Active noise reduction electret MIC circuit applied to far-field voice

Abstract

The utility model relates to an active noise reduction electret MIC circuit applied to far-field voice, which comprises an electret MIC module and a main control module, and further comprises a first filter of which the input end is connected to a bias power supply VCCS1 and the output end is connected to the output end of the electret MIC module through a resistor R2, and the first filter is used for filtering power supply noise in the bias power supply VCCS1; the input end of the second filter is connected with the output end of the electret MIC module, and the second filter is used for filtering low-frequency noise in an output signal of the electret MIC module; the input end of the third filter is connected to the output end of the second filter, the output end of the third filter is connected to the main control module, and the third filter is used for further filtering high-frequency noise in output signals of the electret MIC module. According to the active noise reduction electret MIC circuit of the utility model, high-frequency and low-frequency noise and DC bias power supply noise are effectively suppressed through triple filtering design, the accuracy and reliability of far-field speech recognition are significantly improved, the system cost and complexity are reduced, and the stability and reliability of the circuit are improved.

Description

TECHNICAL FIELD

[0001] The utility model relates to the technical field of voice noise reduction, especially to an active noise reduction electret MIC circuit applied to far-field voice. BACKGROUND

[0002] With the continuous development of smart home, Internet of Things and artificial intelligence technology, far-field speech recognition technology has been widely used in smart speakers, smart home, medical intercom and other fields. Far-field speech recognition technology enables users to interact with smart devices at a distance, greatly improving the intelligence level of the device and user experience. However, in the practical application of far-field speech recognition, noise interference and signal attenuation have become the main factors affecting the accuracy and reliability of speech recognition.

[0003] Electret microphones (MIC) are widely used in far-field speech acquisition devices due to their low cost, flexible connection and good durability. However, in a far-field speech environment, the signal is often subject to many noise disturbances, especially during long-distance transmission, the electret microphone (MIC) output signal is easily affected by high-frequency noise, low-frequency noise and DC bias power supply noise. These noises have a serious impact on the clarity and recognizability of the signal. In the prior art, although the register is configured to increase the ADC channel gain to improve the microphone signal amplitude, the gain is increased, which also brings the enhancement of noise, especially power supply noise and high-frequency noise, resulting in a decrease in signal-to-noise ratio, and thus affecting the accuracy of speech recognition and the stability of the system. Therefore, in a far-field speech device, how to effectively suppress these noises without increasing the complexity of the circuit, while not affecting the amplitude of the signal, maintaining the integrity and stability of the signal, is a technical problem that needs to be solved in the current far-field speech recognition system. SUMMARY

[0004] The inventors found in the process of researching the utility model that in a far-field speech intercom circuit, the sound wave attenuates during transmission, and the attenuation factor is proportional to the transmission distance, so the sound attenuation of far-field speech is more serious than that of near-field, resulting in a too small MIC output signal amplitude. In order to compensate for this amplitude attenuation, a register configuration is usually needed to increase the ADC channel gain, and the register gain of the input channel is configured to the maximum to ensure that the signal amplitude meets the algorithm processing requirements. However, after increasing the gain, the noise also increases significantly, and it is found in debugging that the noise comes from the bias power supply of the electret MIC, and these noises cover the frequency band of 0-20 kHz.

[0005] To solve the above problems, the inventors made various attempts, such as using an additional low dropout regulator (LDO) to provide a bias power supply for the electret microphone, and equipping a filter capacitor at the output end thereof; adding an RC filter circuit on the microphone channel, and finally connecting a DC blocking capacitor in series for signal filtering and DC isolation; when the noise is still large, a microphone with better anti-noise performance is replaced. However, these methods have many limitations in practical application. Although the RC filter circuit has a certain noise reduction effect under high gain conditions, a large resistance will affect impedance matching, and a large capacitor will affect the signal rising edge, change the signal waveform, and it is difficult to effectively filter out power noise and high-frequency noise while ensuring signal quality. The complex active filter circuit relies on multiple operational amplifiers, has more peripheral elements, increases the circuit cost and maintenance difficulty, and once the element fails, it may cause instability of the audio signal. In addition, although increasing the filtering algorithm can reduce the hardware cost, it occupies memory resources and increases the processing delay, and is not suitable for use in an MCU system with limited resources. Therefore, the above-mentioned various schemes are difficult to balance between cost control and reliability, and cannot effectively suppress the power noise and high-frequency noise introduced due to the gain amplification of the ADC, resulting in that the signal-to-noise ratio is difficult to reach the ideal level.

