JPH08256222A - Tone detector - Google Patents

Abstract

(57) [Abstract] [Purpose] In a facsimile machine equipped with a telephone capable of answering an answering machine, it is difficult to erroneously detect a response message as a facsimile call signal, and the automatic switching from incoming call to facsimile reception can be performed accurately. Make sure it is possible. [Structure] A CNG signal and a response message (voice signal) are combined and input to the BPF 16. BPF16 is CN
Frequencies near the frequency 1100 Hz of the G signal (frequency 1
Frequencies other than (060 Hz to 1140 Hz) are removed,
The gain controller 21 amplifies the signal to a constant level. The band signal including the constant CNG signal is input to the CNG detection unit 22, and further rectified by the rectifier 22b through the BPF 22a. When this DC level exceeds the reference voltage E in the comparator 22c, a high (H) level detection signal indicating that the CNG signal has been detected is output.

Description

Detailed Description of the Invention

[0001]

[Field of Industrial Application] The present invention is for incoming calls and absences (absence).
Receiving a fax by responding to, or using a fax machine that selects only incoming fax,
The present invention relates to a tone detection device that detects a facsimile call (CNG) signal (single frequency signal) for automatically switching from incoming call to receiving fax.

[0002]

2. Description of the Related Art Conventionally, a facsimile machine has a telephone mode having only a telephone function. In addition, there are an answering reply facsimile reception mode in which an answering message of absence (absence) is sent to receive a facsimile, and a facsimile reception mode in which only a facsimile reception function is provided, and these modes can be selected by the user. .

FIG. 2 is a block diagram showing a switching section in this type of facsimile apparatus. In FIG.
In this example, the facsimile machine 1 accommodating the office line L and the facsimile machine 1 are connected to each other. For example, when the user is out of the office and cannot answer the telephone, a response message prompting facsimile transmission is sent and the calling side is sent from the calling side. And an answering machine 2 for recording the message.

The switching unit of the facsimile apparatus 1 includes a current detector 3 for detecting the current of the office line L and an answering machine 2.
A relay 4 for selecting a voice message signal from the telephone or a telephone signal of the office line L, a line transformer 5, and an answering machine 2.
And a high impedance transformer 6 for transmitting a response message signal from the telephone or a telephone signal of the office line L.

Further, an analog switch 7 for selecting a response message signal from the answering machine 2 or a telephone signal of the office line L, and a CNG signal [Calling Tone: facsimile call signal, 1100 Hz ( Frequency tolerance ± 38Hz), 500
ms on / 3 s off (timing allowable value ± 15%)], a tone detector (CNG detector) 8, and a controller 9 for controlling automatic switching to facsimile reception in the answering machine facsimile reception mode. , And a communication control device 10 for processing facsimile transmissions. The configuration of the facsimile device other than the communication control device 10 is omitted.

FIG. 3 is a block diagram showing the configuration of the tone detecting device 8 shown in FIG. In FIG. 3, the tone detection device 8 is roughly configured by a gain control unit 11 and a tone detection unit 12, and the gain control unit 11 has a signal Sb obtained by automatically controlling the gain of an input signal Sa to a constant level (AGC). And a variable gain amplifier 11a for outputting
Circuit 11b for constant closed-loop control of the gain of
Are provided.

The tone detector 12 includes a narrow band CN including the CNG signal in the signal Sb from the gain controller 11.
A bandpass filter (BP for extracting the G signal Sc)
F) 12a and a rectifier 12b that envelope-rectifies (detects) the CNG signal Sc that has passed through the BPF 12a and outputs the DC component. Further, the DC level from the rectifier 12b is compared with a reference voltage (threshold level) E, and this DC level is compared with the reference voltage E.
High (H) level detection signal is output when
Low (L) level detection signal S when reference voltage E or lower
and a comparator 12c that outputs d.

FIG. 4 is a frequency characteristic diagram of the BPF 12a shown in FIG. In FIG. 4, in this example, the frequency tolerance value of the CNG signal is ± 38 Hz, and the frequency is 1100 Hz.
With the center frequency being − (−) 3 dB, the frequency points are 1060 Hz and 1140 Hz, respectively. It has an attenuation characteristic for blocking the voice signal component (band Wt) of the response message from the answering machine 2 other than the pass band Wc, and has a steep skirt characteristic (frequency characteristic).

