JPH0522980Y2 - - Google Patents

Description

[Detailed explanation of the invention] (1) Purpose of the invention [Field of industrial application] This invention is designed to prevent inductive noise in communication lines and improve home equipment, especially facsimile machines and no-ringing terminals (16Hz
The present invention relates to an improvement in a noise blocking filter for a communication line to prevent malfunctions in a terminal (terminal that generates incoming calls without using a paging signal).

[Prior Art] Some home devices that connect to communication lines to send and receive information operate not on normal incoming signals (approximately 16 Hz and 70 V) but on signals at other specific frequencies. For example, a facsimile that is part of a facsimile network operates at a frequency of 1300Hz. It is designed to operate with a weak power level of about -40 dB (0 dB = 1 mW). Several mV when converted to voltage
It will start up when a 1300Hz signal of about 100Hz arrives for a certain period of time. In addition, in systems that remotely examine consumption of gas, water, etc. using communication lines, a center periodically calls a meter reading terminal to compile the meter readings. Since this terminal is installed in a branch with a regular telephone, the telephone uses a different signal (for example, 1200Hz) from the normal incoming call signal of 16Hz in order to ring only the meter reading terminal without ringing.

[Problems that the invention aims to solve] On the other hand, since the in-home equipment side is not in a line loop state when it is on standby, the impedance seen from the line side is higher than when it is in the communication state, and the noise is high compared to the external noise on the communication line. It is susceptible to induction.
Therefore, there is a risk that noise induced into the communication line from power lines, electric motors, etc. may cause the facsimile to automatically start up, causing a malfunction. However, even after automatic activation, the facsimile will time out after a certain period of time because a normal signal does not arrive.

In order to prevent this, it is effective to insert a noise blocking filter into the terminal line. The filter is generally of the type in which a toroidal core made of a ferrite material or an E-shaped core is wound, and a capacitor is connected in parallel with a capacitor so that its resonance point is matched to the stopping frequency. If such a normal filter is used, the transmitting and receiving signal level will also be attenuated because it will function as a filter even when a communication state is established. For example, in the case of the facsimile mentioned above, normally the transmission speed is 9600 bits/s, but if a filter of about 10 dB is inserted, the line quality is considered to be degraded and the transmission speed is reduced.
This will reduce the speed to 4800bit/S or 2400bit/S.

As described above, there is a drawback that the signal level is attenuated to the level in the communication state (state in which a line loop is formed).

This system uses a noise blocking filter that has line signal attenuation characteristics in the standby state (state where no line loop is formed) but does not have such attenuation characteristics in the communication state (telephone current flows) to prevent erroneous activation of facsimile machines, etc. It is an object of the present invention to provide a noise blocking filter for communication lines that is effective and suitable for the purpose of the present invention.

(2) Structure of the invention [Means for solving the problem] In the communication line noise blocking filter of this invention, the magnetic properties of the core are saturated by the applied current of the communication line (usually at least 20 mA) and the inductance is reduced. By using a coil, the filter attenuation characteristics are changed between the standby state and the communication state, increasing the attenuation in the former and lowering the attenuation in the latter, making it possible to change the conventional filter to a filter that always has a constant attenuation at the communication current level. The main feature is that it solves the drawbacks that have only been realized before.

[Example] An embodiment of the present invention will be described with reference to FIG.

Figure 1 is a configuration circuit diagram of the communication line noise rejection filter F of the present invention, in which 1 is a chiyoke coil;
2 is a capacitor, 3 is also a capacitor, X1 and X2 are communication line connection terminals, and Y1 and Y2 are home equipment connection terminals.

The impedance between the input and output increases at a specific frequency by utilizing the LC resonance between the choke coil 1 and the capacitor 2, thereby forming a band rejection filter that increases the amount of attenuation at that frequency.

