CN114928335A - Low-noise audio amplifier and equipment - Google Patents
Low-noise audio amplifier and equipment Download PDFInfo
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- CN114928335A CN114928335A CN202210350361.3A CN202210350361A CN114928335A CN 114928335 A CN114928335 A CN 114928335A CN 202210350361 A CN202210350361 A CN 202210350361A CN 114928335 A CN114928335 A CN 114928335A
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F1/00—Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements
- H03F1/26—Modifications of amplifiers to reduce influence of noise generated by amplifying elements
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/181—Low frequency amplifiers, e.g. audio preamplifiers
- H03F3/183—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/181—Low frequency amplifiers, e.g. audio preamplifiers
- H03F3/183—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only
- H03F3/185—Low frequency amplifiers, e.g. audio preamplifiers with semiconductor devices only with field-effect devices
Abstract
The embodiment of the application provides a low noise audio amplifier and equipment, the amplifier includes: the buffer circuit comprises a first filter circuit, a buffer adjusting circuit, a first feedback circuit and a signal amplifying circuit; the first filter circuit comprises a first capacitor and a first resistor, the first capacitor is used for isolating the direct current level of an input sound source from the direct current level of a chip in the audio amplifier, the buffer adjusting circuit is arranged between the first capacitor and the first resistor to reduce the output noise of the audio amplifier, one end of the first resistor, which is far away from the first capacitor, is connected with the input end of the signal amplifying circuit, and the output end of the signal amplifying circuit is connected with the loudspeaker; the first feedback circuit is connected with the signal amplification circuit in parallel, the first end of the first feedback circuit is connected with the input end of the signal amplification circuit, the second end of the first feedback circuit is connected with the output end of the signal amplification circuit, and the first feedback circuit is used for feeding back the output signal of the signal amplification circuit to the input end of the signal amplification circuit. The audio amplifier provided by the embodiment of the application can reduce the output noise of the audio amplifier under the condition that the low-frequency sound source is not attenuated by the input end.
Description
Technical Field
The embodiment of the application relates to the technical field of audio amplifiers, in particular to a low-noise audio amplifier and equipment.
Background
Noise is a very important index in an audio amplifier, and the lower the noise is, the more the audio amplifier can distinguish a very small sound source signal, the wider the dynamic range is, and the clearer the output music is.
The capacitance value of the blocking capacitor of the existing audio amplifier is smaller, so that in order to enable a low-frequency sound source to be more input into the audio amplifier, the output noise of the audio amplifier is very large, and therefore the audio amplifier is urgently needed to be researched and developed, the low-noise output is achieved on the premise that the low-frequency sound source is guaranteed not to enter the audio amplifier in an attenuated mode, and a consumer can hear music with clearer resolution.
Disclosure of Invention
Therefore, the embodiment of the application provides a low-noise audio amplifier and equipment, so as to solve the technical problem that the output noise of the audio amplifier is relatively large after a low-frequency sound source enters the audio amplifier in the prior art.
In order to achieve the above object, the embodiments of the present application provide the following technical solutions:
according to a first aspect of embodiments of the present application, an embodiment of the present application provides a low noise audio amplifier, including: the buffer circuit comprises a first filter circuit, a buffer adjusting circuit, a first feedback circuit and a signal amplifying circuit;
the first filter circuit comprises a first capacitor and a first resistor, the first capacitor is used for isolating the direct current level of an input sound source from the direct current level of a chip in the audio amplifier, the buffer adjusting circuit is arranged between the first capacitor and the first resistor to reduce the output noise of the audio amplifier, one end of the first resistor, which is far away from the first capacitor, is connected with the input end of the signal amplifying circuit, and the output end of the signal amplifying circuit is connected with the loudspeaker;
the first feedback circuit is connected with the signal amplification circuit in parallel, the first end of the first feedback circuit is connected with the input end of the signal amplification circuit, the second end of the first feedback circuit is connected with the output end of the signal amplification circuit, and the first feedback circuit is used for feeding back the output signal of the signal amplification circuit to the input end of the signal amplification circuit.