Next, the operation of this conventional example will be described. 2 to 4, the facsimile apparatus 1
Is normally set to phone mode. Alternatively, the answering machine facsimile reception mode is set (hereinafter, referred to as standby). During this standby, the operator presses a selection button (not shown), and the input control signal is input to the control unit 9. Based on this input control signal, the movable contacts of the relay 4 and the analog switch 7 are switched so as to select the fixed contact on the a side by the switching instruction signal from the control unit 9. Further, the operator presses a facsimile reception selection button (not shown), and the input control signal is input to the control unit 9. In this case, the movable contact of the relay 4 and the analog switch 7 is switched under the control of the control unit 9 so as to select the fixed contact on the b side.

During this standby, the answering machine 2 is connected to the office line L through the relay 4 and the current detector 3, and the call signal of the incoming call from the office line L is input to the answering machine 2 and the line ( The central office line L) is closed, and a response message recorded in advance in a solid-state memory element in the answering machine 2 is sent. That is, a response message prompting facsimile transmission is sent when an incoming call cannot be answered due to absence. When the current is detected by the current detector 3, the control unit 9 recognizes that the answering machine 2 has closed the line (station line L). The tone detection device 8 detects the CNG signal in order to determine whether the incoming call through the central office line L is an incoming call or a facsimile transmission.

In the tone detecting device 8, the variable gain amplifier 11a of the gain control section 11 sends out the signal Sb in which the gain of the input signal Sa is made constant by the closed loop control of the control circuit 11. Further, a band component having a frequency of 1060 Hz to 1140 Hz is extracted from the signal Sb through the BPF 12a, and this band component is envelope-rectified (detected) by the rectifier 12b. This rectified DC level is used as a comparator 12c.
In comparison with the reference voltage E, a high (H) level detection signal is output when the DC level exceeds the reference voltage E.

When the DC level is lower than the reference voltage E, a low (L) level detection signal is output. here,
In the case of a facsimile incoming call in which the CNG signal has been detected, the comparator 12c of the tone detection device 8 inputs a high (H) level detection signal to the control unit 9. When the control unit 9 captures this high (H) level detection signal, the control unit 9
Performs switching control for selecting the movable contact of the relay 4 and the analog switch 7 as the fixed contact on the b side.

After that, the communication control device 10 processes the facsimile reception by the facsimile transmission procedure (for example, G3). If the CNG signal cannot be detected,
A low (L) level detection signal is input to the control unit 9 from the comparator 12c of the tone detection device 8. The control unit 9 holds the selection of the fixed contact on the a side of the movable contacts of the relay 4 and the analog switch 7, and continues the operation in the telephone mode.

Next, the operation of the tone detecting device 8 will be described in detail. To the tone detector 8, the CNG signal is input to the tone detector 8 via the relay 4, the high impedance transformer 6 and the analog switch 7, and the response message signal from the answering machine 2 is also input to the tone detector 8.

FIG. 5 is a gain characteristic diagram showing the variable gain with respect to the level of the input signal Sa of the variable gain amplifier 11a in the gain controller 11. FIG. 6 is a gain characteristic diagram showing the level of the output signal (signal Sb) with respect to the input signal Sa of the variable gain amplifier 11a.

Referring to FIGS. 5 and 6, the variable gain amplifier 1
The variable gain at 1a changes from 0 dB to plus (+) 40 dB in steps of 0.5 dB with respect to the level of the input signal Sa, and the signal Sb is minus (−) 0.5 d.
Closed-loop control is performed by the control circuit 11b so that it falls within the range of B to 0 dB. Here, in the comparator 12c shown in FIG. 3, the threshold level (threshold value by the reference voltage E) at the time of comparison is set to -3.5 dB.

A case where only the CNG signal is input to the tone detector 8 will be described. First, when the level of the CNG signal in the input signal Sa through the analog switch 7 is, for example, −25 dBm, the gain of the variable gain amplifier 11a in the gain control unit 11 is +, as shown in FIG.
Controlled to 25 dBm, its output signal (signal Sb)
Becomes 0 dBm as shown in FIG. This signal Sb is input to the tone detector 12 shown in FIG. BPF12
The level of the CNG signal Sc from a is approximately 0 dB because the transmission loss is small. Therefore, since the CNG signal Sc becomes equal to or higher than the threshold level (reference voltage E) of -3.5 dB, the comparator 12c outputs a high (H) level detection signal. Input signal Sa is -40 dBm
In the range of 0 dBm, the same operation is performed as shown in FIG.

