KR100369601B1 - Dtmf signal receiving apparatus and method - Google Patents

Abstract

PURPOSE: A DTMF(Dual Tone Multi Frequency) signal receiving apparatus and method are provided to minimize processing time with a filter having the lowest order by using a digital signal processor. CONSTITUTION: A data converter(112) converts an input data into a linear data. A first AAF(114) receives and filters the linearized data to a DTMF signal band. A sub-sampler(116) receives the DTMF band signal and sub-samples it. A second AAF(118) receives an output of the sub-sampler(116), filters a low frequency DTMF band signal from the DTMF band signal, and outputs it. A sub-sampler(120) receives and samples the DTMF low band signals to 2KHz frequency. A HBF(122) receives and filters the low band signals of the DTMF band to remove a signal overlap in a dial tone band. A limiter(126) receives an output of the HBF(122) and detects a minimum detection level of a DTMF reception format. A low-pass DTMF filter(128) separately extracts corresponding low band frequencies 697Hz, 770Hz, 852Hz and 941Hz from the low band DTMF signals outputted from the limiter(126). A rectifier(130) rectifies low band DTMF signals and outputs DC signals. A low-pass filter(132) filters an output of the rectifier(130) to a DC signal and outputs it. A judging unit(160) receives an output of the low-pass filter(132), judges the received signal, analyzes information of the received DTMF signal and reports it to an upper level.

Description

DTMF signal receiver and method

The present invention relates to an apparatus and a method for receiving a DTMF signal, and more particularly, to an apparatus and a method for receiving a DTMF signal using a digital signal processor.

In general, a DTMF (Dual Tone Multi Frequency) signal is used as an input signal for controlling telephone number information and various functions.

The DTMF signal is composed of a dual frequency in which a series of high and low frequencies is combined. A DTMF receiver for receiving such DTMF signals and converting them into digital data is constituted by a combination of filters. The DTMF receiver as described above is manufactured and sold as a separate chip, and is also implemented by a digital signal processor.

Currently, a large number of electronic switchboards serve many subscribers, so the faster the DTMF signal processing speed, the better the service quality. For this purpose, many DTMF receivers should be provided in the exchange system, or the processing speed of DTMF receivers should be increased.

Accordingly, an object of the present invention is to provide a DTMF receiving apparatus and method capable of minimizing processing time with a filter having a lowest order using a digital signal processor.

In order to achieve the objects of the present invention, a device for receiving a DTMF signal includes means for subsampling after filtering a band of a DTMF signal in a voice band signal, and subtracting a DTMF signal of a low frequency group from the DTMF band signal, A means for sampling, a means for filtering a DTMF signal of a high frequency group to the DTMF band signal, and a band-filtered DTMF signal for the low frequency group at a separately set cutoff frequency, and then converting the signal into a DC signal to convert the first to fourth low frequencies. Means for extracting the DTMF signal of the high frequency group, means for extracting the DTMF signal of the first to fourth high frequencies by converting the DTMF signals of the high frequency group into the DC signal after individually band-passing them, respectively; Means for generating a dial tone component signal by filtering a dial tone signal band to a DTMF signal of the present invention and converting it into a direct current signal; Means for converting each DTMF signal into a direct current signal and outputting a high frequency group and a low frequency group signal component for determining the standard condition of the signal level difference between the two groups; and converting the voice band signal into a direct current signal and specifying a signal to noise ratio. Means for outputting a total input signal component for judging a condition, a signal level difference between the transmission tone component signal, a high frequency group and a low frequency group, and a total input signal component of the first to fourth low frequencies And determining means for analyzing and converting the DTMF signal and the DTMF signals of the first to fourth high frequencies into corresponding data.

Hereinafter, preferred embodiments of the present invention will be described in detail with the chopsticks of the accompanying drawings. It should be noted that the same parts in the figures represent the same reference signs wherever possible.

According to the present invention, a DTMF receiver implemented using a digital signal processor can process multi-channel DTMF signals while reducing processing time. For this purpose, use of the proper anti-aliasing filter using the constituent characteristics of DTMF signal, the application of subsampling theory, and the filter of the lowest order that meets the specification by the use of limiter circuit. It consists of filters with optimal structure.