As a preferred embodiment of the present application, the signal amplifying circuit includes an operational amplifying circuit and a power amplifying circuit, one end of the first resistor, which is far away from the first capacitor, is connected to an input end of the operational amplifying circuit, an output end of the operational amplifying circuit is connected to an input end of the power amplifying circuit, and an output end of the power amplifying circuit is connected to a speaker;
the first end of the first feedback circuit is connected with the input end of the operational amplification circuit, and the second end of the first feedback circuit is connected with the output end of the power amplification circuit.
As a preferred embodiment of the present application, the audio amplifier further includes a second filter circuit, the second filter circuit includes a second capacitor and a second resistor, the adjusting circuit is disposed between the second capacitor and the second resistor to reduce the output noise of the audio amplifier, and one end of the second resistor, which is far away from the second capacitor, is connected to the input end of the signal amplifying circuit.
As a preferred embodiment of the present application, the audio amplifier further includes a second feedback circuit, a first end of the second feedback circuit is connected to the input end of the signal amplification circuit, a second end of the second feedback circuit is connected to the output end of the signal amplification circuit, and the second feedback circuit is configured to feed back an output signal of the signal amplification circuit to the input end of the signal amplification circuit.
As a preferred embodiment of the present application, the audio amplifier further includes a first integrating circuit, the first integrating circuit is connected in parallel with the operational amplifier circuit, a first end of the first integrating circuit is connected to an input end of the operational amplifier circuit, and a second end of the first integrating circuit is connected to an output end of the operational amplifier circuit.
As a preferred embodiment of the present application, the audio amplifier further includes a second integrating circuit, the second integrating circuit is connected in parallel with the operational amplifier circuit, a first end of the second integrating circuit is connected to the input end of the operational amplifier circuit, and a second end of the second integrating circuit is connected to the output end of the operational amplifier circuit.
As a preferred embodiment of the present application, the buffer adjusting circuit is a buffer.
As a preferred embodiment of the present application, the buffer is composed of an active amplifier of CMOS transistors.
Compared with the prior art, under the condition that the capacitance value of the first capacitor is limited, the resistance value of the first resistor cannot be too small, otherwise a low-frequency sound source enters the audio amplifier, and therefore the output noise of the audio amplifier is large. The first capacitor and the first resistor are isolated through the buffer adjusting circuit, so that the resistance value of the first resistor is not limited by the first capacitor, and the first resistor can select a resistance value with a small resistance value to reduce the output noise of the audio amplifier; and the buffer adjusting circuit has very large impedance to the input sound source, so that the cut-off frequency of the filter circuit is very low, and the low-frequency sound source is not attenuated by the input end, therefore, the output noise of the audio amplifier is reduced under the condition that the low-frequency sound source is not attenuated by the input end.
In a second aspect, an embodiment of the present application further provides an apparatus, including the low noise audio amplifier according to the first aspect.
Compared with the prior art, the beneficial effects of the device provided by the embodiment of the present application are the same as those of the low noise audio amplifier provided by the first aspect, and are not described herein again.
Drawings
In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below. It should be apparent that the drawings in the following description are merely exemplary, and that other embodiments can be derived from the drawings provided by those of ordinary skill in the art without inventive effort.
The structures, ratios, sizes, and the like shown in the present specification are only used for matching with the contents disclosed in the specification, so as to be understood and read by those skilled in the art, and are not used to limit the conditions that the present application can be implemented, so that the present specification has no technical essence, and any structural modifications, changes in the ratio relationship, or adjustments of the sizes, should fall within the scope that the technical contents disclosed in the present application can cover without affecting the effects that the present application can produce and the purposes that the present application can achieve.
Fig. 1 is a schematic circuit diagram of a low noise audio amplifier provided in the prior art;
FIG. 2 is a schematic diagram of another low noise audio amplifier circuit provided in the prior art;
FIG. 3 is a graph illustrating the variation of the cut-off frequency of a filter circuit according to the prior art;
fig. 4 is a schematic circuit diagram of a low noise audio amplifier according to an embodiment of the present application;
FIG. 5 is a graph illustrating the variation of the cut-off frequency of the filter circuit according to the embodiment of the present disclosure;
fig. 6 is a schematic circuit diagram of a low noise audio amplifier according to another embodiment of the present application;
fig. 7 is a schematic circuit diagram of a low noise audio amplifier according to another embodiment of the present application;
fig. 8 is a schematic circuit diagram of a low noise audio amplifier according to another embodiment of the present application.
