JPH04220862A - Tone detection circuit - Google Patents

Abstract

PURPOSE:To prevent a 2100Hz tone detection circuit from causing malfunction at the reception of a 400Hz tone. CONSTITUTION:A switch circuit is provided between a 1st detector for a 2100Hz signal component and a 1st level conversion circuit and the switch circuit is controlled by an output signal of a 2nd level conversion circuit corresponding to the 400Hz signal component. When the 400Hz tone has a high input level and a harmonic distortion component, the harmonic component passes through a 2100Hz band filter and is detected by a detector 4. The harmonic component signal detected by the detector 4 is inputted to a next stage of switch circuit 6 and since the switch circuit 6 is controlled to be opened at the detection of the 400Hz tone, the detection signal of the harmonic component is not sent to a level conversion circuit 8, and then not outputted at a 2100Hz detection output terminal 9.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tone detection circuit, and more particularly to prevention of tone detection malfunction in a switched line modem having a network control function.

0002

2. Description of the Related Art In a conventional tone detection circuit, when a 2100 Hz tone is received at a tone receiving input terminal 11, a 2100 Hz band filter 12 detects a
Noise outside the 0Hz band is removed and a 2100Hz component is extracted, this extracted 2100Hz component is detected by the wave detector 14, and the waveform is shaped by the level conversion circuit 18 and converted to a constant DC voltage level that does not include ripples. death,
It is output to the 2100Hz detection output terminal 19.

Similarly, when a 400Hz tone is received, a 400Hz band filter 13 removes noise outside the 400Hz band and extracts a 400Hz component, and a detector 15 detects the extracted 400Hz component to determine the level. The conversion circuit 17 shaped the waveform and converted it into a constant level DC voltage level that does not include ripples, and output it to the 400 Hz detection output terminal 20.

0004

However, in the conventional tone detection circuit described above, when a high level 400Hz tone is received, the harmonic distortion components of the 400Hz tone enter the band of the 2100Hz bandpass filter 12, and thereby the 2100Hz The detection circuit 14 side also operates, and 2100
There was a problem that the Hz detection circuit side would malfunction.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore, an object of the present invention is to provide a novel tone detection circuit capable of solving the above-mentioned problems inherent in the conventional technology. There is a particular thing.

[0006]

[Means for Solving the Problems] In order to achieve the above object, a tone detection circuit according to the present invention has a tone detection circuit of 2100 Hz and 4
first and second bandpass filters that receive a tone signal from a telephone exchange line transmitted at one of the frequencies of 00Hz and extract a 2100Hz signal component and a 400Hz signal component, respectively; and the first and second bandpass filters. first and second detectors that detect each signal component of the filter, and first and second detectors that waveform-shape the detection outputs of the first and second detectors and convert them into DC voltage signals of a constant level, respectively. a tone detection circuit having a level conversion circuit, the tone detection circuit having a switch circuit between the first detector corresponding to the 2100 Hz signal component and the first level conversion circuit; The switch circuit is controlled by the output signal of the second level conversion circuit.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention.

Referring to FIG. 1, tone reception input terminal 1
When a 400 Hz tone is received, a 400 Hz bandpass filter 3 removes noise outside the 400 Hz band and extracts a 400 Hz component, and a detector 5 detects the extracted 400 Hz component and converts it to a DC signal level. Furthermore, this DC signal level is converted by the next level conversion circuit 7 into a waveform-shaped DC voltage containing no ripples and outputted to a 400 Hz detection output terminal 10.

[0010] Here, if a 400Hz tone has a high input level and has a harmonic distortion component, this harmonic component will be 210
The signal passes through a 0Hz bandpass filter 2 and is detected by a detector 4. The harmonic component signal detected by the detector 4 is input to the next switch circuit 6, and when a 400 Hz tone is detected at the 400 Hz detection output terminal 10, the switch circuit 6 is controlled to open the switch. The detected signal of the harmonic component is not transmitted to the level conversion circuit 8, and therefore is not detected and outputted to the 2100 Hz detection output terminal 9.

On the other hand, 2100Hz is input to the tone reception input terminal.
When the tone is received, the 2100 Hz band filter 2 removes noise outside the 2100 Hz band and
The Hz component is extracted, detected by a wave detector 4, and converted to a DC level. At this time, even if the input level of the 2100 Hz tone is high, the harmonic distortion component does not include a frequency component in the 400 Hz band, so the 400 Hz tone detection circuit does not enter the detection state. Therefore, the switch of the switch circuit 6 is in a closed state, and the output of the detector 4 passes through the switch circuit 6 and is converted into a ripple-free waveform-shaped DC voltage of a constant level by the level conversion circuit 8, and the output is a 2100Hz detection output. It is output to terminal 9.

0012

As explained above, according to the tone detection circuit of the present invention, when receiving a 400Hz tone,
It is possible to prevent the Hz tone detection circuit from malfunctioning, and as a result, it is possible to perform connection operations in network control without malfunction.

[Brief explanation of the drawing]

Claims (2)

[Claims] 1. First and second bandpass filters that receive a tone signal from a line transmitted at a frequency of either 2100 Hz or 400 Hz and extract a 2100 Hz signal component and a 400 Hz signal component, respectively;
first and second detectors that respectively detect each of the signal components, and first and second detectors that waveform-shape the detection outputs of the first and second detectors and convert them into DC voltage signals each having a constant level. In the tone detection circuit having a level conversion circuit, a first tone detection circuit corresponding to the 2100Hz signal component;
A tone detection circuit comprising a switch circuit between the detector and the first level conversion circuit, the switch circuit being controlled by an output signal of the second level conversion circuit corresponding to the 400 Hz signal component. . 2. When the input level of the 400 Hz tone is high and has a harmonic distortion component, and when the output of the second level conversion circuit is in a 400 Hz tone detection state, the second level conversion circuit 2. The tone detection circuit according to claim 1, further comprising controlling said switch circuit to open based on an output of said switch circuit.