JPH0456483B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and more particularly to signal level control of a mixing amplifier circuit that mixes and extracts a plurality of signals.

FIG. 1 shows an amplifier circuit for multi-channel microphone mixing. This mixing amplifier circuit is equipped with a variable resistor 4 that adjusts the output level of each of the plurality of microphones 2 ₁ , 2 ₂ . . . 2 _N.
The level-adjusted signals are applied to the amplifiers 6 ₁ , _{6 2} .

Conventionally, in this type of mixing amplifier circuit, the audio input level is adjusted by operating the variable resistor 4, but it is very time-consuming to obtain the desired level by operating the variable resistor 4 in this way. It takes.
For example, in a portable mixing amplifier circuit, when instantaneous recording is enabled, each microphone 2 ₁ , 2 ₂ . . .
...2 It is difficult to immediately grasp the level of the audio signal arriving at _N , and it is difficult to set its recording level.

In addition, when the circuit is composed of semiconductor integrated circuits,
The variable resistor 4 is an external component, which may lower the reliability of signal level adjustment and increase the set price.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an amplifier circuit that adjusts the signal level to be mixed according to the level of input signals from a plurality of signal sources, and achieves mixing of the level-adjusted input signals.

That is, the amplifier circuit of the present invention includes a plurality of signal sources 12 ₁ and 12 ₂ that generate input signals to be mixed.
. . . 12 _N , a microphone 12, a resistor 13 installed for each signal source and inserted in a signal path receiving the input signal from each signal source, and a buffer circuit (second
amplifier 14 ₁ , 14 ₂ ... 14 _N , amplifier 14)
and a rectifier circuit (diode 16 and capacitor 18) that rectifies the output signal of this buffer circuit and extracts a DC voltage representing the level of the output signal.
A differential pair is installed in which the emitters of first and second transistors 32 and 34 are common, and when the DC voltage is applied to the base from the rectifier circuit, an operating current corresponding to the DC voltage is applied to the differential pair. A third transistor 36 is installed on the emitter side of the differential pair, and an output section (transistors 38, 40, 42, 4
4, 46, 48), the output part of which is connected to the base of the first transistor and the input part of the buffer circuit, and a constant bias voltage is applied to the second transistor. By setting, a resistor circuit (resistors 49, 50) having a resistance value corresponding to the DC voltage is formed, and the buffer circuit is electronic volume circuit 20 ₁ that suppresses the signal level for
20 ₂ . . . 20 _N , and a mixing circuit 8 for adding and extracting each output signal obtained from each of the buffer circuits.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings.

FIG. 2 shows an embodiment of the amplifier circuit of the present invention,
The same parts as the circuit shown in FIG. 1 are given the same reference numerals. First amplifiers 6 ₁ , 6 2 ... 6 _N are installed corresponding to the plurality of signal sources 12 ₁ , 12 ₂ ... 12 _N , and the mixing circuit 8 and each amplifier 6 ₁ , _{6 2 ...} 6 _N are connected to each other. Second amplifiers 14 ₁ , 14 ₂ . . . 14 _N as buffer circuits are installed between them via a first resistor 13 inserted in the input signal path.
A diode 16 for rectifying the output is installed on the output side of each amplifier 14 ₁ , 14 _{2 .} Electronic volume circuits 20 ₁ , 20 _{2 .} . . 20 _N are installed, and the input levels of the amplifiers 14 ₁ , _{14 2} . That is, electronic volume circuits 20 ₁ , 20 ₂
. . . 20 _N has an impedance adjusted by the output signal level of the amplifiers 14 ₁ , 14 _{2 .} The circuit constitutes a voltage circuit, and the voltage division ratio with respect to the resistor 13 changes as the resistance value changes, thereby controlling the input signal level to the amplifiers 14 ₁ , 14 ₂ . . . 14 _N.