Detailed Description
The present disclosure is not intended to be limited to the particular embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.
An audio amplifier as provided in the prior art shown in fig. 1, the audio amplifier comprising a first filter circuit, a first feedback circuit 105 and a signal amplification circuit;
the first filter circuit comprises a first capacitor 101 and a first resistor 102, one end, far away from the first capacitor 101, of the first resistor 102 is connected with an input end of a signal amplification circuit, an output end of the signal amplification circuit is connected with a loudspeaker, the signal amplification circuit comprises an operational amplification circuit 103 and a power amplification circuit 104, namely, one end, far away from the first capacitor 101, of the first resistor 102 is connected with the operational amplification circuit 103, an output end of the power amplification circuit 104 is connected with the loudspeaker 106, and the first capacitor 101 is a blocking capacitor and is used for isolating a direct current level of an input source from a direct current level of a chip in an audio amplifier.
The first feedback circuit 105 is connected in parallel with the signal amplification circuit, a first end of the first feedback circuit 105 is connected to an input end of the signal amplification circuit, a second end of the first feedback circuit 105 is connected to an output end of the signal amplification circuit, the first feedback circuit 105 is configured to feed an output signal of the signal amplification circuit back to the input end of the signal amplification circuit, in this embodiment, the first feedback circuit 105 is a resistor, where V is V cmin For input common mode voltage, V cmout Is the output common mode voltage.
In the audio amplifier provided by the prior art shown in fig. 1, the output noise V of the audio amplifier noise_out The calculation is performed by the following formula (i):
wherein, V noise_out Is the output noise of the audio amplifier, R fb Is a resistance value, R, of the first feedback circuit 105 in Is the resistance value of the first resistor 102, V noise_opa K is a boltzmann constant, and T is an internal temperature of a chip in the audio amplifier, which is a noise value of the operational amplification circuit 103.
Wherein the noise V of the operational amplifier circuit 103 noise_opa Mainly by the thermal noise of the input transistors
Noise component, where f is the frequency of the signal amplification circuit, and f is typically between 20Hz and 20kHz, i.e., the range of audible frequencies that can be heard by humans, in modern semiconductor manufacturing processes, V is added only by adding a certain acceptable area and proper circuit design noise_opa Will be so small that it is over the whole V noise_out The calculation is negligible, namely: output noise V of audio amplifier noise_out The calculation is performed by the following formula (ii):
in addition, the amplification gain of the audio amplifier is controlled by the resistor R of the first feedback circuit 105 fb And a resistance R of the first resistor 103 in Is determined by the ratio of (a):
when g is 1, the gain of the corresponding audio amplifier is 0dB, and when g is 10, the gain of the corresponding audio amplifier is 20dB, resulting in V noise_out The calculation formula (iii) is as follows:
as can be seen from formula (III), R in The smaller the resistance value of (a), the smaller the corresponding resistance thermal noise, so the smaller the noise output by the audio amplifier, and in practical applications, the capacitance value of the first capacitor 101 is generally not very large due to the limitations of manufacturing process and cost.
As shown in fig. 2, on the basis of fig. 1, a second capacitor 208, a second resistor 209 and a second feedback circuit 207 are added to implement differential input, one end of the second resistor 209 away from the second capacitor 208 is connected to an input end of a signal amplification circuit, an output end of the signal amplification circuit is connected to a speaker 206, the signal amplification circuit includes an operational amplification circuit 203 and a power amplification circuit 204, that is, one end of the second resistor 209 away from the second capacitor 208 is connected to the operational amplification circuit 203, an output end of the power amplification circuit 204 is connected to the speaker 206, and the second capacitor 208 is a dc blocking capacitor for isolating a dc level of an input sound source from a dc level of a chip in the audio amplifier.
The second feedback circuit 207 is connected in parallel with the signal amplification circuit, the first end of the second feedback circuit 207 is connected to the input end of the signal amplification circuit, the second end of the second feedback circuit 207 is connected to the output end of the signal amplification circuit, the second feedback circuit 207 is configured to feed back the output signal of the signal amplification circuit to the input end of the signal amplification circuit, and in this embodiment, the second feedback circuit 207 is a resistor.
