KR100248002B1 - Dtmf detection device using correlation method - Google Patents

Abstract

The present invention discloses a DTMF detector using a correlation technique.

The DTMF detector using the correlation technique according to the present invention comprises: a memory unit for sequentially storing and reading three reference signals having a phase difference of π / 3 for each frequency of a row and a column of telephone tones to be detected; A correlator for correlating a received signal with the reference signal read from the memory unit; An adder / maximum value selector which adds correlated values for each frequency introduced from the correlator and then selects a signal having the largest value; A level comparator for outputting the signal when the signal selected by the addition / maximum value selecting unit is equal to or greater than a predetermined level; And a determination unit for determining a tone number and a valid signal for the signal output from the level comparator.

As described above, according to the present invention, the number of data of the reference signal is set to a predetermined different size for each DTMF frequency so that the phase changes continuously when processing subsequent frames, and the correlation value of the maximum value is added after adding the correlation value for each frequency. By selecting, you can detect DTMF tones more accurately.

Description

DFM detector using correlation method

The present invention relates to a dual tone multifrequency (DTMF) detector, and more particularly to a DTMF detector using a correlation technique.

In general, the public telephone network uses DTMF as a signaling method for connecting to the receiving telephone when the user presses the telephone number button. DTMF signaling is developed by Bell Labs and is widely used by AT & T.

As shown in Fig. 1, the four row frequencies are 697 KHz, 770 KHz, 852 KHz, and 941 KHz, respectively, and the frequency of the low frequency band of 1 KHz or less is set, and the four column frequencies are 1209 KHz, respectively. , 1336 KHz, 1477 KHz, and 1633 KHz are set to frequencies in the high frequency band between 1 KHz and 2 KHz. Here, the symbol of each button of the telephone consists of the sum of the frequencies of the rows and columns of the matrix intersection.

A common method for detecting DTMF when a button on the phone is pressed is to calculate energy for eight frequency signals from the received signal, and to calculate energy for each of these frequency signals, fast fourier transform (FFT), DFT (discrete fourier transform) and bandpass filters are used.

When using FFT, 256 samples are required to detect eight frequencies of a row and a column. In this case, energy for each signal of 256 frequencies is calculated. Since only eight frequencies are used for DTMF detection, there is a problem in that a complex number needs to be calculated.

On the other hand, the method of using the bandpass filter has the advantage that the calculation of the complex number is not necessary. The DTMF detection algorithm using the bandpass filter first calculates the energy and total energy of the eight frequency signals through the bandpass filter, and then the high frequency band and the low frequency among the energy of the signal having each frequency through the eight bandpass filters. Find the maximum energy of each in the band. After determining the presence of tone by measuring the ratio between total energy and the maximum energy of each band, if the tone signal is present, check the maintenance period. When all the conditions, such as the tone signal holding period and the stopping period, are satisfied, the DTMF detection operation is completed.

On the other hand, various methods have been studied as a DTMF detection method using a correlation method, and among them, there is a method of correlating a received signal with a sine and cosine signal of a frequency to be detected. Several methods have been proposed to reduce the complexity of the algorithm.

FIG. 2 is a block diagram illustrating a DTMF detector using a method proposed by A.S. Ekinci among DTMF detection methods using a conventional correlation technique.

In FIG. 2, a read only memory (ROM) 21 includes three sine signals having a phase difference of π / 3 for each frequency of a row and a column of telephone tones to be detected, sgn (sin2πf ₀ t) and sgn ( sin2πf ₀ t + π / 3) and sgn (sin2πf ₀ t + 2π / 3) are stored, and each reference signal has a fixed size of 100 sampled data at a predetermined period (for example, 125usec).

The counter 20 is operated by a clock flowing from the outside to output the reference signals for the rows and columns to the correlator 22. At this time, the received signal temporarily stored in the input register not shown is output to the correlator 22. The correlator 22 injects the reference signal and the received signal, sgn (sin2πf ₀ t), sgn (sin2πf ₀ t + π / 3), which is three sine signals having a phase difference of π / 3 of the received signal and frequency. Correlate the sgn (sin2πf ₀ t + 2π / 3) signal.