1 is a view showing a structure for receiving a DTMF signal according to the present invention, the data conversion unit 112 performs a function for converting the input data into linearized data to match the operation function. The first AAF 114 inputs the output of the data converter 112 and low-passes the linearized data into the DTMF signal band. The order of the first AAF114 is the second order, the sampling frequency (fs) is 8KHz, and the cut off frequency (fo) is configured to 2KHz. The subsampler 116 inputs a signal of the DTMF band output from the first AAF114, and subsamples the DTMF band signal to eliminate signal aliasing and reduce signal processing time. The ratio of the subsampler 116 is set to two. The configuration is configured to extract signals of the DTMF band from the received data.

The second AAF118 receives the output of the subsampler 116 and filters the low-frequency group DTMF band signal from the DTMF band signal. The order of the second AAF118 is 2, the sampling frequency is 4KHz, and the cutoff frequency is 1KHz. The subsampler 120 receives the output of the second AAF118 and performs the function of sampling the DTMF low-band signals by 2 KHz frequency call. The ratio of the subsampler 120 is two. The HBF122 receives the output of the subsampler 120 and filters out low-band group signals in the DTMF band to remove signal overlap in the dial tone band. The order of HBF122 is 2, the sampling frequency is 2, and the cutoff frequency is 500 Hz. The configuration as described above is configured to extract the low pass DTMF signal from the DTMF band signal.

The HBF124 receives the output of the subsampler 116 and filters the DTMF signal band signal of the high frequency group from the DTMF band signal.

Limiter 126 receives the output of the HBF122. It performs the function of detecting the minimum detection level of DTMF reception standard. The low pass DTMF filter 128 separately extracts the corresponding low pass frequencies 697 Hz, 770 Hz, 852 Hz, and 941 Hz from the low pass DTMF signals output from the limiter 126, respectively. The filter 128 consists of four filters. The rectifier 130 includes a number corresponding to the number of the filters 128. The rectifier 130 rectifies the low pass DTMF signals output from the filter 128 and outputs the DC signals. The rectifier 130 includes a number corresponding to the number of the filters 128. The low pass filter 164 has the order 1, the sampling frequency is 2 KHz, the cutoff frequency is 100 Hz, and the output of the rectifying unit 130 is filtered by the DC signal. The above configuration performs the function of individually filtering the low-frequency group DTMF signals to determine whether the low-frequency DTMF signal is received.

The limiter 142 receives the output of the HPF124 and detects the minimum detection level of the DTMF reception standard. The high frequency DTMF filter 136 separately extracts corresponding low frequency frequencies 1209 Hz, 1336 Hz, 1477 Hz, and 1633 Hz from the high frequency group DTMF signals output from the limiter 134, respectively. The filter 136 consists of four filters. The rectifier 138 includes a number corresponding to the number of the filters 136. The rectifier 138 rectifies the low-frequency DTMF signals output from the filter 136 and outputs the DC signals. The rectifier 138 is configured with a number corresponding to the number of the filters 136. The low pass filter 140 has a degree 1, a sampling frequency of 4 KHz, a cutoff frequency of 100 Hz, and filters the output of the rectifying unit 138 as a DC signal. The above configuration is performed by individually filtering the DTMF signals of the high frequency group to determine the reception of the high frequency DTMF signal.

The dial tone detection filter 142 receives the output of the HBF122 and performs a function of filtering a signal exceeding the dial tone band in the DTMF signal band of the low band output from the HBF122. The rectifier 144 rectifies and outputs the output of the dial tone detection filter 142. The low pass filter 146 has an order of 1, a sampling frequency of 4 KHz, and a cutoff frequency of 100 Hz. The low pass filter 146 filters and outputs the output of the rectifying unit 146 as a DC signal. The above configuration performs a function of determining whether or not a signal of a dial tone band is received in the DTMF band.

The rectifier 148 rectifies the output of the HBF124 and outputs a signal for determining whether a high-frequency signal is detected. The low pass filter 150 is of order 1, has a sampling frequency of 4KHz, and a cutoff frequency of 100Hz. The low pass filter 150 filters and outputs the output of the rectifying unit 146 as a DC signal. The above configuration is a signal indicating the presence or absence of the detection of the high frequency group DTMF signal in the DTMF band signal.

The rectifier 152 rectifies the output of the LBF124 and outputs a signal for determining whether a high frequency signal is detected. The low pass filter 154 has an order of 1, a sampling frequency of 4 KHz, and a cutoff frequency of 100 Hz. The low pass filter 154 filters and outputs the output of the rectifying unit 152 as a DC signal. The above configuration is a signal indicating whether or not the low-pass group DTMF signal is detected in the DTMF band signal.