With this configuration, the signal sources 12 ₁ , 12 ₂ . . .
... _12N , the signal given from the first amplifier 6
₁ , 6 ₂ ... 6 _N , and the amplified output is amplified by the second amplifier 14 ₁ , 14 ₂ ... 14
given to _N. This amplifier 14 ₁ , 14 ₂ ...1
The amplified output of 4 _N is rectified by a diode 16, smoothed by a capacitor 18, and then
The DC level generated corresponds to the signal input level. This DC level becomes the control input for the electronic volume circuits 20 ₁ , 20 ₂ . . . 20 _N ,
Its impedance is controlled according to the input signal level. As a result, amplifiers 14 ₁ , 14 ₂ . . .
14 _N input levels are adjusted and each amplifier 14 ₁ ,
As a result of adjusting the output level of 14 ₂ ...14 _N ,
The signals with uniform levels are applied to the mixing circuit 8, and mixing is performed. Therefore, the audio playback output or recording signal level can be automatically adjusted to a desired level without the need for individual manipulation of conventional variable resistors. Moreover, the signal sources 12 ₁ , 12 ₂ . . .
This circuit can automatically adjust fluctuations in the output level when electrical characteristics such as sensitivity of ...12 _N are non-uniform.

Moreover, compared to conventional level adjustment using variable resistors, reliability can be improved, and all circuits can be constructed from semiconductor integrated circuits.
The cost can also be reduced by omitting the variable resistor, which is an external component.

FIG. 3 shows a specific example of the circuit configuration of the amplifier circuit of the present invention, and the same reference numerals are given to the same parts as in the above embodiment. This embodiment shows a channel in one signal system, and when multiple signals are input, a plurality of circuits of this embodiment are installed.

In this embodiment, the signal source 12 is composed of a microphone, and a resistor 22, a capacitor 24, and a resistor 2 are connected between the output point of the second amplifier 14 and the reference potential point.
6 are connected in series, the divided voltage output generated at the resistor 26 is rectified by the diode 16, the rectified output is received by the resistor 28, and is smoothed by the capacitor 18 to obtain a DC level according to the input signal level. , its DC level is given to control input terminals 30A and 30B of the electronic volume circuit 20.
Further, the electronic volume circuit 20 constitutes a full feedback differential amplifier, one input of which is set at a reference level, and its operating current is controlled by the DC level. That is, this electronic volume circuit 20 includes first and second transistors 3 forming a differential pair whose emitters are commonly connected.
2, 34, and first and second transistors 32,
Transistor 3 is connected to the emitter side of transistor 3 and transmits an operating current according to the DC voltage applied to the base.
2, 34, transistors 38, 40, 42, 44, 46, 48 forming an output section that combines the outputs taken out from the collectors of transistors 32, 34, It consists of resistors 49 and 50 that set a constant bias voltage, and the power supply terminal 5
A drive voltage V _CC is applied to 2, and the input point of the amplifier 14 is commonly connected to the volume terminal 54 .

The operation in such a configuration will be explained. The audio input from the microphone 12 is amplified by the amplifier 6 and then given to the amplifier 14.
It is applied to the volume terminal 54 of the electronic volume circuit 20. The output of amplifier 14 is developed at resistor 26, but this signal is rectified by diode 16,
The signal is smoothed by a capacitor 18 and converted into a DC level corresponding to the signal level. This DC level is
This becomes a control input for the transistor 36 of the electronic volume circuit 20, and the current of the transistor 36 corresponds to the DC level. That is, the operating current of the differential amplifier composed of the pair of transistors 32 and 34 is determined by the current of the transistor 36, and the DC potential of the base of the transistor 34 is determined by the current of the transistor 36.
It is held constant by the midpoint potential of 9 and 50. Therefore, when capturing a transient operating point, the ratio of current flowing through the transistors 32 and 34 changes in comparison with the signal level applied to the base of the transistor 32, and the current output changes from the current output to the transistor 40,
The outputs of the current mirror circuit consisting of transistors 42 and 42 and the current mirror circuit consisting of transistors 38 and 44 are combined into currents by the current mirror circuit of transistors 46 and 48, and if the input signal level is large, a It acts to suppress the applied signal level. Furthermore, when the input signal level is low, such effects can be suppressed. This electronic volume circuit 2
0 will be described in detail. When a DC voltage corresponding to the output signal level is applied to the base of the transistor 36, a current corresponding to the base input flows through the transistor 36. This current is shunted to each transistor 32, 34 as an operating current of the transistor 32, 34 forming a differential pair. A constant bias voltage is set at the base of the transistor 34 by a voltage dividing circuit including resistors 49 and 50, and the current flowing through the transistor 34 is regulated by this bias voltage. Therefore, the current flowing into the transistor 36 is
Although the current is divided into transistors 2 and 34, one of them is regulated by the bias voltage, so that the transistor 32
A current will flow due to the balanced operation of both. The current flowing through each transistor 32, 34 is
The signals are taken out through a current mirror circuit and combined by transistors 44 and 48. That is, the transistor 48 sinks a current according to the input voltage, and when viewed in terms of resistance change, it is equivalent to a variable resistance for the resistor 13. As a result, a variable resistor is connected to the resistor 13 having a constant resistance value, and an input signal corresponding to the output signal level is taken out at a voltage dividing point between the two.

