CN203840514U - Active noise elimination circuit for earphone - Google Patents

Abstract

The utility model discloses an active noise elimination circuit for an earphone, after each sound channel environment noise signal is collected by the earphone microphone, the sound channel environment noise signal is respectively processed by at least 2 microphone amplification filter circuits, the processed noise signals and audio signals enter a mixer to be mixed, and then are amplified by an amplifier and transmitted into a loudspeaker; each microphone amplification and filtering circuit includes a variable gain microphone amplifier and a filter. The utility model discloses can improve the noise elimination effect to have the advantage of practicing thrift cost, earphone size is little, power consumption is low, be suitable for mass production.

Description

An Active Noise Cancellation Circuit for Headphones

technical field

The utility model relates to an active noise elimination circuit for earphones, which belongs to the technical field of audio equipment noise reduction.

Background technique

Noise cancellation is used to prevent unwanted sound waves from reaching the listener's eardrums. Active Noise Cancellation (ANC) technology uses electronic means to generate sound waves with the same amplitude as the ambient noise but with a phase difference of 180 degrees, and eliminates the ambient noise through destructive interference. Generally use feedforward, feedback or hybrid (feedforward + feedback) circuits.

Figure 16 is a typical circuit of active noise cancellation technology applied to feedforward or feedback headphones. The environmental noise signal of each channel is collected by a microphone and processed by a microphone amplifier and filter circuit. The processed noise signal and audio signal enter the mixer for mixing, and then are amplified by the amplifier and then transmitted to the speaker; the microphone amplifies The filtering circuit includes a variable gain microphone amplifier and a filter. Its noise canceling effect is very dependent on the acoustic response of the earphone, especially if the sound pressure level (sound pressure level) of the earphone is relatively low in certain frequency ranges, then the sound waves produced by it can only cancel the frequency Part of the range of ambient noise, which affects the noise cancellation effect. As shown in Figure 17, there is a 6dB difference in the sound pressure level of the headphones at a frequency of 50 Hz versus a frequency of 500 Hz. As shown in Figure 18, the amplitude of the anti-phase sound wave generated at the 50Hz frequency is 100% of the environmental noise, so all noise can be eliminated; as shown in Figure 19, the amplitude of the anti-phase sound wave generated at the 500Hz frequency is 100% of the environmental noise 50%, so only part of the noise is removed. It can be seen that the overall noise cancellation effect may be high in some frequency ranges, but low in some frequency ranges.

In addition, typical feed-forward or feedback-type headphones generally only produce a maximum noise cancellation effect of about 20 dB (as shown in Figure 11). In order to increase the noise cancellation effect to greater than 30dB, a hybrid (feedforward + feedback) configuration is required, but it requires two microphones, which increases component count, product size, and cost, and regardless of digital (DSP) or analog noise reduction technology, both require higher power consumption.

Utility model content

The purpose of this utility model is to provide an active noise canceling circuit for earphones, which can improve the noise canceling effect, and has the advantages of cost saving, small earphone size, low power consumption, and is suitable for mass production.

The technical scheme of the present utility model: an active noise cancellation circuit for earphones, comprising sequentially connected microphones, at least 2 microphone amplification filter circuits, a mixer, amplifiers and speakers, each microphone amplification filter circuit includes a Variable-gain microphone amplifier and filter; the ambient noise signal of each channel is collected by the microphone of the earphone, and then processed by the microphone amplifier and filter circuit, and the processed noise signal and audio signal enter the mixer for mixing, and then After being amplified by the amplifier, it is transmitted to the speaker; among them, the variable gain microphone amplifier is used to adjust the size of the microphone signal, and can achieve the best level of the out-of-phase or anti-phase signal.

Preferably, the active noise cancellation circuit for earphones includes sequentially connected microphones, 2 microphone amplifier filter circuits, mixers, amplifiers and speakers, and each microphone amplifier filter circuit includes a variable gain microphone amplifier and filter After the environmental noise signal of each channel is collected by the microphone of the earphone, it is processed by two microphone amplification filter circuits respectively, and the noise signal after each channel processing enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier. into the speakers.

In the aforementioned active noise cancellation circuit for earphones, a preamplifier is set between the microphone and the microphone amplifier filter circuit; the preamplifier can support multiple signal paths of microphone amplifiers and filter combinations to realize modulation of multiple frequency bands, To maintain the integrity of the microphone signal.

In the aforementioned active noise cancellation circuit for earphones, a lower-cost buffer can be used instead of the preamplifier, that is, a buffer is set between the microphone and the microphone amplification filter circuit. The voltage gain of the buffer is one, and the input cannot be amplified. The voltage of the signal can only amplify the current of the input signal.

In the foregoing active noise cancellation circuit for earphones, the filter is arranged between the variable-gain microphone amplifier and the mixer.

In the foregoing active noise cancellation circuit for earphones, the filter is arranged between the microphone and the variable-gain microphone amplifier.

