field-effect transistor T1 is an N-channel MOSFET with a switching speed of nS level.

[0014] Furthermore, the microphone circuit further includes:

[0015] The filter capacitor C2 has one end coupled to the positive output of the microphone and the other end coupled to the negative output of the microphone for filtering out high-frequency noise.

[0016] Furthermore, the microphone circuit further includes an electrostatic protection diode D1 , which is coupled to both ends of the load resistor R2 .

[0017] The beneficial effects of the utility model are as follows:

[0018] This microphone circuit eliminates proximity effect and loudspeaker distortion. At a preset frequency, the circuit's impedance is approximately equal to the internal resistance of the DC bias power supply. When the microphone input signal is overloaded, the low-resistance field-effect transistor conducts, reducing the loop impedance to less than the internal resistance of the DC bias power supply. This leads to circuit mismatch and a drop in bias voltage. Consequently, the microphone output circuit's gain decreases due to the drop in bias voltage, reducing output amplitude and effectively suppressing distortion. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 FIG. 1 is a circuit diagram of an embodiment of a microphone circuit of the present invention. DETAILED DESCRIPTION

[0020] The following describes embodiments of the present invention in more detail with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0021] In the following embodiments, a single resistor in the circuit diagram can be replaced by multiple resistors in series or parallel in the actual circuit, but the present invention is not limited thereto. A high-voltage capacitor can also be replaced by multiple high-voltage capacitors in series or parallel.

[0022] See attached Figure 1 The present invention provides a microphone circuit for eliminating proximity effect and loudspeaker distortion, comprising:

[0023] A condenser microphone MIC is coupled to a DC bias power supply for providing a bias voltage, wherein the positive output and the negative output are respectively coupled to a load resistor R2, and the audio signal voltage is taken out across the load resistor R2;

[0024] A low-resistance field-effect transistor T1, whose drain is coupled to the positive output of the microphone via a resistor R1, and whose source is coupled to the negative output of the microphone;

[0025] The overload shunt circuit has an input end coupled to the positive output and the negative output of the microphone, and an output end coupled to the gate of the low-resistance field-effect transistor T1, for controlling the switching of the low-resistance field-effect transistor T1 based on the output voltage of the microphone.

[0026] As a preferred embodiment, in this embodiment, the overload shunt circuit includes a capacitor C1 and a resistor R3 connected in series, wherein one end of the capacitor C1 is coupled to the positive output of the microphone, and the other end is coupled to the gate of the low-resistance field-effect transistor T1 and one end of the resistor R3, and the other end of the resistor R3 is coupled to the negative output of the microphone.

[0027] As a preferred implementation scheme, in this embodiment, the output impedance of the condenser microphone is 800Ω to 3000Ω, the output voltage is 1-20mV@1KHz@1Pa, and the signal sensitivity is -30dB@1KHz@1Pa to -6030dB@1KHz@1Pa.

[0028] The DC bias power supply is provided by a built-in power supply of a computer, tablet or mobile phone, and the bias voltage is 1.8V@1mA.

[0029] The low-resistance field-effect transistor T1 is an N-channel MOSFET with a switching speed of nS level.

[0030] As a preferred embodiment, the microphone circuit in this embodiment further includes a filter capacitor C2, one end of which is coupled to the microphone's positive output and the other end to the microphone's negative output. C2 is a nF decoupling capacitor with an impedance of approximately 8kΩ at the upper audio frequency limit of 20kHz. It acts as a high-pass noise filter for audio, filtering out high-frequency hissing noise.

[0031] In this embodiment, the microphone circuit further includes an electrostatic protection diode D1 coupled to both ends of the load resistor R2.

[0032] When the microphone is operating normally, the low-resistance field-effect transistor T1 is turned off, and the impedance characteristic of the microphone output circuit is close to the internal resistance of the DC bias power supply at a preset frequency;

[0033] When the output voltage of the microphone rises above a preset threshold due to proximity effect or strong noise, the overload shunt circuit outputs voltage / current to turn on the low-resistance field-effect transistor T1. The loop impedance of the microphone output circuit is less than the internal resistance of the DC bias power supply, causing the bias voltage to drop, thereby reducing the gain of the microphone and reducing distortion.

[0034] The following combination Figure 1 The working principle of the microphone circuit for eliminating proximity effect and loudspeaker distortion shown in this embodiment is further described in detail.

[0035] Typically, the bias voltage provided by a computer / tablet / mobile phone to the microphone MIC is typically 1.8V, 1mA, and the internal resistance of the power supply is equivalent to 1800Ω.

[0036] The microphone MIC is a condenser microphone with an output impedance between 800Ω and 3000Ω, with a typical value of 2000Ω. The typical signal sensitivity is -30dB@1kHz@1Pa to -6030dB@1kHz@1Pa, that is, the output voltage is between 1-20mV@1kHz@1Pa and is superimposed on the microphone bias DC voltage, which is 1.8V@1mA.

[0037] The low-resistance field-effect transistor T1 is an N-channel MOSFET with a typical DS value of 1.6Ω@0.36A, a switching speed of nS level, a junction capacitance of pF level, and an Igs current of uA level.

