An automatic muting circuit

Abstract

The utility model relates to an automatic mute circuit, including a field effect tube Q2, a signal detection circuit and a signal control circuit, the field effect tube Q2 includes grid G, drain D and source S, drain D is connected with audio signal input end IN, the source S is connected with audio signal output end OUT, the grid G is connected with the output of signal control circuit, the signal detection circuit, its input is connected with drain D, and its output is connected with the input of signal control circuit, the utility model discloses according to the absence of the power amplifier of the external audio signal input to the detection, controls the intercommunication and the cut-off of the circuit of the external audio signal output to the power amplifier, has realized the function of automatic mute when no signal input, has eliminated the background noise of traditional power amplifier standby, has promoted the signal to noise ratio.

Description

Technical Field

[0001] This utility model relates to audio circuits, and in particular to an automatic mute circuit. Background Technology

[0002] A traditional power amplifier is an electronic device whose core function is to amplify the weak audio signal from an audio source (such as a CD player, microphone, etc.) by increasing its voltage and current, so that it has enough power to drive the speaker to produce sound.

[0003] However, while traditional power amplifiers should theoretically remain completely silent when there is no signal input (i.e., in standby mode), due to the inherent characteristics of the circuit itself (such as component thermal noise, power supply ripple, ground interference, etc.), a slight background noise (such as a hissing or humming sound) will still exist at its output. This noise will be amplified and played back by the connected speakers or monitoring equipment. Especially in high-end audio systems or high-sensitivity monitoring environments (such as recording studios), this background noise will interfere with the listening experience and reduce the purity of the sound quality.

[0004] Therefore, there is an urgent need to propose a circuit that can automatically mute the power amplifier and improve its signal-to-noise ratio when there is no signal input. Utility Model Content

[0005] Based on this, the purpose of this utility model is to overcome the defects or deficiencies of the prior art and provide an automatic mute circuit.

[0006] An automatic mute circuit includes a field-effect transistor Q2, a signal detection circuit, and a signal control circuit; The field-effect transistor Q2 includes a gate G, a drain D, and a source S. The drain D is connected to the audio signal input terminal, and the source S is connected to the audio signal output terminal. The gate G is connected to the output terminal of the signal control circuit. The signal detection circuit has its input terminal connected to the drain D and its output terminal connected to the input terminal of the signal control circuit.

[0007] The audio signal output terminal is connected to the power amplifier. When the signal detection circuit detects the presence of an external audio signal input, the signal control circuit will not output a control signal to the gate G of the field-effect transistor Q2. At this time, the drain D and source S are connected, meaning that the external audio signal is input from the audio signal input terminal and connected to the circuit of the audio signal output terminal, and the external audio signal can be output to the power amplifier. When the signal detection circuit of Q2 detects the absence of an external audio signal input, the signal control circuit outputs a control signal to the gate G of the field-effect transistor. At this time, the drain D and source S are disconnected, meaning that the circuit from the audio signal input terminal to the audio signal output terminal is cut off.

[0008] Compared with the prior art, the automatic mute circuit provided by this utility model controls the connection and disconnection of the circuit from which the external audio signal is output to the power amplifier based on the presence or absence of the detected external audio signal input to the power amplifier, thereby realizing the function of automatic mute when there is no signal input, eliminating the background noise of traditional power amplifiers in standby mode, and improving the signal-to-noise ratio.

[0009] In one embodiment, a Zener diode Q2 is also included, wherein the anode of the Zener diode Q2 is connected to the source S, and the cathode is connected to the drain D.