[0006] Therefore, the inventors finally provide an active noise reduction electret MIC circuit applied to far-field voice, which can effectively filter out high-frequency noise and power noise in the output signal of the electret microphone, improve the purity of the signal, and avoid the loss of signal amplitude, thereby improving the signal-to-noise ratio and stability of the voice recognition system.

[0007] The purpose of the utility model is realized through the following technical schemes, the utility model discloses a kind of active noise reduction electret MIC circuit applied to far-field voice, and the circuit includes:

[0008] First filter, input end is connected to bias power supply VCC_S1, and output end is connected to the output end of the electret MIC module through resistance R2, for filtering out power noise in the bias power supply VCC_S1;

[0009] Second filter, input end is connected with the output end of the electret MIC module, for filtering out low-frequency noise in the output signal of the electret MIC module;

[0010] Third filter, input end is connected to the output end of the second filter, and the output end of the third filter is connected to the main control module, for further filtering out high-frequency noise in the output signal of the electret MIC module.

[0011] Optionally, the first filter includes:

[0012] The triode Q1 has its collector connected to a bias power supply VCC_S1, its base connected to an external power supply VCC_S1 through a resistor R1, and its emitter connected to an output terminal of the electret MIC module through a resistor R2.

[0013] Optionally, the first filter further comprises:

[0014] a capacitor C2 having one end connected between the collector of the triode Q1 and the resistor R1 and the other end grounded;

[0015] a capacitor C3 having one end connected between the emitter of the triode Q1 and the resistor R2 and the other end grounded;

[0016] a capacitor C4 having one end connected between the emitter of the triode Q1 and the resistor R2 and the other end grounded.

[0017] Optionally, the second filter comprises:

[0018] an operational amplifier U1 having its positive terminal connected to an output terminal MIC_OUT of the electret MIC module through a capacitor C6, its negative terminal connected to an output terminal of the operational amplifier U1, and the output terminal of the operational amplifier U1 connected to the third filter;

[0019] the positive input terminal of the operational amplifier U1 is connected to a bias power supply VCC_S2, and the negative input terminal is grounded.

[0020] Optionally, the second filter further comprises:

[0021] a resistor R3 having one end connected between the positive terminal of the operational amplifier U1 and the capacitor C6 and the other end connected to the bias power supply VCC_S2;

[0022] a resistor R5 having one end connected between the positive terminal of the operational amplifier U1 and the capacitor C6 and the other end grounded;

[0023] a capacitor C1 having one end connected to the bias power supply VCC_S2 and the other end grounded;

[0024] a capacitor C5 having one end connected to the bias power supply VCC_S2 and the other end grounded.

[0025] Optionally, the third filter comprises a resistor R4, a capacitor C7, and a capacitor C8;

[0026] the resistor R4 has one end connected to an output terminal of the second filter and the other end connected to an OUTPUT port through the capacitor C7;

[0027] the capacitor C8 has one end connected between the resistor R4 and the capacitor C7 and the other end grounded.

[0028] Optionally, the OUTPUT port is connected to the ADC input channel of the main control module.

[0029] Optionally, the resistance value of the resistor R1 is set to any value in the range of 33kΩ to 100kΩ, and the capacitance value of the capacitor C2 is set to any value in the range of 10uF to 22uF.

[0030] Optionally, the first filter is placed near the electret MIC module, and the second and third filters are placed near the main control module.

[0031] Optionally, the cutoff frequency of the first filter is set below 80Hz, the cutoff frequency of the second filter is set to 80Hz, and the cutoff frequency of the third filter is set to 8kHz.

[0032] Compared with the prior art, the present invention has the following beneficial effects:

[0033] This invention relates to an active noise-canceling electret microphone circuit for far-field speech recognition. Through precise filter circuit design, it effectively filters out high-frequency noise, low-frequency noise, and DC bias power supply noise from the electret microphone output signal, avoiding the noise amplification problem caused by increasing ADC gain in traditional solutions. By setting multiple filters, particularly the first filter which filters out DC bias power supply noise, the second filter which effectively suppresses low-frequency noise, and the third filter which further optimizes signal quality, ensuring signal purity, this circuit design improves the signal-to-noise ratio without significantly affecting the signal amplitude, thereby improving the accuracy and reliability of far-field speech recognition. Furthermore, compared to existing active filtering schemes, this invention reduces the number of active components, lowering system complexity and cost.

