Microphone anti-interference circuit applied to wireless camera

Abstract

The invention belongs to the technical field of microphones, and discloses a microphone anti-interference circuit applied to a wireless camera. Comprising a main control SoC, a microphone interface J1 and an anti-interference front-end network arranged between the main control SoC and the microphone interface J1, and the front-end network comprises a microphone signal node, a bias power supply branch, a blocking capacitor C60, a ground bypass suppression unit and an electrostatic protection device D2; a microphone bias voltage end of the bias power supply branch is connected with a microphone signal node through a series current-limiting resistor; the blocking capacitor C60 is connected in series between a microphone signal node and a signal network MICP; the to-ground bypass suppression unit is composed of capacitors which are arranged between a microphone signal node and a system ground in parallel; and the electrostatic protection device D2 is arranged between the microphone signal node and the system ground in parallel. According to the invention, the multi-branch ground bypass network is established and the electrostatic clamp is combined, so that the discharge of a radio frequency interference component and the suppression of transient overvoltage are realized, and the pickup noise is reduced.

Description

Technical Field

[0001] This invention relates to the field of microphone technology, and more specifically, to a microphone anti-interference circuit for use in wireless cameras. Background Technology

[0002] Existing wireless surveillance cameras typically integrate WiFi and / or cellular communication modules, along with RF front-ends and antenna structures. To meet size and cost requirements, the antenna, main control processor, and audio acquisition circuitry are often compactly arranged on the same motherboard or adjacent boards. The microphone pickup link is also usually connected to the audio input of the main control SoC in a high-impedance, low-amplitude analog manner, and electret microphones need to be powered by a bias branch. The signal nodes and bias nodes are quite sensitive to external electromagnetic disturbances.

[0003] During camera operation, scenarios such as WiFi connection, uplink streaming, link reconnection, and cellular network dwell and switching can cause periodic or sudden changes in antenna RF transmission. RF energy can easily couple into microphone signal nodes, bias power supply branches, or ground reference networks through spatial radiation, near-field coupling, or wire conduction. This energy then undergoes detection and rectification in the microphone body, ESD structure, or nonlinear structure of the main control input, converting high-frequency RF components into audible envelope noise or low-frequency disturbances. Consequently, the audio pickup link may exhibit abnormal noise related to wireless communication status, such as current hum, popping sounds, or firecracker-like noises, reducing voice clarity and the reliability of remote intercom and evidence collection. This problem is particularly pronounced when the antenna and microphone are close together, the board layout is dense, and the ground return path is complex. Furthermore, the interference frequency band changes with the communication standard, making it difficult for a single device or a single frequency band suppression method to meet the needs of multiple operating conditions.

[0004] In view of this, the present invention proposes a microphone anti-interference circuit for wireless cameras to solve the above problems. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art and to achieve the above objectives, the present invention provides the following technical solution: a microphone anti-interference circuit for a wireless camera, comprising:

[0006] The main control SoC, microphone interface J1, and anti-interference front-end network set between microphone interface J1 and main control SoC;

[0007] The anti-interference front-end network includes a microphone signal node, a bias power supply branch, a DC blocking coupling unit, a ground bypass suppression unit, and an electrostatic protection unit.

[0008] The bias power supply branch includes a microphone bias voltage terminal and a series current limiting resistor. The microphone bias voltage terminal is connected to the microphone signal node through the series current limiting resistor.

[0009] The DC blocking coupling unit includes a DC blocking capacitor C60, which is connected in series between the microphone signal node and the signal network MICP.

[0010] The ground bypass suppression unit includes capacitors C61, C439, C440, and C441, which are all connected in parallel between the microphone signal node and the system ground.

[0011] The electrostatic discharge protection unit includes an electrostatic discharge protection device D2, which is connected in parallel between the microphone signal node and the system ground.

[0012] Furthermore, the pickup end of the microphone interface J1 is a first pin, which is connected to the microphone signal node; the reference end of the microphone interface J1 is a second pin, which is connected to the system ground, so that the electret microphone forms a pickup loop with the system ground as a reference and provides a reference ground return path for the microphone signal node.

[0013] Furthermore, the microphone interface J1 also includes a first shielding end and a second shielding end, both of which are connected to system ground to provide a shielded grounding path at the microphone interface and reduce the impact of external electromagnetic coupling on the pickup link.

[0014] Furthermore, the main control SoC is equipped with an analog audio input pin MICLP. The analog audio input pin MICLP is connected to the DC blocking capacitor C60 through the signal network MICP, so that the AC component of the pickup signal coupled by the DC blocking capacitor C60 is input to the analog audio input pin MICLP through the signal network MICP for sampling processing.

