JPH0218785B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a side sound level control method for a side sound prevention circuit.

[Technical background of the invention and its problems]

A conventional side sound prevention circuit has two variable impedance balanced circuit networks, and optimal side sound characteristics are obtained in the following manner. First, one of the two balanced circuit networks is connected to a speech path, and the other balanced circuit is controlled to produce a side tone smaller than that obtained by the balanced circuit network connected to the above communication path. At this point, replace the balanced network connected to the communication path and control the balanced network not connected to the communication path so that the balanced network connected to the above communication path At this point, the balanced circuitry connecting the communication path is replaced. Thereafter, the operation is repeated in the same manner until the sidetone does not become any smaller.

However, this side sound prevention circuit requires two variable impedance balanced circuit networks, is expensive, and requires a lot of time to control, making it impractical.

Therefore, one balanced network is fixed, and the other
A side sound protection circuit with variable balanced circuit networks has been proposed. This sidetone prevention circuit initially connects a fixed impedance balanced circuit network to the communication path, changes the impedance of the variable impedance balanced circuit network to a plurality of preset values, and then changes the sidetone level in that case. and compare the sidetone level when the sidetone level is at its minimum with the sidetone level obtained by a fixed impedance balanced circuit network.
When the sidetone level caused by the fixed impedance balanced circuit network is small, it is left as is, and when the sidetone level caused by the variable impedance balanced circuit network is small, the impedance of the variable impedance balanced circuit network is set to the value when the sidetone is minimum, and this variable impedance balanced circuit is changed. It connects the circuit network to the communication path.

However, in the side sound prevention circuit adopting this method, the timing at which the above-described operation is started coincides with, for example, when the power is turned on, so that the impedance once set cannot be changed.
Therefore, even if the call becomes a conference call, the line impedance changes, and the sidetone level increases during the call, the characteristics are not corrected. Moreover, before the DC loop of the line is formed, sidetone level measurements are started, and a balanced network of incorrect impedance is connected to the speech line, which therefore does not function well as a sidetone protection circuit. There was a possibility that I wouldn't get it.

[Purpose of the invention]

The present invention has been made in view of the above-mentioned circumstances, and its purpose is to provide a side sound level control method for a side sound protection circuit to always maintain the optimum characteristics of the side sound protection circuit. .

[Summary of the invention]

Therefore, in the present invention, a first bridge circuit having a fixed impedance balanced circuit network, a second bridge circuit having a variable impedance balanced circuit network, and one of the signals passing through the first and second bridge circuits is received. a switch for switching so that the signal reaches the transmission line; a transmitting circuit that outputs a transmitting signal; and a transmitting circuit that outputs a transmitting signal so that the signal that initially passed through the first bridge circuit reaches the receiving transmission line; inputting a signal and a signal resulting from the output signal of the transmitter circuit passing through the first and second bridge circuits;
Determining the sidetone level based on these signals, and determining the sidetone level by varying the impedance of the variable impedance balancing circuit network,
The variable impedance balancing circuit network is controlled so that the impedance corresponds to the minimum value among the determined sidetone levels, and the switch is switched so that the signal passing through the second bridge circuit reaches the reception transmission line. In the side sound prevention circuit comprising a control section, the operation of the control section for determining the side sound level is started by an operation start instruction signal other than a signal caused by turning on the power.

[Embodiments of the invention]

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a block diagram of an embodiment of a side sound prevention circuit to which the method of the present invention is applied. In the figure, 1
indicates line impedance (Z _L ). A sensor 2 is connected to the line impedance 1 to detect whether or not the DC loop of the line is closed.
It is now being sent to This sensor 2
A line transformer 3 is connected to the line transformer 3 to allow only AC signals to pass therethrough. The signal flowing through this line transformer is directly transmitted to the differential amplifiers 10 and 11.
The input terminals are connected to one input terminal of each of the input terminals. Further, a resistor 4 is connected to the line transformer 3, and a transmitting circuit 7 is connected to the resistor 4. A resistor 6 is connected between the connection point between the resistor 4 and the transmitter circuit 7 and an input terminal of the differential amplifier 10 that is not directly connected to the line transformer 3. A resistor 5 is connected between the connection point of the differential amplifier 11 and an input terminal of the differential amplifier 11 that is not directly connected to the line transformer 3 .

Further, a variable impedance balanced network 8 is connected to the connection point between the resistor 5 and the differential amplifier 11, and a fixed impedance balanced network 9 is connected to the connection point between the resistor 6 and the differential amplifier 10. There is.

The output terminal of the differential amplifier 10 is connected to the switch 19, the output terminal of the differential amplifier 11 is connected to the switch 20, the output sides of the switches 19 and 20 are wired-OR connected, and this connection point is connected to the receiver. It is connected to the transmission line terminal 21.

In the above configuration, the resistors 4 and 6, the fixed impedance balanced network 9, and the differential amplifier 10 are
The resistors 4 and 5, the variable impedance balanced circuit network 8, and the differential amplifier 11 constitute a second bridge circuit.

15 indicates a control section. This control section 15 includes a microcomputer and controls each section shown in the figure. That is, the signal that has passed through the first bridge circuit is input via the signal line 12, and the signal that has passed through the first bridge circuit is input.
3, the output signal of the transmitter circuit 7 is inputted via the signal line 14, and the output signal from the transmitter circuit 7 is inputted via the signal line 16 to the sensor 2.
Input the output signal of Then, the control unit 15
If the input from the signal line 14 is A, the input from the signal line 12 is B, and the input from the signal line 13 is C, then
B/A and C/A are determined as sidetone levels. Further, the control unit 15 outputs a control signal from the signal line 17, controls the variable impedance balancing circuit network 8 so as to achieve a plurality of preset impedances, and calculates the C/A at each impedance.