[0034] Furthermore, this invention enhances the circuit's noise filtering capability by using a combination of transistor Q1 and multiple capacitors in the first filter, while reducing the negative impact on circuit impedance and transient response. In the second filter, the use of an operational amplifier optimizes impedance matching and noise suppression between the preceding and following stages, avoiding distortion problems caused by impedance mismatch that may occur in traditional circuits. The design of the third filter further improves the circuit's high-frequency suppression capability, enabling it to exhibit superior noise reduction performance in complex far-field speech environments. In addition, this invention reduces system cost and complexity by rationally arranging the filter circuit while ensuring noise reduction performance. Attached Figure Description

[0035] Figure 1 A schematic diagram of an active noise-canceling electret MIC circuit for far-field speech according to an embodiment of the present invention is shown.

[0036] Figure 2 This diagram illustrates an active noise-canceling electret microphone circuit for far-field speech according to an embodiment of the present invention.

[0037] Figure 3 A circuit diagram of an active noise-canceling electret microphone applied to far-field speech is shown according to another embodiment of the present invention. Detailed Implementation

[0038] To make the above-mentioned objectives, features, and advantages of this utility model more apparent and understandable, the specific embodiments of this utility model will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are only for explaining this utility model and not for limiting it. Furthermore, it should be noted that, for ease of description, only the parts related to this utility model are shown in the drawings, not all of the structure. Based on the embodiments of this utility model, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this utility model.

[0039] The terms "comprising" and "having," and any variations thereof, used in this invention, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0040] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of the present invention. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0041] Figure 1 A schematic diagram of an active noise-canceling electret microphone circuit for far-field speech according to an embodiment of the present invention is shown. Figure 1 As shown, the active noise-canceling electret MIC circuit for far-field speech includes an electret MIC module 104 and a main control module 105. The active noise-canceling electret MIC circuit for far-field speech also includes:

[0042] The first filter 101 has its input connected to the bias power supply VCC_S1 and its output connected to the output of the electret MIC module 104 via resistor R2, and is used to filter out power supply noise in the bias power supply VCC_S1.

[0043] The input end of the first filter 101 is directly connected to the bias power supply VCC S1, which provides the required power supply for the electret microphone. The output end of the first filter 101 is connected to the output end of the electret MIC module 104 through a resistor R2. The resistor R2 functions to match the output impedance of the electret MIC, so that the output signal has a suitable dynamic range. The first filter 101 is connected between the bias power supply and the microphone, and mainly functions to filter out the noise in the DC bias power supply of the MIC, and to provide a relatively clean DC bias power supply for the electret MIC module 104. In the working state of the electret microphone, the microphone is easily disturbed by power supply noise, and these noises will increase with the increase of the gain of the ADC channel, and affect the subsequent signal processing. The first filter 101 effectively filters out these unnecessary high-frequency components and DC bias power supply noise through low-pass or band-pass filtering, and ensures that the signal output is more pure.

[0044] By setting the first filter 101, the signal quality can be significantly improved, the noise in the DC bias power supply of the electret MIC is filtered out, the disturbance of these noises on the subsequent signal processing is avoided, and a stable DC bias power supply is provided for the electret MIC module 104. Through the filtering in this stage, the signal clarity is ensured, and the complexity of the subsequent processing is reduced.

[0045] The second filter 102 is connected to the output end of the electret MIC module 104, and is used to filter out low-frequency noise in the output signal of the electret MIC module 104.

[0046] The input end of the second filter 102 is connected to the output end of the electret MIC module 104, and receives the signal processed by the first filter 101. The main function of the second filter 102 is to remove low-frequency noise (such as power fluctuations or low-frequency environmental noise) in the output signal of the electret microphone. These low-frequency noises may still remain after the first filter 101 processing, affecting the clarity of the signal. The second filter 102 uses appropriate low-pass filtering to ensure that these low-frequency disturbances are removed, thereby providing a cleaner signal input for the third filter 103. By effectively removing low-frequency noise, the second filter 102 further improves the quality of the signal, reduces the interference source, and provides a pure signal for subsequent processing. This not only improves the clarity of the speech signal, but also improves the accuracy of speech recognition, especially in complex noise environments.

