JPS6159029B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a control signal detection device for a facsimile machine that transmits information such as drawings and drawings using a telephone line, and its main purpose is to prevent false detections caused by voices and the like.

Conventionally, efforts have been made to detect only the frequency components of tonal control signals, for example. For example, methods have been used such as detecting the incoming control signal with a filter with a steep curve, or converting the incoming control signal into binary pulses, and measuring the pulse interval to detect the frequency. .

However, since the above-mentioned method simply detects only the frequency component of the control signal, erroneous detection of the control signal due to human voice has occurred due to crosstalk peculiar to telephone lines and misconnection of the line. In other words, in the above detection method, if that frequency component exists,
It is determined that it is a control signal. For example, the control signal has a relatively low frequency (400-500Hz)
Although it is used from high frequencies (2K to 2.5KHz), it also includes high spectral components from male voices to female voices, so if certain music etc. are mixed in, it will definitely malfunction. be.

Therefore, in order to eliminate the above-mentioned disadvantages, the present invention focuses on the fact that voice and music have not only a single frequency but also a certain amount of bandwidth. The control signal is also monitored, and when the level other than the original control signal frequency is large, it is not considered to be a true control signal.

FIG. 1 shows a block diagram of an embodiment of the present invention and will be described.

1 is an input terminal to which an incoming control signal is input. 2 is a detection circuit for a single frequency included in the control signal; 3 is a control signal frequency removal filter;
This output is input to a bandpass filter 4. The output of the band filter 4 enters the average level detection circuit 5,
This output is input to the frequency detection circuit 2 and controls the output of the circuit 2.

First, the operation will be explained with reference to FIG. An incoming control signal is input to the terminal 1 from a telephone line via a network control circuit necessary for line connection. This input enters a frequency detection circuit 2 which detects the single frequency component of the incoming control signal.
On the other hand, the input control signal also enters the control signal frequency removal filter 3, and the control signal itself is removed. The output of the control signal frequency removal filter 3 enters a band filter 4 and is subjected to band limitation.
Furthermore, an average level detection circuit 5 determines whether the output of the band filter 4 is greater than or less than a certain level, and the output of the frequency detection circuit 2 is controlled based on the determination result. Regarding the average level detection circuit 5,
Figure 3 shows its configuration. Reference numeral 51 denotes a detection circuit, which may be a diode, a transistor, or the like as long as it performs a rectifying action. 52 is a filter of a low-pass type. This is for extracting the DC component after rectification. 53 is 2 with threshold level
A threshold level is set in a value conversion circuit, and a high level H or a low level L is output as an output depending on whether the output of the low-pass filter 52 is larger or smaller than the threshold level.

The characteristics of the band filter 4 that limits the band are as follows:
It must be possible to detect audio. As is well known, the spectrum of speech is
It is largely distributed around 1KHz, and its low-level harmonics are distributed in the high range. Therefore, even if there are some differences between men and women, it is possible to detect voices if the band filter has a band characteristic that allows frequencies around 1 KHz to pass.

FIG. 2 is a block diagram of a configuration in which a part of the frequency detection circuit 2 shown in FIG. 1 is replaced by a control signal frequency removal filter 3. Note that the same number is the first
It is the same as the figure. 8 indicates 2 excluding the frequency detection filter. 7 is a subtracter to which the signals of input terminal 1 and control signal frequency removal filter 3 are input, and the output of subtractor 7 is equivalently the one that has passed through a bandpass filter controlled by control signal frequency removal filter 3. .

Other operations are the same as in FIG. 1.

FIG. 4 shows the frequency characteristics of the control signal frequency removal filter 3 and the bandpass filter 4. In the graph, the horizontal axis shows frequency, and the vertical axis shows relative input/output input. A solid line 30 in FIG. 4A shows the characteristics of the control signal frequency removal filter 3, that is, it is designed so that almost no circuit is obtained in the vicinity of the control signal frequency s. A broken line 40 in FIG. 5A indicates bandpass characteristics. As already explained, the bandwidth of the broken line 40 is set to include high components of the audio spectrum. Further, FIG. 4B shows the characteristics when the two filters 3 and 4 are integrated, and shows the case where the filter is designed by combining 3 and 4 in FIG. 1 into one.

Note that the above describes the detailed explanation of the frequency detection method, but this detection method can be
Using a combination of logic elements such as TTL or a microcomputer, etc., a control signal with a constant period is converted into a binary pulse, and the pulse period is further counted using a clock pulse with a smaller period (higher frequency). This can be achieved by determining whether the count is within a permissible value.

In addition, the characteristic diagram in Figure 4 shows that the band-pass type is used, which does not produce output even at low frequencies, because it eliminates the influence of billing pulses on the telephone line (pulses for charge calculation, at public telephones, money is dropped with these pulses). This is to eliminate it.

In the above embodiment, the average level detection circuit 5
The level of the band excluding only the control signal frequency is detected, and if it is higher than a certain threshold level, it is determined that it is a voice etc., and the output of the frequency detection circuit 2 is turned off. Therefore, malfunctions such as mistaking audio or the like for a control signal and emitting a control signal detection signal do not occur at all.

As described above, according to the present invention, the level of the band excluding the control signal is detected, and the output of the control signal is forcibly turned off using this detection signal.
It is an object of the present invention to provide a control signal detection device that does not cause malfunction due to noise in a band including control signals and is particularly effective in signal transmission using a telephone line.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing one embodiment of the present invention;
FIG. 2 is a block diagram showing another embodiment, FIG. 3 is a block diagram showing essential parts of this embodiment, and FIG. 4 is a frequency characteristic diagram. 2...Frequency detection circuit, 3...Control signal frequency removal filter, 4...Band filter, 5...Average level detection circuit, 7...Subtractor.

Claims (1)

[Claims] 1 A control signal detecting means which takes as an input a transmission signal into which a control signal including at least one single frequency is inserted, and detects and outputs the frequency of the control signal; A filter means for removing frequency components and further limiting the band; and a level detecting means for comparing the output of the filter means with a certain set value, the output of the control signal detecting means being controlled by the output of the level detecting means. A control signal detection device characterized in that the output of the control signal detection means is turned off when the output of the filter means is equal to or higher than a certain set value.