JP2010263288A - Voice noise removing circuit and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove howling noise occurring in a received voice due to the change in impedance of an analog line. <P>SOLUTION: A current detection circuit 20 detects the presence/absence of a DC loop current of an analog line 10, and outputs a current detection signal IDet showing the detection result. On the basis of the current detection signal IDet, a muting circuit 21 does not mute a received voice received from the analog line 10 in a period when the DC loop current is detected, and the muting circuit 21 mutes the received voice received from the analog line 10 in a period when the DC loop current is not detected. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a telephone communication technique, and more particularly to a technique for removing voice noise caused by a DC voltage change of an analog line.

In a telephone device that connects an analog line of PSTN (Public Switched Telephone Networks) or PBX (Private Branch eXchange), the DC loop of the analog line is blocked as a circuit configuration for terminating the analog line. An analog line is connected to the 2-wire-4 wire conversion circuit via a loop block circuit or a transformer, and the 2-wire-4 wire conversion circuit separates the transmitted voice and the received voice.
In such a configuration, after the loop is closed, the DC voltage fluctuation of the analog line is input to the transformer and further to the 2-wire-4 wire circuit. Noise is generated.

  Conventionally, as a technique for removing such noise, the delayed voice of the received voice obtained from the two-wire / four-wire circuit is muted on the basis of the period signal generated by detecting the DC voltage change in the analog line. Thus, a technique for removing pulse noise generated in a received voice due to a DC voltage change in an analog line has been proposed (see, for example, Patent Document 1).

JP 2001-320746 A

  However, with such a conventional technique, although it is possible to remove pulse noise generated in the received voice due to the DC voltage change in the analog line, it is not possible to remove the howling noise generated due to the impedance change of the analog line. There was a problem that it was not possible.

  The PSTN exchange or PBX, for example, stops the feeding of the DC loop current that has been supplied to the telephone device until the end of the call, and then feeds the reverse polarity DC loop current to the telephone device. Performs reversal operation. At this time, the impedance of the analog line is not guaranteed in the DC loop current power supply stop period, and greatly changes from the impedance of 600Ω or the like in the normal call state. For this reason, in the 2-wire to 4-wire conversion circuit, impedance balance is lost, and the amount of sneak in the transmitted voice with respect to the received voice increases, which causes howling noise.

  An object of the present invention is to solve such a problem, and an object of the present invention is to provide a voice noise removing circuit and method capable of removing howling noise generated in a received voice due to an impedance change of an analog line.

  In order to achieve such an object, an audio noise elimination circuit according to the present invention is an audio noise elimination circuit used in a telephone device that connects to an analog line and makes a voice call, and is a DC loop current of an analog line. A current detection circuit that detects presence / absence and outputs a current detection signal indicating the detection result, and mutes the received voice received from the analog line during the period when the DC loop current is detected based on the current detection signal. In other words, a mute circuit is provided for muting the received voice received from the analog line during a period in which no DC loop current is detected.

  At this time, when the DC loop current starts flowing in the current detection circuit, the change timing of the current detection signal from no current to current may be delayed by a certain period.

  The voice noise removing method according to the present invention is a voice noise removing method used in a telephone device that connects to an analog line and makes a voice call, and detects the presence or absence of a DC loop current in the analog line, and the detection result. Based on the current detection signal that outputs a current detection signal indicating a DC loop current based on the current detection signal, the DC loop current is detected without muting the received voice received from the analog line. A mute step for muting the received voice received from the analog line during the non-period.

  At this time, when the DC loop current starts flowing in the current detection step, the change timing of the current detection signal from no current to current may be delayed for a certain period.

  According to the present invention, even if the impedance balance of the 2-wire to 4-wire conversion circuit is lost due to the impedance change of the analog line due to the operation of the PSTN switch or the PBX, the wraparound of the transmitted voice to the received voice is prevented. And howling noise can be removed.

It is a block diagram which shows the principal part structure of the telephone apparatus concerning the 1st Embodiment of this invention. It is a circuit diagram which shows the principal part of the noise removal circuit concerning the 1st Embodiment of this invention. It is a timing chart which shows operation | movement of the telephone apparatus concerning the 1st Embodiment of this invention. It is a circuit diagram which shows the principal part of the noise removal circuit concerning the 2nd Embodiment of this invention. It is a timing chart which shows operation | movement of the telephone apparatus concerning the 2nd Embodiment of this invention.