The above configuration generates a signal for checking whether the twist standard satisfies a signal level difference between two frequencies detected in each frequency group signal component.

The rectifier 156 rectifies the signal output from the data converter 112, and the low pass filter 158 filters and outputs the audio band.

The determination unit 160 receives the outputs of the low pass filters 132, 140, 146, 150, and 154, and determines the received signal to analyze information of the received DTMF signal and report the result to a higher level.

The structure of the DTMF receiver according to the present invention has the configuration as shown in FIG. 1, which is configured using a digital signal processor and a programming language.

Such a structure is configured on one subscriber signal channel in the exchange, and the structure and economical benefits can be obtained by configuring such a structure in one digital signal processor. In order to accommodate the maximum number of subscriber data channels inputted by time division during 125 μS, which is the time within the sampling frequency (8KHz), this is achieved by configuring the DTMF signal processing speed in a limited environment to have an optimized structure. Can be. The structure of the DTMF receiving apparatus for satisfying this is as shown in FIG. 1, and the input and input data are 8-bit PCM data, and the finally detected result value satisfies the DTMF signal specification.

Referring to FIG. 1, the data converter 112 linearizes and outputs 8-bit PCM data, which is data of a voice signal band, in accordance with arithmetic functions in a digital signal processor. Therefore, the data output from the data converter 112 becomes linear data. The linearized data is low-pass filtered at the first AAF114 and output. At this time, if the cutoff frequency of the first AAF114 is designed to be 2 KHz, the voice band data is filtered into the DTMF signal band in the first AAF1144 to extract data of the DTMF band. In order to speed up the signal processing, the subsampler 130 removes the signal overlap chip phenomenon from the signal of the DTMF band. Accordingly, the data output from the subsampler 116 becomes DTMF band signals from which signal overlap is removed.

Since the DTMF signal is a dual frequency consisting of the high frequency group and the low frequency group as described above, the DTMF signal should be processed separately from the low frequency group and the high frequency group. To this end, first, the second AAF118 designs a cutoff frequency of 1 KHz and low-pass filters xb12, which is a DTMF signal of a low frequency group, in the DTMF band. The subsampler 120 inputs xb12 to generate data sampled at a frequency of 2 KHz. In addition, the HBF122 designs a cutoff frequency of 500 Hz to prevent signal distortion of a low frequency group caused by a dial tone. Accordingly, the signal output from the HBF122 becomes xlo, which is a DTMF signal of a low frequency group between 500 Hz and 1000 Hz. In addition, HBF124 extracts xhi, which is a DTMF signal of a high frequency group, at a cutoff frequency of 1 KHz from the band of the DTMF signal. Therefore, in the band of the DTMF signal, xlo becomes a low frequency signal and xhi becomes a high frequency signal.

Then, limiters 126 and 134 are used for xlo and xhi, respectively, to detect the minimum detection level of the signal, which is a reception standard of the DTMF signal. It outputs the maximum signal data sample when every input signal is above the minimum detection level, and outputs the minimum signal data sample when the minimum detection level is reached. Therefore, xlo and xhi which output the limiters 126 and 134, respectively, are removed if the signal is below the reference level, and the frequency component is reliably converted if the signal is above the reference level.

The signals of both groups output from the limiters 126 and 134 are separately filtered by the filters 128 and 138 having the frequency constituting the DTMF signal as a variable. Accordingly, the signals of the low frequency group output from the filter 128 become signals of 697 Hz, 770 Hz, 852 Hz, and 941 Hz, and the signals of the high frequency group output from the filter 136 become signals of 1209 Hz, 1336 Hz, 1477 Hz, and 1633 Hz. Therefore, the signals individually output from the filters 128 and 136 become signals capable of determining the existence of frequencies included in each group. The frequency signals output from the filters 128 and 136 are rectified and converted into direct current signals while passing through rectifiers 130 and 138, respectively, and the full-wave rectified signals are passed through low power filters 132 and 140 designed to have low cutoff frequencies. Is converted into a signal. The outputs of the low pass filters 132 and 140 are applied to the determination unit 160 and input as a signal for determining the DTMF signal.

At this time, there are various standards for determining whether to receive a DTMF signal.

In the present invention, the dial tone detection component DCdt, the total input signal component DCfb for determining the standard condition of the signal to noise ratio (signsl / noise ratio), and a twist standard for defining the signal level difference between the two frequency groups are used.