[0047] The third filter 103 is connected to the output end of the second filter 102, and the output end of the third filter 103 is connected to the main control module 105, which is used to further filter out high-frequency noise in the output signal of the electret MIC module 104.

[0048] The third filter 103 further filters out high-frequency noise in the signal to ensure that the signal is not disturbed when entering the main control module 105. After the processing of the first filter 101 and the second filter 102, although the signal is relatively clear, high-frequency noise (such as radio frequency interference, etc.) may still exist. Therefore, the third filter 103 adopts a more refined filtering strategy to ensure that the noise is sufficiently suppressed and that the signal entering the main control module 105 is a pure audio signal. The third filter 103 further filters out high-frequency noise to ensure that the signal quality delivered to the main control module 105 is extremely high, avoiding the influence of noise on subsequent processing (such as ADC conversion, digital signal processing). The effect of this filter significantly improves the speech recognition accuracy of the system, ensuring that the system can also stably and clearly receive voice signals in a far-field environment.

[0049] When the electret microphone outputs a signal, the signal first passes through the first filter 101 to filter out the MIC DC bias power supply noise. The bias power supply VCC_S1 provides a stable power supply for the electret microphone, while avoiding the influence of power supply noise on the signal through the first filter 101. The signal processed by the first filter 101 enters the second filter 102, which removes low-frequency noise (such as power supply noise, environmental noise, etc.) in the signal. Low-frequency noise is often not conducive to the transmission and processing of voice signals, especially in far-field voice applications, removing low-frequency noise is crucial for signal clarity. Finally, the signal passes through the third filter 103 to further remove high-frequency noise, ensuring that the signal sent to the main control module 105 has reached the best purification state. After triple filtering, the noise interference of the final signal is almost completely eliminated, which can ensure that the system can still stably and accurately perform voice recognition in a far-field environment. The circuit of the present application scheme realizes efficient noise suppression through a triple filtering structure, significantly improves signal quality, and enhances voice recognition accuracy and system robustness. Compared with the traditional scheme, it simplifies the circuit design, reduces the dependence on complex components, reduces costs and improves system stability. At the same time, the optimized signal processing improves the accuracy of voice recognition and can work stably in various noise environments, with strong adaptability and flexibility, suitable for multiple application scenarios such as smart home, smart speakers, medical intercom, etc.

[0050] According to the above-mentioned embodiments, by means of the accurate filter circuit design, the high-frequency noise, low-frequency noise and DC bias power supply noise in the electret MIC output signal can be effectively filtered out, and the noise amplification problem caused by increasing the ADC gain in the traditional scheme is avoided. By arranging multiple filters, especially the first filter 101, the MIC DC bias power supply noise can be filtered out, the second filter 102 can effectively suppress the low-frequency noise, and the third filter 103 can further optimize the signal quality and ensure the purity of the signal. The circuit design improves the signal-to-noise ratio of the signal without significantly affecting the signal amplitude, and thus improves the accuracy and reliability of the far-field speech recognition. Meanwhile, compared with the existing technical solutions, the number of active components is reduced, and the complexity and cost of the system are reduced.

[0051] Figure 2 The application relates to an active noise reduction electret MIC circuit applied to far-field speech according to an embodiment of the application. As shown in the figure, Figure 2 The first filter 101 comprises:

[0052] The collector of the triode Q1 is connected to the bias power supply VCC_S1, the base is connected to the external power supply VCC_S1 through the resistor R1, and the emitter is connected to the output end of the electret MIC module 104 through the resistor R2.

[0053] The collector of the triode Q1 is connected to the bias power supply VCC_S1, which provides the required voltage for the circuit and provides a stable working voltage for the subsequent filtering function. The base of the triode Q1 is connected to the external power supply VCC_S1 through the resistor R1, so as to control the switching state and working mode of the triode. The emitter of the triode Q1 is connected to the output end of the electret MIC module 104 through the resistor R2, so as to adjust and filter the microphone output signal. The triode Q1 serves as a core amplification element, filters the DC bias power supply of the MIC, utilizes the principle of base current control of emitter-collector current, realizes the filtering of the collector-emitter through the filtering of the base, and thus reduces the influence of noise in the DC bias power supply. It makes the DC bias power supply of the electret MIC cleaner, that is, the composition of the power supply noise coupled to the signal line becomes extremely small. The structure can suppress the high-frequency noise in the signal, and is especially suitable for filtering the bias power supply noise, so as to provide a clearer signal for the subsequent filter processing.

