JP2927565B2 - Multi-frequency signal receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-frequency signal receiving device used in telephone lines and the like.

[0002]

2. Description of the Related Art A conventional multi-frequency signal (generally called a DTMF, a dual tone multi-frequency signal) receiving apparatus (hereinafter referred to as a DTMF receiver) has recently been used in a data communication system using a telephone line. Used in telemeter systems.

In this telemeter system, meter readings and the like of a terminal device (such as a gas meter) in a remote place are automatically read from a center or data is set. FIG. 9 is a conceptual diagram of a telemeter system using this telephone line. In the figure, reference numeral 11 denotes a center side of a security company, a water service company, an LPG company, or the like. Reference numeral 12 denotes a generally used telephone line network, 13 denotes a central office, 14
Denotes a terminal-side exchange, and 15 denotes a no-ringing trunk of the terminal-side exchange. Reference numeral 16 denotes a terminal device installed in each home, and a sensor device 17 for detecting LPG usage, detecting water usage, and for security is connected to the terminal device 16.

[0004] The terminal device 16 is provided with a DTMF receiver. This DTMF receiver demodulates 16 types of tone pairs consisting of four types of signals (tones) for each of a high group and a low group (see the truth table in FIG. 2).
0. FIG. 10 is a block diagram of a typical DTMF receiver. To explain the schematic operation of receiving a DTMF signal, a signal enters a logarithmic amplifier 21 from a telephone line and is input to a DTMF receiver 22. Thereafter, the light enters a band-pass filter unit 26 composed of a high-group filter 24 and a low-group filter 25 via a pre-filter 23, and is guided to a voltage detection unit 27 for detecting the presence or absence of a tone. The decoder 28 encodes the eight inputs from the voltage detector 27 according to a truth table (see FIG. 2).
These codes are handled by the control circuit 29 as data meaningful to the system. Here, the DTMF signal has data codes 1, 2, 3, 4, 5, 6, 7, 8,
9, 0, *, #, A, B, C, D. That is, the transmission / reception system of the DTMF signal has a different usage from the dial signal used for the connection control of the telephone line, and it is said that the connection is made in the wrong place even if the signal is erroneously recognized. Instead, processing in the communication procedure is performed as a mere data error. That is,
As is evident from the truth table (see FIG. 2), if multiple tones were detected in either the high group, the low group, or both, decoding was not possible and a valid tone pair was detected from decoder 28. Signal (DV in the figure) indicating this is not activated.

[0005]

When the DTMF receiver 22 as described above is used in a telemeter system, the following problems occur. That is, the power supply of the terminal device located farther than the center 11 is mostly a battery, which means that the power supply voltage is low. Also,
Because of the remote location, the signal is attenuated and its level is -4
It may be 0 dBm or less. However, the signal level receivable by the DTMF receiver 22 is 0 dBm to -3.
0 dBm.

On the other hand, when the terminal device 16 is installed near the center 11, the signal peak becomes large and distortion occurs.

That is, if the signal resolution is limited with a low-voltage power supply (higher resolution leads to an increase in the product price), if a signal from -40 dBm to 0 dBm is to be received, the DTMF receiver 22 is placed in front of the DTMF receiver 22. It is necessary to increase the dynamic range by providing a nonlinear amplifier.

However, the provision of the non-linear amplifier leads to distortion, and in particular, when the signal level is large, the saturation occurs in a portion having a large amplitude, and the distortion becomes remarkable. As a result, for example, in a signal having a data code of *, 1477 Hz is generated in addition to the fundamental waves of 941 Hz and 1209 Hz, and the original two frequencies are changed to three frequencies, and two frequencies appear in the same group. Up to DTMF receiver 22 could not receive.

In view of the above, it is an object of the present invention to provide a DTMF receiver which can receive even if two frequency signals appear in the same group.

[0010]

Means for Solving the Problems] SUMMARY According to claim 1 of the present invention, through a frequency signal having a predetermined frequency
High according to the value of the frequency of the frequency signal to be passed.
Multiple band filters classified into groups and low groups respectively
26 and the frequency signal passing through the band filter 26
Priority circuit 3 for preferentially selecting one of the frequency signals
And the priority circuit 31 has a different frequency.
A plurality of frequency signals passed through the band filter 26
Sometimes, in the high group, the frequency signal having the lower frequency
The frequency signal having the higher frequency is preferentially selected in the low group by selecting first . Specifically, billing
As in item 2, the priority circuit 31 corresponds to the high group and the low group
It is constituted by a logic circuit provided as such.

[0011] Further , a solution to the problem according to claim 3 of the present invention.
The stage passes a frequency signal having a predetermined frequency, and
High and low depending on the frequency value of the frequency signal
A plurality of band filters 26 each classified into groups,
One of the frequency signals passing through the band filter 26
And a priority circuit 31 for preferentially selecting the frequency signal of
The priority circuit 31 has a plurality of circuits having different frequencies.
When the wave number signal passes through the band filter 26,
Group and low group, respectively,
The priority is selected.

