JPS5937737A - Automatic controlling circuit of volume of received voice - Google Patents

Abstract

PURPOSE:To prevent an excessive voice due to the attack delay time of a volume controlling circuit, by differentiating and applying a DC voltage to a variable control circuit and controlling the amount of passing attenuation. CONSTITUTION:When a switch is closed associatively with a key switch which is closed by operating the trunk-line button switch of a key telephone set, the DC voltage signal (d) is supplied to a differentiating circuit 12, which differentiates it with a time constant of hundreds of milliseconds. The resulting signal is applied as a control signal (c) to a variable attenuating circuit 4 through a diode 13 and the circuit 4 varies in the amount of attenuation according to the signal (c); the amount of attenuation right after the switch 11 is closed is extremely large and then decreased gradually thereafter. Consequently, the generation of an excessive voice due to the attach delay of the volume controlling circuit consisting of a rectifying circuit 8, holding circuit 9, etc., is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in an automatic volume control circuit for telephones and the like.

[Technical background of the invention and its problems]

1. Conventionally, an automatic voice volume adjustment circuit employed in, for example, a button telephone has been constructed as shown in FIG. In the figure, l is a subscriber line terminal, 2 is a power switch (for example, a central office line button switch) that opens and closes the connection with the subscriber line,
3 is a line transformer, 4 is a variable attenuation circuit that performs attenuation control of the signal obtained from the line transformer 3, 5 is an amplifier circuit, 6 is a speaker, 7 is a power amplifier circuit for driving the speaker 6, 8 is an amplifier circuit 5 a rectifier circuit that rectifies the output of
9 is a holding circuit that smoothes and holds the output from the rectifier circuit 8. Further, the variable attenuation circuit 4, the amplification circuit 5, the rectification circuit 8, and the holding circuit 9 constitute a volume control circuit.

The receiver back cover eye movement adjustment circuit configured as described above performs the following operations. First, electric switch 2 is closed,
The receiving signal a input from the subscriber line terminal 1 is input to the amplifier circuit 5 via the line transformer 3 and the variable attenuation circuit 4, and is amplified here.The amplified output of the amplifier circuit 5 is the rectifier circuit 8. It is held in the holding circuit 9 after being rectified by
The attenuation signal C is supplied to the variable attenuation circuit 4. Since the attenuation amount of the variable attenuation circuit 4 changes in response to this attenuation signal C (DC voltage), the output level of the amplifier circuit 5 remains unchanged even if the input level input via the subscriber line terminal l changes. remains constant.

Therefore, even if the input level input via the subscriber line terminal 1 fluctuates, the input level of the power amplifier circuit 7 is kept constant by the variable attenuation circuit 4, the amplifier circuit 5, the rectifier INr 8, and the holding circuit 9. Therefore, the volume of the received sound emitted from the speaker 6 is always kept constant.

However, in particular, in such a conventional automatic listening volume adjustment circuit, the rectified signal input to the holding circuit 9 is input to the variable attenuation circuit 4 with a delay time when the power switch 2 starts to close. This causes a delay in the automatic volume adjustment operation by the variable attenuation circuit 4 and the like, and as shown in FIG. 2, the level due to the attack response of the output of the amplifier circuit 5 increases significantly when a signal is applied or increased. For this reason, for example, when you make a call by operating the central office line button switch on a 1-phone switch, the beginning of the dial tone received from the exchange (υ after the line is connected) is abnormally thick (and the audibility is poor). 1. A problem occurred during use.In order to prevent this problem, simply shortening the delay time of the holding circuit 9 results in The feedback loop became unstable, causing problems such as shooting and level fluctuations, and in some cases oscillation and freezing.

[Purpose of the invention]

The present invention focuses on the above-mentioned circumstances, and is capable of preventing excessive noise immediately after a line is connected with a simple configuration.
It is an object of the present invention to provide an automatic adjustment circuit for receiving a sound that is advantageous in use.

[Summary of the invention]

Therefore, the present invention generates a differential signal in conjunction with a first switch connected to a wired communication line and controls connection to the wired line, and uses this differential signal as an attenuation signal.
The above objective is achieved by applying f to the variable attenuation circuit.