[0054] In some embodiments, referring to Figure 2 The first filter 101 further comprises:

[0055] The capacitor C2 has one end connected between the collector of the triode Q1 and the resistor R1 and the other end grounded.

[0056] The capacitor C2 plays a role of high-frequency noise suppression in the filtering process and functions to smooth the power signal. It can effectively filter out the noise from the bias power supply VCC_S1 and prevent the noise from being transmitted to the electret microphone output through the direct current bias, thereby avoiding its influence on the subsequent signal processing.

[0057] In some embodiments, the resistance R1 is set to any value in the range of 33kΩ-100kΩ, and the capacitance C2 is set to any value in the range of 10uF-22uF.

[0058] The resistance R1 and the capacitance C2 are thus set to ensure that the cutoff frequency of the low-pass filter is extremely low, thereby effectively filtering out the alternating current noise in the direct current bias power supply and improving the purity of the signal. Such a configuration can also effectively isolate the RC filter from the power supply path, avoid negative impact on the impedance matching of the subsequent circuit, and ensure that the filtering effect is not disturbed by the power supply noise, thereby enhancing the noise suppression capability of the overall circuit.

[0059] The capacitor C3 is connected at one end to the emitter of the transistor Q1 and the resistance R2 and grounded at the other end.

[0060] The capacitor C3 functions to filter out the interference of the power supply noise on the microphone signal and ensure that only the required audio signal is transmitted to the subsequent circuit. In combination with the capacitor C4, the filtering effect on the low-frequency noise is enhanced, and the stability of the circuit is improved.

[0061] The capacitor C4 is connected at one end to the emitter of the transistor Q1 and the resistance R2 and grounded at the other end.

[0062] The capacitor C4 works together with the capacitor C3 to further reduce the influence of the direct current bias power supply noise. The setting of the capacitors C3 and C4 also effectively improves the stability of the signal and ensures that the signal maintains its quality and purity during the entire filtering process.

[0063] The first filter 101 effectively filters the high-frequency noise, low-frequency noise and DC bias power supply noise in the output signal of the electret microphone module through the precise configuration of triode Q1 and the cooperation of capacitors and resistors. Triode Q1, as the core amplification element, not only isolates the impedance influence of high-value RC on the latter circuit, but also effectively removes unnecessary noise components. Capacitors C2, C3 and C4 respectively process high-frequency noise and low-frequency noise to ensure the purity and stability of the signal transmission process. Through multi-layer filtering, the first filter 101 greatly improves the signal quality, so that the signal can maintain high purity during subsequent processing, enhancing the accuracy of the speech recognition system in a far-field speech environment. Compared with traditional filter design, this filter not only improves the noise suppression effect, but also reduces the complexity of the circuit, avoids the use of too many active components, and reduces the overall circuit cost and maintenance difficulty.

[0064] In some embodiments, with reference to Figure 2 , the second filter 102 includes:

[0065] The operational amplifier U1 has its positive terminal connected to the output end MIC_OUT of the electret MIC module 104 through the capacitor C6, and its negative terminal connected to the output end of the operational amplifier U1, and the output end of the operational amplifier U1 connected to the third filter 103.

[0066] The main function of the operational amplifier U1 is to amplify and filter the output signal of the electret microphone. Since the output signal of the electret MIC module 104 contains low-frequency noise, the capacitor C6 and the resistor R5 together form a high-pass filter with very low cutoff frequency, which effectively filters out low-frequency interference signals and also serves as a direct current blocking function to ensure that the alternating component of the input signal can be transmitted normally. The use of the operational amplifier U1 improves the performance of the second filter 102, enabling it to more accurately filter out low-frequency noise and stabilize the signal output.

[0067] The positive input end of the operational amplifier U1 is connected to the bias power supply VCC_S2, and the negative input end is grounded.

[0068] The positive input end of the operational amplifier is connected to the bias power supply VCC_S2, which provides a stable reference voltage for the operational amplifier. The voltage at the positive input end is stabilized at the level of VCC_S2, allowing the operational amplifier to work normally and adapt to other circuits (such as the MIC module). Grounding the negative input end ensures the stability of the input signal relative to ground, avoiding interference from other signal sources or noise, thereby improving the common-mode rejection capability of the operational amplifier.

