JPH0326566B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an amplifier circuit, and particularly to muting 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 .} The amplified output is mixed by the mixing circuit 8, and the mixed output can be taken out from the output terminal 10.

Conventionally, in this type of mixing amplifier circuit, for channels where audio input is not given, the signal is cut off by adjusting the variable resistor 4, or a switch (not shown) is installed to cut off the signal input. This suppresses noise and prevents deterioration of the S/N ratio.

However, in this signal blocking, it is necessary to operate the variable resistor 4 or switch installed for each of the plurality of microphones 2 ₁ , _{2 2} . Therefore, it was difficult to make adjustments according to the signal input.

Therefore, an object of the present invention is to provide an amplifier circuit that realizes mixing control of a plurality of signal sources according to their input levels.

That is, the amplifier circuit of the present invention has a plurality of signal sources 1
2, 12 ₁ , 12 ₂ ... installed corresponding to 12 _N ,
A plurality of first amplifiers (amplifiers 6, _{6 1} , 6 ₂ ... 6 _N
and a voltage divider circuit (resistors 22, 24) installed for each of these first amplifiers to receive the output signal of the first amplifier through the capacitor 20, divide the output signal and take out the voltage, and this voltage divider circuit. a diode 16 for rectifying the voltage-divided output signal through the diode 16;
A smoothing circuit (resistor 26 and capacitor 28) is installed on the output side of this diode and takes out a DC voltage representing the level of the output signal, and a first transistor 34 outputs the DC voltage obtained by this smoothing circuit. a muting control circuit 30, which includes a second transistor 36, which receives a base current through the first transistor and generates a control current according to the DC voltage; , a current mirror circuit including third and fourth transistors 40 and 42 having a common emitter, and a current mirror circuit having the base and collector of the fifth transistor 44 and the base of the sixth transistor 46 in common; 2
The control current flowing through the fifth transistor
By causing a current corresponding to the control current received by the base and collector of the transistor to flow through the sixth transistor, an operating current is supplied to the third and fourth transistors through the sixth transistor, and the operating current is supplied to the third and fourth transistors through the sixth transistor. The output signal of the first amplifier is applied to the base of the transistor No. 3, and
By feeding back the muting output to the base of the fourth transistor, the output taken out from the collector side of the third transistor and the output taken out from the collector side of the fourth transistor are combined. a second amplifier (operational amplifier 32) that generates the muting output;
It also includes a mixing circuit 8 which receives and synthesizes the respective outputs of the second amplifier.

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 ,
These amplifiers 6 ₁ , 6 ₂ ...6 _N and the mixing circuit 8
Muting circuits 14 ₁ , 14 ₂ ...1 are connected between
4 _N is installed. These muting circuits 14 ₁ , 14 _{2 .} . . 14 _N each include amplifiers 6 ₁ , 6 _{2 .}
A control input obtained by converting the output of . . . 6 _N to a DC level with a diode 16 is provided. That is, when the muting circuits 14 ₁ , 14 _{2 .} . . 14 _N are not given audio input _,
...6 It is composed of a switch that opens depending on the output level of _N , or an amplifier that has a gain of 0.

With this configuration, when the audio input is at a low level, the muting circuits 14 ₁ , _{14 2} . The mixing circuit 8 can mix and extract only the audio signals of the
ratio can be improved. Furthermore, since the operation of unnecessary channels is stopped, the battery life of portable devices powered by batteries can be extended.

Figure 3 shows the muting circuit 14 ₁ , 14 ₂ ...1
_4N is shown, and parts common to those in the previous embodiment are given the same reference numerals. 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 constituted by a microphone, and the first amplifier 6 amplifies the audio input thereof.
Connected between the output terminal 70 and the reference potential point terminal 18 are resistors 22 and 24 that constitute a voltage dividing circuit that receives the output signal of the amplifier 6 through a capacitor 20 and divides the output signal. The signal output obtained at the voltage dividing point is rectified by a diode 16, the rectified output is received by a resistor 26, and is smoothed by a capacitor 28 to obtain a DC level corresponding to the input signal level.

Further, the muting circuit 14 includes a muting control circuit 30 and a differential amplifier 32 as a second amplifier whose gain is adjustable. The muting control circuit 30 is a capacitor 2
Differential amplifier 32 depending on the DC level generated at 8
The first and second transistors 34, 34,
36 and a resistor 38. Differential amplifier 32 constitutes a full feedback amplifier.

Third and fourth transistors 40, 42 having a common emitter, these transistors 40, 42
A fifth transistor 4 having a common base and collector serves as a current mirror circuit that flows an operating current to
4. A sixth transistor 46 having a common base with the base collector of this transistor 44 is installed, and transistors 48, 50, 5
2, 54, 56, 58 and resistance 60, 62, 64
A constant DC bias is applied to the base of the transistor 40 by resistors 60, 62, and 64, and the amplified output of the amplifier 6 is applied via a DC blocking capacitor 66. A drive voltage Vcc is applied to the power supply terminal 68, and a signal output taken out from the output terminal 70 is applied to the mixing circuit 8.

