JPS60112348A - Anti-side tone circuit - Google Patents

Abstract

PURPOSE:To enable wide setting of an impedance variable area only by making one impedance out of two balanced circuit networks variable and to obtain appropriate antiside tone characteristics, by determining a ratio between a transmission output level and a side tone level as side tone attenuation and setting impedance of the optimum balanced circuit network. CONSTITUTION:The first bridge circuit is composed of the first and second resistors 21 and 22, a fixed impedance balanced circuit network 24 and a differential amplifier 26. The second bridge circuit consists of the first and third resistors 21 and 23, a variable impedance balanced circuit network 25 and a differential amplifier 27. A signal made into anti-side tone is sent out by the fixed impedance balanced circuit network 24 between call-receiving transmission line connection terminals 2 and 2'. ON the other hand, a controller 29 sends out a signal to the network 25 via a signal line 30a, converts the impedance into a prescribed value, determines a signal level of an output point E to a signal level of an output point C, and stores the ratio in a register. When data of the predetermined number of ratio are prepared at end by repeating the above- mentioned procedure, a controller 29 compares the ratio data in the register as side tone attenuation, and searches ratio data denoting the maximum attenuation to set a circuit network 25 to impedance corresponding to said data.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to an improvement in a side sound protection circuit applied to a communication network terminal such as a telephone.

[Technical background of the invention]

2. Description of the Related Art In a terminal connected to a telephone line and equipped with an amplifier, such as a loudspeaker telephone, howling occurs because the transmitting signal leaks into the receiving circuit (this is called sidetone). Therefore, in this type of terminal device, reducing side noise (this is called side sound prevention) is an important issue, and various side sound prevention circuits have been proposed in the past.

A conventional side sound prevention circuit will be explained with reference to FIG.

In FIG. 1, 1.1' indicates a line impedance connection terminal, and 2.2' indicates a reception transmission line connection terminal. Here, the signal sent from the line side is sent from the reception transmission line connection terminals 2, 2' to the reception circuit (not shown) via the circuit shown in the figure.

In addition, the line impedance connection terminal 1 is connected to the bridge circuit 4
, 5, and a transmitter output circuit 3 is connected between the transmitter circuit connectors of the bridge circuits 4 and 5 and the line impedance connection terminal 1'.
.

The two-manpower changeover switch 7 is connected to a balanced network 8□, 8□+s3+---+8n having n different impedances. Furthermore, balanced circuit networks 8□, 8□.

83r ---e 8H is connected to a signal line connecting the line impedance connection terminal 1' and the reception transmission line connection terminal 2'.

Reference numeral 12 denotes a control unit, and this control unit 12 connects point A of the signal line connecting the bridge circuit 4 and the changeover switch 6 and point B of the signal line connecting the bridge circuit 5 and the changeover switch 6.
The side noise prevention characteristics of the balanced circuit networks connected to the bridge circuit 4 and the bridge circuit 5 via the two-manpower changeover switch 7 are compared. Then, in order to leave the one with the lower side noise as it is and select the one with the louder side noise, a switching signal is output to the two-man switch 7 via the signal line 9, and another balanced circuit network is set. Select and compare side sound protection characteristics. Repeat this process to find the optimal balanced network. Since the call must not be interrupted during this operation, the control unit selects a balanced circuit network with superior characteristics between the balanced circuit network connected to the bridge circuit 4 and the balanced circuit network connected to the bridge circuit 5. In order to adopt the side, a switching signal is sent to the changeover switch 6 via the signal line 10, and the changeover switch 6 is changed over.

Thus, finally, the balanced network 8□, 8□.

The circuit is constructed so that the side sound damping operation is performed by the optimum balanced circuit network during 83+=--+8H.

[Problems with background technology]

However, if we try to sufficiently reduce side noise using such conventional side sound prevention circuits, the number of balanced circuit networks must be reduced to 1.
Requires 0 or more. Therefore, the configuration becomes complicated and large. Therefore, such a side sound prevention circuit is not suitable for small-sized equipment.

[Purpose of the invention]

The present invention was made in view of the above-mentioned drawbacks of the conventional side sound prevention circuit, and its purpose is to provide a side sound prevention circuit that is simple in configuration and has excellent side sound prevention characteristics. be.