[0010] In one embodiment, the signal detection circuit includes a precision rectifier circuit and a voltage comparator circuit connected in series. The precision rectifier circuit is used to convert an external AC signal into a DC signal, and the voltage comparator circuit is used to compare the voltage signal output by the precision rectifier circuit with a reference voltage, and output different voltage signals to the signal control circuit according to the different comparison results. In one embodiment, the precision rectifier circuit includes a resistor R1, an operational amplifier U1A, diodes D1 and D2, and a resistor R2. One end of the resistor R1 is connected to the audio signal input terminal, and the other end is connected to the inverting input terminal of the operational amplifier U1A. The non-inverting input terminal of the operational amplifier U1A is grounded. The two power supply terminals of the operational amplifier U1A are respectively connected to a positive power supply voltage and a negative power supply voltage. The anode of diode D1 is connected to the inverting input terminal of the operational amplifier U1A, and its cathode is connected to the anode of diode D2. The anode of diode D2 is also connected to the output terminal of the operational amplifier U1A, and the cathode of diode D2 is connected to the voltage comparator circuit in the subsequent stage. One end of the resistor R2 is connected to the inverting input terminal of the operational amplifier U1A, and the other end is connected to the cathode of diode D2. In one embodiment, the voltage comparison circuit includes a comparator U2A, resistors R4 and R5 connected in series, and a positive power supply voltage connected to the other end of resistor R4. The other end of resistor R5 is grounded. A first connection point is established between resistors R4 and R5, and the voltage at this first connection point can be set by adjusting the power supply voltage and the resistance values ​​of resistors R4 and R5. The positive input terminal of comparator U2A is connected to the first connection point, and its inverting input terminal is connected to the negative terminal of diode D2 in the preceding precision rectifier circuit. The two power supply terminals of comparator U2A are connected to the positive and negative power supply voltages, respectively. The output terminal of comparator U2A is connected to the subsequent signal control circuit.

[0011] In one embodiment, the signal control circuit includes a PNP transistor Q3, resistors R6, R7, R8, R9, and capacitor C3; wherein the emitter of the PNP transistor Q3 is connected to the output terminal of the comparator U2A in the preceding voltage comparison circuit, and a resistor R6 is connected in series between the emitter and the output terminal of the comparator U2A; the base of the PNP transistor Q3 is connected to the resistor R7, the other end of the resistor R7 is grounded, and the collector of the PNP transistor Q3 is connected to the resistor R8; the other end of the resistor R8 is connected to the gate G of the field-effect transistor Q2, and the other end of the resistor R8 is also connected to the resistor R9, the other end of the resistor R9 is connected to the positive power supply voltage; and the capacitor C3 is connected in parallel with the resistor R9.

[0012] In one embodiment, the system further includes a capacitor C1, one end of which is connected to the negative terminal of the diode D2, and the other end of which is grounded; and a resistor R3 connected in parallel with the capacitor C1.

[0013] In one embodiment, a capacitor C2 is also included in parallel with the resistor R5.

[0014] In one embodiment, the positive power supply voltage is 15V, and the negative power supply voltage is -15V; The resistance of resistor R1 is 33KΩ, the resistance of resistor R2 is 100KΩ, the resistance of resistor R3 is 100KΩ, the resistance of resistor R4 is 10KΩ, the resistance of resistor R5 is 47Ω, the resistance of resistor R6 is 10KΩ, the resistance of resistor R7 is 470Ω, the resistance of resistor R8 is 5.1KΩ, and the resistance of resistor R9 is 47KΩ. The capacitance of capacitor C1 is 4.7μF, the capacitance of capacitor C2 is 0.1μF, and the capacitance of capacitor C3 is 1μF.

[0015] To better understand and implement this invention, the following detailed description is provided in conjunction with the accompanying drawings. Attached Figure Description

[0016] The present invention will now be described in detail with reference to the accompanying drawings.

[0017] Figure 1 A schematic diagram of an automatic mute circuit according to this utility model. Detailed Implementation

[0018] like Figure 1As shown, an automatic mute circuit of this utility model includes a field-effect transistor Q2, a signal detection circuit 10, and a signal control circuit 20. The field-effect transistor Q2 includes a gate G, a drain D, and a source S. The drain D is connected to the audio signal input terminal IN, and the source S is connected to the audio signal output terminal OUT. The gate G is connected to the output terminal of the signal control circuit 20. The input terminal of the signal detection circuit 10 is connected to the drain D, and the output terminal is connected to the input terminal of the signal control circuit 20.

