JPH0247908B2 - BOSOKUONKAIRONOSAITEKIINPIIDANSUKENSHUTSUHOHO - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a method for detecting the optimum impedance of a side sound protection circuit applied to a terminal of a communication network, such as a telephone.

[Technical background of the invention and its problems]

Conventional side sound protection circuits include two variable impedance balanced networks. This side sound prevention circuit connects one variable impedance balanced circuit network to the communication path side, changes the impedance of the other variable impedance balanced circuit network,
This variable impedance balanced circuit network controls so that a sidetone smaller than that obtained by the variable impedance balanced circuit network connected to the communication line side is obtained, and when the sidetone is obtained, the variable impedance balance circuit is connected to the communication line side. Convert the net and repeat the same operation again. In this way, optimal side sound protection characteristics can be obtained, but this method requires two variable impedance balanced circuit networks, is complicated, and requires many control procedures, making it impractical.

Therefore, a side sound protection circuit including one variable impedance balanced circuit network as shown in FIG. 1 has been proposed.

That is, the signal arriving from the line impedance 1 reaches one input terminal of each of the differential amplifiers 8 and 9. Further, a first resistor 2 is connected to the line impedance 1, and this first resistor 2 is connected to the line impedance 1.
A second resistor 4 is connected between the resistor 2 and the other input terminal of the differential amplifier 8. Further, a third resistor 3 is connected between the first resistor 2 and the other input terminal of the differential amplifier 9. the first resistance and the second,
A transmitter output circuit 5 is connected to the third resistor 4, 3.
is connected, and the other end of the transmitter output circuit 5 is grounded. A fixed impedance balanced network 7 is connected between the input terminal of the differential amplifier 8 and ground, and a variable impedance balanced network 6 is connected between the input terminal of the differential amplifier 9 and ground. There is.

Further, the output signals of the differential amplifiers 8 and 9 are sent to the communication line terminal 18 via the switches SW1 and SW2 of the switch section 16.

Further, the control section 13 is adapted to take in the output signals of the differential amplifiers 8 and 9 from the signal lines 10 and 11, respectively, and take in the output signal of the transmitting output circuit 5 from the signal line 12. Then, if the input from the signal line 10 is A, the input from the signal line 11 is B, and the input from the signal line 12 is C, then A, B,
A/C and B/C are calculated from C and stored. Although there are analog approximation methods for this division, here, for simplicity, it is assumed that the division is performed by converting it into a digital value. Furthermore, the control unit 13
sends a signal via the signal line 14 to the variable impedance balancing network 6 instructing it to change the impedance to a plurality of predetermined impedances. Then, every time the impedance is changed, the control section 13 calculates B/C and stores it all.

During this operation, the control unit 13 sends a switching signal from the signal line 15, and the switch SW of the switch unit 16 is activated.
Turn on switch SW1 and turn off switch SW2.

When the B/C calculation results for a plurality of predetermined impedances are stored, the control unit 13 compares all the ratios. This ratio can be considered as sidetone attenuation, so find the impedance with the maximum sidetone attenuation (minimum ratio value), for example, B/
If there is a desired impedance in C, signal line 14
to set the impedance of the variable impedance balancing network 6 to the above searched impedance value. After that, the control unit 13 sends a switching signal via the signal line 15,
The switch SW1 of the switch section 16 is turned off, and the switch SW2 is turned on. Of course, the above A/C
If applicable, leave the switch section 16 as it was. By doing so, it is possible to realize a side sound protection circuit with optimal impedance.

By the way, the conventional method for finding the optimum impedance in such a side sound prevention circuit is as follows.

For example, the possible impedances Z=R+jX of the variable impedance balanced network 6 are Z ₁₁ , Z ₁₂ ,..., Z ₁₉ , Z ₂₁ , Z ₂₂ ,..., Z ₂₉ , shown in FIG.
Z ₃₁ , Z ₃₂ ,…, Z ₃₉ , Z ₄₁ , Z ₄₂ ,…, Z ₄₉ , Z ₅₁ ,
Assuming that there are 45 values of Z ₅₂ , ..., Z ₅₉ , in the conventional method, all of these 45 impedance values are randomly realized by the variable impedance balancing circuit network 6, and the above-mentioned ratio (B/
C) was being calculated.

For this reason, in an attempt to obtain good side sound protection characteristics,
When the impedance value to be varied is increased, the time required to reach the optimum value becomes longer.On the other hand, when the impedance value is decreased, although the time can be shortened, the sidetone may not be sufficiently reduced.

[Purpose of the invention]

The present invention was made in view of the shortcomings of the conventional methods, and its purpose is to provide an optimal impedance detection method for a side sound prevention circuit that can reach sufficient side sound prevention characteristics in a short time. .

[Summary of the invention]

Therefore, in the present invention, the optimum impedance of the side sound protection circuit is detected by the method described below.

First, the impedance of the variable impedance balanced circuit network is changed to one predetermined impedance in each complex impedance area divided into a plurality of areas that do not overlap with each other, and the bridge including the variable impedance balanced network is The ratio of the output signal of the circuit to the output signal output from the transmitter output circuit is determined. Then, the impedance at which the maximum sidetone attenuation amount is reached is detected.

Furthermore, the impedance of the variable impedance balanced circuit network is set to one predetermined impedance in each of the complex impedance regions that are divided into a plurality of regions that do not overlap with each other regarding the complex impedance region to which the obtained impedance belongs. The ratio is determined by changing the ratio. Then, the impedance at which the maximum sidetone attenuation amount is reached is detected.

Thereafter, the optimum impedance is detected by similarly narrowing the complex impedance region.