[0015] Furthermore, the bias power supply branch also includes a filter and voltage regulator capacitor C64, which is connected in parallel between the microphone bias voltage terminal and the system ground to decouple the microphone bias voltage terminal and suppress the coupling of bias branch ripple and transient disturbances to the microphone signal node.

[0016] Furthermore, the ground bypass suppression unit shares a microphone signal node with the electrostatic protection unit to provide a ground bypass channel for radio frequency interference components and a ground clamping channel for abnormal voltages at the microphone signal node.

[0017] The technical effects and advantages of the microphone anti-interference circuit for wireless cameras proposed in this invention are as follows:

[0018] The microphone anti-interference circuit of this invention integrates bias current limiting and filtering voltage regulation, DC blocking coupling, ground bypass suppression and electrostatic clamping protection at the microphone signal node. This allows RF interference coupled into the pickup link by WiFi or antenna to be discharged to ground at the source and the amplitude entering the main control SoC input terminal to be reduced. This suppresses abnormal noises such as current noise and popping sound caused by audible RF. At the same time, it stabilizes the microphone working bias, isolates DC components and improves anti-static and interface reliability. The structure is simple and easy to integrate at the board level, and is suitable for various working environments of wireless cameras. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the main control SoC circuit in Embodiment 1 of the present invention;

[0020] Figure 2 This is a schematic diagram of the anti-antenna interference filtering circuit in Embodiment 1 of the present invention;

[0021] Figure 3 This is a schematic diagram of the signal transmission path of the microphone anti-interference circuit in Embodiment 1 of the present invention. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] Please see Figures 1-3 This embodiment provides a microphone anti-interference circuit for a wireless camera, including:

[0025] The main control SoC, microphone interface J1, and anti-interference front-end network set between microphone interface J1 and main control SoC.

[0026] The main control SoC has an analog audio input pin MICLP, which is connected to the anti-interference front-end network through the signal network MICP, and is used to receive microphone pickup signals and perform subsequent sampling processing.

[0027] The anti-interference front-end network includes a bias power supply branch, a DC blocking coupling unit, a ground bypass suppression unit, and an electrostatic protection unit.

[0028] The microphone interface J1 is used to connect an electret microphone. The pickup end of the microphone interface J1 is a first pin, which is connected to the microphone signal node. The reference end of the microphone interface J1 is a second pin, which is connected to the system ground. The microphone interface J1 also includes a first shield end and a second shield end, both of which are connected to the system ground, thereby forming a pickup loop with the system ground as a reference and providing a shielded grounding path.

[0029] The electrostatic discharge protection unit includes an electrostatic discharge protection device D2, which is connected in parallel between the microphone signal node and the system ground. It is used to clamp electrostatic discharge and discharge energy to the system ground, thereby improving the microphone input node's tolerance to electrostatic discharge and transient overvoltage and reducing the overvoltage risk of the subsequent main control SoC input port.

[0030] The DC blocking coupling unit includes a DC blocking capacitor C60, which is connected in series between the microphone signal node and the signal network MICP. The first end of the DC blocking capacitor C60 is connected to the microphone signal node, and the second end is connected to the signal network MICP. Through the DC blocking capacitor C60, the DC component of the electret microphone side is prevented from entering the main control input side, while the AC component of the pickup signal is coupled to the signal network MICP and input to the analog audio input pin MICLP, thereby reducing the impact of the DC component on the main control SoC input.

[0031] The bias power supply branch includes a microphone bias voltage terminal VCC_2V8, a series current-limiting resistor R29, and a filter and voltage-stabilizing capacitor C64 connected in parallel to ground. The microphone bias voltage terminal VCC_2V8 is connected to the microphone signal node through the series current-limiting resistor R29, which is used to provide operating bias for the electret microphone and limit the current flowing through the electret microphone; the filter and voltage-stabilizing capacitor C64 is connected in parallel between the microphone bias voltage terminal VCC_2V8 and system ground, which is used to filter and stabilize the microphone bias voltage, thereby reducing the coupling effect of ripple and transient disturbances in the bias branch on the microphone signal node.

[0032] The ground bypass suppression unit includes capacitors C61, C440, C439, and C441 connected in parallel. These capacitors are all connected in parallel between the microphone signal node and the system ground. The multiple parallel capacitors together form an anti-antenna interference filtering circuit to establish a multi-branch ground bypass channel at the microphone signal node.