[0019] The audio signal output terminal OUT is connected to the power amplifier. When the signal detection circuit 10 detects the presence of an external audio signal input, the signal control circuit 20 will not output a control signal to the gate G of the field-effect transistor Q2. At this time, the drain D and source S are connected, meaning that the external audio signal is input from the audio signal input terminal IN and connected to the circuit from the audio signal output terminal OUT, allowing the external audio signal to be output to the power amplifier. When the signal detection circuit 10 detects the absence of an external audio signal input, the signal control circuit 20 outputs a control signal to the gate G of the field-effect transistor Q2. At this time, the drain D and source S are disconnected, meaning that the circuit from the audio signal input terminal IN to the audio signal output terminal OUT is cut off, achieving the effect of automatic mute when there is no external audio signal input.

[0020] To prevent excessively high voltage from appearing between the source S and drain D of the field-effect transistor Q2, thereby protecting Q2 from damage, a Zener diode Q2 is also included. The anode of the Zener diode Q2 is connected to the source S, and its cathode is connected to the drain D.

[0021] In this application, the field-effect transistor Q2 is model number 2SK3018.

[0022] The signal detection circuit 10 includes a precision rectifier circuit 11 and a voltage comparison circuit 12 connected in series. The precision rectifier circuit 11 is used to convert an external AC signal into a DC signal. The voltage comparison circuit 12 is used to compare the voltage signal output by the precision rectifier circuit 11 with a reference voltage and output an intermediate signal to the signal control circuit 20 according to the comparison result.

[0023] The precision rectifier circuit 11 includes a resistor R1, an operational amplifier U1A, diodes D1 and D2, and a resistor R2. One end of the resistor R1 is connected to the audio signal input terminal IN, and the other end is connected to the inverting input terminal of the operational amplifier U1A. The non-inverting input terminal of the operational amplifier U1A is grounded. The two power supply terminals of the operational amplifier U1A are connected to the positive power supply voltage V+ and the negative power supply voltage V-, respectively. The anode of the diode D1 is connected to the inverting input terminal of the operational amplifier U1A, and its cathode is connected to the anode of the diode D2. The anode of the diode D2 is also connected to the output terminal of the operational amplifier U1A, and the cathode of the diode D2 is connected to the voltage comparator circuit 12 in the subsequent stage. One end of the resistor R2 is connected to the inverting input terminal of the operational amplifier U1A, and the other end is connected to the cathode of the diode D2.

[0024] Specifically, the positive power supply voltage V+ is 15V, and the negative power supply voltage V- is -15V.

[0025] Specifically, the voltage output of the precision rectifier circuit 11 can be changed by adjusting the ratio of resistor R1 to resistor R; in this application, the resistance of resistor R1 is 33KΩ and the resistance of resistor R2 is 100KΩ.

[0026] Specifically, the diodes D1 and D2 are of type 1N4148.

[0027] Specifically, the operational amplifier U1A is model NJM4580M.

[0028] Furthermore, in order to filter out any AC signals that may exist after processing by the precision rectifier circuit 11, a capacitor C1 is included, one end of which is connected to the negative terminal of the diode D2, and the other end of which is grounded; furthermore, a resistor R3 is included in parallel with the capacitor C1. In this application, the capacitance of the capacitor C1 is 4.7μF, and the resistance of the resistor R3 is 100KΩ.

[0029] The voltage comparison circuit 12 includes a comparator U2A, resistors R4 and R5 connected in series, and a positive power supply voltage V+ connected to the other end of resistor R4. The other end of resistor R5 is grounded. A first connection point is established between resistors R4 and R5, and the voltage at this first connection point can be set by adjusting the power supply voltage and the resistance values ​​of resistors R4 and R5. The positive input terminal of comparator U2A is connected to the first connection point, and its inverting input terminal is connected to the negative terminal of diode D2 in the preceding precision rectifier circuit 11. The two power supply terminals of comparator U2A are connected to the positive power supply voltage V+ and the negative power supply voltage V-, respectively. The output terminal of comparator U2A is connected to the subsequent signal control circuit 20.

[0030] In this application, the resistance of resistor R4 is 10KΩ and the resistance of resistor R5 is 47Ω.

[0031] Furthermore, in order to stabilize the voltage at the first connection point, a capacitor C2 is also included in parallel with the resistor R5. In this application, the capacitance of the capacitor C2 is 0.1μF.

