JP4421993B2 - Howling reduction device - Google Patents

Description

  The present invention relates to a howling reduction device, and more particularly, to a howling reduction device combined with a telephone interface to which an analog single telephone is connected.

  A hybrid circuit of a telephone interface (analog extension interface) is a primary circuit when an analog single telephone connected to the secondary side is in a call state with an opposite terminal connected to the primary side (that is, in an off-hook state). It is designed so that the impedance of the side and the secondary side can be balanced. For this reason, when the analog single telephone is on hook, the impedance balance between the primary side and the secondary side of the hybrid circuit is lost.

  When the analog single telephone changes from the talking state to the on-hook state, if the telephone interface and the opposite terminal are still in the talking state, the audio signal from the opposite terminal is transmitted from the receiving side to the transmitting side on the primary side of the hybrid circuit. Wrap around. In this case, if the opposite terminal is a terminal having a high level of sound wrapping (a terminal in which the sound of the receiving speaker easily enters the transmitting microphone, such as a hands-free terminal or a door phone), a closed loop is formed and howling occurs. .

  The telephone interface is configured to determine that the analog single telephone has been on-hook when the on-hook state of the analog single telephone has continued for a predetermined time (for example, several hundred milliseconds) in order to detect dial pulses and hooking from the analog single telephone. . For this reason, if the analog single telephone is on-hook before the opposite terminal, the above-described howling may occur. Howling that lasts for hundreds of milliseconds is a noise that cannot be ignored by humans. Thus, techniques for preventing and reducing such howling have been proposed.

  As shown in FIG. 5, the conventional howling mitigation device includes a Zener diode 512 connected to a secondary winding of a transformer 511 included in a telephone interface 510 (see, for example, Patent Document 1).

  In the telephone interface 510 of FIG. 5, when the loop detector 513 detects the on-hook of the single telephone 550, the control unit 514 controls the communication path switch 515 to end the call. At this time, the Zener diode 512 matches the impedance between the primary winding side and the secondary winding side of the transformer 511 until the call is terminated by the control of the communication path switch 515 after the single telephone 550 is on-hooked. Preventing howling at the other party's terminal.

  Further, as shown in FIG. 6, another conventional howling mitigation device is configured by an end-of-call impedance circuit 610 including a call detection circuit configured by a photocoupler PC1 (see, for example, Patent Document 2). .

  When the on-hook impedance circuit 610 in FIG. 6 detects the on-hook state of the key telephone 620 by the photocoupler PC1, the transistor TR1 is turned on for a predetermined time (that is, until the capacitor C1 is charged) and maintains the impedance balance state.

Japanese Utility Model Publication No. 05-080076 (in particular, FIG. 1) Japanese Utility Model Publication No. 07-001640 (in particular, FIGS. 1 and 2).

  Since the conventional howling mitigation device matches impedance, there is a problem that a special circuit that is difficult to design and adjust is necessary.

  An object of the present invention is to provide a howling reduction device that can prevent or reduce howling with a simple circuit configuration without using a special circuit.

The present invention relates to a howling reduction apparatus used together with a hybrid circuit included in a telephone interface, a loop detection unit for detecting on / off of a loop current flowing on the secondary side of the hybrid circuit , and a detection signal from the loop detection unit And a howling reduction unit that cuts off or suppresses an audio signal input to the primary side of the hybrid circuit and / or an audio signal output from the primary side as soon as the loop current is turned off , The howling reduction unit includes: a changeover switch connected to a primary side of the hybrid circuit; and a plurality of selection paths that are alternatively selected by the changeover switch and have different resistance values. To do.

Further, according to the present invention, instead of a howling mitigation unit including the changeover switch and a plurality of selection paths, a howling mitigation unit realized using a CODEC or DSP included in the telephone interface, or the telephone interface. A howling mitigation unit realized by using a connected call path control unit can be used.

  According to the present invention, when the telephone connected to the secondary side of the hybrid circuit included in the telephone interface is on-hook, the voice signal that wraps around on the primary side of the hybrid circuit is immediately blocked or suppressed. Generation of howling can be prevented or reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an analog extension interface (telephone interface) 10 including a howling mitigation apparatus according to an embodiment of the present invention and an analog single telephone 20 connected thereto.