Next, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
First, a telephone apparatus according to a first embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram showing a main configuration of the telephone device according to the first embodiment of the present invention.

The telephone device 100 is a telephone device that performs voice communication by connecting to an analog line 10 of PSTN or PBX. As an interface circuit 1 connected to the analog line 10, a rectifier circuit 11, a current blocking circuit 12, a capacitive element 13, A transformer 14, a 2-wire to 4-wire conversion circuit 15, a receiving amplifier 16, a transmitting amplifier 17, and a codec 18 are provided.
In the present embodiment, the interface circuit 1 includes a current detection circuit 20 and a mute circuit 21 as the noise removal circuit 2.

The rectifier circuit 11 is composed of a rectifier circuit such as a diode bridge, and has a function of rectifying the DC loop current IL flowing through the analog line 10.
The current blocking circuit 12 is made up of a constant current circuit using, for example, a transistor. When the analog line 10 is captured, the DC output terminal of the rectifier circuit 11 is closed with a high impedance with respect to the audio signal, and a DC loop current IL flows. It has a function.
The capacitive element 13 has a function of blocking the DC loop current IL to the transformer 14 and allowing the audio signal to pass.

The transformer 14 is connected to the DC output terminal of the rectifier circuit 11 via the capacitive element 13 and has a function of performing impedance conversion between the analog line 10 side and the 2-wire-4 wire conversion circuit 15. Note that there is a configuration in which the transformer 14 is not provided when impedance conversion is unnecessary.
The 2-wire to 4-wire conversion circuit 15 is composed of, for example, a bridge circuit, and outputs the reception voice signal received from the analog line 10 to the reception amplifier 16 and outputs the transmission voice signal from the transmission amplifier 17 to the analog line 10. By doing so, it has a function to suppress the wraparound of the transmitted voice signal with respect to the received voice signal.

The reception amplifier 16 has a function of amplifying the reception voice signal from the two-wire / four-wire conversion circuit 15 and outputting the amplified signal to the codec 18.
The transmission amplifier 17 has a function of amplifying the transmission voice signal from the codec 18 and outputting the amplified signal to the 2-wire-4 wire conversion circuit 15.
The codec 18 encodes the reception voice signal from the reception amplifier 16 into the reception voice data DR and outputs the encoded voice signal DR, and decodes the received reception voice data DT into the transmission voice signal and outputs it to the transmission amplifier 17. And have.

The current detection circuit 20 is made of, for example, a photocoupler, and is provided between the DC output terminal of the rectifier circuit 11 and the current blocking circuit 12, detects the presence or absence of the DC loop current IL, and a current detection signal indicating the detection result. It has a function of outputting IDet.
The mute circuit 21 includes an analog switch using a MOSFET, for example, and is provided between the two-wire / four-wire conversion circuit 15 and the reception amplifier 16 and is based on the current detection signal IDet output from the current detection circuit 20. Thus, the received voice received from the analog line 10 is not muted during the period when the DC loop current IL is detected, and the received voice received from the analog line is muted during the period when the DC loop current is not detected. It has a function.

  FIG. 2 is a circuit diagram showing the main part of the noise removal circuit. Here, a photocoupler PC1 is used as the current detection circuit 20. The light emitting diode of the photocoupler PC1 is connected in series between the DC output positive terminal + of the rectifier circuit 11 and the input terminal of the current blocking circuit 12, and emits light according to the presence or absence of the DC loop current IL. The light receiving transistor of the photocoupler PC1 has a collector terminal connected to the power supply voltage Vc, an emitter terminal connected to the ground potential GND through the resistance element R, and the potential of the emitter terminal is the current detection signal IDet. Is output to the mute circuit 21.

Therefore, when the DC loop current IL flows through the current blocking circuit 12, the light-emitting diode of the photocoupler PC1 emits light and the light-receiving transistor is turned on, so that the current detection signal IDet becomes the power supply potential Vc indicating that there is a current and muted. The circuit 21 is muted off.
On the other hand, when the DC loop current IL is stopped, the light emitting diode of the photocoupler PC1 is extinguished and the light receiving transistor is turned off, so that the current detection signal IDet becomes the ground potential GND indicating no current, and the mute circuit 21 is muted on. .

