JPS6242404B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an audio signal transmission circuit that mixes one of the audio signals from two audio signal sources with priority over the other audio signal using a simple circuit configuration. It is an object of the present invention to provide an audio signal transmission circuit which is capable of switching output with a small number of nozzles, can suitably mix and transmit one of the above audio signals with another audio signal, and is particularly suitable when implemented as an integrated circuit. purpose.

2. Description of the Related Art Various audio signal transmission circuits have been known in the past that can switch or mix one of audio signals from two audio signal sources and output the resulting signal, such as those shown in FIGS. 1 and 2, for example. In the conventional audio signal transmission circuit shown in FIG. 1, 1 is a jack into which a microphone plug (not shown) is inserted, and 2 is a line input terminal. Microphone (not shown)
In use, when the microphone plug is inserted into the jack 1, the movable contact piece 1a inside the jack 1 is pushed and separated from the contact 1b. As a result, the audio signal from the microphone passes through the contact 1b in the jack 1 and the shield wire 3, and then is supplied to the amplifier (microamp) 4 via a circuit consisting of a load resistor Ra and a capacitor Ca for high frequency removal. is amplified to the required level. The output audio signal of amplifier 4 is connected to capacitor Cc and resistor Rc.
are connected in series to the variable resistor VR ₁ , where the level is adjusted to the desired level, and then the variable resistor
It is output from the slider of VR ₁ via the coupling capacitor Cd from the output terminal 5.

On the other hand, input terminal 2 is connected to a tape recorder or
An audio signal from another device comes in at the audio line input terminal of the VTR, and is supplied to variable resistor VR ₁ via resistor Rb and capacitor Cb in series, where the level is adjusted to the desired level. , is output from the output terminal 5 from the slider via the capacitor Cd. Therefore, in the conventional circuit shown in FIG.
Audio signal from microphone and line input terminal 2
When one of the audio signals from another device is input, that audio signal is output, and when both are input, they are mixed and output.

Therefore, the conventional circuit shown in Fig. 1 cannot output only the audio signal from the microphone preferentially when audio signals are received from other devices, and even when the microphone is not in use, the amplifier cannot be output. There was a drawback that the noise of No. 4 was mixed into the input audio signal of the input terminal 2.

Further, in the conventional audio signal transmission circuit shown in FIG. 2, 6 is a jack, and when a microphone plug (not shown) is inserted, the contact 6a is grounded via a movable contact piece 6b. A normally closed contact 6c is connected to one end of the shielded wire 8, and a contact 6d is opened. As a result, when the microphone plug is not inserted, when an audio signal is supplied to the line input terminal 7 from another device,
This audio signal is supplied to the variable resistor VR ₂ via the resistor Rd, capacitor Ce, shield wire 8, contact 6c, and shield wire 10, where the level is adjusted, and then output from the output terminal 13 through the coupling capacitor Ci. .

On the other hand, when the microphone plug is inserted into the jack 6, the contact 6a is electrically connected to the microphone plug, and at the same time, the shield wire 12 is connected to the shield wire 10 via the contact 6d, and the normally closed contact 6c and the shielded wire 10 are disconnected. Therefore, the audio signal from the microphone is transmitted through a circuit consisting of the contact 6a, the shield wire 9, the high frequency removal capacitor Cf, and the resistor Re, and the capacitor Cg.
are supplied to the amplifier (microphone amplifier) 11, where they are amplified to the required level, and then supplied to the variable resistor VR ₂ through the capacitor Ch, the resistor Rf, the shield wire 12, the contact 6d, and the shield wire 10, respectively. The level is adjusted to the desired level. The microphone audio signal whose level is adjusted by the variable resistor VR ₂ and taken out is outputted from the output terminal 13 through the coupling capacitor Ci. Therefore, according to this conventional circuit, when audio signals from the microphone and other devices arrive at the same time, only the audio signal from the microphone is preferentially output from the output terminal 13.

However, this conventional circuit has disadvantages in that the number of shielded wires connected to the jack 6 is four, making it expensive, and since the input and output of the amplifier 11 are supplied to the jack 6, problems such as oscillation are likely to occur. It was hot.

