JPS6181056A - Noise eliminating circuit - Google Patents

Abstract

PURPOSE:To prevent the erroneous detection of signals due to noise by generating a discriminating signal which is turned on when the variation of the rise of an input signal is larger than that of the noise and is turned off when the variation of the fall of the input signal is larger than that of the noise and transmitting or not transmitting the input signal to a noise eliminating circuit in accordance with turning-on or off of the discriminating signal. CONSTITUTION:An input signal 4 to a FAX is inputted to a logarithmic amplifier 6 and is subjected to a logarithmic amplification. When this signal is inputted to a differentiating circuit 8, the differentiating circuit 8 outputs a signal which becomes as shown in a figure (a) by the rise of the input signal and becomes as shown in a figure (b) by the fall of the input signal. When this signal is inputted to a comparator 10, an RS flip flop 12 is set through an operational amplifier 1001 by the signal shown in the figure (a) and is reset through an operational amplifier 1002 by the signal shown in the figure (b) because a voltage corresponding to >=10dB variation of the input signal is applied to the (+) terminal of the operational amplifier 1001 and the (-) terminal of the operational amplifier 1002.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a noise removal circuit for preventing false detection of received signals due to noise in network control of facsimile machines.

Technical background of the invention] As shown in FIG. 8, the t2 control section of the facsimile machine
It consists of a network control unit (hereinafter referred to as NCU) 100 that serves as an interface with a line, a modem 102 that performs modulation and demodulation, and a main control unit (hereinafter referred to as CPU) 104 that controls them.

The input signal passes through NCUl 00, which is switched to the facsimile machine (hereinafter referred to as FAX) side, and is sent to modem 1.
02 is input. The modem 102 receives a demodulated signal of the input signal and a signal indicating that the signal is being received (hereinafter referred to as C).
D) is input to CPU IQ,1.

The CPU104 monitors the CD, and when this signal is on, it does not send a signal itself, which is an inexpensive and easy way to prevent signal collision.

[Problems with background technology]

By the way, ideally, the modem 102 transfers the CD to the CPU 104 only when it receives a signal related to a FAX signal.
It is desirable to enter the following information. However, conventionally modem 1
When a signal reaches a level that modem 102 can receive, it outputs all CDs and tells CPUIO4 that a signal is coming from the other station.For this reason, when noise enters the reception range of modem 102, it outputs a CD. There was an inconvenience that the signal was not sent out by itself in order to send the signal to the CPUIO4.

In this way, in conventional facsimile dialing, the presence or absence of a signal was determined based on the level, so if noise came within the modem's reception range, it would be judged as a signal from the other station, and the signal would be transmitted from the own station. There was a problem in that it did not give a signal.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a noise removal circuit capable of eliminating the above-mentioned problems and detecting only a signal even if there is noise or the like within the reception level.

[Summary of the invention]

In the present invention, a discrimination signal is generated that is turned on when the amount of change in the rising edge of the input signal is greater than the amount of change in the noise, and is turned off when the amount of change in the falling edge of the input signal is greater than the amount of change in the noise. The above object is achieved by disconnecting or disconnecting the transmission of the input signal to this circuit in accordance with the on/off state of the discrimination signal.

[Embodiments of the invention]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below based on the drawings. FIG. 1 is a block diagram of a circuit according to an embodiment of the present invention. In FIG. 1, 2 is an input signal line to this circuit, 4 is an input signal line to it FAX, 6 is two operational amplifiers, A log amplifier consisting of a resistor and a transistor, 8 a known differentiating circuit, 10 a comparator consisting of a resistor and operational amplifiers 1001 and 1002, 12 an RS flip-flop, and 14 transmitting the CD signal generated by this embodiment. 16 is a switching circuit, and 18 is a main circuit line.

The log amplifier 6 is used to convert the decibel input from the line into a linear voltage value. FIGS. 2 and 3 show input and output signals of the log amplifier 6, with the vertical axis representing voltage and the horizontal axis representing dBm. As shown in the figure, for example, -4QdBm
The amount of change in input level from -30dBm to LOdB
Even if the amount of change from m to OdBm is different, the amount of change in the output voltage is -4QdBm to -30dBm, and -1Qd
It becomes equal between Bm and 068m.

