Communication cable for reducing electromagnetic wave interferen

Electrical transmission or interconnection systems – Anti-induction or coupling to other systems – Magnetic or electrostatic field control

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174 32, 333167, H03H 700

Patent

active

056568720

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to a communication cable for connecting a computer main body with a monitor, and more particularly, to a communication cable for reducing electromagnetic wave interference.


DESCRIPTION OF THE PRIOR ART

Recently, as home-use computers are generally distributed, a considerable amount of higher harmonics being electromagnetic wave signals has been being generated to interfere with the operations of the other electromechanical apparatuses. Thus, most of the countries have the provisions in which an interference wave signal output should be attenuated from such an interference signal generating source so as to reduce a signal output of the interference wave.
A method or an apparatus for reducing the interference wave signal output has been disclosed in a variety of the prior art references. A filter using a ferrite sleeve of U.S. Pat. No. 4,144,509 or a filter using a structure of a monolithic capacitor having ferrite or not having ferrite of U.S. Pat. No. 3,538,464 can be enumerated as such an example.
However, such an apparatus is too expensive to be used in an inexpensive electronic product such as a personal computer. Thus, an inexpensive filter is required so as to be capable of satisfactorily attenuating an electromagnetic signal having an ultra high frequency, that is, frequencies up to 1,000 MHz. An available efficient filter attenuates an electromagentic signal having a frequency of 1,000 MHz by 30 decibel (dB).
In the other methods of smoothly transmitting a signal and removing such an interference wave component, a method for bypassing an interference wave using a capacitive filter or a method for enlarging an alternative resistance Using an inductive filter (a choke coil) can be used.
However, such a method using the capacitive filter or inductive filter causes several problems. That is, the method for largely reducing noise using a capacitor having a large capacitance greatly attenuates the signal waveform to cause a circuit to misoperate, while the method for reducing noise using an inductor having a large inductance greatly attenuates the signal waveform to cause the signal waveform to be distorted.
Moreover, such a capacitive filter or inductive filter has a good effect on removing the noise at a comparatively low frequency. However, at the high frequencies, an inductive coupling due to the residual inductance dependent upon a structure of a lead wire or an electrode and a drift capacitance which exists between lines become resonant at a particular frequency between several mega hertz and several tens of mega hertz. Accordingly, the effect of removing noise with respect to a particular high frequency has been lowered.
A combination filter using both a capacitive element and an inductive element can be used to transmit a desired frequency band for a load and prevent an undesired wave from being radiated. FIG. 1 shows such an example, in which an inductive element 12 which is inserted in series with respect to a load 16 causes a large impedance component with respect to an alternating component, while a capacitive element 14 which is connected in parallel to the load 16 plays a role of bypassing the alternating component.
Thus, since the components more than a predetermined frequency among a signal applied between input ends "A" and "B" are blocked by inductive element 12 and bypassed by capacitive element 14, only a signal from which the components more than a predetermined frequency are attenuated is transmitted for load 16.
However, when a characteristic impedance Z.sub.O of the line and an intrinsic impedance Z.sub.L Of the load 16 are not matched to each other, a reflected wave is generated from the load and is transmitted toward input ends "A" and "B". However, since such a reflected wave is bypassed by capacitive element 14 and is blocked by inductive element 12, the reflected wave is not transmitted toward input ends "A" and "B", but circulates a closed circuit constituted by load 16, capacitive element 14 and inductive element 12, t

REFERENCES:
patent: 4144509 (1979-03-01), Boutros
patent: 4215325 (1980-07-01), Sansone
patent: 5168251 (1992-12-01), Zennamo, Jr. et al.
patent: 5519434 (1996-05-01), Fasquel

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