In the aforementioned active noise cancellation circuit for earphones, the filter is a band-pass, high-pass or low-pass filter to select the frequency band of the signal that needs to be inverted.

In the aforementioned active noise cancellation circuit for earphones, the filter is a first-order filter, a second-order filter or a multi-order filter.

In the aforementioned active noise cancellation circuit for earphones, the earphones are earphones or earphones.

Compared with the prior art, the microphone noise signal path (i.e. microphone amplifier filter circuit) of the present utility model adopts the combined circuit of more than 2 variable gain microphone amplifiers+filters, so that the amplification gains of different levels are applied to different microphone signals. band. That is to say, if the acoustic response of the earphone is high in the low frequency band and low in the middle frequency band, after applying the utility model, a low level of amplification gain can be applied to the low frequency band and a high level of amplification can be applied to the mid frequency band Gain, which compensates the inhomogeneity of the acoustic response of the earphone in different frequency bands; if the sensitivity of the microphone is low in the low frequency band and high in the high frequency band, after applying the utility model, a high level of amplification gain can be applied to the low frequency band, And a low level of amplification gain is applied to the high frequency band, which compensates for the unevenness of the microphone sensitivity in different frequency bands. Each filter tuning process only needs to take care of a relatively narrow frequency band, which makes the tuning process easier and faster to achieve a high level of noise cancellation in all frequency bands.

The utility model does not need to adopt a hybrid circuit (that is, a microphone is installed inside and outside the earmuffs of the earphone), but only one microphone (that is, a feedforward type or a feedback type) is required, and its noise elimination effect is equivalent to that of the hybrid type, or even better. good.

With the emergence and popularization of portable audio/video equipment, such as MP3, mobile phone, music player, portable media player (PMP), notebook computer, netbook computer, etc., headphones and earphones have become quite a part of people's daily life. Important electronic equipment accessories. Since the noisy environment in public places will greatly reduce the accuracy of people using headphones to receive sound information, people pay more attention to the noise cancellation function, size, power consumption and other aspects of headphones. The active noise cancellation circuit described in the utility model can be applied to various earphones (including wired and wireless earphones), and the earphones using this circuit have low manufacturing cost, small size, light weight, low power consumption, and are suitable for mass production Etc.

Description of drawings

Fig. 1, Fig. 2, Fig. 3 are active noise elimination circuit diagrams of the present utility model;

Fig. 4 is the active noise cancellation circuit diagram of embodiment 1;

Fig. 5 is the active noise cancellation circuit diagram of embodiment 2;

Fig. 6 is the active noise cancellation circuit diagram of embodiment 3;

Fig. 7 is the active noise cancellation circuit diagram of embodiment 4;

Fig. 8 is the active noise cancellation circuit diagram of embodiment 5;

Fig. 9 is the active noise cancellation circuit diagram of embodiment 6;

Fig. 10 is a filter circuit frequency response diagram of the prior art;

Fig. 11 is an effect diagram of active noise cancellation in the prior art;

Fig. 12 is the filter circuit frequency response figure of embodiment 1, embodiment 2, embodiment 3;

Fig. 13 is an effect diagram of active noise cancellation in Embodiment 1, Embodiment 2, and Embodiment 3;

Fig. 14 is the filter circuit frequency response figure of embodiment 4, embodiment 5, embodiment 6;

Fig. 15 is an effect diagram of active noise cancellation in Embodiment 4, Embodiment 5, and Embodiment 6;

Fig. 16 is a prior art active noise cancellation circuit diagram;

Figure 17 is a diagram of the acoustic response of the earphone;

Figure 18 and Figure 19 are schematic diagrams of noise cancellation at frequencies of 50Hz and 500Hz respectively.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is described further.

Embodiment 1 of the present utility model: a kind of active noise canceling circuit that is used for earphone, as shown in Figure 4, after the ambient noise signal of each sound channel is collected by microphone, is processed through 2 microphone amplification filter circuits respectively, each channel The processed noise signal enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplification and filtering circuit includes a variable gain microphone amplifier and a filter, and the filter is set in the variable gain microphone Between the amplifier and the mixer; a preamplifier is set between the microphone and the microphone amplification filter circuit.

Embodiment 2 of the present utility model: a kind of active noise canceling circuit that is used for earphone, as shown in Figure 5, after the ambient noise signal of each sound channel is collected by microphone, is processed through 2 microphone amplification filter circuits respectively, each channel The processed noise signal enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplifier filter circuit includes a variable gain microphone amplifier and filter, and the microphone and the microphone amplifier filter circuit The preamp is set, and the filter is set between the preamp and the variable-gain mic amplifier.

Embodiment 3 of the present utility model: a kind of active noise canceling circuit that is used for earphone, as shown in Figure 6, after the environmental noise signal of every sound channel is collected by microphone, is processed through 2 microphone amplification filter circuits respectively, each channel The processed noise signal enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplifier filter circuit includes a variable gain microphone amplifier and filter, and the microphone and the microphone amplifier filter circuit The preamplifier is set, and the filter is set between the preamplifier and the variable-gain microphone amplifier and between the variable-gain microphone amplifier and the mixer.

