JP2853841B2 - DTMF signal judgment circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a DTMF (Dual-To-To) used for a facsimile machine, a multifunctional telephone, and the like.
ne Multi Frequency) circuit.

[0002]

2. Description of the Related Art A DTMF signal is a signal used for transmitting a dialed number or the like from a push-button telephone to a telephone office. Recently, a DTMF signal is also used for exchanging information after a line is connected. For this reason, some facsimile machines and multifunctional telephones connected to the public telephone network have a DTMF receiver.

[0003] The DTMF is composed of a combination of four tones belonging to a low group and four tones belonging to a high group. F _a = 697 Hz, f _b = 7 for tones belonging to the low group
Four frequencies of 70 Hz, f _c = 852 Hz, and f _d = 941 Hz are allocated. F _e = 1209Hz the tone belonging to the high _{group, f f = 1336Hz, f g} = 147
Four frequencies of 7 Hz and f _h = 1633 Hz are allocated. For example, the DTMF signal indicating the dial “1” is composed of a 697 Hz tone and a 1209 Hz tone.

FIG. 3 shows an example of a conventional DTMF receiver. The DTMF receiver in FIG. 3 has eight bandpass filters 110 to 117, and these bandpass filters 110 to 117 are connected to the input terminal 100. Each bandpass filter corresponds to one of the above eight types of tones. Each band-pass filter uses the frequency of the corresponding tone as the center frequency of its pass band. Each bandpass filter has a multiplier 120-1.
27 are respectively connected. Bandpass filter 1
The outputs of 10 to 117 are output from multipliers 120 to 127, respectively.
Is squared. Each multiplier is connected to a low-pass filter for smoothing 130 to 137, respectively. Output signals of the smoothing low-pass filters 130 to 137 are input to level detectors 140 to 147, respectively. Output signals of the level detectors 140 to 147 are output to a coder (encoder) 15.
Input to 0. The coder 150 includes a level detector 140
A code indicating that a DTMF signal has been input is output based on the output signals of .about.147.

[0005]

A signal other than a DTMF signal (a signal such as a voice signal or white noise) may be input to a DTMF receiver, and these input signals include a component of the DTMF signal. . Therefore, even though these input signals are not DTMF signals, the DTMF receiver may output a code indicating that these input signals are DTMF signals (malfunction may occur). This malfunction of the DTMF receiver prevents normal operation of the system using the DTMF receiver.

SUMMARY OF THE INVENTION The present invention has been made in view of such circumstances, and is intended to prevent a system using a DTMF receiver from malfunctioning even when a signal other than the DTMF signal is input to the DTMF receiver. It is an object of the present invention to provide a DTMF signal determination circuit for determining whether or not this input signal is a DTMF signal.

[0007]

SUMMARY OF THE INVENTION A DTMF signal determination circuit according to the present invention extracts a signal having a frequency outside a DTMF detection frequency band from an input signal and calculates the power of the extracted signal. Means for extracting a signal having a high group of frequencies within the DTMF detection frequency band from the input signal and calculating the power of the extracted signal
TMF band high group signal power calculation means, and a DTMF for extracting a signal having a low group frequency within a DTMF detection frequency band from an input signal and calculating the power of the extracted signal
An in-band low group signal power calculating means, a calculation result output from the DTMF in-band high group signal power calculating means, and the DTMF
Receiving the calculation result output by the in-band low-group signal power calculation means, processing the two calculation results, and converting the processing result to D
DTM output as the calculation result of power in TMF band
F-band power processing means, compares the calculation result output by the DTMF in-band power processing means with the calculation result output by the DTMF out-of-band signal power calculation means, and determines whether the input signal is a DTMF signal. A first power comparison / judgment means for judging, and a comparison between the calculation result output from the DTMF high group signal power calculation means in the DTMF band and the calculation result output from the low group signal power in the DTMF band; A second power comparison / judgment means for judging whether or not the signal is a DTMF signal; a judgment result outputted by the first power comparison / judgment means and a judgment result outputted by the second power comparison / judgment means; There is provided a general judgment means for judging whether the signal is a signal or not, thereby achieving the above object.

[0008]

FIG. 1 is a block diagram showing a DTMF signal determination circuit according to the present invention.

The DTMF signal determination circuit 8 includes a DTMF out-of-band signal power calculation means 1, a DTMF high-group signal power calculation means 2, an DTMF low-group signal power calculation means 3, a first power comparison and determination means 4, and a DTMF. It comprises an in-band power processing means 5, a second power comparison / determination means 6, and a comprehensive determination means 7.