[Embodiments of the invention]

Hereinafter, the present invention will be explained in detail with reference to the drawings.

The side sound prevention circuit to which the present invention is applied is shown in FIG. 1, so a detailed explanation will be omitted. , differential amplifier 9 and further line impedance 1 function as a bridge circuit including a variable impedance balancing network 6.

It is also assumed that the variable impedance balanced circuit network 6 is designed so that the sidetone changes monotonically when its impedance value is changed in the complex impedance plane. That is, specifically, the impedances Z ₁₁ , Z ₂₁ , Z ₃₁ ,
Assuming that the sidetone is the smallest when the impedance is _Z51 among _{Z41 and Z51} , the variable impedance balanced circuit network 6 is designed so that the sidetone is the smallest near the impedance _Z51 . In the above case, this means that the sidetone will not be the smallest near the impedance _Z11 . An example of such a variable impedance balanced network 6 is a six-element circuit as shown in FIG. That is, the circuit consists of variable resistors 42, 43, variable capacitors 44, 45, fixed resistor 46, and fixed capacitor 47, and terminal 48 is the third
The terminal 49 is connected to the resistor 3, the terminal 49 is grounded, and the signal line 1 extending from the control unit 13 is connected to the terminals 50 and 51.
4 is connected. Then, while the variable resistors 42 and 43 take the same resistance value according to the signals given from the terminals 50 and 51, the variable capacitors 44 and 4
5 can be changed while maintaining the same capacitance value. Furthermore, the area within the broken line 41 can be implemented as an LSI.

Using such a variable impedance balanced circuit network 6, the control unit 13 sets the impedance values of the variable impedance balanced circuit network 6 to Z ₁₁ , Z ₂₁ , . . .
Z ₅₁ (random order) and calculate B/C at each time. For example, assume that the impedance value _Z51 indicates the maximum amount of sidetone attenuation. Then, the control unit 13 changes the variable impedance balancing circuit network 6 to predetermined impedances Z ₅₂ , Z ₅₃ , ..., Z ₅₉ for the impedance value Z ₅₁ (again, the order is random), respectively. Calculate B/C when . and,
For example, if the impedance value Z ₅₅ indicates the maximum sidetone attenuation, then this impedance value Z ₅₅ is the optimum impedance, and the sidetone attenuation (B/C) at this time and the fixed impedance balanced circuit 7, and set the switch unit 16 so that the attenuation amount becomes larger.
Switch SW1 and SW2 inside. Of course, the control unit 13 sets the impedance of the variable impedance balancing network 6 to Z ₅₅ by the signal on the signal line 14. By doing so, it is guaranteed that a call can be made using the side sound protection circuit having the optimum side sound protection characteristics.

Note that the timing at which the control unit 13 inputs the signal is when the transmitter output circuit 5 is outputting an output signal.
It is assumed that the control section 13 does not perform any input when the reception signal arrives. This operation is performed by the control unit 1
3 is realized by monitoring the level on the signal line 12 and capturing the signal only when a transmitting signal whose level is relatively higher than that of the receiving signal appears.

Further, in the embodiment, the number of impedances is five in the first stage and nine in the second stage, but there is no limitation on the number of impedances or the number of stages to be determined.

〔Effect of the invention〕

According to the present invention as explained above, as is clear from the comparison between FIG. 2 and FIG. 3, the conventional method required operation for all impedances (45 in the example), but according to the present invention It is necessary to perform operations for far fewer impedances (13 in the example), and the time required to detect the optimal impedance can be shortened.

In addition, instead of detecting the optimal impedance from among fixed impedance values as in the past, the method gradually narrows the range of minute changes to detect the optimal impedance, so variable impedance balance is achieved. It becomes possible to relax the accuracy conditions required for the circuit network.

In addition, as in this embodiment, the impedances used at each stage of an operation that is generally repeated sequentially are placed in a complex impedance plane region (the region surrounded by the broken line in FIG. 3) that does not overlap with each other. It is set to include multiple impedances used in the next step.

[Brief explanation of drawings]

Fig. 1 is a block diagram of the side sound prevention circuit, Fig. 2 is a diagram showing a complex impedance plane for explaining the conventional method, and Fig. 3 is a diagram showing a complex impedance plane for explaining the embodiment of the present invention. , FIG. 4 is a circuit diagram illustrating an example of a variable impedance balancing network used in accordance with the present invention. 2...First resistance, 3...Third resistance, 4...
Second resistor, 5... Sending output circuit, 6... Variable impedance balanced circuit network, 7... Fixed impedance balanced circuit network, 8, 9... Differential amplifier, 13...
...control section, 16...switch section.

Claims (1)

[Claims] 1. The ratio of the output signal of the bridge circuit including the variable impedance balanced circuit network to the output signal output from the transmitting output circuit is regarded as the amount of sidetone attenuation,
In the detection method of detecting the impedance at which the amount of sidetone attenuation is maximum as the optimum impedance of the sidetone prevention circuit, the impedance of the variable impedance balanced circuit network is divided into a plurality of regions, each of which does not overlap with each other, as a complex impedance. The ratio is determined by changing the impedance to a predetermined impedance of 1 in each region, and the impedance at which the maximum sidetone attenuation is obtained is detected, and the complex impedance to which this determined impedance belongs is determined. changing the impedance of the variable impedance balancing circuit network to one predetermined impedance in each complex impedance region divided into a plurality of regions, each of which does not overlap with each other, and determining the ratio; A method for detecting an optimum impedance for a side sound protection circuit, characterized in that the optimum impedance is detected by performing the operation of detecting the impedance when the maximum side sound attenuation amount is reached in required steps.