JPH04200157A - Dtmf signal receiving circuit - Google Patents

Abstract

PURPOSE:To obtain a valid DTMF signal without causing malfunction due to a harmonic component of a dial signal by providing a dial tone signal detecting circuit to the receiving circuit and discriminating whether or not a DTMF signal is to be outputted based on an output of the detecting circuit. CONSTITUTION:When a caller side hooks on and recognizes a harmonic of a dial tone signal as a DTMF signal, a recognizing signal is outputted to a discriminating circuit 42. In this case, a dial tone signal detecting circuit 40 detects the dial tone signal and no DTMF recognizing signal is outputted from the discriminating circuit 42 and no malfunction takes place. On the other hand, when the DTMF recognizing signal is normally sent from the caller, since a low level signal is outputted from the dial tone signal detecting circuit 40, the discriminating circuit 42 outputs the DTMF recognizing signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a DTMF signal receiving circuit, and particularly to a circuit configuration for effectively extracting a DTMF signal from a received signal transmitted from a telephone line.

[Prior Art] A telephone with an answering machine function can remotely control various devices by operating an external telephone.
TMF (Dual Tone Multipl
eFrequency) signal.

FIG. 4 shows the circuit blocks inside the answering machine, and the hook switch 10 includes a ringer circuit 12 and a speech network circuit 14 for adjusting the level of the audio signal.
is connected to this speech network circuit 14, and D
TMF signal receiving circuit 16 and speech network circuit 1
A recording/reproducing circuit 18 for recording and reproducing the audio information obtained through the four steps, and a dial circuit 20 are provided, and these circuits are controlled by a control circuit 22.

The DTMF signal receiving circuit 16 detects a DTMF signal based on the received signal from the speech network circuit 14, decodes the received DTMF signal, converts it into data such as 4 bits, and outputs it to the control circuit 22. . For example, when remotely controlling an answering machine or the like, a code number made up of DTMF signals is first supplied from an external telephone or the like, and then a remote control signal of DTMF signals is supplied.

Therefore, the control circuit 22 performs recording/playback operations, etc. using the remote control signal, and can also output remote control signals to various devices to control household devices, control home security, etc. .

[Problems to be Solved by the Invention] However, in the above conventional DTMF signal receiving circuit,
For example, if the calling side performs an on-hook operation or the like and the telephone line loop is broken after the calling side supplies the recitation number but before the remote control signal is supplied, the DTMF signal receiving circuit 16 There was a problem in that a dial tone signal (monitoring signal - a signal indicating the connection status between the telephone and the station) was supplied, causing malfunctions of various devices.

That is, the dial tone signal is 400Hz±15
It consists of a fundamental frequency component of Hz, and the width of this fundamental frequency component varies depending on various conditions such as the telephone line, but as shown in Fig. 5, for example, when the fundamental frequency component is 395Hz, the width of the DTMF signal In the receiving circuit 16, one-harmonic □ wave components that are twice or three times the fundamental frequency appear.

This harmonic is 790Hz, 1185H as shown in the figure.
z, and these harmonic signals are present in the band of the DTMF signal. Therefore, the DTMF receiving circuit 16 will detect a harmonic signal similar to the DTMF signal, and this harmonic signal may cause malfunction.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a DTMF signal receiving circuit that does not malfunction due to harmonic components of a dial tone signal.

[Means for Solving the Problems] In order to achieve the above object, the present invention includes a dial tone signal detection circuit that detects a dial tone signal from a received signal, and a DTMF signal based on the output of the dial tone signal detection circuit. The present invention is characterized in that it includes a determination circuit that determines whether or not to output a signal of the decoding result.

[Operation] According to the above configuration, when a dial tone signal is detected by the dial tone signal detection circuit, a signal to that effect is output to the determination circuit, but the determination circuit does not detect the dial tone signal. For example, a DTMF recognition signal for outputting a DTMF signal is output only when a dial tone signal is detected, and the DTMF recognition signal is not output when a dial tone signal is detected. Therefore, the decoded DTMF signal is sent to the microprocessor only if no dial tone signal is detected.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows the configuration of a DTMF signal receiving circuit, and as shown in the figure, an input filter 24 for amplifying and filtering the received signal (DTMF signal included) is provided. Part filter 24 is an input buffer, 60Hz
It is composed of a removal filter, an AGC circuit, an antialiasing filter, a dial tone filter, etc. A high group filter 26 and a low group filter 28, which are bandpass filters, are provided at the next stage of the manual section filter 24, and the DTMF
The signal is divided into a low frequency group of signals and a high frequency group of signals. Zero-cross comparators 30 and 32 are connected to the next stage of both filters 26 and 28, respectively, and the DTMF signal is converted into a binary signal by these comparators 30 and 32.