DTMF out-of-band signal power calculating means 1
First, a signal having a frequency outside the DTMF detection frequency band is extracted from the input signal. Next, the power of the extracted signal is calculated (for example, square calculation). The result of this calculation is DTM
The power of the extracted signal outside the F detection frequency band.
Then, a signal indicating the power of the signal outside the DTMF detection frequency band is output to the first power comparison / determination means 4.

DTMF in-band high group signal power calculation means 2
Extracts a signal having a high frequency group within the DTMF detection frequency band from the input signal. Next, the power of the extracted signal is calculated. The result of this calculation is the power of the high-group extracted signals within the DTMF detection frequency band. The signal indicating the power of the high-group signal in the DTMF detection frequency band is transmitted to the DTMF band power processing means 5 and the second signal.
It is output to the power comparison and determination means 6.

DTMF in-band low group signal power calculation means 3
Extracts a signal having a low group of frequencies within the DTMF detection frequency band from the input signal. Next, the power of the extracted signal is calculated. The result of this calculation is the power of the low-group extracted signals within the DTMF detection frequency band. The signal indicating the power of the low group of signals in the DTMF detection frequency band is transmitted to the DTMF band power processing means 5 and the second signal.
It is output to the power comparison and determination means 6.

The DTMF in-band power processing means 5 includes a DTMF
Calculation result of MF high band signal power calculation means 2 and DT
Receiving the calculation result of the low-group signal power calculation means 3 in the MF band, processing the two calculation results, and using the processing result as the calculation result of the power of the DTMF signal in the first band;
The signal is output to the power comparison / determination means 4.

The first power comparison / determination means 4 receives the calculation result of the DTMF out-of-band signal power calculation means and the calculation result output by the DTMF in-band power processing means 5 and calculates the difference or ratio between the two powers. Then, the result of the calculation is compared with a predetermined threshold. Based on the result of this comparison, the first power comparison and determination means 4 determines whether the input signal to the DTMF signal determination circuit 8 is a DTMF signal.

The second power comparison / determination means 6 receives the calculation result of the DTMF high group signal power calculation means 2 in the DTMF band and the calculation result of the low group signal power calculation means 3 in the DTMF band, and calculates the difference or ratio between the two powers. The required calculation is performed, and then the calculated result is compared with a predetermined threshold. Based on the result of this comparison, the second power comparison and determination means 6 determines whether or not the input signal to the DTMF signal determination circuit 8 is a DTMF signal.

Finally, the comprehensive judgment means 7 receives the judgment result of the first power comparison judgment means 4 and the judgment result of the second power comparison judgment means 6, and determines whether the input signal to the DTMF signal judgment circuit is a DTMF signal. And outputs this determination result to the output terminal 11.

[0017]

EXAMPLES The present invention will be described with reference to examples. FIG. 2 shows an embodiment of the present invention.

The DTMF signal judgment circuit 8 of the present embodiment
TMF out-of-band signal power calculation means 1, DTMF in-band high group signal power calculation means 2, DTMF in-band low group signal power calculation means 3, first power comparison / determination unit 4, DTMF in-band power processor 5, and second power It is composed of a comparison judging device 6 and a general judging device 7.

DTMF out-of-band signal power calculation means 1
DTMF out-of-band signal extraction filter 1a and power calculator 1
b and a smoothing low-pass filter 1c. DT
The MF band high group signal power calculation means 2 includes a high group tone signal extraction filter 2a, a power calculator 2b, and a smoothing low-pass filter 2c. The DTMF low-group signal power calculation means 3 includes a low-group tone signal extraction filter 3
a, a power calculator 3b, and a smoothing low-pass filter 3c.

The input terminal 10 of the DTMF receiver 9 is
It is connected to a TMF out-of-band signal extraction filter 1a, a high group tone signal extraction filter 2a, and a low group tone signal extraction filter 3a. Outputs of the signal extraction filters 1a, 2a, 3a are connected to power calculators 1b, 2b, 3b, respectively. The outputs of the power calculators 1b, 2b, 3b are
They are connected to the low-pass filters for smoothing 1c, 2c, 3c, respectively. The output of the smoothing low-pass filter 1c is
One input of the first power comparison / determination unit 4 is connected to the first power comparison / determination unit 4. Outputs of the smoothing low-pass filters 2c and 3c are connected to a DTMF in-band power processor 5 and a second power comparison / determination unit 6, respectively. The output of the DTMF in-band power processor 5 is connected to the first power comparison / determination unit 4 as another input of the first power comparison / determination unit 4. The output of the first power comparison / determination unit 4 is used as one input of the
It is connected to the. The output of the second power determiner 6 is connected to the overall determiner 7 as another input of the overall determiner 7. The output of the general determinator 7 is connected to the output terminal 11. The output of the DTMF receiver 9 is connected to an output terminal 12
It is connected to the.