The present invention eliminates the above-mentioned drawbacks,
Each embodiment will be described below with reference to FIGS. 3 and 4.

FIG. 3 shows the first audio signal transmission circuit according to the present invention.
A circuit diagram of an example is shown. In the figure, 14 is a jack into which a microphone plug is to be inserted, a contact 14a that contacts the microphone plug, and a normally closed contact 14 when no microphone plug is inserted.
b and is connected to the contact 14c during the period when the microphone plug is inserted.
It is composed of One end of the movable contact piece 14d is grounded, and the contact point 14a is connected to the shield wire 16.
through resistor R ₁ and high frequency rejection capacitor C ₁
connected to each non-ground terminal of the
It is connected to the non-inverting input terminal of operational amplifier 17 via _C2 . The operational amplifier 17 has an inverting input terminal connected to ground via a resistor R ₃ , a feedback resistor R ₄ , and an output terminal connected to an input terminal of an electronic switch circuit 18 . The electronic switch circuit 18 is configured to be opened and closed by a signal from the contact 14c, and its output terminal is connected to one end of a variable resistor _VR3 via a capacitor _C4 .

On the other hand, 15 is the line input terminal, and the capacitor
Variable resistor VR ₃ via C ₃ and resistor R ₂ in series, respectively.
connected to one end of the The other end of the variable resistor VR ₃ is grounded, and the slider is connected to the output terminal 19 via a coupling capacitor C ₅ . Therefore,
The number of shield wires is 16 in total (shield wire 1)
It consists only of books.

Here, the impedance when looking at the electronic switch circuit 18 side from the variable resistor VR ₃ is when the electronic switch circuit 18 is on (when the microphone plug is inserted).
If we call it Z _MIC , the Z _MIC is selected to have a low impedance of, for example, several tens of Ω, and
If the electronic switch circuit 18 is off (when the microphone plug is not inserted) and is Z _MUTE , then Z _{MU
The TE} is selected to have a high impedance of, for example, several hundred kΩ. Further, the electronic switch circuit 18 is turned off (opened) when the contact 14c is open;
It is configured to be turned on (closed) when 4c is grounded.

In the circuit shown in FIG. 3, the operation when the microphone plug is not inserted into the jack 14 will be explained first.
etc.), this audio signal is passed through capacitor C ₃ and resistor R ₂ to variable resistor.
The level is adjusted to a desired level by VR ₃ and output from the output terminal 19. Here, the impedance Z _MUTE when the microphone plug is not inserted is
500kΩ, the value of resistor R ₂ is 82kΩ, and the resistance value R of variable resistor VR ₃ is 15kΩ, the line input audio signal is (RZ _MUTE ) / {R ₂ + (RZ _MUTE )} = 0.151 = -16.43 (dB ) (1) is output to the output terminal 19 after being attenuated as follows. On the other hand, the nozzle from the microphone audio signal input side at this time receives an attenuation amount of (R ₂ R)/{Z _MUTE + (R ₂ R)} = 0.0247 = -32.13 (dB) (2). Therefore, when the microphone plug is not inserted into the jack 14, the incorporation of noise from the microphone audio signal transmission system is virtually no problem, and the audio signal that enters the line input terminal 15 is sent to the output terminal with a high S/N ratio. 19.

Next, the operation when the microphone plug is inserted into the jack 14 will be explained. At this time, the electronic switch circuit 18 is turned on. When the impedance Z _MIC is 15Ω, the line input audio signal is attenuated by the following attenuation: (RZ _MIC )/{R ₂ +(RZ _MIC )} = 0.000182 = −74.76 (dB) (3). This can be seen by comparing equations (1) and (3).
The incoming audio signal will be muted by 58.33 dB, which means that even if it enters the input terminal 15, it will not be output to the output terminal 19.

On the other hand, the output audio signal of the operational amplifier (microphone amplifier) 17 is given an extremely small amount of attenuation: (R ₂ R) / {Z _MIC + (R ₂ R)} = 0.9988 = -0.01 (dB) (4) It is output to the output terminal 19 almost as is. That is, the audio signal from the microphone is switched and outputted to the output terminal 19 at a high S/N ratio, giving priority to the line input signal.