Next, the case where the CNG signal and the response message (voice signal) are simultaneously input to the tone detector 8 will be described. Here, the level of the CNG signal is -25 dB.
m. Further, as shown in FIG. 4, the response message (voice signal) is in the band Wt, and its level is -15.
dBm. Further, the level of the band Wc of the response message (voice signal) is set to -50 dBm.

In this case, the tone detector 8 uses the CNG.
The gain controller 11 controls the signal obtained by combining the signal and the response message (voice signal) to a constant gain. in this case,
Level (-1 of band Wt of response message (voice signal)
5 dBm) is high, the constant gain of the gain control unit 11 is −
It is determined to be 15 dBm.

Therefore, as shown in FIG. 5, the gain of the variable gain amplifier 11a in the gain control section 11 is +15 dB.
The output signal (signal Sb) is controlled to be 0 dBm as shown in FIG. This signal Sb is input to the tone detector 12 shown in FIG. Here, BPF12
The level of only the CNG signal in the CNG signal Sc (band Wc) from a is “−25 dBm + 15 dBm = −10.
dBm ". The level of the audio signal in the CNG signal Sc (band Wc) is “−50 dBm + 15 dBm = −3.
5 dBm ”. Therefore, the combined level of these is -10 dBm.

In this case, the comparator 12c outputs a low (L) level detection signal because the CNG signal Sc becomes lower than the threshold level (reference voltage E) of -3.5 dB. That is, the CNG signal is not detected.

As described above, in the conventional tone detecting device, when the level of the CNG signal exceeds the reference voltage E which is the threshold value, the CNG signal indicating the incoming of the facsimile is detected. Based on this detection, the automatic switching of facsimile reception in the answering machine facsimile reception mode is controlled.

[0023]

However, in the above-mentioned conventional tone detecting apparatus, the CNG signal from the station line L, the relay 4, the high impedance transformer 6 and the analog switch 7 in the answering machine facsimile reception mode and the answering machine 2 are used. Since the response message signal from is input to the tone detection device 8, the CNG signal is erroneously detected.

That is, since the CNG signal and the response message signal are amplified by the gain control unit 11 to a constant level and the tone detection unit 12 detects the CNG signal, the CNG signal and the CNG signal are not detected even when the CNG signal is not input. A response message signal (voice signal) having the same frequency (1060 Hz to 1140 Hz) is also amplified to a certain level, and this response message signal is easily erroneously detected as a CNG signal.

By the erroneous detection of the tone detecting device 8,
In the facsimile apparatus 1 shown in FIG. 2, the control unit 9 determines that the call is received by the facsimile although the call is received from the office line L, and the relay 14 and the analog switch 7 are connected.
Was switched to select the fixed contact on the b side,
There was a drawback that malfunctions occurred.

The present invention solves the above-mentioned drawbacks of the prior art. For example, in a facsimile machine equipped with a telephone capable of answering machine answering, a voice signal (wideband signal) of a response message is converted into a CNG signal. It is an object of the present invention to provide a tone detection device that makes it difficult to erroneously detect as a (single frequency signal) and automatically and accurately enables automatic switching from telephone call reception to facsimile reception.

[0027]

In order to achieve the above object, the tone detecting device according to claim 1 has a single frequency signal in the voice domain and a frequency spectrum in the voice domain including the single frequency signal. A tone detection device for detecting a single frequency signal when a wide band signal is simultaneously input, a first filter for extracting a band component including the single frequency signal, and a band extracted by the first filter The variable gain amplifying means for setting the component to a constant level and the detection result transmitting means for transmitting the detection signal indicating that the signal from the variable gain amplifying means is detected as the single frequency signal are configured.

A tone detecting apparatus according to a second aspect of the present invention comprises a second filter having a frequency band for passing a single frequency signal between the output end of the variable gain amplifying means and the input end of the detection result sending means. I am trying.

According to a third aspect of the present invention, in the tone detecting device, the detecting result transmitting means includes a converting means for converting the signal from the variable gain amplifying means into a direct current and a direct current level converted by the converting means exceeds a reference level. And a comparison means for transmitting a detection signal indicating that a single frequency signal has been detected.

A tone detecting device according to a fourth aspect of the present invention is such that the tone detecting device is provided in a facsimile device for detecting a facsimile calling signal as a single frequency signal for automatically switching from incoming telephone call to facsimile reception. There is.