[0069] In some embodiments, with reference to Figure 2 , the second filter 102 further includes:

[0070] Resistor R3, one end connected between the positive terminal of operational amplifier U1 and capacitor C6, the other end connected to the bias power supply VCC_S2.

[0071] Resistor R5, one end connected between the positive terminal of operational amplifier U1 and capacitor C6, the other end grounded.

[0072] The main role of resistor R3 is to provide a suitable static operating point for operational amplifier U1, ensuring its stable operation in the best bias state. Capacitor C6 is responsible for isolating the DC signal, preventing the DC component from entering the operational amplifier input, thereby protecting the normal operation of the circuit. Resistor R5 and capacitor C6 together form a low cutoff frequency high-pass filter. With the impedance isolation characteristics of the front and rear stages of operational amplifier U1, the resistance of R5 can be designed to be larger, thereby achieving a lower cutoff frequency (lower than 80Hz). This design can effectively filter out low-frequency noise without affecting the human voice frequency signal (80Hz~8kHz), improving the purity and overall signal-to-noise ratio of the audio signal.

[0073] Capacitor C1, one end connected to the bias power supply VCC_S2, the other end grounded.

[0074] Capacitor C5, one end connected to the bias power supply VCC_S2, the other end grounded.

[0075] Capacitors C1 and C5 are connected to the bias power supply VCC_S2 and grounded. Capacitors C1 and C5 play a decoupling role, filtering out high-frequency noise in the bias power supply VCC_S2. They are connected in parallel to prevent the high-frequency noise of the power supply from affecting the filtering effect, further purifying the signal of the bias power supply, and ensuring the power quality of the entire circuit. The use of capacitors C1 and C5 can effectively reduce the interference of power supply noise, reduce the influence of power supply fluctuations on the operation of the entire circuit, ensure the stability of the signal and the effectiveness of the filtering effect, and optimize the power management and noise suppression of the circuit.

[0076] In some embodiments, the capacitance of capacitor C6 is set in the range of 560nF~680nF, which can effectively filter out low-frequency noise while ensuring the transmission stability of the signal in the required frequency band. The capacitance of capacitor C1 is set to 1uF, and the capacitance of capacitor C5 is set to 0.1uF, further optimizing the filtering effect and improving the decoupling and high-frequency noise suppression capability of the power supply. The resistance of resistor R5 is set to 10k, which helps to stabilize the operating point of the operational amplifier while ensuring the effectiveness of the filtering circuit. The power supply of VCC_S2 is set in the range of 3V~5V, which can provide appropriate operating voltage for the operational amplifier, ensure the stable operation of the circuit, control the power consumption, and adapt to the needs of different working environments.

[0077] In some embodiments, reference Figure 2The third filter 103 includes a resistor R4, a capacitor C7, and a capacitor C8.

[0078] One end of the resistor R4 is connected to the output end of the second filter 102, and the other end is connected to the OUTPUT port through the capacitor C7.

[0079] The OUTPUT port is connected to the ADC input channel of the main control module 105.

[0080] The resistor R4 and the capacitor C7 form an RC filter network, which optimizes the signal path and suppresses unwanted frequency components. By adjusting the resistance value, the filtering effect can be precisely controlled to ensure smooth signal transmission. The resistor R4 prevents excessive amplification or attenuation of the signal, ensuring that the output signal is within the appropriate amplitude range, avoiding loss or interference affecting the ADC input channel of the main control module 105. The capacitor C7, together with the resistor R4, forms a low-pass filter that filters the passing signal and removes high-frequency noise. It will only allow signals of a specific frequency band to pass according to the designed cutoff frequency, suppressing high-frequency interference and noise.

[0081] One end of the capacitor C8 is connected between the resistor R4 and the capacitor C7, and the other end is grounded.

[0082] The main function of the capacitor C8 is to filter out the DC component in the system, preventing it from affecting subsequent signal processing and ensuring that the signal passing through the ADC is a pure AC signal, avoiding potential errors caused by DC bias power supply noise.

[0083] The resistor R4, together with the capacitors C7 and C8, ensures that the signal is filtered and optimized during transmission, removing high-frequency noise, low-frequency noise, and DC bias power supply noise. The third filter 103 effectively removes noise, especially high-frequency components, improving signal quality and providing clearer voice signals for the ADC input of the main control module 105.

