JPH05236522A - Tone receiver circuit - Google Patents

Abstract

PURPOSE:To reduce the chip size and the current consumption by switching the characteristic of a filter circuit in accordance with an inputted signal to filter a DTMF signal and a busy tone signal with one filter circuit. CONSTITUTION:Only when the signal inputted to a discriminating circuit 1 from a telephone line through an input terminal has a prescribed frequency or lower, this signal passes a low-pass filter 2 and is converted to the high level by a detecting circuit 3 with respect to DC and is outputted to a data latch circuit 4. The data latch circuit 4 latches the converted signal and outputs signals D and the inverse of D to a switching means 5 to switch the characteristic of a filter circuit 6. In this case, the busy signal passes the low-pass filter but the DRMF signal cannot pass it. Consequently, signals D and the inverse of D outputted from the data latch circuit 4 are turned on and off respectively and are outputted to the switching means 5 when the signal inputted from the telephone line is the busy signal, and signals D and the inverse of D are turned off and on respectively and are outputted to the switching means 5 when it is the DTMF signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tone receiver circuit for detecting a DTMF signal and a busy tone signal.

[0002]

2. Description of the Related Art In a conventional tone receiver circuit,
A filter circuit having the characteristic of filtering a DTMF signal;
The filter circuit having the characteristic of filtering the busy signal was separately provided.

[0003]

However, in the conventional tone receiver circuit, it is necessary to always operate the two filter circuits even though the DTMF signal and the busy tone signal are not simultaneously input. Therefore, there is a problem that the current consumption is large and the chip size is large.

An object of the present invention is to provide a tone receiver circuit capable of filtering a DTMF signal and a busy tone signal with one filter circuit by switching the characteristics of the filter circuit according to the input signal. It is in.

[0005]

A tone receiver circuit of the present invention includes a filter circuit having a characteristic of selectively filtering a DTMF signal or a busy tone signal from a signal input from a telephone line, and an input signal. A discriminating circuit for discriminating the level of the specific frequency; and, when the discriminating circuit discriminates that the input signal is higher than the specific frequency, the filter circuit DT
A switching means for setting the MF signal to a characteristic for filtering and setting the filter circuit to a characteristic for filtering the busy tone signal when it is determined that the input signal is lower than a specific frequency. ..

[0006]

In the present invention, when the signal inputted from the telephone line is judged to be higher than the specific frequency by the judging circuit,
The switching means sets the characteristics of the filter circuit to filter the DTMF signal. On the other hand, if the discrimination signal determines that the input signal from the telephone line is lower than the specific frequency,
The characteristics of the filter circuit are set by the switching means so as to filter the busy tone signal. Generally, the DTMF signal has a frequency of 6
90 to 1640 Hz, busy tone signal is 400 ± 10% Hz
Therefore, the specific frequency may be set to about 500 Hz, for example.

[0007]

1 is a diagram showing the configuration of a tone receiver circuit according to an embodiment of the present invention.

The tone receiver circuit is composed of a discrimination circuit 1 including a low-pass filter 2, a detection circuit 3 and a data latch circuit 4, and a switching means 5 and a filter circuit 6 which is switched by the switching means 5 to a characteristic according to an input signal. ing.

Discrimination circuit 1 from the telephone line via the input terminal
The signal input to the signal passes through the low-pass filter 2 only for signals having a frequency of 500 Hz or less, is converted to an H level in terms of DC by the detection circuit 3, and is output to the data latch circuit 4. The data latch circuit 4 latches the converted signal and outputs the signals D and D * (* is synonymous with bar (upper line), the same applies hereinafter) to the switching means 5 to switch the characteristics of the filter circuit 6. The frequency of the signal input from the telephone line is 690 to 1640 Hz for the DTMF signal and 400 ± 10 for the busy tone signal.
Since it is% Hz, it is the busy tone signal that passes through the low-pass filter 2, and the DTMF signal cannot pass through. Therefore, when the signal input from the telephone line is the busy tone signal, when the signal output from the data latch circuit 4 is D on and D * is off and is output to the switching means 5 and is the DTMF signal. Is output to the switching means 5 when D is off and D * is on.

The switching means 5 receives passive signals C1, C2 and R according to the signals D and D * inputted from the discrimination circuit 1.
Select 1 or R2 with analog switch, and filter circuit 6
Switch the characteristics of.

The filter circuit 6 constitutes a band-pass filter for passing the busy tone signal of frequency 400 Hz by C2 and R1 when the switching means 5 has a characteristic of detecting the busy tone signal, and the busy signal is inputted. The unnecessary frequency component of the sound signal is removed. The busy signal output from the filter circuit 6 is pulse-converted in the 0-cross circuit 7 and output.

On the other hand, when the switching means 5 is set to have the characteristic of detecting the DTMF signal, the filter circuit 6 causes the C1 and R2
A bandpass filter for passing a DTMF signal having a frequency of 690 to 1640 Hz is configured by
The unnecessary frequency component of the MF signal is removed. Filter circuit 6
The DTMF signal output from is input to the frequency reading circuit 8, the actual frequency is read, and then 4-bit data determined from the combination of the two frequencies is output.

As described above, since the tone receiver circuit of the present invention switches the characteristics of the filter circuit 6 according to the signal discriminated by the discrimination circuit 1, the busy tone signal and the DTMF signal are detected by one filter circuit. It can be carried out.

[0014]

As described above, according to the present invention, the DTMF signal and the busy tone signal can be filtered by one filter circuit by switching the characteristics of the filter circuit according to the input signal. The chip size can be reduced and the current consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a tone receiver circuit according to an embodiment of the present invention.

[Explanation of symbols]

 1 discrimination circuit 5 switching means 6 filter circuit

Claims (1)

[Claims] 1. DTMF from a signal input from a telephone line
A filter circuit having a characteristic of selectively filtering a signal or a busy signal, a discrimination circuit for discriminating the level of an input signal and a specific frequency, and discriminating that the input signal is higher than the specific frequency in the discrimination circuit. Switching means for setting the filter circuit to the characteristic of filtering the DTMF signal, and setting the filter circuit to the characteristic of filtering the busy tone signal when it is determined that the input signal is lower than a specific frequency. Tone receiver circuit characterized by