[Operation of First Embodiment]
Next, the operation of the telephone apparatus according to the first embodiment of the present invention will be described with reference to FIG. FIG. 3 is a timing chart showing the operation of the telephone device according to the first embodiment of the present invention. Here, an operation will be described as an example in the case where the other party telephone device hangs up from a state in which the telephone device 100 performs a voice call with the other party telephone device via the analog line 10 of the PSTN switch.

Prior to time T1, telephone device 100 is in a voice call state with the other telephone device. Therefore, a negative DC voltage is supplied to the analog line 10 from the PSTN switch, and a DC loop current IL flows through the current blocking circuit 12.
The current detection circuit 20 detects the DC loop current IL, and becomes a power supply potential Vc indicating that there is a current, that is, mute off, as the current detection signal IDet. For this reason, the mute circuit 21 does not mute the received voice signal, and the received voice signal from the two-wire / four-wire converter circuit 15 is input to the received amplifier 16 and output from the receiver.

On the other hand, when the call termination operation is performed at the other telephone apparatus at time T1, the supply of the negative DC voltage from the PSTN switch to the analog line 10 is temporarily stopped, the line voltage VL becomes zero, and the DC loop current Also stop.
In response to this, the current detection circuit 20 detects the stop of the DC loop current IL and outputs a value indicating no current as the current detection signal IDet. For this reason, the mute circuit 21 mutes the received voice signal, and the received voice signal from the two-wire / four-wire converter circuit 15 is not input to the receiver amplifier 16 and is not output from the receiver.

Thereafter, at time T 2, a positive DC voltage is supplied from the PSTN switch to the analog line 10 by the reversing operation of the PSTN switch, and a DC loop current IL flows through the current blocking circuit 12.
The current detection circuit 20 detects the DC loop current IL and outputs a value indicating the presence of current as the current detection signal IDet. For this reason, the mute circuit 21 does not mute the received voice signal, and the received voice signal from the two-wire / four-wire converter circuit 15 is input to the received amplifier 16 and output from the receiver.

[Effect of the first embodiment]
As described above, according to the present embodiment, during the period in which the DC loop current is stopped and the impedance of the analog line 10 is unstable due to the operation of the PSTN switch or the PBX, the current detection signal IDet is used. The received voice signal is muted by the mute circuit 21.
For this reason, even if the impedance balance of the 2-wire to 4-wire conversion circuit is lost due to the impedance change of the analog line due to the operation of the PSTN switch or the PBX, it is possible to prevent the transmitted voice from wrapping around the received voice. , Howling noise can be removed.

  Such changes in the line status such as inversion, depolarization, and disconnection of DC loop current are problems inherent to analog lines and do not occur in ISDN lines or IP lines. According to the present invention, since howling noise that occurs in response to such a change in line status can be removed, an analog line can be controlled in the same manner as an ISDN line or an IP line. For this reason, when developing control software for a telephone device connected to various lines, it is not necessary to handle only analog lines, reducing the software development burden and reducing development costs.

  Also, in an IP telephone apparatus that performs digital processing of voice processing, an echo canceller is often used for a two-wire line such as an analog line or a door phone communication path. In such an echo canceller, the operation of the echo canceller is not effective when the amount of return of voice changes greatly or noise is mixed due to a change in the line condition such as inversion, depolarization, or disconnection of the DC loop current. Since the automatic learning function for learning the return amount of the voice becomes stable or the operation starts, the call quality is deteriorated. In the present invention, since howling due to the change in the line condition can be suppressed, the echo canceller can be stably operated, and the above-described deterioration in call quality does not occur.

[Second Embodiment]
Next, a telephone device according to a second embodiment of the present invention will be described with reference to FIG. FIG. 4 is a circuit diagram showing a main part of a noise removing circuit according to the second embodiment of the present invention.

In the first embodiment, the case where the mute of the received voice signal in the mute circuit 21 is canceled when the supply of the DC voltage to the analog line 10 is resumed and the DC loop current starts flowing has been described. In the present embodiment, a case will be described in which the mute of the received voice signal in the mute circuit 21 is canceled after a lapse of a certain time from the time when the DC loop current starts to flow.
Compared to the first embodiment, in this embodiment, a timer circuit that delays the rising of the current detection signal IDet for a certain time is added to the current detection circuit 20. Other configurations are the same as those in the first embodiment, and detailed description thereof is omitted here.