[Embodiments of the invention] Hereinafter, the present invention will be explained in detail with reference to the drawings.

FIG. 3 is a diagram showing an embodiment of the present invention applied to a reception amplification circuit of a button telephone set, and the same main parts as in FIG. In the figure, 10 is a DC power supply, 11 is a switch 2 which is opened when the storm switch 2 is opened and closed when it is closed, and 12 is a switch 1.
13 is a diode.

Also, these DC power supply 10, switch 11° differential circuit 12
．． and a diode 13 constitute a click prevention circuit.

Next, the operation of this embodiment will be explained with reference to the signal waveforms of each part shown in FIG. In conjunction with this, the switch 11 is also closed. Thereafter, the dial tone from the exchange that is input via the subscriber line terminal 1 is transmitted to the line transformer 3, variable attenuation circuit 4,
The signal passes through the amplifier circuit 5, is amplified by the power amplifier circuit 7, and drives the speaker 6. At this time, the switch 11 is also closed in conjunction with the power switch 2, and the attenuation signal C is introduced to the control input terminal of the variable attenuation circuit 40 via the ode 13. In the variable attenuation circuit 4, the attenuation jt (passage loss) changes based on the attenuation signal C (DC voltage n), so the switch 11
The amount of attenuation (loss) immediately after closing is extremely small and gradually decreases. Also, in the volume control circuit composed of the rectifier circuit 8, the holding circuit 9, etc., the gain is at the minimum in the initial state, so the volume set by the amplifier circuit 5 and the power amplifier circuit 7 is emitted from the speaker 6. .

Therefore, in the conventional circuit shown in FIG. 1, for a period of about several hundred m5 from this initial state to a steady state in which attenuation i (passage loss) is set based on attenuation signal C,
The amplified output of the amplifier circuit 5 was obtained at a level higher than the steady level. However, in the circuit according to this embodiment, during this divisor 100 m8 due to the delay of the holding circuit 9, the differential signal e
is supplied to the control input terminal of the variable attenuation circuit 40, so the amplified output of the amplifier circuit 5 will not become large as described above (and no excessive sound will be emitted from the speaker 6).

Furthermore, the clicking noise caused by the closing of the DC loop with the father exchanger when a wired communication line is connected can also be suppressed by this temporary change in attenuation amount.

Incidentally, during normal operation, the diode 13 is reverse biased and has a direct current potential applied thereto, and is in a cut-off state, and the electrical connection between the volume control circuit and the click prevention circuit is cut off. Therefore, during normal operation, there is no influence between the volume control circuit and the click prevention circuit.

By the way, the present invention is not limited to the above embodiment, and the switches 2 and 11 may be a central line switching relay of an automatic dialing device. Further, these switches 2 and 11 may be electronic switches other than the 5 mechanical interlocking switches.

〔Effect of the invention〕

As described above, according to the present invention, excessive sound caused by the attack delay time of the volume control circuit can be prevented, and call characteristics are improved.

Furthermore, click backs that occur immediately after a wired communication line is connected can be reduced, further improving call characteristics.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional automatic listening volume adjustment circuit, FIG. 2 is a diagram showing signal waveforms of each part, FIG. 3 is a block diagram showing an embodiment of the present invention, and FIG. It is a figure which shows the signal waveform of each part. 2...Electric switch, 4...Variable attenuation circuit,
5... Amplifier circuit, 8... Rectifier circuit, 9...
Holding circuit, 10... DC power supply, 11... Switch, 12... Differential circuit, 13... Diode,
C...attenuation signal, e...9 differential signal

Claims (1)

[Claims] A first switch connected to a wired communication line to control connection to the wired communication line, a variable attenuation means for controlling attenuation of a signal transmitted via the first switch, and an output of the variable attenuation means. a second switch connected to a DC power supply and interlocked with the first switch; and a DC voltage applied when the second switch is closed. click prevention means comprising a differentiating means for forming a differentiated signal and outputting the differentiated signal as an attenuation signal for a predetermined time through a control input of the variable attenuation means. Autoregulating circuit.