[0032] Specifically, the comparator U2A is model LM393D.

[0033] When an external audio signal is present, the voltage at the inverting input terminal of comparator U2A is greater than the voltage at its non-inverting input terminal, and comparator U2A outputs a negative power supply voltage V-; when no external audio signal is present, the voltage at the inverting input terminal of comparator U2A is less than the voltage at its non-inverting input terminal, and comparator U2A outputs a positive power supply voltage V+.

[0034] The signal control circuit 20 includes a PNP transistor Q3, resistors R6, R7, R8, R9, and capacitor C3. The emitter of the PNP transistor Q3 is connected to the output of comparator U2A in the preceding voltage comparison circuit 12, and resistor R6 is connected in series between the emitter and the output of comparator U2A. The base of the PNP transistor Q3 is connected to resistor R7, the other end of which is grounded. The collector of the PNP transistor Q3 is connected to resistor R8. The other end of resistor R8 is connected to the gate G of the field-effect transistor Q2, and also to resistor R9, the other end of which is connected to a positive power supply voltage. Capacitor C3 is connected in parallel with resistor R9.

[0035] In this application, the resistance of resistor R6 is 10KΩ, the resistance of resistor R7 is 470Ω, the resistance of resistor R8 is 5.1KΩ, the resistance of resistor R9 is 47KΩ, and the capacitance of capacitor C3 is 1μF.

[0036] In this application, the PNP transistor Q3 is model BC857C.

[0037] Furthermore, a resistor R10 and a capacitor C4 are connected in series between the source S and the power amplifier; in this application, the resistance of the resistor R10 is 2.2KΩ and the capacitance of the capacitor C4 is 22μF.

[0038] When an external audio signal is present, the negative power supply voltage V- output by the comparator U2A cannot trigger the connection between the emitter and collector of the PNP transistor Q3. Therefore, no additional voltage is applied to the gate G of the field-effect transistor Q2. At this time, the drain D and source S are connected, that is, the circuit for outputting the external audio signal to the power amplifier is connected, and the external audio signal can be output to the power amplifier.

[0039] When there is no external audio signal, the comparator U2A outputs a positive power supply voltage V+, which first passes through resistor R6 and is then output to the emitter of the PNP transistor Q3, triggering the connection between the emitter and collector. Therefore, an additional voltage can be applied to the gate G of the field-effect transistor Q2, which in turn causes the drain D and source S to disconnect, that is, the circuit for outputting the external audio signal to the power amplifier is cut off, achieving the effect of automatic mute when there is no external audio signal input.

[0040] Compared with the prior art, the automatic mute circuit provided by this utility model controls the connection and disconnection of the circuit from which the external audio signal is output to the power amplifier based on the presence or absence of the detected external audio signal input to the power amplifier, thereby realizing the function of automatic mute when there is no signal input, eliminating the background noise of traditional power amplifiers in standby mode, and improving the signal-to-noise ratio.

[0041] The terminology used in the embodiments of this application is for the purpose of describing particular embodiments only and is not intended to limit the embodiments of this application. The singular forms “a,” “the,” and “the” used in the embodiments and claims of this application are also intended to include the plural forms, unless the context clearly indicates otherwise. It should also be understood that, unless otherwise stated, “a plurality” means two or more; the terms “first,” “second,” “third,” etc., are used only to distinguish and not to describe a particular order or sequence, nor should they be construed as indicating or implying relative importance. The term “and / or” as used herein refers to and includes any or all possible combinations of one or more associated listed items. When the above description relates to drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. In the description of this application, those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0042] The embodiments described above are merely examples of several implementations of this utility model, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the utility model patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this utility model, and these modifications and improvements all fall within the protection scope of this utility model.

Claims

1. An automatic muting circuit, characterized by, include: A field-effect transistor Q2, a signal detection circuit, and a signal control circuit; The field-effect transistor Q2 includes a gate G, a drain D, and a source S. The drain D is connected to the audio signal input terminal, and the source S is connected to the audio signal output terminal. The gate G is connected to the output terminal of the signal control circuit. The signal detection circuit has its input terminal connected to the drain D and its output terminal connected to the input terminal of the signal control circuit.