Where sgn is defined as in Equation 1 below.

The value correlated in the correlator 22 selects the tone signal having the maximum value among the absolute values of the correlation values accumulated for the three phases in the absolute / maximum value selecting section 23. This operation is performed on the eight frequencies assigned to the rows and columns. The level comparator 25 outputs to the determination unit 26 when the signal having the maximum value of the correlated value is high compared to a predetermined threshold. The determination unit 26 checks the on-time by counting the number of consecutive frames with respect to the signal determined by the level comparator 25, and checks the off-time by counting the number of rejected frames to determine the last detected tone. Determine whether the number and the received signal are valid.

In the correlation method proposed by Ekinci, 100 received data are defined as one frame, and if the same tone is detected in three consecutive frames, then DTMF tones are detected if the tones are not detected in three consecutive frames. do. On the other hand, if the power level detector 24 detects the power of the received signal and outputs it to the determination unit 26, the determination unit 26 invalidates the tone signal when the detected detected power is less than or equal to the reference value.

However, the DTMF detector by the conventional Ekinci's correlation technique is sensitive to the phase error of the received signal, and it is difficult to properly set the threshold value when the multiple of the received frequency almost matches the sampling frequency. The size of the data of the reference signal stored in the ROM 21 for each frequency is fixed at 100 per frame regardless of the frequency, and there is a case where the phase change is severe when correlated by a fixed frame unit, and thus DTMF detection is preferable. It could not be done.

FIG. 3 shows the output of the correlator 22 for the frequency 1633 Hz in the DTMF detector shown in FIG. 2. An error of ± 1.5% is allowed in the detection of DTMF tones, thus allowing an operating frequency of 1608.5 hz to 1657.48 Hz. However, as shown in FIG. 3, since a value correlated with 1633 Hz is asymmetric, setting a threshold value based on a frequency lower than 1633 Hz may ignore frequencies greater than 1663 Hz and less than or equal to 1657.48 Hz. In the opposite case, there was a problem in recognizing a frequency significantly lower than 1608.5 Hz.

Therefore, such a DTMF detector is not only sensitive to the phase error of the received signal, but also cannot detect the tone signal properly because the threshold cannot be properly set when the multiple of the received frequency almost matches the sampling frequency.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a DTMF detector capable of more stably operating on a phase error and more accurately detecting a tone signal.

1 shows frequencies according to each button of a telephone using DTMF.

2 is a block diagram illustrating a DTMF detector proposed by Ekinsey using a conventional correlation technique.

FIG. 3 is a graph showing values correlated to a frequency of 1633 Hz in the DTMF detector shown in FIG. 2.

4 is a block diagram illustrating a DTMF detector using a correlation technique according to the present invention.

FIG. 5 is a graph illustrating a correlation value of a reference signal having a phase difference by π / 3 and a value added to each other in the addition / maximum value selection unit shown in FIG. 2.

6 and 7 are graphs showing the magnitude of a signal along the time axis of DTMF tones detected in the received signal of the detector shown in FIG. 4, respectively.

FIG. 8 is a graph showing a correlation value for a frequency of 1633 Hz in the detector shown in FIG. 4.

In the DTMF detector using the correlation technique according to the present invention for achieving the above object, a reference signal having a phase difference of π / 3 for each frequency of a row and a column of telephone tones to be detected is stored and read sequentially. A memory unit; A correlator for correlating a received signal with the reference signal read from the memory unit; An adder / maximum value selector which adds correlated values for each frequency introduced from the correlator and then selects a signal having the largest value; A level comparator for outputting the signal when the signal selected by the addition / maximum value selecting unit is equal to or greater than a predetermined level; And a determination unit for determining a tone number and a valid signal for the signal output from the level comparator.

Further, preferably, the data size of the reference signal for each frequency of the rows and columns of tones stored in the memory unit is set to a predetermined value different according to the frequency.

The memory unit may include a counter for introducing a clock to output a count value and a ROM for sequentially reading the stored reference signal according to the count value.