[Summary of the invention]

Therefore, the present invention provides a first bridge circuit having a fixed impedance balanced circuit network, a second bridge circuit having a variable impedance balanced circuit network, and the first and second bridge circuits.
The output signal of the bridge circuit and the output signal of the transmitting output circuit are received, and the impedance of the variable impedance balanced circuit network of the second bridge circuit is changed to obtain the output signal of the first transmitting output circuit and the output signal of the transmitting output circuit. a control section that calculates and stores the ratio of the output signals of the second bridge circuit and outputs a switching control signal for the switch based on this result; A side sound prevention circuit is constructed from a switch circuit that selects and passes the output signal of the circuit.

[Embodiments of the invention]

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

FIG. 2 is a block diagram of an embodiment of the present invention, and the same components as in FIG. 1 are given the same numbers and their explanations will be omitted.

In the figure, the first resistor 21 is connected between the line impedance connection terminal l and the output point C of the transmitter output circuit 3. Furthermore, a second resistor is connected in series to the first resistor 21, and a signal line connects this second resistor n to the line impedance connection terminal 1' and the reception transmission line connection terminal 2'. A fixed impedance balanced network is connected between them.

Furthermore, a series circuit of a third resistor and a variable impedance balanced circuit network 5 is connected to the first resistor 21, and the variable impedance balanced circuit network 5 is connected to the line impedance connection terminal 1' and the receiving transmission line connection. It is connected to the signal line connecting terminal 2'.

Further, the signal arriving at the line impedance connection terminal 1 is configured to be applied to one input terminal of each of the differential amplifiers 26 and 27. Further, the other input terminal of the differential amplifier section is configured to receive a signal from the connection point between the second resistor n and the fixed impedance balanced circuit network, and the other input terminal of the differential amplifier section is provided with a signal from the connection point between the second resistor n and the fixed impedance balanced circuit network. , a signal is applied from a connection point between the third resistor and the variable impedance balancing network 5.

In the configuration described above, the first resistor 21 and the second resistor n1
The fixed impedance balanced network u1 differential amplifier 26 is
The first resistor 21, the third resistor 31, the variable impedance balanced circuit network 5, and the differential amplifier ρ constitute a second bridge circuit.

Reference numeral 4 in FIG. 2 is a control unit, which includes, for example, a microprocessor, a memory storing program data used by the microprocessor, and an interface with other parts. And, this control;
It also takes in signals from the output point C of the transmitter output circuit 3, and based on these signals, outputs a switching control signal to the changeover switch A, which is a switch circuit, via the signal line 30B. be.

Specifically, since the fixed impedance balanced circuit network is configured to have standard sidetone protection characteristics for normal calls, the control unit 29 initially operates the telephone with: A switching control signal instructing to turn the switch toward the differential amplifier 26 is output from the signal line 30B.

As a result, a side noise-blocking signal is transmitted between the reception transmission line connection terminals 2 and 2' (C is the fixed impedance balanced circuit network 2/IK).

On the other hand, the control unit 4 includes a circuit that log-converts the signals taken in from each of the output points C, D, and E, respectively, and converts them to a DC level. The resulting DC level is A/
D conversion, output point by microprocessor, E
The data corresponding to the output point C is subtracted from the data corresponding to the output point C, and each result is stored in a register (memory). This result is approximately equal to the ratio of the level of the signal at the output point E to the transmitting signal output (that is, the signal level at the output point C).

Therefore, in addition to the above-mentioned circuit, there are also problems such as speed and complexity of the structure, but direct division may be used.

Next, the control unit 4 sends a signal to the variable impedance balance network 5 via the signal line 30A to change the impedance to a predetermined value 5, so that the signal level at the output point E corresponds to the signal level at the output point C. Find the ratio in the same way as above and store it in the register. Thereafter, the impedance is changed a predetermined number of times in the same way, and the ratio is similarly stored in the register.

Finally, when a predetermined number of ratio data is collected, the control unit 4 compares the ratio data in the register as the sidetone attenuation amount, and compares the ratio data in the register with the ratio data indicating the maximum attenuation amount. is found, and the variable impedance balancing circuit network 5 is set to the impedance corresponding to this. And signal line 30
A switching control signal is sent to the selector switch section via B, and the output signal from the differential amplifier n side is passed through.

Of course, when the amount of sidetone attenuation by the variable impedance balanced circuit network 5 is smaller than the amount of sidetone attenuation by the fixed impedance balanced circuit network 5, for example, the changeover switch path may be left as is and the operation is terminated, or the sidetone attenuation may become louder again. Adjust the amount of attenuation and repeat the operation described above.

Regarding the problem of how to change the impedance of the variable impedance balancing circuit network 5 to find the impedance point where the amount of sidetone attenuation is large, please refer to the circuit configuration of the variable impedance balancing circuit network section and the westward direction of the control section. The configuration is variable depending on the microprocessor program, but for example, the configuration is as follows.

