JPS6080311A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To improve the S/N by providing a muting circuit at each signal source to an input side of a mixing circuit so as to apply mixing control in response to an input signal level. CONSTITUTION:Muting circuits 141-14N to which a control input obtained by converting an output of amplifiers 61-6N into a DC level by a diode 16 are provided between amplifiers 61-6N provided at each signal source and the mixing circuit 8. When the input signal goes to a low level further, the titled circuit is constituted so that the muting circuits 141-14N are controlled to a open or low gain state. As a result, only a desired signal is extracted while mixing it at the mixing circuit 8, the effect of unnecessary noise component is avoided and the S/N is improved.

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 21,22...2N, and provides the level-adjusted signal to the amplifier 61,62...6N. The amplified output is mixed by a mixing circuit 8, and the mixed output can be taken out from an output terminal 10.

Conventionally, in this type of mixing amplifier circuit, for channels to which no audio input is given, the signal is cut off by adjusting the variable resistor 4, or by placing a switch (not shown) to cut off the signal input. This suppresses noise and prevents deterioration of the S/N ratio.

However, with this signal blocking, multiple microphones 2+,
22...It is necessary to operate the variable resistor 4 or switch installed every 2N by determining the presence or absence of signal input, which is time-consuming, has the risk of erroneous operation, and is difficult to adjust according to the signal input. there were.

An object of the present invention is to provide an amplifier circuit that enables mixing control according to the input levels of a plurality of signal sources.

The present invention is characterized in that a muting circuit is installed for each signal source on the input side of a mixing circuit that mixes signals from a plurality of signal sources, and the muting circuit is operated according to the signal level.

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, and the same parts as those in the circuit shown in FIG. 1 are given the same reference numerals. Amplifiers 61.62...6N are installed corresponding to the plurality of signal sources 12+, 122...12N, and the amplifiers 61.
62...6N and the mixing circuit 8 are provided with muting circuits 1411142...14N. This muting circuit 141.142...
- 14N is given a control input obtained by converting the outputs of the amplifiers 61, 62, . That is, the muting circuits 141, 142, . . . , 14N are composed of switches that open according to the output levels of the amplifiers 6I, 62, . . . , 6N, or amplifiers whose gain becomes 0 when no audio input is applied. .

With this configuration, when the audio input is at a low level, the muting circuit 141 .
As a result of selectively controlling 142...14N to an open state or a low gain state, only the desired audio signal can be mixed and extracted by the mixing circuit 8, avoiding the influence of unnecessary noise components, and reducing the SN ratio can be improved. Also,
Since the operation of unnecessary channels is stopped, the battery life of battery-powered portable devices can be extended.

Figure 3 shows muting circuits 141, 142...1
A specific example of the circuit configuration of 4N is shown, and parts common to those in the previous embodiment are given the same reference numerals. This embodiment shows channels in one signal system, and for multiple signal inputs, a plurality of circuits of this embodiment will be installed.

In this embodiment, the signal source 12 is composed of a microphone,
A capacitor 20, a resistor 22, .
24 is connected, the signal output obtained at the voltage dividing point of resistor 22.24 is rectified by diode 16, and the rectified output is connected to resistor 2.
6 and 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 whose gain is adjustable. The muting control circuit 30 controls the differential amplifier 32 according to the DC level generated in the capacitor 28.
It adjusts the gain of and performs muting control, and is composed of transistors 34 and 36 and a resistor 38.

Differential amplifier 32 constitutes a full feedback amplifier.

Transistor 40.42.44.46.48.50°5
2.54.56.58 and resistors 60, 62.64, and the base of the transistor 40 has a resistor 60.62.
．． A constant DC bias is applied at 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, and the DC level exceeds the threshold level of the transistor 34. If so, 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. For this reason,
The output of the amplifier 6 is sent to the output terminal 70 via the differential amplifier 32.
taken from.

However, when no audio input is given to the microphone 12, the output level of the amplifier 6 decreases by 5, and the capacitor 2
Since the DC level generated at 8 is below the threshold level of transistor 34, transistor 34 becomes non-conductive and differential amplifier 32 becomes inactive.

Figure 4 shows the output with respect to the input signal level, Vs
is a reference level that cuts 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 as described above, by cutting off the output, unnecessary noise output can be avoided and the S/N ratio can be improved.

FIG. 5 shows the muting circuits 141, 142...
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 via a resistor 72 between the emitters of transistors 40, 42 and the reference potential line. The differential amplifier 32 of this embodiment differs from the differential amplifier 32 in FIG. 3 in that it is configured to provide amplification gain.

A resistor 76 is connected between the output point and the reference potential line.
and a capacitor 78 are installed.

According to such a configuration, as shown in FIG.
By setting the output voltage VO to increase linearly with respect to It can be taken out.

Although each embodiment is explained using microphone mixing as an example, the same effect can be expected even if this invention is used as an amplification means for mixing signal sources 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 switch operations and volume operations as in the past, reducing the number of steps required for adjustment operations and the SN ratio due to erroneous operations. Deterioration can be prevented.

[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 block diagram showing a specific circuit configuration example of the amplifier circuit of the present invention. 4 is an explanatory diagram showing its operating characteristics, FIG. 5 is a circuit diagram showing another specific circuit configuration example of the amplifier circuit of the present invention, and FIG. 6 is an illustration of the amplifier circuit shown in FIG. 5. FIG. 7 is an explanatory diagram showing the input/output characteristics of the muting circuit, and FIG. 7 is an explanatory diagram showing the operating characteristics of the amplifier circuit shown in FIG. 8...Mixing circuit, 12.12+, 122...
12N...Signal source, 14.14+, 142...1
4N...muting circuit.

Claims (1)

[Claims] An amplifier circuit characterized in that a muting circuit is installed for each signal source on the input side of a mixing circuit that mixes signals from a plurality of signal sources, and the muting circuit is operated according to the signal level.