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

4 is a block diagram illustrating a DTMF detector according to the present invention.

A memory section including a counter 40 for introducing and counting clocks and a ROM 41 for reading a reference signal having a phase difference of π / 3 for each frequency of rows and columns of telephone tones sequentially according to the counted values ( 41, the correlator 43 correlating the received signal with the reference signal read from the memory unit 41, and the correlator 43 adds the correlated values for the respective frequencies and then selects the signal having the largest value. The maximum value selector 44, the power level detector 45 for detecting the power level of the received signal, and the addition / maximum value selector 44 compares whether the signal selected is greater than or equal to a predetermined level. A level comparator 46 for outputting a signal and a determination unit 47 for determining a tone number and valid signal for the signal output from the level comparator 46.

Referring to the operation according to the configuration shown in FIG. 4, the counter 40, the ROM 41, and the correlator 43 perform the same functions as the components of the DTMF detector shown in FIG. 2. However, the data size and frame size for the reference signal having three π / 3 phase differences for each frequency are stored in the ROM 41 as shown in Table 1 below.

Frequency (Hz) Reference signal data size Frame size 697 149 137 770 156 138 852 141 133 941 153 133 1209 159 115 1336 150 108 1477 157 107 1633 147 99

By varying the data size of the reference signal for each frequency, as shown in Table 1, in processing one frame and then processing the next frame, the phase change is continuous to reduce errors in DTMF detection.

The adder / maximum value selector 44 introduces a correlation value output from the received signal and the correlator 43, adds correlation values for three phases for each frequency, and selects and outputs the correlation value having the largest value. Thereafter, the detection step detects DTMF through a processing step similarly to the conventional detector shown in FIG.

In this case, the effect of setting the maximum value by adding the correlation values in the addition / maximum value selection unit 44 is well illustrated in FIG. 5.

FIG. 5 shows phases of reference signal phases (a, b, c) having a phase difference of π / 3 according to the present invention and an addition signal d obtained by adding correlation values to the phases, as shown in FIG. As can be seen, the added signal is not sensitive to errors depending on the phase difference. Accordingly, since the phase of the received signal changes randomly, if the phases of the three reference signals are slightly different from each other, the maximum value is small at the output of the correlator 43, but the sum of the correlation values is added even though the phase changes slightly. It can be seen that the results do not change significantly.

6 and 7 are graphs showing the magnitude of a signal along the time axis of DTMF tones detected in the received signal of the detector shown in FIG. 4, respectively.

FIG. 8 shows that the graph of the correlation value for the frequency 1633 Hz according to the present invention is better symmetrically compared with the conventional correlation value shown in FIG. 3.

As described above, according to the present invention, the number of data of the reference signal is set to a predetermined different size for each DTMF frequency so that the phase changes continuously when processing subsequent frames, and the correlation value of the maximum value is added after adding the correlation value for each frequency. By selecting, you can detect DTMF tones more accurately.

Claims (4)

In a DTMF detector using a correlation technique, A memory unit for sequentially storing and reading a reference signal having a phase difference of π / 3 for each frequency of a row and a column of telephone tones to be detected; A correlator for correlating a received signal with the reference signal read from the memory unit; An adder / maximum value selector which adds correlated values for each frequency introduced from the correlator and then selects a signal having the largest value; A level comparator for outputting the signal when the signal selected by the addition / maximum value selecting unit is equal to or greater than a predetermined level; And And a determination unit for determining a tone number and valid signal of the signal output from the level comparator. The DTMF detector according to claim 1, wherein the data size of the reference signal for each frequency of rows and columns of tones stored in the memory unit is set to a predetermined value different according to each frequency. The data size of the reference signal according to the frequency and the size value of the frame according to claim 2, Frequency (Hz) Reference signal data size Frame size 697 149 137 770 156 138 852 141 133 941 153 133 1209 159 115 1336 150 108 1477 157 107 1633 147 99 DTMF detector using a correlation method characterized in that. The method of claim 1, wherein the memory unit And a counter for inputting a clock and outputting a count value, and a ROM for sequentially reading the stored reference signal according to the count value.

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