  As shown in FIG. 1, the analog extension interface 10 includes a hybrid circuit 11, a reception amplifier 12, a transmission amplifier 13, a loop detector 14, and a howling reduction circuit 15. Among these, the loop detector 14 and the howling reduction circuit 15 function as the howling reduction device of the present invention.

  The hybrid circuit 11 includes a transformer Tr and resistors R1, R2, and R3 connected to the primary winding side of the transformer Tr. The primary side of the hybrid circuit 11, that is, the connection point between the resistors R1 and R2, the connection point between the resistors R1 and R3, and the connection point between the resistor R2 and the primary winding of the transformer Tr are respectively reception amplifiers. 12 output terminals and one and the other of a pair of input terminals of the transmission amplifier 13 are connected. Further, the secondary side of the hybrid circuit 11, that is, both ends of the secondary winding of the transformer Tr are connected to a call power supply circuit (not shown) and to the analog single telephone 20. The call power supply circuit and the analog single telephone 20 form a call loop.

  The reception amplifier 12 and the transmission amplifier 13 are connected via a howling reduction circuit 15 to a call path control unit (exchange or main device of an extension telephone system) (not shown).

  The loop detector 14 is a current detection device such as a photocoupler, for example. The loop detector 14 is connected between a call power supply circuit (not shown) and the analog telephone 20 and detects a loop current flowing in a call loop formed by the call power supply circuit and the analog telephone 20. The call loop is closed when the analog single telephone 20 is in an off-hook state, and a loop current flows (turns on) at this time. When the analog single telephone 20 is in the on-hook state, the call loop is opened, and at this time, no loop current flows (turns off). In addition, the loop detector 14 can use the loop detector for detecting a dial pulse, hooking, and off-hook as it is for a howling reduction apparatus as it is.

  The howling reduction circuit 15 is also connected to the loop detector 14, and in response to a detection signal from the loop detector 14, a downlink voice signal (received signal) transmitted from the exchange and input to the primary side of the hybrid circuit 11, and One or both of the upstream audio signals (transmission signals) transmitted from the primary side of the hybrid circuit 11 to the exchange are muted (attenuated) or blocked, and the mute or blocked state is restored to the original state. .

  More specifically, howling reduction circuit 15 mutes or blocks the audio signal (up and / or down) as soon as the detection signal of loop detector 14 indicates that the loop current is off. As a result, after the analog single telephone 20 changes from the off-hook state to the on-hook state, the audio signal can be muted or blocked before several tens of milliseconds have elapsed, and howling can be prevented or reduced. Further, when the detection signal from the loop detector 14 indicates that the loop current is on, the howling reduction circuit 15 immediately cancels the mute or cut-off of the audio signal and returns it to the original state.

  As described above, the howling reduction apparatus according to the present embodiment can prevent or reduce the occurrence of howling when the analog single telephone goes off-hook before the opposite terminal.

  In the present embodiment, the howling reduction circuit 15 is provided in the analog extension interface 10, but it is only necessary to suppress or block an audio signal that wraps around on the primary side of the hybrid circuit 11. It can be installed anywhere. It is also possible to use a call path control unit (not shown) as the howling reduction circuit 15.

In the above embodiment, the howling mitigation unit is configured by only the howling mitigation circuit 15, but the signal converter that converts the detection signal from the loop detector 14 into a control signal of a predetermined signal format, and the control signal The howling mitigation unit may be configured using an execution circuit that is controlled to suppress or block the audio signal. In this case, the loop current OFF state continuation time indicated by the detection signal is measured, the dial pulse or hooking of the analog telephone 20 is determined according to the continuation time, and the corresponding operation is executed by each part of the telephone interface. A time measuring circuit (microcomputer) can be used instead of the signal converter.

  With reference to FIG. 2, a first embodiment of the howling mitigation device of the present invention will be described.