[0084] In some embodiments, the resistance value of the resistor R4 is set within the range of 66Ω to 86Ω, which helps optimize the frequency response of the filter and ensure effective signal transmission while avoiding signal distortion. The capacitance of the capacitor C8 is set to 220nF, and the capacitance of the capacitor C7 is set to 1uF, which can effectively suppress high-frequency noise, enhance the purity of the signal, and ensure stable filtering effect, preventing low-frequency and high-frequency noise from interfering with the system, thereby improving the noise suppression capability and signal quality of the overall circuit.

[0085] In some embodiments, the first filter 101 is placed near the electret MIC module 104, and the second filter 102 and the third filter 103 are placed near the main control module 105.

[0086] The first filter 101 is placed close to the end of the electret MIC module 104, which can filter out noise at the source of the signal, avoiding the noise and interference being further amplified in the signal transmission process. This helps to reduce the loss of the signal and the decline of the signal-to-noise ratio, thereby improving the efficiency of the subsequent filters. The second filter 102 and the third filter 103 are placed close to the end of the main control module 105, which helps to further refine the filtering and ensure that the main control module 105 receives as clear a signal as possible.

[0087] In some embodiments, the cutoff frequency of the first filter 101 is set below 80 Hz, the cutoff frequency of the second filter 102 is set to 80 Hz, and the cutoff frequency of the third filter 103 is set to 8 kHz.

[0088] The cutoff frequency of the first filter 101 is set below 80 Hz, which is mainly used to filter out low-frequency noise (such as 50 Hz power supply noise, vibration noise, etc.) from the bias power supply and the environment. These noises generally interfere with the speech signal and affect the accuracy of speech recognition. By setting the cutoff frequency below 80 Hz, the influence of low-frequency noise on the speech signal can be effectively avoided, thereby improving the purity of the signal. The cutoff frequency of the second filter 102 is set to 80 Hz, which can further filter out small low-frequency noise. This setting ensures that the signal processed by the first filter 101 can be further optimized to remove possible noise components around 80 Hz, ensuring that the signal is not disturbed by low-frequency noise in the next processing stage. Considering that the MIC speech is to capture human voice, and the range of human voice is usually between 80 Hz and 8 kHz, the cutoff frequency of the third filter 103 is set to 8 kHz, which can effectively remove high-frequency noise (such as radio frequency interference, switching noise, etc.). These noises can affect the clarity of the speech signal, especially in far-field speech applications, where the signal is usually amplified, and the noise can also be amplified. By setting the cutoff frequency to 8 kHz, the anti-interference ability of the system can be significantly improved, and the influence of noise on the speech signal can be reduced.

[0089] The application of the active noise reduction electret MIC circuit for far-field speech of the utility model will be further explained and described below with a specific implementation process.

[0090] Figure 3 The application of the active noise reduction electret MIC circuit for far-field speech of the utility model will be further explained and described below with a specific implementation process. Figure 3As shown, the VCC_S1 bias voltage uses a 3.3V voltage source to provide a stable operating voltage for the electret MIC. In the design of the first filter 101, R1 is set to 100kΩ, C2 is configured to 10uF, and a high-efficiency low-pass filter is formed through NPN transistor Q1, and the filtering effect is further optimized by combining capacitors C3 and C4 (both 1uF), to ensure that the DC bias power supply noise of the MIC is removed. Resistor R2 is set to 2.2kΩ, which is used to stabilize the output of the bias power supply. The MIC uses a conventional electret MIC module 104, which has an output resistance of 2.2kΩ. The second filter 102 uses an operational amplifier U1 with model number LMV321, C6 is configured to 680nF, and resistors R3 and R5 are both set to 10kΩ, forming a high-pass filter circuit for filtering out extremely low-frequency noise in the environment or in the circuit. VCC_S2 uses a 5V voltage source to support the operation of the operational amplifier. Capacitors C1 (1uF) and C5 (0uF) are used for filtering and stabilizing the voltage, respectively. The design of the third filter 103 uses resistor R4 (86Ω) and capacitors C7 (1uF) and C8 (220nF) in combination to ensure effective removal of high-frequency noise in the signal, and to transmit clear signals to the ADC input channel through the OUTPUT port. The design of the entire circuit reasonably configures various resistors and capacitors, ensuring the purity of the signal and improving the noise suppression effect and signal quality of the system.