Embodiment 4 of the present utility model: a kind of active noise canceling circuit that is used for earphone, as shown in Figure 7, after the environmental noise signal of each channel is collected by microphone, respectively through 3 microphone amplification filter circuit processings, each channel The processed noise signal enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplification and filtering circuit includes a variable gain microphone amplifier and a filter, and the filter is set in the variable gain microphone Between the amplifier and the mixer; a preamplifier is set between the microphone and the microphone amplification filter circuit.

Embodiment 5 of the present utility model: a kind of active noise canceling circuit that is used for earphone, as shown in Figure 8, after the environmental noise signal of each sound channel is collected by microphone, respectively through 3 microphone amplification filter circuits processing, each channel The processed noise signal enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplifier filter circuit includes a variable gain microphone amplifier and filter, and the microphone and the microphone amplifier filter circuit The preamp is set, and the filter is set between the preamp and the variable-gain mic amplifier.

Embodiment 6 of the present utility model: a kind of active noise canceling circuit that is used for earphone, as shown in Figure 9, after the ambient noise signal of each sound channel is collected by microphone, respectively through 3 microphone amplification filter circuit processings, each channel The processed noise signal enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplifier filter circuit includes a variable gain microphone amplifier and filter, and the microphone and the microphone amplifier filter circuit The preamplifier is set, and the filter is set between the preamplifier and the variable-gain microphone amplifier and between the variable-gain microphone amplifier and the mixer.

Except the microphone noise signal paths of 2 roads and 3 roads shown in the above-mentioned embodiments, more than 3 road microphone noise signal paths can also be used, as shown in Fig. 1, Fig. 2 and Fig. 3 (N>3 in the figure) .

In the above-mentioned embodiment, the preamplifier can be replaced by a buffer, that is, a buffer is provided between the microphone and the microphone amplification filter circuit; the filter can be a band-pass, high-pass or low-pass filter to select the signal frequency band that needs to be inverted; The filter can be a first-order filter, a second-order filter or a multi-order filter.

The active noise cancellation circuit described in the above-mentioned embodiments can be realized by discrete electronic components, analog signal integrated circuits, digital signal integrated circuits or mixed signal (analog + digital) integrated circuits; Outer), feedback (microphone inside the earcup) or hybrid (feedforward + feedback) noise-canceling headphones (over-ear, in-ear).

Fig. 10, 12, 14 are prior art, embodiment 1-3, embodiment 4-6 respectively filter circuit frequency response figure; Fig. 11, 13, 15 are respectively prior art, embodiment 1-3, embodiment Active noise cancellation renderings in 4-6. As can be seen from Fig. 13 and Fig. 15, when each microphone noise signal path (i.e. microphone amplifier filter circuit) adopts 2 or 3 variable gain microphone amplifier+filter combination circuits in Embodiment 1-6, the environment noise ( Frequency 100～500HZ) the maximum elimination effect can reach 30 decibels, which is much better than the noise reduction effect (the maximum value is about 20 decibels) of the typical noise elimination circuit of the prior art shown in FIG. 11 .

Claims (9)

1. An active noise cancellation circuit for earphones, characterized in that: after the ambient noise signal of each sound channel is collected by the microphone of the earphone, it is processed by at least 2 microphone amplification filter circuits respectively, and the noise signal after each road process Together with the audio signal, it enters the mixer for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplification and filtering circuit includes a variable gain microphone amplifier and a filter. 2. The active noise cancellation circuit for earphones according to claim 1, characterized in that: after the ambient noise signal of each sound channel is collected by the microphone of the earphone, it is processed by 2 microphone amplification and filter circuits respectively, and each channel is processed The final noise signal enters the mixer together with the audio signal for mixing, and then is amplified by the amplifier, and then transmitted to the speaker; each microphone amplification and filtering circuit includes a variable gain microphone amplifier and a filter. 3. The active noise cancellation circuit for earphones according to claim 1 or 2, characterized in that: a preamplifier is set between the microphone and the microphone amplification filter circuit. 4. The active noise cancellation circuit for earphones according to claim 1 or 2, characterized in that a buffer is provided between the microphone and the microphone amplification and filtering circuit. 5. The active noise cancellation circuit for earphones according to claim 1, wherein the filter is arranged between the variable gain microphone amplifier and the mixer. 6. The active noise cancellation circuit for earphones according to claim 1 or 5, characterized in that the filter is arranged between the microphone and the variable gain microphone amplifier. 7. The active noise cancellation circuit for earphones according to claim 6, wherein the filter is a band-pass, high-pass or low-pass filter. 8. The active noise cancellation circuit for earphones according to claim 7, wherein the filter is a first-order filter, a second-order filter or a multi-order filter. 9. The active noise cancellation circuit for earphones according to claim 8, wherein the earphones are earphones or earphones.