2. The automatic mute circuit according to claim 1, characterized in that: It also includes a field-effect transistor Q2, whose anode is connected to the source S and whose cathode is connected to the drain D.

3. The automatic mute circuit according to claim 1, characterized in that: The signal detection circuit includes a precision rectifier circuit and a voltage comparator circuit connected in series. The precision rectifier circuit is used to convert an external AC signal into a DC signal. The voltage comparator circuit is used to compare the voltage signal output by the precision rectifier circuit with a reference voltage and output different voltage signals to the signal control circuit according to the different comparison results.

4. The automatic mute circuit according to claim 3, characterized in that: The precision rectifier circuit includes a resistor R1, an operational amplifier U1A, diodes D1 and D2, and a resistor R2. One end of resistor R1 is connected to the audio signal input terminal, and the other end is connected to the inverting input terminal of operational amplifier U1A. The non-inverting input terminal of operational amplifier U1A is grounded. The two power supply terminals of operational amplifier U1A are connected to a positive power supply voltage and a negative power supply voltage, respectively. The anode of diode D1 is connected to the inverting input terminal of operational amplifier U1A, and its cathode is connected to the anode of diode D2. The anode of diode D2 is also connected to the output terminal of operational amplifier U1A, and the cathode of diode D2 is connected to the voltage comparator circuit in the subsequent stage. One end of resistor R2 is connected to the inverting input terminal of operational amplifier U1A, and the other end is connected to the cathode of diode D2.

5. The automatic mute circuit according to claim 4, characterized in that: It also includes a capacitor C1, one end of which is connected to the negative terminal of the diode D2, and the other end is grounded; and a resistor R3 connected in parallel with the capacitor C1.

6. The automatic mute circuit according to claim 5, characterized in that: The voltage comparison circuit includes a comparator U2A, resistors R4 and R5 connected in series, and a positive power supply voltage connected to the other end of resistor R4. The other end of resistor R5 is grounded. A first connection point is established between resistors R4 and R5. The voltage at this first connection point can be set by adjusting the power supply voltage and the resistance values ​​of resistors R4 and R5. The positive input terminal of comparator U2A is connected to the first connection point, and its inverting input terminal is connected to the negative terminal of diode D2 in the preceding precision rectifier circuit. The two power supply terminals of comparator U2A are connected to the positive and negative power supply voltages, respectively. The output terminal of comparator U2A is connected to the subsequent signal control circuit.

7. The automatic mute circuit according to claim 6, characterized in that: It also includes a capacitor C2 connected in parallel with the resistor R5.

8. The automatic mute circuit according to claim 6, characterized in that: The signal control circuit includes a PNP transistor Q3, resistors R6, R7, R8, R9, and capacitor C3. The emitter of PNP transistor Q3 is connected to the output of comparator U2A in the preceding voltage comparison circuit, and resistor R6 is connected in series between the emitter and the output of comparator U2A. The base of PNP transistor Q3 is connected to resistor R7, the other end of which is grounded. The collector of PNP transistor Q3 is connected to resistor R8. The other end of resistor R8 is connected to the gate G of field-effect transistor Q2 and also to resistor R9. The other end of resistor R9 is connected to a positive power supply voltage. Capacitor C3 is connected in parallel with resistor R9.

9. The automatic mute circuit according to claim 7, characterized in that: The positive power supply voltage is 15V, and the negative power supply voltage is -15V; The resistance of resistor R1 is 33KΩ, the resistance of resistor R2 is 100KΩ, the resistance of resistor R3 is 100KΩ, the resistance of resistor R4 is 10KΩ, and the resistance of resistor R5 is 47Ω. The capacitance of capacitor C1 is 4.7μF, and the capacitance of capacitor C2 is 0.1μF.

10. The automatic mute circuit according to claim 8, characterized in that: The positive power supply voltage is 15V; The resistance of resistor R6 is 10KΩ, the resistance of resistor R7 is 470Ω, the resistance of resistor R8 is 5.1KΩ, and the resistance of resistor R9 is 47KΩ. The capacitance of capacitor C3 is 1μF.

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