The operation of such electronic volume circuit 20 is as follows.
Electronic volume circuit 2 corresponding to the input signal level
This is equivalent to varying the impedance on the 0 side, and functions to suppress the signal when the signal level is high, and to reduce the degree of suppression when the signal level is low. As a result, the signal input level of the amplifier 14 is adjusted to a constant level, and the output level of the amplifier 14 becomes constant and is input to the mixing circuit 8.

Since the signal level input to the mixing circuit 8 is adjusted in accordance with the input signal level using the electronic volume circuit 20, the mixing output is balanced for each signal, eliminating the inconvenience of conventional resistance adjustment. In addition to eliminating the noise, it also improves the reliability of signal mixing, making it suitable for recording mixing, etc.
Another advantage is that irregularities in the characteristics of the microphones 12 can be adjusted within the electronic circuit. In the case of this embodiment, all the circuits except for the capacitors 18 and 24 are constructed of semiconductor integrated circuits, and the conventional variable resistor can be removed to simplify the construction. Furthermore, when using the electronic volume circuit 20, it is impossible to immediately set a desired signal level using a conventional variable resistor.
With IC, the output signal level can be immediately fed back to the input signal level side, and level control can be performed according to the amount of feedback, allowing for stable level control and mixing operation. In particular, the electronic volume circuit 20 shown in FIG. 3 can be integrated into an IC together with the amplifier 14, and since it is composed of a differential amplifier and a current mirror circuit, stable operation can be achieved with an extremely simple configuration. can get.

Although microphone mixing has been described in the embodiment, the present invention can be utilized for mixing signals from various signal sources other than microphones, and similar effects can be expected.

As explained above, according to the present invention, it is possible to adjust each level of a plurality of input signals added from each signal source to be mixed to an appropriate level, and also to adjust the input signal level to the mixing circuit to an electronic volume circuit. In addition, compared to the case of using conventional variable resistors, there is no need to perform level adjustment individually, and semiconductor integrated circuits are compact and require less external components. Automatic level adjustment can improve the reliability of mixing, and the reduction in variable resistors can simplify the circuit configuration and reduce manufacturing costs.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional mixing amplifier circuit, FIG. 2 is a block diagram showing an embodiment of the amplifier circuit of the present invention, and FIG. 3 is a specific example of the circuit configuration of the amplifier circuit of the present invention. It is a circuit diagram. 8... Mixing circuit, 12, 12 ₁ , 12 ₂ ...
...12 _N ... Signal source, 13 ... First resistor, 14,
14 ₁ , 14 ₂ ... 14 _N ... Second amplifier (buffer circuit), 16 ... Diode (rectifier circuit), 2
0,20 ₁ ,20 ₂ ...20 _N ...Electronic volume circuit, 32...First transistor, 34...Second transistor, 36...Third transistor, 38,40,42,44,46 , 48...transistor (output section).

Claims (1)

[Claims] 1. A plurality of signal sources that generate input signals to be mixed; a resistor installed for each signal source and inserted in a signal path for receiving the input signal from each signal source; and this resistor. a buffer circuit that receives the input signal through the buffer circuit; a rectifier circuit that rectifies the output signal of the buffer circuit to extract a DC voltage representing the level of the output signal; A third transistor is installed on the emitter side of the differential pair, and a third transistor is installed on the emitter side of the differential pair, and the DC voltage is applied to the base from the rectifier circuit, and an operating current corresponding to the DC voltage flows through the differential pair.
An output section is installed to combine and output outputs taken out from the collector sides of the first and second transistors, and this output section is connected to the base of the first transistor and connected to the input section of the buffer circuit. By connecting and setting a constant bias voltage to the second transistor, a resistance circuit is formed having a resistance value according to the DC voltage, and the resistance value of this resistance circuit and the resistance value of the resistance are An amplification characterized by comprising: an electronic volume circuit that suppresses a signal level to the buffer circuit by a voltage division ratio according to the above, and a mixing circuit that adds and extracts each output signal obtained from each of the buffer circuits. circuit.