[0031]

According to the tone detecting device of the first aspect of the present invention, the bandpass component is extracted by the first filter and then set (amplified) to a certain level to detect a single frequency signal. Sending a detection signal. That is, even if the single frequency signal is not input, the wideband signal having the same frequency as the single frequency signal is not set (amplified) to a constant level, and this wideband signal is less likely to be erroneously detected as the single frequency signal. . That is, the single frequency signal is accurately and reliably detected.

Thus, for example, in a facsimile machine equipped with a telephone capable of answering an answering machine, it becomes difficult to erroneously detect a voice signal (wideband signal) of a response message as a CNG signal (single frequency signal), and a facsimile is received from a telephone call. The automatic switching to reception becomes possible accurately and surely.

According to a second aspect of the present invention, there is provided a tone detecting device, wherein a second filter having a frequency band for passing a single frequency signal is provided between the output end of the variable gain amplifying means and the input end of the detection result converting / transmitting means. Therefore, the extraction accuracy of the single frequency signal is further improved. For example, in a facsimile machine equipped with a telephone capable of answering an answering machine, the voice signal (wideband signal) of the response message is converted into a facsimile call (CNG) signal (single signal). It becomes more difficult to erroneously detect the frequency signal), and the automatic switching from the incoming call to the facsimile reception becomes possible more accurately and surely.

Since the tone detecting device according to the third aspect sends the detection signal indicating that the single frequency signal is detected when the direct current level obtained by converting the single frequency signal exceeds the reference level. No more erroneous detection of noise or the like as a single frequency signal. For example, in a facsimile machine equipped with a telephone capable of answering machine answering, a facsimile call (CNG) signal (single frequency signal) is detected more accurately, The automatic switching from the incoming call to the facsimile reception becomes possible accurately and surely.

A tone detecting apparatus according to a fourth aspect of the invention detects a facsimile call signal for automatically switching the tone detecting apparatus from a telephone call to a facsimile reception, and when the telephone call is received, a facsimile transmission is made to the calling side. It is provided in a facsimile machine which sends out a response message which is a broadband signal prompting. Therefore, in a facsimile machine equipped with a telephone capable of answering an answering machine, it is difficult to erroneously detect a voice signal of a response message as a CNG signal (single frequency signal), and automatic switching from incoming call to facsimile reception is accurate and reliable. Done.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of the tone detecting device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of a tone detecting device of the present invention. In addition,
The tone detecting device 15 detects a facsimile call (CNG) signal when automatically switching from a telephone call to a facsimile reception by a facsimile device or the like as described with reference to FIG. Corresponding to the tone detection device 8 of. Here, the following description will be given by using the previous FIG.

In FIG. 1, the tone detector 1 of this example is shown.
Reference numeral 5 is a bandpass filter (BPF) 16 for extracting a CNG signal from an input signal Sa which is a CNG signal and a voice signal of a response message (for example, frequency 300 Hz to 3400 Hz shown in FIG. 4), and a constant CNG signal from the BPF 16. Gain control unit 21 for automatic gain adjustment (AGC)
And a CNG signal from the gain control unit 21, which determines its level and sends out a detection signal indicating the CNG signal.
The detection unit 22 and the detection unit 22 are roughly configured.

The gain control unit 21 outputs a variable gain amplifier 21a which outputs a signal Sb obtained by automatically adjusting the gain of the input signal Sa to a constant value (AGC), and a constant gain closed loop control for controlling the gain of the variable gain amplifier 21a. The control circuit 21b is provided.

The CNG detection unit 22 cuts off frequency components other than the CNG signal in the signal Sb from the gain control unit 21 and extracts the CNG signal Sc from the BPF 22a.
And a rectifier 22b that envelope-rectifies (detects) the CNG signal Sc that has passed through the BPF 22a and outputs the DC component. Furthermore, the DC level from the rectifier 22b is set to a reference voltage (threshold level).
Comparator 22c that compares with E and outputs a detection signal of high (H) level when it exceeds the reference voltage E in this comparison, and outputs a detection signal Sd of low (L) level when it is equal to or lower than the reference voltage E. And are provided.

The BPFs 16 and 22a have the same frequency characteristics as in FIG. That is, it has a frequency band of 1060 Hz to 1140 Hz with a frequency of 1100 Hz as a center frequency, and has an attenuation characteristic for blocking the voice signal component (band Wt) of the response message from the answering machine 2 other than the pass band Wc. In addition, BPF16, 22a
Need not have the same frequency characteristics. That is, any frequency characteristic that can pass the frequency 1100 Hz of the CNG signal may be used.