First, referring to the operation of detecting the dial tone, the dial tone detection filter 142 for inputting the xlo of the low frequency group outputs after filtering the frequency of the dial tone band, and the rectifier 144 and the low pass filter 183 convert the components of the dial tone band into a DC signal to determine the determination unit. Output to 160 Secondly, the rectifying unit 156 and the low power filter 158 for inputting the voice band signal output from the data converter 112 rectify and filter the voice band signal component to detect the total input signal component DCfb and output the same to the determination unit 160. And a third rectifier 148 and a low pass filter 150 for inputting the high frequency group xhi signal to rectify and low pass the xhi signal to output the high frequency group signal component DCbh to the determination unit 160 and to input a low frequency group xlo signal. The low pass filter 154 rectifies and low pass filters the xlo signal and outputs the low frequency group signal component DCb1 to the determination unit 160.

Therefore, the determination unit 160 analyzes the output of the filter 132 to check the low frequency of the received DTMF signal, and analyzes the output of the filter 140 to check the pepper wave frequency of the received DTMF signal. At this time, the determination unit 160 analyzes the transmission tone detection component DCdt, the total input signal component DCfb, and the input frequency components DCbh and BCbl of each frequency group to determine the reception standard of the DTMF signal. At this time, by analyzing the signals to determine the standard, the total input signal component DCfb is not a dial tone band, satisfies the standard condition of the set signal-to-noise ratio, and the signal level difference between the high frequency group and the low frequency group satisfies the set twist specification Only when the received DTMF signal is determined to be a normal signal.

As described above, the DTMF receiver of the present invention minimizes signal processing time by using a digital signal processor. To do this, two subsampling processes are used to process DTMF signals, anti-aliasing filters are used to eliminate signal interference caused by subsampling, and to meet acceptable standards to reduce the time required to implement the filter. Implement using the smallest filter order possible.

1 is a diagram showing the structure of an apparatus for receiving a DTMF signal according to the present invention.

Claims (2)

In the apparatus for receiving a DTMF signal, Means for subsampling after filtering the band of the DTMF signal in the audio band signal; Means for subsampling a DTMF signal of a low frequency group from the DTMF band signal and then subsampling; Means for filtering a high frequency group DTMF signal to the DTMF band signal; Means for extracting the first-fourth low-frequency DTMF signals by band-filtering the low-frequency group DTMF signals at individually set cutoff frequencies and then converting them into direct-current signals; Means for extracting the first-fourth high-frequency DTMF signals by band-filtering the DTMF signals of the high-frequency group at respective cutoff frequencies and converting them into direct current signals; Means for generating a dial tone component signal by filtering a dial tone signal band to a DTMF signal of the low frequency group and converting the signal into a direct current signal; Means for converting the DTMF signals of the high frequency group and the low frequency group into DC signals, respectively, and outputting the high frequency group and the low frequency group signal components for determining the standard condition of the signal level difference between the two groups; Means for converting the voice band signal into a direct current signal and outputting a total input signal component for determining a standard condition of a signal-to-noise ratio; When the transmission sound component signal, the signal level difference between the high frequency group and the low frequency group, and the charging input signal component satisfy the set standard condition, the first-fourth low frequency DTMF signals and the first-fourth high frequency DTMF signals are analyzed and responded to. DTMF receiver characterized in that it is composed of a determination means for converting and outputting the data. In the method for receiving a DTMF signal, Filtering the received voice band signal into the band of the DTMF signal, Filtering the DTMF band signal from a low frequency group DTMF signal, and filtering a high frequency group DTMF signal; Filters the transmission tone signal band to the DTMF signal of the low frequency group, and generates a signal for determining the standard condition of the signal level difference between the high frequency group and the low frequency group, and converts the voice band signal into a DC signal to reduce the signal to noise ratio. Generating a total input signal component for determining a standard condition; Extracting the first-fourth low-frequency DTMF signals by converting the low-frequency group DTMF signals into band cut-offs at individually set cutoff frequencies and converting them into direct-current signals; Extracting the DTMF signals of the first to fourth high frequencies by converting the DTMF signals of the high frequency group into band signals at respective set cutoff frequencies and converting them into DC signals; The first-fourth low frequency DTMF signals and the first-fourth high frequency DTMF signals are input when the set tone condition signal, the signal level difference between the high frequency group and the low frequency group, and the total input signal component are satisfied. DTMF signal receiving method characterized in that consisting of a process of determining the output to convert to the corresponding data by analyzing.