Fig. 2 shows a specific example of the chiyoke coil 1 used in the present invention, and Fig. 2a shows the overall configuration, Fig. 2b shows an exploded view, and Fig. 2c shows a central vertical section taken along line c-c in Fig. 2a. Figures are shown respectively. In the figure, 4 is a bobbin made of an insulating material, 5 is a winding wire, and 6 is a magnetic thin film. magnetic thin film 6
should be thin and have high magnetic permeability, specifically
A thin wire material with high magnetic permeability such as permalloy material with a thickness of about 0.1 mm or Ni-based amorphous material with a thickness of 0.05 mm is recommended.
Such a magnetic thin film 6 is folded from one side of the bobbin 4 and inserted into the inner hole 4a from the bottom to the top, and then folded from the top to the same side as shown by the imaginary line in FIG. 2b to form an overlapping loop. to create a magnetic closed circuit.

[Operation] The present invention is constructed as described above. Here, in FIG. 3, the connection terminal A of the chiyoke coil 1 of FIG.
The inductance characteristics with respect to the direct current flowing through B are shown. In the figure, the vertical axis represents the coil inductance (mH), the horizontal axis represents the direct current (mA), and the measurement frequency is 1.3kHz. When there is no DC bias current, the inductance L of the coil is L = 40 mH, but as DC is applied, the magnetic flux in the magnetic material becomes saturated at about 10 mA, and the coil L decreases to 2 mH or less. represents the characteristic that

Looking at the DC current in a communication line, when the equipment in the home is in standby mode, no current flows, but when a loop is formed by receiving or sending a call, a DC current of about 20 to 100 mA flows. Therefore, if the filter F in Figure 1 is configured with the filter F in Figure 1 using the characteristic coil 1 as shown in Figure 3, and the capacitance of the capacitor 2 is appropriately selected (approximately 0.3 μF), it will attenuate at a predetermined frequency during standby when there is no superimposed current. The amount can be increased.

FIG. 4 shows the attenuation characteristics of the filter F shown in FIG. 1. In the figure, the vertical axis shows the attenuation (dB) and the horizontal axis shows the frequency (kHz), and the correlation characteristic line α when there is no superimposed current and the superimposed current (20 mA to 100 mA DC)
A comparison was made with the correlation characteristic line β in the case of . When the filter F of the present invention is used with direct current applied, the inductance L of the choke coil 1 is significantly reduced, so that the attenuation characteristic becomes as shown by the dotted line, and no loss is caused to the line signal.

That is, when inserted into a communication line, the in-home device exhibits attenuation characteristics when it is in a standby state, but when a loop is formed and it enters a communication state, the amount of attenuation decreases and does not affect signal transmission and reception.

(3) Effects of the invention In this way, this proposal has the following effects when viewed in terms of the frequency band of communication lines (for example, 500Hz to 3.5kHz for analog lines).
The attenuation of the filter is large when no DC bias current is applied, but the attenuation decreases when a DC of 20 mA or more is applied, so it is possible to block induced noise from the line when in-home equipment is on standby. It has excellent practicality and usefulness, such as being able to communicate normally without attenuating the signal once it is in a communication state.

[Brief explanation of the drawing]

Fig. 1 is a schematic diagram of the circuit configuration of the communication line noise blocking filter of the present invention, and Fig. 2 is an example of the structure of the chiyoke coil used in the present invention. FIG. 3 is an inductance characteristic diagram of the same chiyoke coil, and FIG. 4 is an attenuation characteristic diagram of the filter of the present invention. 1...Chiyoke coil, 2, 3...Capacitor, 4...Bobbin, 5...Winding wire, 6...High permeability magnetic thin film, X1, X2...Communication line connection terminal, Y
1, Y2...In-house equipment connection terminal.

Claims (1)

[Scope of utility model registration request] Connect the chiyoke coil and capacitor in parallel,
In a communication line band rejection filter that is inserted in series in a communication line, the inductance is large when no DC current is applied, and the inductance decreases when the DC bias current that is superimposed when the communication current is applied exceeds a specified value. A noise blocking filter for communication lines that uses a chiyoke coil.