Note that the control unit 15 initially controls the switch 1
A control signal is outputted via the signal line 18 so that the switch 9 is closed and the switch 20 is opened. Also, when determining the sidetone levels B/A and C/A, the signal line 12
The control unit 15 uses the inputs A, B, and C as valid only when the input B from the signal line 13 and the input C from the signal line 13 are at a significant level. That is, when the input signals B and C from the signal lines 12 and 13 are lower than the level of the signal output from the transmitting circuit 7, the input signals A, B, and C are discarded.

The sidetone level found in the above manner is
When all the sidetone levels are memorized and finally all the sidetone levels are determined, the control unit 15 compares them and
If there is a smallest one in C/A, signal line 17
A control signal is outputted from the switch to control the variable impedance balancing circuit network 8 so as to obtain the corresponding impedance value, and a control signal is output from the signal line 18 to open the switch 19 and close the switch 20. control as follows.

As described above, close switch 19, switch 2
The operation start instruction signal that instructs the start of the operation from the control to open the switch 19 to the control to close the switch 20 is generated by the sensor 2 and the sidetone level control performed by the control unit 15. The control unit 15 operates according to the flow chart obtained by measurement and shown in FIG. 2, for example.

That is, when the power is turned on, the control section 15 outputs a control signal via the signal line 18, and the switch 1 is turned on.
9 is closed and switch 20 is opened. Then, the output signal of the sensor 2 is taken in from the signal line 16,
In the judgment step of “Is the DC lube closed?”
This determination is repeated until a signal from sensor 2 indicating that the DC loop of the line is closed is obtained.
When a signal indicating that the DC loop of the line is closed is obtained, the "operation" routine is entered and the operation as described above is performed. Then, switch 19 is opened and switch 20 is closed. Therefore, in the flow up to this point, the operation start instruction signal has been output from the sensor 2.

Next, the control unit 15 executes the step "Has the sidetone level reached the reference value?" in FIG. 2. That is, the memory in the control unit 15 stores a predetermined reference value (for example, a value slightly smaller than the sidetone level B/A by the fixed impedance balanced circuit network 9).
is stored, and the control unit 15 compares this with the minimum value of the sidetone level (minimum value in C/A) obtained in the above operation, and if the reference value has not been reached, the control unit 15 switches the switch 19. Close the switch 20, open the switch 20, and restart the operation from the step "Is the DC loop closed?" in FIG.

In addition, if the reference value has been reached, the control unit 1
5, for example, calculates C/A at regular intervals using a built-in timer, and first compares it with the finally determined sidetone level to ask, "Has the sidetone level increased?" This is done in the following steps. If YES, the switch 19 is closed, the switch 20 is opened, and the following operations are performed again: "Is the DC loop closed?"

If the sidetone level has not increased, the process returns to the step "Has the sidetone level reached the reference value?" and performs the following operations according to the flowchart.

The sensor 2 used in the above explanation is a loop current detection circuit used in, for example, a telephone. Further, the variable impedance balanced circuit network 8 is
For example, assume that a balanced network known as a six-element configuration is used. Furthermore, when the control section 15 obtains the sidetone levels B/A and C/A, it is possible to convert the captured analog signal into a digital signal and calculate it using a microcomputer. A rectifier circuit and a log conversion circuit are provided, the input analog signal is converted into a DC level signal, this is log converted, and the difference is calculated by a microcomputer to approximately obtain B/A,
Try to find C/A.

〔Effect of the invention〕

As described above, according to the present invention, the operation to maintain the side sound level at an optimum level is performed at appropriate timing, so that the side sound prevention circuit always has optimum characteristics.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an embodiment of a side sound prevention circuit using the method of the present invention, and FIG. 2 is a flowchart for explaining the method of the present invention. 1...Line impedance, 2...Sensor,
3... Line transformer, 4, 5, 6... Resistor, 7...
...Talking circuit, 8...Variable impedance balanced circuit network, 9...Fixed impedance balanced circuit network, 1
0, 11...Differential amplifier, 15...Control unit, 1
9,20...Switch.

Claims (1)

[Claims] 1. A first circuit having a fixed impedance balanced network.
a bridge circuit, a second bridge circuit having a variable impedance balanced circuit network, a switch for switching so that one of the signals passing through the first and second bridge circuits reaches the receiving transmission line, and a transmitting signal. and a signal that initially passed through the first bridge circuit to reach the receiving transmission line, and the output signal of the transmitting circuit and the output signal of the transmitting circuit are connected to the first bridge circuit. and the signal resulting from passing through the second bridge circuit, and determine the sidetone level based on these signals, and change the impedance of the variable impedance balanced circuit network to determine the sidetone level. controlling the variable impedance balancing circuit network so that the impedance corresponds to the minimum value among the sidetone levels determined, and switching the switch so that the signal passing through the second bridge circuit reaches the reception transmission path; A side sound prevention circuit comprising: a side sound prevention circuit comprising: an operation start instruction signal other than a signal caused by power-on to start the operation of determining the side sound level of the control section; Level control method. 2. A patent characterized in that the operation start instruction signal is an output signal of a sensor that detects whether the DC loop of the line is closed, and the operation of the control unit is started when the DC loop of the line is closed. A side sound level control system for a side sound prevention circuit according to claim 1. 3. The side sound prevention signal according to claim 1, wherein the operation start instruction signal is emitted when the side sound level determined by the control unit based on the first operation does not reach a reference value. Circuit sidetone level control method. 4. The sidetone level control system for a sidetone protection circuit according to claim 1, wherein the operation start instruction signal is issued when the sidetone level increases after reaching a reference value.