  FIG. 2 is a block diagram showing a configuration of a howling reduction circuit 15 used in the howling reduction device of the present embodiment.

  The howling reduction circuit 15 shown in the figure has an analog switch (path selection switch) 21 and selection paths 22 and 23 in front of the reception amplifier 12, and an analog switch (path selection switch) 24 in front of the transmission amplifier 13. Selection paths 25 and 26 are provided. Note that the analog switch 21 may be arranged in the subsequent stage of the selection paths 22 and 23. Similarly, the analog switch 24 may be disposed in the subsequent stage of the selection paths 25 and 26. Further, any one of the set of the analog switch 21 and the selection circuits 22 and 23 and the set of the analog switch 24 and the selection circuits 25 and 26 can be omitted.

  The analog switch 21 is directly connected to the loop detector 14 if the logic matches that of the loop detector 14. If the logic does not match, the signal is connected to the loop detector 14 via a signal converter (or control circuit (microcomputer)). The analog switch 21 performs path switching according to a detection signal from the loop detector 14 (or a control signal from a signal converter or a control circuit (microcomputer)), and uses the selected path 22 or 23 as a call path. The selection paths 22 and 23 have different resistance values, one of which causes the input audio signal to be input to the transmission amplifier 12 with almost no attenuation, and the other significantly attenuates (mutes) the audio signal. That is, when the loop detector 14 detects that the loop current is off, the analog switch 21 selects the selection path 22 (23) for attenuating the audio signal. When the loop current is detected, the analog switch 21 passes the audio signal almost as it is. The selection path 23 (22) for selecting is selected.

  Since the analog switch 22 and the selection paths 25 and 26 are the same as the analog switch 21 and the selection paths 22 and 23, description thereof is omitted.

  As described above, in this embodiment, the primary side audio current of the hybrid circuit can be suppressed when the loop current is turned off with a simple configuration of a selection path and a selection switch having different resistance values. , Howling can be prevented.

  A second embodiment of the howling mitigation device of the present invention will be described with reference to FIG.

FIG. 3 shows a case where a CODEC (encoder / decoder) or a DSP (digital signal processor) provided in the telephone interface 10 is used as the howling reduction circuit 15 of the howling reduction device of this embodiment.

  The CODEC or DSP 31 is connected to the front stage of the reception amplifier 12 and the rear stage of the transmission amplifier 13 in the analog extension interface 10. The CODEC or DSP 31 has an Enable / Disable terminal for switching the enable / disable of the function. If the logic of the CODEC or DSP 31 matches the logic of the loop detector 14, the output terminal of the loop detector 14 is directly connected to this Enable / Disable terminal. If these logics do not match, the loop detector 14 is connected to the enable / disable terminal via a signal converter (or control circuit (microcomputer)).

  The CODEC or DSP 31 enables / disables the operation according to the detection signal from the loop detector 14 (or the control signal from the converter or the control circuit (microcomputer)), and outputs the audio signal when the loop current is turned off. Cut off. Thus, in the present embodiment, when the loop current is turned off, the primary side audio current of the hybrid circuit can be cut off, and howling can be prevented.

  Thus, in this embodiment, howling can be prevented or suppressed without providing a special circuit.

  With reference to FIG. 4, a third embodiment of the howling mitigation device of the present invention will be described.

FIG. 4 shows a speech path control unit (switch or main apparatus) 41 to which an analog extension interface 10 is connected as a howling reduction circuit 15 of the howling reduction apparatus of this embodiment, and a control apparatus (analog extension interface 10) for controlling it. may be provided within.) is a diagram showing a case of using and 42.

  The call path control unit 41 includes a cross point switch in the case of an analog system, and a time switch that connects PCM data paths in the case of a digital system.

  The control device 42 receives the detection signal from the loop detection unit 14 and immediately controls the call path control unit 41 to disconnect the call path when the loop current is turned off. Further, as soon as the loop current is turned on, the call path control unit 41 is controlled to restore the call path.