In the current detection circuit 20 shown in FIG. 4, a timer circuit using charging / discharging of the capacitive element C is used.
The light emitting diode of the photocoupler PC2 is connected in series between the DC output positive terminal + of the rectifier circuit 11 and the input terminal of the current blocking circuit 12, and the light emitting diode operates according to the presence or absence of the DC loop current IL. The light receiving transistor of the photocoupler PC2 has an emitter terminal connected to the ground potential GND and a collector terminal connected to the base terminal of the NPN transistor Q.

  The base terminal of the transistor Q is pulled up to the power supply voltage Vc through the resistance element R1, and the collector terminal is pulled up to the power supply voltage Vc through the resistance element R2, and the emitter terminal of the transistor Q Is connected to the ground potential GND. In addition, the capacitive element C is connected in parallel between the collector terminal and the emitter terminal of the transistor Q, and the electron at the collector terminal of the transistor Q, that is, the potential of the capacitive element C is output to the mute circuit 21 as the current detection signal IDet. The

[Operation of Second Embodiment]
Next, the operation of the telephone device according to the second embodiment of the present invention will be described with reference to FIG. FIG. 5 is a timing chart showing the operation of the telephone device according to the second embodiment of the present invention. Here, an operation will be described as an example in the case where the other party telephone device hangs up from a state in which the telephone device 100 performs a voice call with the other party telephone device via the analog line 10 of the PSTN switch.

Prior to time T1, telephone device 100 is in a voice call state with the other telephone device. Therefore, a negative DC voltage is supplied to the analog line 10 from the PSTN switch, and a DC loop current IL flows through the current blocking circuit 12.
At this time, in the current detection circuit 20, the light emitting diode of the photocoupler PC2 emits light according to the DC loop current IL, and the light receiving transistor is turned on. Thereby, the transistor Q is turned off, the capacitive element C is charged via the resistor R2, and the current detection signal IDet maintains the power supply potential Vc indicating that there is a current. Therefore, the mute circuit 21 does not mute the received voice signal, and the received voice signal from the 2-wire / four-wire conversion circuit 15 is input to the received amplifier 16 and output from the receiver.

On the other hand, when the call termination operation is performed at the other telephone apparatus at time T1, the supply of the negative DC voltage from the PSTN switch to the analog line 10 is temporarily stopped, the line voltage VL becomes zero, and the DC loop current Also stop.
At this time, in the current detection circuit 20, the light emitting diode of the photocoupler PC2 is extinguished and the light receiving transistor is turned off. As a result, the transistor Q is turned on, the capacitive element C is immediately discharged, and the current detection signal IDet becomes the ground potential GND indicating no current. Accordingly, the mute circuit 21 mutes the received voice signal, and the received voice signal from the 2-wire / four-wire conversion circuit 15 is not input to the received amplifier 16 and is not output from the receiver.

Thereafter, at time T 2, a positive DC voltage is supplied from the PSTN switch to the analog line 10 by the reversing operation of the PSTN switch, and a DC loop current IL flows through the current blocking circuit 12.
In the current detection circuit 20, the light emitting diode of the photocoupler PC1 emits light, the light receiving transistor is turned on, the transistor Q is turned off, and charging of the capacitive element C is started via the resistor R2.

  At this time, the current detection signal IDet gradually rises to the power supply potential Vc based on the time constants of the resistance element R2 and the capacitance element C. As a result, there is a delay in raising the current detection signal IDet to the potential indicating the presence of current, and at this time T3 after a certain time has elapsed from time T2 when the DC loop current has started to flow, The mute for the audio signal is cancelled.

[Effect of the second embodiment]
As described above, according to the present embodiment, the mute of the received voice signal in the mute circuit 21 is released after a lapse of a certain time from the time when the DC loop current starts to flow. For this reason, even when the line voltage VL in the analog line 10 greatly changes at the start of the supply of the DC voltage from the PSTN switch or the PBX to the analog line 10, the line noise generated according to the change is removed from the received voice. can do.

In particular, the line noise caused by the disconnection signal sent from the exchange in response to the call-ending operation at the other party's telephone device is very annoying noise and generates an acoustic shock. According to the present embodiment, such line noise can be effectively removed.
Further, it is only necessary to add a timer circuit using charging / discharging of the capacitive element C to the first embodiment, and an extremely simple configuration without requiring an expensive circuit such as a delay circuit for received voice. This makes it possible to remove line noise.

  Therefore, both the influence of howling that occurs during the period when the DC loop current stops and the impedance of the analog line 10 becomes unstable and the influence of line noise that occurs when the DC loop current resumes thereafter are suppressed. Therefore, it is possible to effectively remove noise mixed in the received voice due to the operation of the PSTN exchange or the PBX.