[0033] In a preferred embodiment of the present invention, capacitors C61, C440, C439, and C441 respectively correspond to radio frequency interference suppression branches in different frequency bands, so as to reduce the amplitude of radio frequency interference components entering the main control SoC input terminal along the main signal path in different frequency bands; the capacitance value of capacitor C441 is preferably 0.75pF, the capacitance value of capacitor C439 is preferably 10pF, the capacitance value of capacitor C440 is preferably 33pF, and the capacitance value of capacitor C61 is preferably 8.2pF.

[0034] Different capacitance values ​​cause the microphone signal nodes to exhibit different ground bypass impedance characteristics for different frequency band radio frequency components, thereby forming a discharge channel covering multiple frequency bands; the capacitance value can be selected according to the target radio frequency band range and board-level parasitic parameters.

[0035] In a preferred embodiment of the present invention, capacitor C441 is used to suppress interference in the 5G WiFi band, capacitor C439 is used to suppress interference in the 2.4G WiFi band, capacitor C440 is used to suppress interference in the 800MHz to 900MHz band of 4G communication, and capacitor C61 is used to suppress environmental common-mode interference.

[0036] In this embodiment, the signal transmission path of the anti-interference front-end network is as follows: the electret microphone outputs a pickup signal via microphone interface J1 and converges at the microphone signal node; the microphone signal node obtains a working bias through a bias power supply branch; interference components on the microphone signal node are discharged via a ground bypass channel provided by a ground bypass suppression unit, and electrostatic discharge and transient overvoltage are clamped and discharged via electrostatic protection device D2; subsequently, the AC component of the pickup signal is coupled to the signal network MICP via DC blocking capacitor C60 and input to the analog audio input pin MICLP of the main control SoC for sampling and processing. Through the above structure and connection relationship, the bias power supply, RF bypass suppression, and electrostatic clamping are centrally located at the microphone signal node, and the AC component of the pickup signal is sent to the main control input terminal through DC blocking coupling, thereby suppressing the impact of antenna coupling interference on the pickup link during the operation of the wireless communication unit, and improving the pickup stability and audio availability of the wireless camera.

[0037] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

[0038] In conclusion, the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A microphone anti-interference circuit for use in wireless cameras, characterized in that, include: The main control SoC, microphone interface J1, and anti-interference front-end network set between microphone interface J1 and main control SoC; The anti-interference front-end network includes a microphone signal node, a bias power supply branch, a DC blocking coupling unit, a ground bypass suppression unit, and an electrostatic protection unit. The bias power supply branch includes a microphone bias voltage terminal and a series current limiting resistor. The microphone bias voltage terminal is connected to the microphone signal node through the series current limiting resistor. The DC blocking coupling unit includes a DC blocking capacitor C60, which is connected in series between the microphone signal node and the signal network MICP. The ground bypass suppression unit includes capacitors C61, C439, C440, and C441, which are all connected in parallel between the microphone signal node and the system ground. The electrostatic discharge protection unit includes an electrostatic discharge protection device D2, which is connected in parallel between the microphone signal node and the system ground.

2. The microphone anti-interference circuit for a wireless camera according to claim 1, characterized in that, The microphone interface J1 has a pickup end as a first pin, which is connected to the microphone signal node; the microphone interface J1 has a reference end as a second pin, which is connected to the system ground, so that the electret microphone forms a pickup loop with the system ground as a reference and provides a reference ground return path for the microphone signal node.

3. The microphone anti-interference circuit for a wireless camera according to claim 2, characterized in that, The microphone interface J1 also includes a first shielding end and a second shielding end, both of which are connected to system ground to provide a shielded grounding path for the microphone interface and reduce the impact of external electromagnetic coupling on the pickup link.

4. The microphone anti-interference circuit for a wireless camera according to claim 1, characterized in that, The main control SoC has an analog audio input pin MICLP. The analog audio input pin MICLP is connected to the DC blocking capacitor C60 through the signal network MICP, so that the AC component of the pickup signal coupled by the DC blocking capacitor C60 is input to the analog audio input pin MICLP through the signal network MICP for sampling processing.

5. The microphone anti-interference circuit for a wireless camera according to claim 1, characterized in that, The bias power supply branch also includes a filter and voltage regulator capacitor C64, which is connected in parallel between the microphone bias voltage terminal and the system ground to decouple the microphone bias voltage terminal and suppress the coupling of bias branch ripple and transient disturbances to the microphone signal node.

6. The microphone anti-interference circuit for a wireless camera according to claim 1, characterized in that, The ground bypass suppression unit and the electrostatic protection unit share a microphone signal node to provide a ground bypass channel for radio frequency interference components and a ground clamping channel for abnormal voltages at the microphone signal node.

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