In the audio amplifier provided by the prior art shown in fig. 2, the output noise V of the audio amplifier noise_out The calculation is performed by the following formula (iv):
wherein, V noise_out Is the output noise of the audio amplifier, wherein the resistance values of the first feedback circuit 205 and the second feedback circuit 207 are the same, R fb Is the resistance value of the first feedback circuit 205 or the second feedback circuit 207, wherein the resistance values of the first resistor 102 and the second resistor 109 are the same, R in Is the resistance value, V, of the first resistor 202 or the second resistor 209 noise_opa K is a boltzmann constant, and T is an internal temperature of a chip in the audio amplifier, which is a noise value of the operational amplification circuit 203.
Wherein the noise V of the operational amplifier circuit 203 noise_opa Mainly by the thermal noise of the input transistors
Noise component, where f is the frequency of the signal amplifying circuit, and f is generally between 20Hz and 20kHz, i.e. the range of sound frequency that can be heard by human, in modern semiconductor manufacturing process, only a certain acceptable area and frequency range need to be addedProper circuit design, V noise_opa Will be so small that it is over the whole V noise_out The calculation can be ignored, namely: output noise V of audio amplifier noise_out The calculation is performed by the following formula (v):
in addition, the amplification gain of the audio amplifier is controlled by the resistor R of the first feedback circuit 205 fb And the resistance R of the first resistor 203 in Is determined by the ratio of (a):
when g is 1, the gain of the corresponding audio amplifier is 0dB, and when g is 10, the gain of the corresponding audio amplifier is 20dB, thereby obtaining V noise_out The calculation formula (iv) is as follows:
as can be seen from the formula (IV), R in The smaller the resistance value of (2), the smaller the corresponding resistance thermal noise, so the smaller the noise output by the audio amplifier, and in practical applications, the capacitance value of the first capacitor 201 is not usually very large.
FIG. 3 shows the cut-off frequency f of the filter circuit, as shown in FIGS. 1 and 3 -3db In which the abscissa f -3db In order to cut-off frequency of the filter circuit, the ordinate V is the amplitude of the input audio signal, wherein, as in fig. 1, the first capacitor 101 and the first resistor 102 form a filter circuit, as in fig. 2, the first capacitor 201 and the first resistor 202 form a filter circuit, and the second capacitor 208 and the second resistor 209 form a filter circuit, wherein f -3db For the cut-off frequency of the filter circuit, the cut-off frequency is specifically calculated by the formula (vii):
wherein, in the audio amplifier of FIG. 1, for R in the formula (VII) in Is the resistance value of the first resistor 101, C in Is the capacitance value of the first capacitor 102.
In the audio amplifier of fig. 2, R is the same for the resistance values of the first resistor 102 and the second resistor 209 in formula (vii) in The capacitance of the first capacitor 101 and the capacitance of the second capacitor 208 are the same, C is the resistance of the first resistor 102 or the second resistor 209 in Is the capacitance value of the first capacitor 101 or the second capacitor 208.
If f is -3db The lower the frequency, the more the audio of lower frequencies is allowed to enter the audio amplifier without being attenuated, thus resulting in the output noise V of the audio amplifier noise_out It will be very large. At C in In the case where the capacitance value of (2) is limited, R in Must not be too small, otherwise low frequency signals enter the audio amplifier, which results in an output noise V of the audio amplifier noise_out It will be very large.
The low-noise audio amplifier is provided to solve the technical problem that the output noise of the audio amplifier is relatively large when the audio amplifier in the prior art allows the audio with lower frequency to enter the audio amplifier.
Example 1
As shown in fig. 4, an embodiment of the present application provides a low noise audio amplifier, where the audio amplifier includes: a first filter circuit, a buffer adjustment circuit 407, a first feedback circuit 107 and a signal amplification circuit;
the first filter circuit comprises a first capacitor 401 and a first resistor 402, the adjusting circuit 407 is arranged between the first capacitor 401 and the first resistor 402 to reduce noise of the audio amplifier, one end of the first resistor 401 far away from the first capacitor 402 is connected with an input end of the signal amplifying circuit, and an output end of the signal amplifying circuit is connected with the loudspeaker 406.