[Extended embodiment]
In each of the embodiments described above, the case where the mute circuit 21 is provided between the two-wire / four-wire converter circuit 15 and the receiver amplifier 16 has been described as an example of a specific configuration for muting the received voice. It is not limited to. For example, a mute circuit 21 may be provided between the reception amplifier 16 and the codec 18, and the mute function of the reception amplifier 16 may be used instead of the mute circuit 21. The received voice data DR output from the codec 18 may be muted by a mute circuit. In this case, in the mute circuit, when the received voice is muted, silence data corresponding to the coding rule used in the codec 18 may be output as the received voice data DR.

  In each of the embodiments, the mute circuit 21 performs the mute control on only the received voice. However, the transmission voice may be muted. For example, the mute circuit 21 may be added before or after the transmission amplifier 17 and the mute control of the transmission voice signal may be performed based on the current detection signal IDet. As a result, transmission of the transmitted voice can be stopped during a period when the impedance of the analog line 10 is in an unstable state, and an increase in the amount of transmitted voice wraparound with respect to the received voice can be suppressed.

  In each of the embodiments, the operation when the other party telephone apparatus ends the call from the state in which the telephone apparatus 100 makes a voice call with the other party telephone apparatus via the analog line 10 of the PSTN exchange has been described as an example. However, the present invention is not limited to this. For example, even when the telephone apparatus 100 calls the other party telephone apparatus via the analog line 10 of the PSTN switch and starts a voice call in response to the other party's response, the impedance change of the analog line occurs due to the operation of the PSTN switch or the PBX. Therefore, howling noise can be removed even in such a case.

  Further, in the second embodiment, the rising delay amount of the current detection signal IDet by the timer circuit of the current detection circuit 20 is experienced according to the state of occurrence of line noise at the start of DC voltage supply of the analog line 10. It is sufficient to make a decision. In particular, when the DC loop current of the analog line 10 is temporarily stopped at the start of a voice call, the other party's voice at the start of the call may be interrupted if the delay amount is too large. For example, there is a service that outputs voice guidance in response to the start of a call. Such a case can be dealt with by making the delay amount variable without being fixed. For the configuration in which the delay amount is variable, a known technique such as changing the values of the resistor element R2 and the capacitor element C under the control of the CPU may be used.

  Although the present invention has been described with reference to the embodiment, the present invention is not limited to the above embodiment. Various changes that can be understood by those skilled in the art can be made to the configuration and details of the present invention within the scope of the present invention.

  DESCRIPTION OF SYMBOLS 100 ... Telephone apparatus, 1 ... Interface circuit, 10 ... Analog line, 11 ... Rectifier circuit, 12 ... Current block circuit, 13 ... Capacitance element, 14 ... Transformer, 15 ... 2-wire-4 wire conversion circuit, 16 ... Receiving amplifier, DESCRIPTION OF SYMBOLS 17 ... Transmitting amplifier, 18 ... Codec, 2 ... Noise removal circuit, 20 ... Current detection circuit, 21 ... Mute circuit, VL ... Line voltage, IL ... DC loop current, IDet ... Current detection signal

Claims (4)

An audio noise removal circuit used in a telephone device that connects to an analog line and makes a voice call,
A current detection circuit that detects the presence or absence of a DC loop current of the analog line and outputs a current detection signal indicating the detection result;
Based on the current detection signal, the incoming voice received from the analog line is not muted during a period when the DC loop current is detected, and the analog line is not detected during a period when the DC loop current is not detected. And a mute circuit for muting the received voice received from the voice. The audio noise removal circuit according to claim 1,
The audio noise elimination circuit according to claim 1, wherein the current detection circuit delays a change timing of the current detection signal from no current to current present for a certain period when the DC loop current starts to flow. An audio noise removal method used in a telephone device that connects to an analog line and makes a voice call,
Detecting the presence or absence of a DC loop current of the analog line, and outputting a current detection signal indicating the detection result; and
Based on the current detection signal, the incoming voice received from the analog line is not muted during a period when the DC loop current is detected, and the analog line is not detected during a period when the DC loop current is not detected. And a mute step for muting the received voice received from the voice. In voice noise removal according to claim 3,
In the current detection step, when the DC loop current starts to flow, the change timing of the current detection signal from no current to current is delayed by a certain period.

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