When the current level changes, the differentiating circuit 8 changes it to a no level according to a certain time constant if the change is at a high level;
If it is low level, it changes to low level for a certain amount of time.

This signal is shown in FIG. 4, where the vertical axis represents voltage and the horizontal axis represents time. The portion a indicates that the signal has changed upward from the current level, and the portion b indicates that the signal has changed downward from the current level.

The comparator 10 has thresholds determined for each of the signal 2 (signal ON) and the signal b (signal OFF') shown in FIG. 4, and voltages are divided in advance using resistors.

That is, the (10) terminal of operational amplifier 1001 and operational amplifier 1
For example, a voltage of 0.24V is applied to the (-) terminal of 002.

The output of 1001 million pampers is the RS flip-flop 1
It is connected to the S (sect) terminal of 2, and the operational amplifier 1002
The output of is connected to the R (reset) terminal of the RS flimb flow knob 12.

CD14 which is the output signal of the R, S flipflop 12
is input to the switching circuit 16, and in this switching circuit 16, C
When DI 4 is at low level, the contact of switching circuit 16 is B.
When the CD 14 becomes high level, the contact piece of the switching circuit 16 is connected to the A side, and the input signal 2 is transmitted to the main circuit line 18.

Next, the operation of this embodiment will be explained.

FIG. 5 is a time chart of an input signal with noise within the receiving range of the modem, and FIG. 6 is a time chart of a meaningful input signal, where the vertical axis represents dBm and the horizontal axis represents time. Now, as shown in FIG. 6, a case will be considered in which a signal that changes by 1QdB or more is a meaningful signal, and this signal is input to the log amplifier 6. The input signal 4 to the FAX is input to the log amplifier 6 and is logarithmically amplified as described above.

In other words, a 1QdB change in the input signal will result in the same change in the output voltage no matter where it changes due to the log amplifier 6. Next, this signal is input to the differentiating circuit 8. Then, in the differentiating circuit 8, the input signal At the rising edge of the signal, the signal shown in FIG. 4a is obtained, and at the falling edge of the input signal, the signal shown in FIG. 4 is outputted.

Next, when a signal as shown in iC1 FIG. .24V
) Kaohe 77p1001 (7) Since the voltage is applied to the (+) terminal and the (-2 terminal of the operational amplifier 1002, the 4th
The signal shown in FIG. 4 sets the RS flip-flop 12 via the operational amplifier 1001, and the signal shown in FIG.

However, if there is an input signal as shown in Figure 6ζ,
The output signal CD of the RS flip-flop 12 is at a high level only during the period Δt shown in the figure, and at a low level during other periods.

When this CD signal is input to the switching circuit 16, the contact piece of the switching circuit 16 connects to A only when CD is at a high level, and the input signal 2 is transmitted to the main circuit 18.

However, when there is an input signal shown in Fig. 6,
The signal represented by this circuit 18 is as shown in FIG.

〔Effect of the invention〕

As described above in detail and specifically, according to the present invention, no signal is input to this circuit when no meaningful signal is input, and only when a meaningful signal is input. Since the signal is input to this circuit, false detection of the signal due to noise can be prevented.

Further, the present invention allows determining the presence or absence of a meaningful input signal,
Since the switching circuit is switched, it can be easily applied not only to FAX machines but also to network control units of data transmission devices.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a noise removal circuit according to an embodiment of the present invention, FIGS. 2 and 3 are graphs showing input signals and output signals of a log amplifier, and FIG. 4 is an output of a differentiating circuit. Graphs showing signals; Figure 5 is a time chart showing an input signal with noise within the receiving range of the MODEM; Figure 6 is a time chart showing meaningful input signals; Figure 7 is a signal represented by this circuit. Time chart showing 8th
The figure is a block diagram showing the configuration of a network control section of a facsimile machine. 6... Log amplifier, 8... Differential circuit, 10... Comparator, 12... RS flip-flop, 16.
switching circuit. Figure 2 t □ Figure 5... Cape t □

Claims (1)

[Claims] (1) means for generating a discrimination signal that turns on when the amount of change in the rising edge of the input signal is greater than the amount of change in noise; and turns off when the amount of change in the falling edge of the input signal becomes greater than the amount of change in noise; , and switching means for connecting or disconnecting transmission of the input signal to the circuit according to whether the discrimination signal is turned on or off.