That is, as shown in FIG. 3, the variable impedance network 5 includes variable resistors 32, 33 with equal resistance values, variable capacitors 34, 35, . . . with equal capacitances. It has a well-known six-element configuration consisting of a capacitor 36 and a resistor 37. A signal 30A sent from the control section 29 is input to input terminals 38 and 39, and the values of the variable resistors 32 and 33 and the variable capacitors A and 35 are determined. change each.

The method of change is that on the complex impedance plane in FIG. 4, arrow F is the direction in which the diameter of the line becomes thicker, and arrow F is the direction in which the length of the line becomes longer, so for example, the characteristic curve z1 p z, ,z, t z4t z.

Above z1□v Z21 p Z3□t Z41p ZB
The impedance of the variable impedance balanced circuit network section is changed so as to move with the line diameter, and the optimum characteristic curve Zi for the line diameter is first determined. Further, a variable impedance balanced circuit network 25 is arranged along the characteristic curve z1 in the direction of the arrow.
Finally, the optimum impedance is found. Of course, other methods may be used to find the optimum impedance.

In addition, the output point and the timing of receiving the signal from N.

Accurate measurement of sidetone attenuation is performed only when the transmitting signal is output to the output point C of the transmitting output circuit 3 (generally, when the level of the signal is higher than the level of the receiving signal). shall be carried out.

〔Effect of the invention〕

As explained above, according to the present invention, the number of impedance balancing circuit networks can be reduced to two, and moreover, for example, 3 in FIG.
Since the parts shown in 1 can be implemented as an LSI, it is possible to provide a small and simplified side sound prevention circuit. Furthermore, in the present invention, the ratio between the transmitting output level and the sidetone level is taken as the amount of sidetone attenuation, and based on this, the impedance of the optimally balanced circuit network is set. By making only one of the 92 balanced circuit networks variable, which is different from when comparing balanced circuit networks, it is possible to set a wide impedance variable range and obtain appropriate side sound protection characteristics. Furthermore, the control section uses a microprocessor and has a circuit configuration suitable for LSI implementation, making it extremely effective for manufacturing small-sized devices.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional example, FIG. 2 is a block diagram of an embodiment of the present invention, and FIG. 3 is a block diagram of the main parts of the present invention. iii!
FIG. 4 is a diagram for explaining the operation of the circuit of the present invention. 3.--Talking output circuit 21...First resistor n...
Second resistor n...Third resistor...Fixed impedance balanced circuit network 5...Variable impedance balanced circuit network 26, 27...Differential amplifier path...Switch switch Z4. ... Control Department Agent Patent Attorney Book 1) Takashi Figure 1 Figure 2 Figure 3rA Figure 4 υ Large Glaze

Claims (3)

[Claims] (1) A first bridge circuit having a fixed impedance balanced circuit network, a second bridge circuit having a variable impedance balanced circuit network, and the output signals of the first and second bridge circuits and the first and second bridge circuits. The output signal of the transmitting output circuit connected to the bridge circuit of the second bridge circuit is taken in, and the impedance of the variable impedance balanced circuit network of the second bridge circuit is changed. Calculate and store the ratio of the output signals of the bridge circuit,
A control unit that outputs a switch switching control signal based on this result, and a switch circuit that selects and passes the output signal of the first or second bridge circuit based on the switching control signal of the control unit. Sidetone circuit. (2) The control unit controls the second output signal for the output signal of the transmitter output circuit.
The ratio of the output signal of the first bridge circuit and the ratio of the output signal of the first bridge circuit to the output signal of the transmitting output circuit are compared as the amount of sidetone attenuation, and the bridge having the largest amount of sidetone attenuation is selected. The side sound protection circuit according to claim 1, wherein a switching control signal is output to select an output signal of the circuit. (3) The first bridge circuit includes a second resistor connected in series to a first resistor connected to one side of the line, and a second resistor connected between the second resistor and the other side of the line. The second bridge circuit comprises a fixed impedance balanced circuit network, and a differential amplifier inputting a signal at a connection point between the second resistor and the fixed impedance balanced network and a signal from one side of the line. , a third resistor connected in series with the first resistor and in parallel with the second resistor, and a variable impedance connected between the third resistor and the other side of the line. It consists of a balanced circuit network, and a differential amplifier that inputs a signal at a connection point between the third resistor and the variable impedance balanced network and a signal from one side of the line, and
, wherein the transmitting output circuit is connected between a connection point with a third resistor and the other side of the line. Side sound circuit.