[0091] According to the above embodiment, the combination of the transistor Q1 and the plurality of capacitor elements in the first filter further enhances the ability of the circuit to filter out DC bias power supply noise. In the second filter, the use of the operational amplifier optimizes impedance matching and noise suppression effect, avoiding signal distortion problems that may occur in traditional circuits. The design of the third filter effectively improves the stability and reliability of the circuit, making it perform better in complex far-field speech environments. In addition, while ensuring noise reduction performance, the present application reduces the cost and complexity of the system by reasonably arranging the filter circuit.

[0092] The technical features of the above-described embodiments can be combined in any manner. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described, but as long as the combinations of the technical features do not contradict, they should be considered within the scope of the present application.

[0093] The above-described embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. An active noise reduction electret MIC circuit applied to far-field speech, comprising an electret MIC module and a master control module, characterized in that, The circuit further comprises: a first filter, an input end of which is connected to a bias power supply VCC_S1, and an output end of which is connected to an output end of the electret MIC module through a resistor R2, for filtering out power supply noise in the bias power supply VCC_S1; a second filter, an input end of which is connected to the output end of the electret MIC module, for filtering out low-frequency noise in the output signal of the electret MIC module; a third filter, an input end of which is connected to an output end of the second filter, and an output end of which is connected to the main control module, for further filtering out high-frequency noise in the output signal of the electret MIC module.

2. An electret MIC circuit for active noise reduction of far-field speech according to claim 1, wherein, The first filter comprises: a triode Q1, a collector of which is connected to the bias power supply VCC_S1, a base of which is connected to an external power supply VCC_S1 through a resistor R1, and an emitter of which is connected to the output end of the electret MIC module through a resistor R2.

3. An electret MIC circuit for active noise reduction of far-field speech according to claim 2, wherein, The first filter further comprises: a capacitor C2, one end of which is connected between the collector of the triode Q1 and the resistor R1, and the other end of which is grounded; a capacitor C3, one end of which is connected between the emitter of the triode Q1 and the resistor R2, and the other end of which is grounded; a capacitor C4, one end of which is connected between the emitter of the triode Q1 and the resistor R2, and the other end of which is grounded.

4. An electret MIC circuit for active noise reduction of far-field speech according to claim 1, wherein, The second filter comprises: an operational amplifier U1, a positive pole of which is connected to the output end MIC_OUT of the electret MIC module through a capacitor C6, and a negative pole of which is connected to an output end of the operational amplifier U1, and the output end of the operational amplifier U1 is connected to the third filter; a positive input end of the operational amplifier U1 is connected to a bias power supply VCC_S2, and a negative input end is grounded.

5. An electret MIC circuit for active noise reduction of far-field speech according to claim 4, wherein, The second filter further comprises: a resistor R3, one end of which is connected between the positive pole of the operational amplifier U1 and the capacitor C6, and the other end of which is connected to the bias power supply VCC_S2; a resistor R5, one end of which is connected between the positive pole of the operational amplifier U1 and the capacitor C6, and the other end of which is grounded; a capacitor C1, one end of which is connected to the bias power supply VCC_S2, and the other end of which is grounded; a capacitor C5, one end of which is connected to the bias power supply VCC_S2, and the other end of which is grounded.

6. An active noise cancelling electret MIC circuit for far-field voice in accordance with claim 1, wherein, The third filter comprises a resistor R4, a capacitor C7, and a capacitor C8; one end of the resistor R4 is connected to the output end of the second filter, and the other end of the resistor R4 is connected to an OUTPUT port through the capacitor C7; one end of the capacitor C8 is connected between the resistor R4 and the capacitor C7, and the other end of the capacitor C8 is grounded.

7. An active noise cancelling electret MIC circuit for far-field voice in accordance with claim 6, wherein, The OUTPUT port is connected to an ADC input channel of the main control module.

8. An active noise cancelling electret MIC circuit for far-field voice in accordance with claim 3, wherein, The resistor R1 is set to have a resistance value in a range of 33kΩ-100kΩ, and the capacitor C2 is set to have a capacitance value in a range of 10uF-22uF.

9. The active noise cancelling electret MIC circuit for far-field voice of claim 1, wherein, The first filter is placed close to the electret MIC module, and the second filter and the third filter are placed close to the main control module.

10. An active noise cancelling electret MIC circuit for far-field speech according to any one of claims 1-9, characterized in that, The first filter is set to have a cut-off frequency below 80Hz, the second filter is set to have a cut-off frequency of 80Hz, and the third filter is set to have a cut-off frequency of 8kHz.

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