[0038] Resistor R1 is preferably 5.1 kΩ. Together with the DS channel resistance of low-resistance field-effect transistor T1, it forms a variable resistor with a resistance range from 5.1 kΩ to several tens of megaohms. This resistance is controlled by the overload shunt circuit composed of capacitor C1 and resistor R3. The midpoint current of the overload shunt circuit varies with the output signal voltage of the parallel-connected microphone MIC. During normal MIC operation, the maximum output peak voltage is approximately 250 mV. During applause, the peak voltage can reach 350 mV, and during proximity effect, the peak voltage can reach 500 mV.

[0039] When the microphone MIC is operating normally, the GS voltage of low-impedance FET T1 is in the pV range, the current is zero, and it is effectively grounded. Low-impedance FET T1 is in the cutoff state, and its DS open-circuit resistance is over tens of MΩ, unaffecting the MIC's output impedance. At this point, the impedance of the entire circuit is MIC / / R2, which is approximately 1.81 kΩ, roughly equal to the power supply impedance. This impedance matches the DC bias voltage, and the output voltage remains unchanged.

[0040] When the proximity effect occurs (or when receiving a sudden, strong noise), the output voltage of microphone MIC rises above 300mV. The response time of the overload shunt circuit formed by capacitor C1 and resistor R3 is approximately 5mS. For a 1kHz, 300mV disturbance audio voltage, the signal voltage generated at the G terminal of low-impedance FET T1 is (XC1 / XC1+R3)*(300mV+1800mV), which is approximately 63.5mV. This voltage generates a current of approximately 12.5uA in resistor R3, which flows into the gate of low-impedance FET T1, ending the cutoff state of DS and entering the conduction state. Its on-resistance is proportional to the magnitude of the overload audio voltage signal, ranging from several Ω to tens of Ω. Its switching time is related to the switching time parameters of low-impedance FET T1. The low-impedance FET T1 selected here is of the nanosecond class. When low-impedance FET T1 turns on due to an overloaded audio signal, the output impedance of the microphone MIC changes to (T1's on-resistance is in Ω): MIC1 / / R1 + T1 / / R2, which is approximately 1.34 kΩ. This impedance mismatches the DC bias voltage, causing the bias voltage to drop. This drop in bias voltage reduces the microphone MIC circuit gain, offsetting the audio signal voltage overload caused by the proximity effect, effectively suppressing output distortion. When the proximity effect disappears (or the sudden noise disappears), low-impedance FET T1 returns to its cutoff state due to the reduced gate voltage / current. The output circuit impedance of the microphone MIC returns to matching the DC bias voltage impedance, returning the microphone to its ideal design.

[0041] The embodiments of the present invention are intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention shall be included in the scope of protection of the present invention.

Claims

1. A microphone circuit for eliminating proximity effect and loudspeaker distortion, characterized in that: include: A condenser microphone is coupled to a DC bias power supply for providing a bias voltage, wherein the positive output and the negative output are respectively coupled to a load resistor R2, and the audio signal voltage is taken out across the load resistor R2; A low-resistance field-effect transistor T1, whose drain is coupled to the positive output of the microphone via a resistor R1, and whose source is coupled to the negative output of the microphone; an overload shunt circuit, having an input end coupled to the positive output of the microphone and the negative output of the microphone, and an output end coupled to the gate of the low-resistance field-effect transistor T1, for controlling the switching of the low-resistance field-effect transistor T1 based on the output voltage of the microphone; When the microphone is operating normally, the low-resistance field-effect transistor T1 is turned off, and the impedance characteristic of the microphone output circuit is close to the internal resistance of the DC bias power supply at a preset frequency; When the output voltage of the microphone rises above a preset threshold due to proximity effect or strong noise, the overload shunt circuit outputs voltage / current to turn on the low-resistance field-effect transistor T1. The loop impedance of the microphone output circuit is less than the internal resistance of the DC bias power supply, causing the bias voltage to drop, thereby reducing the gain of the microphone and reducing distortion.

2. The microphone circuit for eliminating proximity effect and loudspeaker distortion according to claim 1, wherein: The overload shunt circuit includes a capacitor C1 and a resistor R3 connected in series, wherein one end of the capacitor C1 is coupled to the positive output of the microphone, the other end is coupled to the gate of the low-resistance field-effect transistor T1 and one end of the resistor R3, and the other end of the resistor R3 is coupled to the negative output of the microphone.

3. The microphone circuit for eliminating proximity effect and loudness distortion according to claim 1, wherein: The output impedance of the condenser microphone is 800Ω to 3000Ω, the output voltage is 1-20mV@1KHz@1Pa, and the signal sensitivity is -30dB@1KHz@1Pa to -6030dB@1KHz@1Pa.

4. The microphone circuit for eliminating proximity effect and loudspeaker distortion according to claim 3, wherein: The DC bias power supply is provided by a built-in power supply of a computer, tablet or mobile phone, and the bias voltage is 1.8V@1mA.

5. The microphone circuit for eliminating proximity effect and loudspeaker distortion according to claim 1, wherein: The low-resistance field effect transistor T1 is an N-channel MOSFET with a switching speed of nS level.

6. The microphone circuit for eliminating proximity effect and loudness distortion according to any one of claims 1 to 5, characterized in that: Also includes: The filter capacitor C2 has one end coupled to the positive output of the microphone and the other end coupled to the negative output of the microphone for filtering out high-frequency noise.

7. The microphone circuit for eliminating proximity effect and loudspeaker distortion according to claim 6, wherein: The device further includes an electrostatic protection diode D1 coupled to both ends of the load resistor R2 .

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