[0012]

In the above means for solving the problems, different frequencies are used.
Frequency signals passing through the bandpass filter 26
In the high group, the frequency signal having the lower frequency is selected.
Selected. In the low group, the frequency having the higher frequency
A number signal is selected. This is the case in the high and low groups
When one frequency signal is selected, two
The frequency signal containing the difference component of the two regular frequency signals is
In the high group, low frequencies at higher frequencies than the normal frequency signal
Occurs at frequencies lower than the normal frequency signal in the population
It focuses on that. Also have different frequencies
Are passed through the bandpass filter 26.
Frequency in the high and low groups
A number signal is selected. This also means that each group
In addition to the frequency signal to be selected,
Frequency signal is generated, the normal frequency signal is distorted.
Frequency signal is higher than the
Only a few signals can be reliably selected.

[0013]

[0014]

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the conceptual diagram of the telemeter system using the telephone line of FIG. The same functional parts as the conventional constituent parts shown in FIG. 10 are denoted by the same reference numerals.

FIG. 1 shows a DTM according to the present invention.
FIG. 2 is a diagram showing a truth table of the DTMF receiver, FIG. 3 is a diagram showing a distortion analysis table, FIG. 4 is a diagram showing a distortion analysis graph, and FIG. 5 is a diagram showing an input / output table of a decoder.

A DTMF receiver 22 according to the present invention is incorporated in a terminal device 16 of a telemeter system of a data communication system as shown in FIG. 9, and comprises 16 types of signals (tones) of 4 types each for a high group and a low group. Unlike the conventional DTMF receiver shown in FIG. 10, when a plurality of signals are detected in the same frequency band of the high group or the low group, as shown in FIG. A priority circuit 31 for preferentially selecting one signal is provided.

The priority circuit 31 is a logical priority circuit that operates in the same group, and includes a voltage detection unit 27 and a decoder 2.
8 correspond to the auxiliary decoders 31a and 31b. By employing the auxiliary decoders 31a and 31b, a communication system with less communication errors can be provided.

Specifically, the priorities are determined based on the following concept. The high group frequency and the low group frequency of the DTMF signal component, and the frequency of the difference component generated therefrom are superimposed on the signal component as a distortion component of the amplifier (logarithmic amplifier 21). In other words, the logarithmic signal from the telephone line amplifier 2
At this time , if the input level is low, there is no distortion during this period, but if the input level is high, the distortion is input to the DTMF receiver 22.

When f _H (high group frequency) −f _L (low group frequency) = Δf, a component of f _H + Δf, f _L −
Since the component of Δf appears, the data code * shown in FIG.
In the signal, as shown in FIG. 3, f _H + Δf = 1477
Hz, which is the same as other high group frequencies. F _L −
Since Δf = 673 Hz, which is only about 20 Hz apart from the normal low frequency of 697 Hz, it may be accepted as a signal component. FIG. 3 shows an analysis table for each frequency.

Therefore, the configuration of the auxiliary decoder 31a on the high group side in FIG.
When the two frequencies appear, the function of giving priority to 1209 Hz is provided.
It is understood that when 41 Hz appears, a function of giving priority to 941 Hz may be provided. Therefore, if the above function is given to the auxiliary decoder, even if a plurality of frequencies are detected,
Since only one signal is selected, decoding becomes possible, and a valid tone pair is detected from the decoder 28 and becomes active. FIG. 5 shows a state where the data is coded by the decoder 31b. The decoder 31a uses a truth table in which a and d and b and c are interchanged in FIG. And the auxiliary decoder 31
The information coded by a and 31b is coded by the decoder 28, and this code is handled as data meaningful to the system by the control circuit 29. However, since the subsequent operation is not directly related to the present invention, Description is omitted.

It is needless to say that the specific configuration of the priority circuit 31 can be configured by a gate circuit or the like, and thus the description thereof is omitted. In addition, the configuration of each part of the DTMF receiver includes various products, and is well-known, so that detailed description is omitted.

<Second Embodiment> FIG. 6 is a block diagram of a DTMF receiver according to a second embodiment of the present invention, FIG. 7 is a block diagram of a variable voltage detection unit, and FIG. 8 is a flowchart of a micro computer of a detection voltage control circuit. It is.

In recent years, the progress of electronics has been remarkable, and it has become possible to execute complicated processing at a speed never before conceivable. The second embodiment of the present invention is made possible by such advanced technology.

That is, the voltage detecting section shown in the block diagram of the second embodiment shown in FIG. 6 is a priority circuit which makes the signal having the largest amplitude among the signals detected in the same group a valid signal. ing. That is, as shown in FIG. 7, the voltage detection unit is a variable voltage detection circuit 27a, and the detection voltage of the variable voltage detection circuit 27a can be set and is usually set to a predetermined (normally high sensitivity) level. Now, when two frequencies appear in the same group due to distortion and come out after the band-pass filter 26, the two elements are naturally activated also in the detection element 271 in the variable voltage detection circuit 27a. Therefore, the detection voltage control circuit 272 works so that when the plurality of detection elements 271 are activated, the respective detection levels become low sensitivity.
It has a function of sequentially lowering the sensitivity and maintaining this level when only one element becomes active. As a result, the decoder 28 at the next stage can output a code according to the truth table of FIG.