The first feedback circuit 405 is arranged in parallel with the signal amplification circuit to feed back the output signal of the signal amplification circuit to the signalThe first end of the first feedback circuit 405 is connected to the input end of the signal amplification circuit, the second end of the first feedback circuit 405 is connected to the output end of the signal amplification circuit, in this embodiment, the first feedback circuit 405 is a resistor, and the output noise V of the audio amplifier provided in this embodiment is the output noise V of the audio amplifier provided in this embodiment noise_out Calculated by the following formula (viii):
wherein, V noise_out Is the output noise of the audio amplifier, R fb Is a resistance value, R, in the first feedback circuit 405 in Is the resistance value of the first resistor 402, V noise_buf To buffer the noise value, V, of the conditioning circuit 407 noise_opa Is a noise value of the operational amplifier circuit 403. Wherein the noise value V of the operational amplifier circuit 403 noise_opa Mainly by input-side transistor thermal noise and
the noise component, where f is the frequency of the signal amplification circuit, and f is typically between 20Hz and 20kHz, i.e., the range of sound frequencies that can be heard by a human.
In the embodiment of the present application, the buffer adjusting circuit 407 may be a buffer, the buffer is composed of an active amplifier of CMOS transistors and does not include a passive resistor, and in a modern semiconductor manufacturing process, the power amplifying circuit 404V only needs to be added with a certain acceptable area and a proper circuit design noise_opa Will be so small that the output noise V at the whole audio amplifier noise_out The calculation is negligible, and the buffer adjusting circuit 307 is noisy V by the semiconductor manufacturing process noise_buf Designed to be so small that the buffer adjustment circuit 307 noise V noise_buf Output noise V at the whole audio amplifier noise_out The calculation is negligible, so in the embodiment of the present application, the output noise V of the audio amplifier noise_out Calculated by the following formula (ix):
in addition, the amplification gain g of the audio amplifier is obtained by the resistance R of the first feedback circuit 405 fb And the resistance R of the first resistor 303 in Is determined by the ratio of (A) to (B):
when g is 1, the gain of the corresponding audio amplifier is 0dB, and when g is 10, the gain of the corresponding audio amplifier is 20dB, thereby obtaining V out_noise The calculation formula (iii) is as follows:
since the buffer adjustment circuit 407 is formed of an active amplifier of a CMOS transistor, the impedance to the input sound source is large, resulting in a low cut-off frequency of the filter circuit, so that the low frequency sound source is not attenuated by the input terminal, and the cut-off frequency f of the filter circuit is low -3db Is calculated by the formula (iv):
wherein, C in Is the capacitance value, R, of the first capacitor 402 in Is the resistance value of the first resistor 403.
FIG. 5 shows the cut-off frequency f -3db Graph of (2), wherein the abscissa f -3db For the cut-off frequency of the filter circuit, the ordinate V is the amplitude of the input audio signal, because the buffer adjusting circuit 407 is disposed between the first capacitor 401 and the first resistor 402 in the embodiment of the present application, the buffer adjusting circuit 407 plays a role in isolating the first capacitor 401 from the first resistor 402, the resistance value of the first resistor 402 in the filter circuit is not influenced by the capacitance value C of the first capacitor 401 of the filter circuit at the input end in So that the first resistance402 a very low resistance value can be selected, as can be seen from equation (iii), the audio amplifier output noise V out_noise Is low, thereby realizing a low noise audio amplifier in which the first capacitor 401 and the first resistor 402 constitute a filter circuit.
In an embodiment of the present application, the signal amplifying circuit includes an operational amplifying circuit 403 and a power amplifying circuit 404, one end of the first resistor 401 away from the first capacitor 402 is connected to an input end of the operational amplifying circuit 403, an output end of the operational amplifying circuit 403 is connected to an input end of the power amplifying circuit 404, and an output end of the power amplifying circuit 404 is connected to the speaker 306; the first feedback circuit 405 is arranged in parallel with the operational amplifier circuit 403 and the power amplifier circuit 404 so as to feed back an output signal of the signal amplifier circuit to an input terminal of the signal amplifier circuit, a first end of the first feedback circuit 405 is connected to the input terminal of the operational amplifier circuit 403, and a second end of the first feedback circuit 405 is connected to an output terminal of the power amplifier circuit 404.