According to such a configuration, the DC level obtained by rectifying the output of the amplifier 6 with the diode 16 and smoothing it with the capacitor 28 is applied to the base of the transistor 34;
, the transistor 34 becomes conductive. As a result, the transistor 36 becomes conductive, an operating current flows to the transistor 46 via the transistor 36, and the differential amplifier 32 performs normal amplification operation. As a result, the outputs of the transistors 40 and 42 are taken out through the transistors 48 and 50, combined and taken out by the output circuit of the transistors 52, 54, 56, and 58, and the input signal from the amplifier 6 is taken out through the differential amplifier 32. The signal is taken out from the output terminal 70 through the terminal.

However, when no audio input is given to the microphone 12, the output level decreases to the output level of the amplifier 6, and the DC level generated in the capacitor 28 becomes below the threshold level of the transistor 34, so the transistor 34 is in a non-conducting state. Then,
Differential amplifier 32 becomes inactive.

FIG. 4 shows the output with respect to the input signal level, where V _S is a reference level that shuts off the output when no audio input is provided, and corresponds to the threshold level of the transistor 34.
Therefore, when the input signal level is low like this,
By cutting off the output, unnecessary noise output can be avoided and the SN ratio can be improved.

FIG. 5 shows the mutating circuits 14 ₁ and 14 ₂
. . . _14N is shown, and the same parts as in the embodiment shown in FIG. 3 are given the same reference numerals. In this embodiment, the muting control circuit 30 is constituted by a buffer amplifier, and is applied to the base of a transistor 74 connected through a resistor 72 between the emitters of transistors 40 and 42 and a reference potential line. The operational amplifier 32 of this embodiment differs from the operational amplifier 32 in FIG. 3 in that it is configured to provide amplification gain. A resistor 76 and a capacitor 78 are installed between the output point and the reference potential line.

According to such a configuration, as shown in FIG. 6, when the input/output characteristics of the muting control circuit 30 are set such that the output voltage V _O increases linearly with respect to the input voltage V _IN , the input signal Muting control of the differential amplifier 32 can be performed according to the level, and the output of the differential amplifier 32 can be taken out as shown in FIG.

Although each embodiment is described using microphone mixing as an example, the same effects can be expected even if the present invention is utilized as an amplification means for mixing signal inputs from various signal sources other than microphones.

As explained above, according to the present invention, it is possible to perform mixing control according to the input signal level, eliminating the need for conventional switch operations and volume control, as well as simplifying the configuration and omitting adjustment operations. It is possible to prevent deterioration of the SN ratio due to erroneous operation.

[Brief explanation of drawings]

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. A circuit diagram, FIG. 4 is an explanatory diagram showing its operating characteristics, and FIG. 5 is a circuit diagram showing another specific example of the circuit configuration of the amplifier circuit of the present invention.
FIG. 6 is an explanatory diagram showing the input/output characteristics of the muting circuit in the amplifier circuit shown in FIG. 5, and FIG. 7 is an explanatory diagram showing the operating characteristics of the amplifier circuit shown in FIG. 6. 6, 6 ₁ , 6 ₂ ...6 _N ... first amplifier, 8 ...
Mixing circuit, 12, 12 ₁ , 12 ₂ ...12 _N ...
... Signal source, 14, 14 ₁ , 14 ₂ , ... 14 _N ... Muting circuit, 16 ... Diode, 20 ...
... Capacitor, 22, 24 ... Resistor (voltage divider circuit),
26... Resistor (smoothing circuit), 28... Capacitor (smoothing circuit), 30... Muting control circuit,
32... Differential amplifier (second amplifier), 34...
1st transistor, 36...2nd transistor, 40...3rd transistor, 42...4th transistor
transistor, 44...fifth transistor (part of the current mirror circuit), 46...6th transistor (part of the current mirror circuit).

Claims (1)

[Scope of Claims] 1. A plurality of first amplifiers installed corresponding to a plurality of signal sources and receiving input signals to be mixed from each signal source; and a plurality of first amplifiers installed for each of these first amplifiers, 1
Receives the output signal of the amplifier through a capacitor,
A voltage divider circuit that divides the voltage of the output signal and extracts it; a diode that rectifies the output signal divided through the voltage divider circuit; a smoothing circuit to take out; a first transistor that receives the DC voltage obtained by the smoothing circuit; a second transistor that receives a base current through the first transistor and generates a control current according to the DC voltage; and third and fourth transistors installed corresponding to the first amplifier and having a common emitter, and connecting the base and collector of the fifth transistor to the base and collector of the sixth transistor. A current mirror circuit having a common base is provided, the control current flowing through the second transistor is received by the base collector of the fifth transistor, and a current corresponding to the control current is caused to flow through the sixth transistor. By this, an operating current is supplied to the third and fourth transistors through the sixth transistor, the output signal of the first amplifier is applied to the base of the third transistor, and the output signal of the first amplifier is applied to the base of the third transistor. By feeding back the muting output to the base of the transistor, the output taken out from the collector side of the third transistor and the output taken out from the collector side of the fourth transistor are combined to generate the muting output. An amplifier circuit comprising: a second amplifier that receives and combines outputs of the second amplifier; and a mixing circuit that receives and combines outputs of the second amplifier.