Further, a detection circuit and a code converter 34 are connected to the next stage of the comparators 30 and 32, and the detection circuit and code converter 34 detect whether or not a DTMF signal is received. The two received DTMF signals obtained by the high group filter 26 and the low group filter 28 are decoded and converted into 4-bit data which is remote control information. Further 1. :, the above detection circuit and code converter 34
includes a steering circuit 36 and a shift register evening circuit 3.
8 is connected to the detection circuit and code converter 3.
4 outputs an enable signal when it detects a valid TMF signal, so the tearing circuit 36 receives this enable signal and outputs a DTMF recognition signal.

A dial tone signal detection circuit 40 is connected to the input filter 24, and a determination circuit 42 is provided which inputs the output of the dial tone signal detection circuit 40 and the DT'MF recognition signal output from the steering circuit 36. It will be done. Note that the determination circuit 42 and shift register 38 are connected to the host microprocessor through printed wiring.

FIG. 2 shows two examples of the internal circuit of the dial tone signal detection circuit 40, and FIG. This dial tone detection circuit 40 detects a dial tone signal when the output of the band pass filter 40H becomes larger than a predetermined value.

In the case of FIG. 2(b), a zero-cross type comparator 40c is used to select the signal amplitude level near the frequency of 400 Hz.
The dial tone signal can be detected when the integrated value of the integrator 40d becomes larger than a predetermined value.

Further, FIG. 3 shows the internal configuration of the determination circuit 42. This determination circuit 42 consists of an input circuit 42e and an AND circuit 42f, and receives a DT to IF recognition signal and receives a dial tone. D when no detection signal is input
Output the TMF recognition signal to the microprocessor.

The embodiment has the above configuration, and its operation will be explained below.

When the received signal is input to the input section filter 24, the DTMF signal contained in the received signal is divided into two signals, a high frequency group and a low frequency group, by the filter 26.28, and then sent to the detection circuit and code converter 34. Output to. The detection circuit and code converter 34 detects whether or not the DTMF signal has been received, and converts the DTMF signal divided into two types of bands into 4-bit decoded data serving as remote control information. Therefore, the detection circuit and code converter 34 output an enable signal to the steering circuit 36, and this enable signal causes the steering circuit 36 to output a DTMF recognition signal to the determination circuit 4.
At the same time, the 4-bit decoded data is output to the shift register 38.

On the other hand, the received signal input to the input section filter 24 is also supplied to a dial tone signal detection circuit 40, and the dial tone signal is detected by the dial tone signal detection circuit 40 shown in FIG.

For example, if the calling side goes on-hook after outputting a DTMF signal indicating a recitation number, the detection circuit and code converter 34 detect the DTMF signal indicating the recitation number and determine, for example, a DTMF recognition signal of the old GH level. Output to circuit 42.

In this case, when the calling side goes on-hook and recognizes the harmonics of the dial tone signal as a DTMF signal, it similarly outputs a recognition signal to the determination circuit 42.

However, in such a case, the dial tone signal detection circuit 40 detects a dial tone signal, and outputs, for example, a signal at the old gh level to the determination circuit 42. Therefore, as shown in FIG. Su signal (ll
Even if the high level) is output, the dial tone detection circuit (high level inverter 42e
The signal becomes OW level, and no DTMF recognition signal is output from the determination circuit 42, so that no malfunction occurs. On the other hand, if the DTMF recognition signal is normally sent from the calling side, the dial tone signal detection circuit 40 outputs Lo.
Since a signal of w level is output, the determination circuit 42
An MF recognition signal can be output.

Then, when the DTMF recognition signal is output from the determination circuit 42 to the host microprocessor, the host microprocessor outputs a shift pulse for calling serial data to the shift register 38. Therefore, the shift register 38 synchronizes with this and outputs the 4-bit decoded data to the host microprocessor, thereby making various controls possible.

[Effects of the Invention] As explained above, according to the present invention, a dial tone signal detection circuit is provided, and the DT signal is detected based on the output of this detection circuit.
Since it is decided whether or not to output the MF signal,
Even if the telephone line is cut off due to an on-footer or the like on the calling side, a valid TMF signal can be obtained without causing malfunction due to harmonic components of the dial tone signal.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of a DTMF signal receiving circuit according to an embodiment of the present invention, FIG. 2 is a diagram showing two examples of the internal configuration of a dial tone signal detection circuit, and FIG. 3 is a judgment of the embodiment. FIG. 4 is a block diagram showing the circuit structure of a conventional answering machine; FIG. 5 is a diagram showing harmonics of a dial tone signal. 16... DTMF signal receiving circuit 22... Control circuit 34... Detection circuit and code converter 36...
Steering circuit 38... Shift register 40... Dial tone detection circuit 42...
Judgment circuit

Claims (1)

[Scope of Claims] A DTMF signal receiving circuit that receives a DTMF signal, decodes the DTMF signal, and outputs a signal resulting from the decoding, comprising: a dial tone signal detection circuit that detects a dial tone signal from the received signal; A DTMF signal receiving circuit comprising: a determination circuit that determines whether or not to output a signal as a result of decoding the DTMF signal based on the output of the tone signal detection circuit.