The input audio signal is amplified by the operational amplifier circuit 403 to output an audio, the frequency of the input sound source is amplified by the power amplifier circuit 404,
the audio amplifier provided by the embodiment of the application can reduce the output noise of the audio amplifier under the condition that the low-frequency sound source is not attenuated by the input end.
Example 2
As shown in fig. 6, in embodiment 4, the audio amplifier further includes a first integrating circuit 608, the first integrating circuit 608 is disposed in parallel with the operational amplifier circuit 603 and the power amplifier circuit 604, a first end of the first integrating circuit 608 is connected to an input end of the operational amplifier circuit 603, a second end of the first integrating circuit 608 is connected to an output end of the operational amplifier circuit 604, and the signal output from the filter circuit is accumulated by the first integrating circuit 608 and then is operated and output.
In this embodiment, the output noise V of the audio amplifier out_noise The calculation formula is the same as that in the first embodiment, and the filter circuit is cutThe variation graph of the stop frequency f is also the same as the first embodiment, and is not described herein again.
In the embodiment of the present application, since the buffer adjusting circuit 607 is composed of an active amplifier of a CMOS transistor, the impedance to the input sound source is large, so that the cut-off frequency of the filter circuit is low, so that the low-frequency sound source is not attenuated by the input terminal. The buffer adjustment circuit 607 is used to isolate the first capacitor 601 from the first resistor 602, and the resistance of the first resistor 602 in the filter circuit is not affected by the capacitance C of the first capacitor 601 in the filter circuit at the input end in The first resistor 602 can select a resistor with a very small resistance value, so that the output noise of the audio amplifier can be reduced without the low-frequency sound source being attenuated by the input terminal.
The audio amplifier provided by the embodiment of the application can reduce the output noise of the audio amplifier under the condition that the low-frequency sound source is not attenuated by the input end.
Example 3
As shown in fig. 7, in the embodiment 4, in order to realize the differential audio source input, the audio amplifier further includes a second filter circuit, the second filter circuit includes a second capacitor 709 and a second resistor 710, the buffer adjustment circuit 707 is disposed between the second capacitor 709 and the second resistor 710 to adjust the cut-off frequency of the first filter circuit so that the low-frequency audio source is not attenuated, and an end of the second resistor 710 far from the first capacitor 709 is connected to the input end of the operational amplifier circuit 703.
In an embodiment of the present application, the audio amplifier further includes a second feedback circuit 711, the second feedback circuit 711 is disposed in parallel with the operational amplifier 703 and the power amplifier 704, a first end of the second feedback resistor is connected to an input end of the operational amplifier 703, a second end of the second feedback circuit 711 is connected to an output end of the power amplifier 704, and the second feedback circuit 611 is disposed in parallel with the signal amplifier so as to feed back an output signal of the signal amplifier to the input end of the signal amplifier, in an embodiment of the present application, the second feedback circuit 711 is a resistor, and the audio amplifier further includes a first feedback circuit 711, a second feedback circuit, and a third feedback circuit 711, a fourth feedback circuit, and a fourth feedback circuit, where the second feedback circuit is disposed in parallel with the signal amplifier 611, and the third feedback circuit is disposed in parallel with the signal amplifier so as to feed back an output signal of the signal amplifier to the input end of the signal amplifierOutput noise V of amplifier noise_out The calculation is performed by the following formula (iv):
wherein, V noise_out The output noise of the audio amplifier is obtained by using the resistance values of the first feedback circuit 705 and the second feedback circuit 707, R fb Is the resistance value of the first feedback circuit 705 or the second feedback circuit 707, wherein the resistance values of the first resistor 702 and the second resistor 709 are the same, R in Is the resistance value of the first resistor 702 or the second resistor 709, V noise_opa To calculate the noise value of the amplifier circuit 703, the frequency of the signal amplifier circuit, k is boltzmann's constant, and T is the internal temperature of the chip in the audio amplifier.