The input signal input to the input terminal 10 of the DTMF receiver 9 is a DTMF out-of-band signal extraction filter 1.
a and the high group tone signal extraction filter 2a and the low group tone signal extraction filter 3a.

The DTMF out-of-band signal extraction filter 1a includes:
A signal having a frequency outside the DTMF detection frequency band is extracted from the input signal. Next, the extracted signal is input to the power calculator 1b. The power calculator 1b calculates the square of the extracted signal to obtain the power. The power signal resulting from this calculation is output to the smoothing low-pass filter 1c. The power signal that has passed through the smoothing low-pass filter 1c is output to the first power comparison / determination unit 4 as a signal indicating the power of the signal outside the DTMF detection frequency band.

The high group tone signal extraction filter 2a extracts a high group tone signal within the DTMF detection frequency band from the input signal. Next, the extracted signal is used as a power calculator 2
b. The power calculator 2b calculates the square of the extracted signal to obtain the power. The power signal resulting from this calculation is output to the smoothing low-pass filter 2c. The power signal that has passed through the smoothing low-pass filter 2c is output to the DTMF in-band power processor 5 and the second power comparison / determination unit 6.

The low group tone signal extraction filter 3a extracts a low group tone signal in the DTMF detection frequency band from the input signal. Next, the extracted signal is used as a power calculator 3
b. The power calculator 3b calculates the square of the extracted signal to obtain the power. The power signal as a result of this calculation is output to the smoothing low-pass filter 3c. The power signal that has passed through the smoothing low-pass filter 3c is output to the DTMF in-band power processor 5 and the second power comparison / determination unit 6.

The DTMF in-band power processor 5 uses the smaller of the power value of the high group tone signal and the power value of the low group tone signal as a signal indicating the power of the signal in the DTMF detection frequency band. Output to the one-power comparison / determination unit 4.

Here, first, a signal indicating the power of the above-mentioned signal outside the DTMF detection frequency band is defined as P ₁ and the DTMF is detected.
A signal indicating the power of the signal in the DTMF detection frequency band output from the in-band power processor 5 is denoted by P ₂ . First
The power comparison / determination unit 4 calculates a difference P between the following two powers:
Calculate ₃

P ₃ = P ₂ -P ₁ Thereafter, the calculation result P ₃ is compared with a predetermined threshold value. Calculation results when P ₃ is greater than the threshold, the input signal is the first power comparison determination unit 4 in the DTMF signal to the DTMF signal judging circuit 8 judges. This determination result is a binary "1".
It is said. When the calculation result P ₃ are equal and less time or calculation result P ₃ and the threshold value than the threshold, DTMF signal judging circuit first power comparison determination unit 4 when the input signal is not the DTMF signal to the 8 judges. The result of this decision is a binary "
0 ". The result of the determination by the first power comparison / determination unit 4 is output to the overall determination unit 7.

Next, a signal indicating the power of a high group of signals in the above-mentioned DTMF detection frequency band is defined as P _4, and DTMF
A signal indicating the power of the low group signal within the detection frequency band is represented by P
_{Assume 5} . In the second power comparison determination unit 6 performs calculation for obtaining the absolute value P ₆ of the difference between the two power shown below.

P ₆ = | P ₄ −P ₅ | Then, the calculation result P ₆ is compared with a predetermined threshold value. When the calculation result P ₆ is smaller than the threshold value, the input signal to the DTMF signal judging circuit 8 is a DTMF signal to the second power comparison determination unit 6 determines. This determination result is a binary "1".
It is said. When the calculation result P ₆ is larger than the threshold value or when the calculation result P ₆ is equal to the threshold value, the second power comparison / determination unit 6 determines that the input signal to the DTMF signal determination circuit 8 is not a DTMF signal. The result of this decision is a binary "
0 ". The result of determination by the second power comparison / determination unit 6 is output to the overall determination unit 7.