The variable gain amplifier 21a in the gain controller 21 has the same variable gain characteristic as shown in FIGS. That is, the variable gain of the variable gain amplifier 21a is between 0 dB and plus (+) 40 dB, and the input signal Sa is
The level is variable in 0.5 dB steps. The input signal Sa is minus (-) 0.5 dB to 0.
The control circuit 21b automatically adjusts the gain to a constant value (AGC) so that the gain falls within the range of dB. That is, the constant signal Sb is output by the closed loop control.

Next, the operation of this embodiment will be described. The switching operation in the facsimile machine equipped with the tone detecting device 15 is the same as that described in FIG. That is, the answering machine 2 is connected to the central office line L through the relay 4 and the current detector 3 during standby in the answering machine facsimile reception mode. In this standby state, an incoming call signal from the office line L is input to the answering machine 2,
At this point, the line (station line L) is closed, and the response message recorded in the solid-state memory element in the answering machine 2 is transmitted. The control unit 9 identifies the current detection by the current detector 3,
Recognize that the answering machine 2 has closed the line (station line L). Then, the tone detector 15 (corresponding to the tone detecting device 8 in FIG. 5) operates to determine whether the incoming call from the central office line L is a telephone call or a facsimile incoming call.
The NG signal is detected.

A response message (voice signal) from the answering machine 2 shown in FIG. 5 is also input. CNG detector 2
0a of the BPF 22a has a frequency of 1100 as shown in FIG.
Extract the CNG signal of Hz. In the tone detector 15, the threshold level (threshold value based on the reference voltage E) of the comparator 22c is set to -3.5 dB.

The detection operation of the tone detector 15 will be described in detail below. A case will be described in which the CNG signal in the answering machine facsimile reception mode and the reply message signal from the answering machine 2 are combined and input to the tone detector 15.

Here, the level of the CNG signal is -25 dB.
m, the frequency spectrum of the response message (voice signal) is in the band Wt as shown in FIG. 4, and
The level is set to −15 dBm. Further, the level of the band Wc of the response message (voice signal) is set to -50 dBm.

The CNG signal and the response message (voice signal) are combined and input to the BPF 16, and the signal component of the band Wc shown in FIG. 4 previously shown in FIG. 4 is extracted from the BPF 16. The signal component of this band Wc has a C level of -25 dBm.
An NG signal and a response message (voice signal) in the band Wc whose level is -50 dBm are included. In this case, BP
The actual extracted signal level from F16 is that the level of the CNG signal (-25 dBm) is higher than the level of the response message (voice signal) of the band Wc (-50 dBm).
The level of the CNG signal is -25 dBm.

The extracted signal in the band Wc having a level of -25 dBm is input to the gain control section 21 and controlled to a constant gain. In this control, the gain of the variable gain amplifier 21a in the gain control unit 21 is +2 as shown in FIG.
The output signal (signal Sb) is controlled to 5 dBm,
It becomes 0 dBm as shown in FIG. This signal Sb
Is input to the CNG detection unit 22 shown in FIG. This CN
In the G detector 22, the BPF 22a is the variable gain amplifier 2
The extracted signal of 0 dBm in which the CNG signal from 1a and the response message (voice signal) are combined is sent to the comparator 22c.

Therefore, the CNG is output from the comparator 22c.
Since the signal Sc becomes equal to or higher than the threshold level (reference voltage E) of −3.5 dB, a high (H) level detection signal indicating that the CNG signal has been detected is output. Further, the CNG signal Sc is -3.5d from the comparator 22c.
When the threshold level of B (reference voltage E) or less, a low (L) level detection signal indicating non-detection of the CNG signal is output. Thus, the CNG signal is accurately detected by setting the threshold level of -3.5 dB. That is, in the facsimile machine,
The level of the CNG signal is relatively high, and, for example, noise or the like is not erroneously detected as a CNG signal.

As described above, in this embodiment, the frequency near the frequency of 1100 Hz (frequency 1060) of the CNG signal in the response message (voice signal) in the facsimile machine.
Frequency other than 100 Hz to 1140 Hz)
Variable gain amplification is performed by removing 0 Hz and frequencies 1140 Hz to 3400 Hz. In this case, since the gains in these frequency bands are reduced, it is difficult to erroneously detect this frequency signal as a CNG signal. Therefore, the automatic switching from the incoming call to the facsimile reception can be performed accurately and surely.