Wherein the noise V of the power amplifying circuit noise_opa Mainly by the thermal noise of the input transistors
Noise component, where f is the frequency of the signal amplifying circuit, and f is generally between 20Hz and 20kHz, i.e. the range of sound frequency that can be heard by human, in modern semiconductor manufacturing process, V is added as long as certain acceptable area and proper circuit design are added noise_opa Will be so small as to be over the entire V noise_out The calculation can be ignored, namely: output noise V of audio amplifier noise_out The calculation is performed by the following formula (v):
in addition, the amplification gain of the audio amplifier is controlled by the resistor R of the first feedback circuit 705 fb And a resistance R of the first resistor 103 in Is determined by the ratio of (a):
when g is 1, the corresponding toneWhen the gain of the frequency amplifier is 0dB and g is 10, the corresponding gain of the audio amplifier is 20dB, and V is obtained noise_out The formula (IV) is calculated as follows:
as can be seen from the formula (IV), R in The smaller the resistance value of (2), the smaller the corresponding resistance thermal noise, so the smaller the noise output by the audio amplifier, and in practical applications, the capacitance value of the first capacitor 101 is not usually very large.
Wherein the cut-off frequency f of the filter circuit -3db The variation graph is the same as that of the first embodiment, and is not repeated herein.
In the present embodiment, since the buffer adjusting circuit 707 is composed of an active amplifier of a CMOS transistor, the impedance to the input sound source is large, and the cut-off frequency of the filter circuit is low, so that the low-frequency sound source is not attenuated by the input terminal. The buffer adjusting circuit 707 isolates the first capacitor 701 from the first resistor 702, and the resistance of the first resistor 702 in the filter circuit is not affected by the capacitance C of the first capacitor 701 in the filter circuit at the input end in Because the first resistor 702 can select a resistor with a very small resistance, the output noise of the audio amplifier can be reduced without the low-frequency sound source being attenuated by the input terminal.
The audio amplifier provided by the embodiment of the application can reduce the output noise of the audio amplifier under the condition that the low-frequency sound source is not attenuated by the input end.
Example 4
As shown in fig. 8, in embodiment 7, the audio amplifier further includes a first integrating circuit 808 and a second integrating circuit 812, the second integrating circuit 812 is connected in parallel with the operational amplifier 803 and the power amplifier 804, a first end of the second integrating circuit 812 is connected to an input end of the operational amplifier 803, a second end of the second integrating circuit 812 is connected to an output end of the operational amplifier 803, and a signal output from the filter circuit is accumulated by the second integrating circuit 812 and then is operated and output.
The first integrating circuit 808 is connected in parallel with the operational amplifier circuit 803 and the power amplifier circuit 804, a first end of the first integrating circuit 808 is connected with an input end of the operational amplifier circuit 803, a second end of the first integrating circuit 808 is connected with an output end of the operational amplifier circuit 803, and signals output by the filter circuit are accumulated by the first integrating circuit 808 and then are operated and output.
In the present embodiment, the first integrator 808 and the second integrator 812 are capacitors.
In this embodiment, the output noise V of the audio amplifier out_noise The calculation formula is the same as that in the first embodiment, and the variation curve of the cut-off frequency f of the filter circuit is also the same as that in the first embodiment, which is not repeated herein.
In the embodiment of the present application, since the buffer adjusting circuit 807 is formed by an active amplifier of a CMOS transistor, the impedance to the input sound source is large, so that the cut-off frequency of the filter circuit is low, so that the low-frequency sound source is not attenuated by the input terminal. The buffer adjustment circuit 807 serves to isolate the first capacitor 801 from the first resistor 802, and the resistance of the first resistor 802 in the filter circuit is not affected by the capacitance C of the first capacitor 801 of the filter circuit at the input terminal in Because the first resistor 802 can select a resistor with a very small resistance, the output noise of the audio amplifier can be reduced without the low-frequency sound source being attenuated by the input terminal.
The audio amplifier provided by the embodiment of the application can reduce the output noise of the audio amplifier under the condition that the low-frequency sound source is not attenuated by the input end.
In a second aspect, an embodiment of the present application further provides an apparatus, which includes the low noise audio amplifier described in the first aspect.
Compared with the prior art, the beneficial effects of the device provided by the embodiment of the present application are the same as those of the low noise audio amplifier provided by the first aspect, and are not described herein again.
Although the present application has been described in detail with respect to the general description and the specific examples, it will be apparent to those skilled in the art that certain changes and modifications may be made based on the present application. Accordingly, such modifications and improvements are intended to be within the scope of this invention as claimed.