The control device 42 also measures the duration that the loop current is off, and determines that it is a dial pulse when it returns to the on state within a first predetermined time (for example, 20-50 ms), When it returns to the ON state within the second predetermined time (for example, several hundred ms), it is determined that it is hooking. Then, when the duration time during which the loop current is off exceeds the second predetermined time (for example, when a time of several hundred ms or more has elapsed), it is determined that the analog telephone is on-hook. The control device 42 controls the analog extension interface and the call path control unit based on the determination result to perform a predetermined operation.

  As described above, also in this embodiment, when the loop current is turned off, the primary side audio current of the hybrid circuit can be cut off, and howling can be prevented.

  Also in this embodiment, a special circuit for preventing or suppressing howling is unnecessary.

It is the schematic which shows the structure of the howling reduction apparatus which concerns on one embodiment of this invention. It is a block diagram which shows the howling reduction circuit used for the howling reduction apparatus of 1st Example of this invention. It is a block diagram which shows the example which uses CODEC or DSP as a howling reduction circuit of the howling reduction apparatus of the 2nd Example of this invention. It is a block diagram which shows the example which uses a speech path control part and a control apparatus as a howling reduction circuit of the howling reduction apparatus of the 3rd Example of this invention. It is a circuit diagram for demonstrating the conventional howling reduction apparatus. It is a circuit diagram for demonstrating other conventional howling reduction apparatuses.

Explanation of symbols

10 telephone interface 11 hybrid circuit 12 receives the amplifier 13 transmission amplifier 14 loop current detector 15 howling reduce circuit 21, 24 analog switches 22, 23, 25, 26 selected paths 31 CODEC or DSP
41 Call path control unit 42 Control device

Claims (6)

In a howling mitigation device used with a hybrid circuit included in a telephone interface,
A loop detection unit for detecting on / off of a loop current flowing on the secondary side of the hybrid circuit;
In response to a detection signal from the loop detection unit, immediately after the loop current is turned off, an audio signal input to the primary side of the hybrid circuit and / or an audio signal output from the primary side is blocked or suppressed. Howling reduction part,
Equipped with a,
The howling reduction unit includes a changeover switch connected to a primary side of the hybrid circuit, and a plurality of selection paths that are alternatively selected by the changeover switch and have different resistance values. A howling mitigation device characterized by that. In a howling mitigation device used with a hybrid circuit included in a telephone interface ,
A loop detection unit for detecting on / off of a loop current flowing on the secondary side of the hybrid circuit;
In response to a detection signal from the loop detection unit, immediately after the loop current is turned off, an audio signal input to the primary side of the hybrid circuit and / or an audio signal output from the primary side is blocked or suppressed. Howling reduction part,
With
The howling reduction device, wherein the howling reduction unit is realized using a CODEC or a DSP included in the telephone interface. In a howling mitigation device used with a hybrid circuit included in a telephone interface ,
A loop detection unit for detecting on / off of a loop current flowing on the secondary side of the hybrid circuit;
In response to a detection signal from the loop detection unit, immediately after the loop current is turned off, an audio signal input to the primary side of the hybrid circuit and / or an audio signal output from the primary side is blocked or suppressed. Howling reduction part,
With
The howling reduction device, wherein the howling reduction unit is realized by using a call path control unit connected to the telephone interface. The howling mitigation device according to claim 1 , 2 or 3 ,
The howling mitigation device, wherein the howling mitigation unit cancels the blocking or suppression of the audio signal as soon as the loop current is turned on in response to a detection signal from the loop detection unit. The howling mitigation device according to any one of claims 1 to 4 ,
The howling reduction device, wherein the howling reduction unit includes a signal conversion unit that converts the detection signal into a control signal of a predetermined format. The howling reduction apparatus according to any one of claims 1 to 5,
The howling mitigation unit includes a time measurement circuit for measuring a duration time of the loop current in an off state, and causing the telephone interface to perform different operations based on the duration time, and a howling mitigation execution circuit, The howling mitigation device, wherein the time measuring circuit causes the howling mitigation execution circuit to execute the blocking or suppression of the audio signal as soon as the loop current is turned off according to the detection signal.

Images