In this embodiment, the automatic switching from the incoming call to the facsimile reception has been described, for example, the present invention is applied to a small household facsimile machine. However, in addition to this, a call using an analog voice signal and a facsimile transmission are used together. It can be applied to the device as it is. For example, it may be installed in an operation control device that is placed side by side with the facsimile storage and exchange device and is capable of telephone communication. Further, it can be applied as it is when the mobile station in a mobile telephone system such as a cellular system is installed side by side with a facsimile apparatus having a function of automatically switching to facsimile reception.

[0051]

As is apparent from the above description, the tone detecting device according to the first aspect extracts the band component by the first filter and then sets (amplifies) it to a constant level to obtain a single frequency signal. When a single-frequency signal is not input, a wide-band signal with the same frequency as the single-frequency signal is not set (amplified) to a certain level when the single-frequency signal is not input. It becomes difficult to erroneously detect as a frequency signal, and a single frequency signal can be accurately and reliably detected.

For example, in a facsimile machine equipped with a telephone capable of answering an answering machine, it becomes difficult to erroneously detect a voice signal (wideband signal) of a response message as a CNG signal (single frequency signal), and a call from a telephone call to a facsimile reception is made. This has the effect of enabling automatic switching accurately and surely.

In the tone detecting device according to the second aspect of the present invention, since the second filter for passing the single frequency signal is provided between the variable gain amplifying means and the detection result converting / transmitting means, the single frequency signal is extracted. The accuracy is improved. For example, in a facsimile machine equipped with a telephone capable of answering an answering machine,
It becomes more difficult to erroneously detect the voice signal (broadband signal) of the response message as a facsimile call (CNG) signal (single frequency signal), and automatic switching from incoming call to facsimile reception becomes more accurate and reliable. Has the effect of becoming.

A tone detecting apparatus according to a third aspect of the present invention compares the DC levels converted from the single frequency signal, and when the DC level exceeds the reference level, outputs a detection signal indicating that the single frequency signal is detected. Since, for example, noise is not erroneously detected as a single frequency signal as a single frequency signal, and in a facsimile machine equipped with a telephone capable of answering machine answering, a facsimile call (CNG) signal (single frequency signal) is generated. This has the effect that it can be detected more accurately, and automatic switching from telephone call reception to facsimile reception can be performed accurately and reliably.

A tone detecting device according to a fourth aspect of the invention detects a facsimile call signal for automatically switching the tone detecting device from a telephone call reception to a facsimile reception, and when the telephone call is received, a facsimile transmission is performed to the calling side. Since it is provided in a facsimile device that sends a response message that is a broadband signal that prompts, a facsimile device equipped with a telephone that can answer a voice mail is less likely to erroneously detect the voice signal of the response message as a CNG signal, and the incoming call The effect is that automatic switching to facsimile reception can be performed accurately and reliably.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a tone detecting device of the present invention.

FIG. 2 is a block diagram showing a switching unit in a conventional facsimile apparatus.

FIG. 3 is a block diagram showing a configuration of the tone detection device shown in FIG.

FIG. 4 is a frequency characteristic diagram of the BPF shown in FIG.

5 is a gain characteristic diagram showing a variable gain with respect to an input signal level in the gain control unit shown in FIG.

6 is a gain characteristic diagram showing an output signal level with respect to an input signal of the variable gain amplifier shown in FIG.

[Explanation of symbols]

 15 tone detector 16, 22a BPF 21 gain controller 22 CNG detector 21a variable gain amplifier 21b control circuit 22b rectifier 22c comparator

Claims (4)

[Claims] 1. A single frequency signal in the voice domain, and
A tone detection device for detecting a single frequency signal when a wideband signal having a frequency spectrum of a voice region including the single frequency signal is simultaneously input, and a band component including the single frequency signal is extracted. A first filter, a variable gain amplifying means for setting the band component extracted by the first filter to a constant level, and a signal from the variable gain amplifying means for detecting that the single frequency signal is detected. And a detection result transmitting means for transmitting the detection signal shown by the above. 2. A second filter having a frequency band for passing a single frequency signal is provided between the output end of the variable gain amplifying means and the input end of the detection result sending means. Tone detector. 3. The detection result sending means, the converting means for converting the signal from the variable gain amplifying means into a direct current, and the single frequency signal when the direct current level converted by the converting means exceeds a reference level. The tone detecting apparatus according to claim 1, further comprising: a comparing unit that sends out a detection signal indicating that the tone has been detected. 4. A tone detecting device, wherein the tone detecting device is provided in a facsimile device for detecting a facsimile calling signal as a single frequency signal for automatically switching from a telephone incoming call to a facsimile receiving.