Claims (9)
1. A low noise audio amplifier, comprising: the buffer circuit comprises a first filter circuit, a buffer adjusting circuit, a first feedback circuit and a signal amplifying circuit;
the first filter circuit comprises a first capacitor and a first resistor, the first capacitor is used for isolating the direct current level of an input sound source from the direct current level of a chip in the audio amplifier, the buffer adjusting circuit is arranged between the first capacitor and the first resistor to reduce the output noise of the audio amplifier, one end of the first resistor, which is far away from the first capacitor, is connected with the input end of the signal amplifying circuit, and the output end of the signal amplifying circuit is connected with the loudspeaker;
the first feedback circuit is connected with the signal amplification circuit in parallel, the first end of the first feedback circuit is connected with the input end of the signal amplification circuit, the second end of the first feedback circuit is connected with the output end of the signal amplification circuit, and the first feedback circuit is used for feeding back the output signal of the signal amplification circuit to the input end of the signal amplification circuit.
2. The low noise audio amplifier of claim 1, wherein the signal amplifying circuit comprises an operational amplifier circuit and a power amplifier circuit, the end of the first resistor away from the first capacitor is connected to an input end of the operational amplifier circuit, an output end of the operational amplifier circuit is connected to an input end of the power amplifier circuit, and an output end of the power amplifier circuit is connected to a speaker;
the first end of the first feedback circuit is connected with the input end of the operational amplification circuit, and the second end of the first feedback circuit is connected with the output end of the power amplification circuit.
3. A low noise audio amplifier according to claim 1, wherein the audio amplifier further comprises a second filter circuit, the second filter circuit comprises a second capacitor and a second resistor, the adjusting circuit is disposed between the second capacitor and the second resistor to reduce the output noise of the audio amplifier, and an end of the second resistor remote from the second capacitor is connected to the input end of the signal amplifying circuit.
4. A low noise audio amplifier according to claim 1, wherein said audio amplifier further comprises a second feedback circuit, a first terminal of said second feedback circuit being connected to said input terminal of said signal amplification circuit, a second terminal of said second feedback circuit being connected to said output terminal of said signal amplification circuit, said second feedback circuit being configured to feed back an output signal of said signal amplification circuit to said input terminal of said signal amplification circuit.
5. A low noise audio amplifier according to claim 2, wherein said audio amplifier further comprises a first integrating circuit, said first integrating circuit is connected in parallel with said operational amplifier circuit, a first end of said first integrating circuit is connected to an input end of said operational amplifier circuit, and a second end of said first integrating circuit is connected to an output end of said operational amplifier circuit.
6. A low noise audio amplifier of claim 5, further comprising a second integrator circuit, said second integrator circuit being arranged in parallel with said operational amplifier circuit, a first terminal of said second integrator circuit being connected to said operational amplifier circuit input, and a second terminal of said second integrator circuit being connected to said operational amplifier circuit output.
7. A low noise audio amplifier according to any of claims 1 to 6, wherein said buffer adjusting circuit is a buffer.
8. A low noise audio amplifier according to claim 7, wherein said buffer is formed by an active amplifier of CMOS transistors.
9. An apparatus comprising a low noise audio amplifier as claimed in any one of claims 1 to 8.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210350361.3A CN114928335A (en) | 2022-04-04 | 2022-04-04 | Low-noise audio amplifier and equipment |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202210350361.3A CN114928335A (en) | 2022-04-04 | 2022-04-04 | Low-noise audio amplifier and equipment |
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| CN114928335A true CN114928335A (en) | 2022-08-19 |
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| CN202210350361.3A Pending CN114928335A (en) | 2022-04-04 | 2022-04-04 | Low-noise audio amplifier and equipment |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116668904A (en) * | 2022-12-21 | 2023-08-29 | 荣耀终端有限公司 | Audio circuit and electronic device |
| CN116668904B (en) * | 2022-12-21 | 2024-04-12 | 荣耀终端有限公司 | Audio circuit and electronic device |
-
2022
- 2022-04-04 CN CN202210350361.3A patent/CN114928335A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116668904A (en) * | 2022-12-21 | 2023-08-29 | 荣耀终端有限公司 | Audio circuit and electronic device |
| CN116668904B (en) * | 2022-12-21 | 2024-04-12 | 荣耀终端有限公司 | Audio circuit and electronic device |
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