Further, according to this embodiment, since the output of the operational amplifier 17 is not supplied to the jack 14, problems such as oscillation in the conventional circuit shown in FIG. 2 do not occur. Furthermore, since the switching control signal for the electronic switch circuit 18 is obtained from the jack 14, both the input audio signal input to the operational amplifier 17 and the output audio signal muting are controlled by the electronic switch circuit 18.
It can be done with just one. Furthermore, by selecting the output impedance of the electronic switch circuit 18 for muting noise from the microphone audio signal transmission system when the microphone plug is not inserted, it can also be used as a microphone audio signal priority switch.

Next, a second embodiment of the present invention will be described. FIG. 4 shows a circuit diagram of a second embodiment of the audio signal transmission circuit according to the present invention. In the figure, the same components as in FIG. 3 are designated by the same reference numerals. This embodiment further adds a circuit section to the first embodiment for mixing a microphone audio signal and a reproduced audio signal via a muting electronic switch circuit for muting the microphone amplifier output, and also integrates a predetermined circuit section. It is a circuit (IC). In FIG. 4, 20 is an IC, the operational amplifier 17,
Electronic switch circuit 18, together with resistors R ₃ and R ₄ ,
Amplifiers 22 and 23, an electronic switch circuit 24, and resistors R ₅ and R ₆ are each incorporated into the same IC.
A, B, C, D and E are terminal pins of IC20.

Reference numeral 21 denotes a reproduced audio signal input terminal, into which, for example, an audio signal reproduced from a magnetic tape by a magnetic head is input. Input terminal 21 is connected to amplifier 22 via capacitor C ₆ and terminal pin D.
Further, the output terminal of the operational amplifier 17 is connected to the input terminal of a switching electronic switch circuit 24 via an amplifier 23. The output terminal of electronic switch circuit 24 is connected to terminal pin E with resistor R ₆ connected to the output terminal of amplifier 22 via resistor R ₅ . The electronic switch circuit 24 is controlled to open and close by a signal from a contact 14c in the jack 14 that enters the terminal pin B, and is configured to be turned off when the contact 14c is open and turned on when the contact 14c is grounded. There is. Furthermore, the audio signal taken out from the output terminal 19 is recorded by the recording and reproducing device to which this circuit is applied, and is not used during reproduction.

Here, in order to mix the reproduced audio signal and the microphone audio signal that enter the input terminal 21, it is preferable to connect the input terminal of the amplifier 23 to the terminal pin C, since the electronic switch circuit 24 is not required. It seems that there is. However, when the electronic switch circuit 18 is off, the line input audio signal from the input terminal 15 enters the terminal pin C, so this line input audio signal is mixed with the reproduced audio signal. Therefore, as in this embodiment, a dedicated muting electronic switch circuit 2
It is necessary to use a configuration using 4.

In FIG. 4, when the microphone plug (not shown) is not inserted into the jack 14,
The electronic switch circuits 18 and 24 are each off,
The output noise of the amplifier 23 is generated by the electronic switch circuit 24.
transmission is blocked (muted) by
It is not mixed with the output audio signal of the amplifier 22.

Next, when the microphone plug is inserted into jack 14, electronic switch circuits 18 and 24 are turned on, respectively. As a result, the audio signal from the microphone is output to the output terminal 19 as described above, and is also supplied to the terminal pin E through the operational amplifier 17, the amplifier 23, the electronic switch circuit 24, and the resistor _R5 . On the other hand, the reproduced audio signal that has entered the input terminal 21 is supplied to the terminal pin E via the capacitor C ₆ , the terminal pin D, the amplifier 22 and the resistor R ₆ . That is, an audio signal obtained by mixing the microphone audio signal and the reproduced audio signal is taken out from the terminal pin E, and is outputted from the output terminal 25 through the capacitor _C7 .

In this embodiment, an electronic switch circuit 18 is used which also serves as a microphone audio signal priority switch as a muting switch for the microphone audio signal transmission system when the microphone plug is not inserted.
The number of terminal pins can be reduced by one, and it is also possible to prevent the line input audio signal from being mixed with the reproduced audio signal when the microphone plug is not inserted.