The operation of changing the detection voltage by the detection voltage control circuit 272 will be briefly described. In this specific example, the detection voltage control circuit 272 is constituted by a microcomputer, and when it is determined that a plurality of terminals are active at the input terminal 272a, the output 272b is changed and the digital output is changed.
The analog output of the analog converter 273 is increased.

As a result, the threshold value of the detecting element 271 increases. When this operation is repeated, a signal exceeding the threshold value is generated at a certain point in time. Since this signal has been eliminated, this operation is performed until one signal becomes active at the input terminal 272a.

Taking the distortion analysis graph of FIG. 4 as an example, 94
Since the amplitudes of the 1 Hz and 1209 Hz signals are the highest in each of the high and low groups, other signals only have to be excluded so that only these two signals are valid.

The microcomputer of the detection voltage control circuit 272 comprises a memory, an input / output device, a central processing unit, etc., and is a well-known microcomputer which reads out an instruction code from the memory and executes various operations. Since the operation itself is not the gist of the present invention, a detailed description of the operation of the microcomputer is omitted. FIG. 8 shows a schematic flowchart of the microcomputer.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that many modifications and changes can be made to the above-described embodiment within the scope of the present invention.

[0030]

As described above, according to the present invention, high groups and
One frequency signal for each of the low and high groups
In some cases, distortion caused by raising the input signal
A frequency signal containing the difference component of the regular frequency signal
Also selects the frequency signal with the lower frequency in the high group
And the lower group selects the frequency signal with the higher frequency
So that a regular frequency signal can be preferentially selected.
it can. Accordingly, there is no problem in that the multi-frequency signal receiving device is installed near the transmission source of the frequency signal, or that a non-linear amplifier or the like is installed far from the transmission source and provided in front of the multi-frequency signal receiving device.

Accordingly, since a multi-frequency signal receiving apparatus having a wide dynamic range can be provided equivalently, the communication performance of a telemeter system or the like can be remarkably improved.

[Brief description of the drawings]

FIG. 1 is a block diagram of a DTMF receiver according to a first embodiment of the present invention.

FIG. 2 is a truth table of a DTMF receiver.

FIG. 3 is an analysis table of the distortion.

FIG. 4 is an analysis graph of distortion.

FIG. 5 is a diagram showing an input / output table of a decoder.

FIG. 6 is a block diagram of a DTMF receiver according to a second embodiment of the present invention.

FIG. 7 is a block diagram of a variable voltage detection circuit.

FIG. 8 is a flowchart of a microcomputer of the detection voltage control circuit.

FIG. 9 is a conceptual diagram of a telemeter system using a telephone line.

FIG. 10 is a block diagram of a typical conventional DTMF receiver.

[Explanation of symbols]

 Reference Signs List 21 logarithmic amplifier 23 pre-filter 24 high-group filter 25 low-group filter 26 band-pass filter 27 voltage detection unit 27a variable-voltage detection circuit 28 decoder 29 control circuit 271 detection element 272 detection-voltage control circuit 273 digital-analog conversion

Continuation of the front page (56) References JP-A-1-74890 (JP, A) JP-A-54-13714 (JP, A) JP-A-52-34607 (JP, A) JP-A-55-64464 (JP) JP-A-56-153897 (JP, A) JP-A-55-3228 (JP, A) JP-A-56-79594 (JP, A) JP-A-58-95487 (JP, A) JP-A-3-132291 (JP, A) JP-A-61-273095 (JP, A) JP-A-61-225994 (JP, A) JP-A-59-161787 (JP, A) U) (58) Fields investigated (Int.Cl. ⁶ , DB name) H04M 11/00 H04Q 1/45 H04L 7/26

Claims (3)

(57) [Claims] 1. Passing a frequency signal having a predetermined frequency
High group according to the frequency value of the frequency signal to be passed
Band filters classified into low and low groups
And one of the frequency signals passing through the band filter
And a priority circuit for preferentially selecting a frequency signal of the plurality of frequency signals having different frequencies.
Is higher in the high group when passing through the band filter
Frequency signal having a frequency of
Preferentially selects the frequency signal with the higher frequency
Multi-frequency signal receiving apparatus, characterized in that that. 2. The multi-frequency signal receiving device according to claim 1, wherein the priority circuits are provided corresponding to the high group and the low group.
Multi-frequency signal receiving device, characterized in that it is a logic circuit . 3. Passing a frequency signal having a predetermined frequency
High group according to the frequency value of the frequency signal to be passed
Band filters classified into low and low groups
And one of the frequency signals passing through the band filter
And a priority circuit for preferentially selecting a frequency signal of the plurality of frequency signals having different frequencies.
When passing through the band filter, the high group and the low group
Now, preferentially select the frequency signal with the largest amplitude
A multi-frequency signal receiving apparatus.