The overall decision unit 7 is a first power comparison decision unit 4
The signal input to the DTMF signal determination circuit 8 is determined to be a DTMF signal only when both the output of the second power comparison determination unit 6 and the output of the second power comparison determination unit 6 are binary “1”. This determination result is a binary number “1”. When the overall decision unit 7 decides that the input signal to the DTMF signal decision circuit 8 is not a DTMF signal, the decision result is a binary "0". The determination result of the comprehensive determiner 7 is output to the output terminal 11.

The DTMF receiver 9 outputs a DTMF code to the output terminal 8. DTMF signal determination circuit 8 and DTMF receiver 9 connected to output terminals 11 and 12
The system at the next stage performs processing of the input signal in accordance with the determination result of the overall determiner 7.

Regarding the DTMF in-band power processor 5,
The signal indicating the power of the signal within the DTMF detection frequency band may be a value obtained by calculating the sum of the power value of the high group tone signal and the power value of the low group tone signal. Also with respect to the first power comparison determination unit 4, even if the comparison with the threshold seeking the ratio of the signal P ₂ indicating the power of the signal P ₁ and the DTMF detection frequency band signal indicating the power of the DTMF detection frequency band signals Good. Regarding the second power comparison / determination unit 6, D
TMF detection ratio may be performed compared to a threshold seeking the signal P ₅ indicating the power of the low group signal of the high group in the signal P ₄ and DTMF detection frequency band indicating the power of the signal in the frequency band.

[0033]

By using a DTMF receiver provided with a DTMF signal judgment circuit according to the present invention,
The noise resistance and the voice cutoff performance of the system using the F receiver are remarkably improved.

More specifically, a user of a system using a DTMF receiver controls a device by sending a DTMF signal to a telephone or a controller of a general home from a place where there is much noise around a public telephone or the like. In such a case, the telephone or the controller, etc.
In the case of a telephone or a controller using a DTMF receiver provided with a TMF signal determination circuit, the user does not need to take measures such as covering the transmitter so as to prevent ambient noise from entering when preventing malfunction of the device. . Further, even when a device with a DTMF control function is connected to a line having a high noise level, such as an international line or a private line, the DTMF according to the present invention can be used.
By using a DTMF receiver having a signal determination circuit, a special device such as a noise remover for obtaining a normal DTMF receiving operation becomes unnecessary.

[Brief description of the drawings]

FIG. 1 is a block diagram of a DTMF signal determination circuit according to the present invention.

FIG. 2 is a block diagram of a DTMF receiver provided with one embodiment of the DTMF signal determination circuit of the present invention.

FIG. 3 is a block diagram of a conventional DTMF receiver.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 DTMF out-of-band signal power calculation means 2 DTMF in-band high group signal power calculation means 3 DTMF in-band low group signal power calculation means 4 first power comparison and determination means 5 DTMF in-band power processing means 6 second power comparison and determination means 7 Comprehensive judgment means 8 DTMF signal judgment circuit 9 DTMF receiver 10 Input terminal 11 Output terminal of DTMF signal judgment circuit 12 Output terminal of DTMF receiver

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-1-188194 (JP, A) JP-A-62-144493 (JP, A) JP-A-51-105212 (JP, A) 36675 (JP, U) Actually open 1953-130912 (JP, U) (58) Field surveyed (Int. Cl. ⁶ , DB name) H04Q 1/45

Claims (1)

(57) [Claims] 1. A DTMF out-of-band signal power calculating means for extracting a signal having a frequency outside the DTMF detection frequency band from an input signal and calculating the power of the extracted signal; DTMF in-band high-group signal power calculating means for extracting a signal having a group frequency and calculating the power of the extracted signal; and extracting a signal having a low-group frequency in a DTMF detection frequency band from the input signal. DT for calculating the power of the extracted signal
MF band low group signal power calculation means, calculation results output by the DTMF high group signal power calculation means, and DT
Receiving the calculation result output from the low group signal power calculation means in the MF band, processing the two calculation results, and outputting the processing result as a calculation result of the power in the DTMF band;
TMF in-band power processing means, and compares the calculation result output by the DTMF in-band power processing means with the calculation result output by the DTMF out-of-band signal power calculation means to determine whether the input signal is a DTMF signal. A first power comparison / judgment means for judging, and a comparison between the calculation result output from the DTMF high group signal power calculation means in the DTMF band and the calculation result output from the low group signal power in the DTMF band; Second to determine whether the signal is a DTMF signal
Power comparison and determination means, and comprehensive determination means for receiving the determination result output by the first power comparison and determination means and the determination result output by the second power comparison and determination means and determining whether the input signal is a DTMF signal DTM with
F signal determination circuit.