Note that if the output impedance of the operational amplifier 17 is increased by inserting and connecting a resistor in series between the connection point of the resistor R ₂ and the variable resistor VR ₃ and the capacitor C ₄ , the microphone audio signal and the line It is possible to obtain a mixed output with the input audio signal, providing a high degree of freedom in design.

Further, in each of the above embodiments, it has been explained that the microphone audio signal is output with priority over the line input audio signal, but the reverse may be done, and furthermore, the type of audio signal source is limited to the above embodiments. Of course, this is not the case (for example, the microphone audio signal may be an input audio signal from a DIN terminal).

As described above, the audio signal transmission circuit according to the present invention uses the output of the amplifier of the transmission system for the first audio signal in order to mute the output of the transmission system for the first audio signal when the first audio signal is not input. The output end of the muting switch circuit provided on the side and the second
The impedance of the switch circuit when viewed from the connection point with the output end of the audio signal transmission system is set so that it is high when the switch circuit is in muting operation and low when muting is not in operation. When the circuit is not muting, only the first audio signal is taken out from the connection point with priority, regardless of whether or not the second audio signal is input, so that the first audio signal and the second audio signal are When only one of the signals is input, the input audio signal can be transmitted with a high SN ratio, and the above switch circuit can also be used as a switch circuit for priority output of the first audio signal. The circuit configuration is simple, and
When integrated into an integrated circuit, the number of terminal pins can be minimized and only one shielded wire can be used, and when a jack is provided at the input end of the first audio signal transmission system. Since there is no need to supply the output audio signal of the amplifier to the jack, problems such as oscillation will not occur, and when the jack is provided at the input end of the first audio signal transmission system, the switch circuit Since the switching control signal is obtained from a predetermined contact point in this jack, it is possible to shoot the input signal of the amplifier and mute the output signal with just one switch circuit. providing a second switch circuit;
Since the first audio signal taken out from the second switch circuit is mixed with the reproduced third audio signal and transmitted, when mixed with the first audio signal taken out from the switch circuit, In comparison, it is possible to mix only the first audio signal with a high signal-to-noise ratio, and by incorporating each of the above circuits into the same integrated circuit, the circuit can be configured at a low cost and in a small size. It has the following features.

[Brief explanation of the drawing]

1 and 2 are circuit diagrams showing respective examples of conventional circuits, and FIGS. 3 and 4 are circuit diagrams showing respective embodiments of the circuit of the present invention. 1, 6, 14...Microphone jack,
2, 7, 15...Line input terminal, 4, 11, 1
7...Amplifier (mic amplifier), 5, 13, 1
9, 25...Output terminal, 18, 24...Electronic switch circuit, 20...Integrated circuit (IC), 21...Reproduction audio signal input terminal, _VR1 to _VR3 ...Variable resistor.

Claims (1)

[Claims] 1. Provided on the output side of the amplifier of the transmission line for the first audio signal in order to mute the output of the transmission system for the first audio signal when the first audio signal is not input. When the switch circuit is viewed from the connection point between the output end of the muting switch circuit and the output end of the second audio signal transmission system, the impedance becomes high during the muting operation by the switch circuit, and the impedance is high when the switch circuit is in the muting operation. When the switch circuit is in operation, it is set to be low, and when the muting of the switch circuit is not in operation, only the first audio signal is taken out from the connection point with priority, regardless of whether or not the second audio signal is input. An audio signal transmission circuit characterized by: 2. A first and second muting circuit provided on the output side of the amplifier of the transmission system for the first audio signal in order to mute the output of the transmission system for the first audio signal when the first audio signal is not input. The impedance of the second switch circuit when viewed from the connection point between the output end of the first switch circuit and the output end of the second audio signal transmission system is It is set to be high when the first switch circuit is muting, and low when the first switch circuit is not muting, regardless of whether or not the second audio signal is input when the first switch circuit is not muting. First, only the first audio signal is taken out as the audio signal to be recorded from the connection point, and the first audio signal taken out from the second switch circuit is used as the reproduced third audio signal. 1. An audio signal transmission circuit characterized in that the circuit is configured to mix and transmit audio signals. 3. A patent characterized in that the amplifier, the first and second switch circuits, and the circuit for mixing the second audio signal with the reproduced third audio signal are built into the same integrated circuit. An audio signal transmission circuit according to claim 2.