Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2001-11-26
2004-03-09
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C361S794000, C361S795000
Reexamination Certificate
active
06703909
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a covering sheet, a triplate line using the sheet, a signal bus for a computer using the sheet, and a covering structure of an electronic circuit using the sheet. Particularly, the present invention relates to a technology for achieving higher pbu of a signal bus mainly for a computer and to an electromagnetic-interference-preventing technology for suppressing unwanted signal radiation observed in signal lines of electronic equipment.
DESCRIPTION OF THE RELATED ART
Generally, the speeding up of central processing units (CPUs) has been pursued in order to increase the clock frequency of computers. However, there is a limit to what is done by increasing the speed of only CPU's, the achievement of the further increased processing-speed of computers requires the increased speed of data exchange between CPU's and peripheral equipment.
As shown in
FIG. 1
, a CPU
10
and peripheral equipment
11
to
14
are usually connected to each other through lines having a plurality of branches and being called a signal bus
15
. The signal bus
15
should be made of non-matched branch lines, because talkers (sending ends) and listeners (receiving ends) change places as required. As a result, there can be troubles such as the delay of pulse build up (pbu) time, caused by the irregularities of pulse shapes resulting from the existence of reflected waves in the lines, and the break down of semiconductor elements due to voltage buildups caused by resonance.
In order to avoid such troubles, conventionally, damping resistance and absorbing type of high-cut filters have been inserted into the circuits. However, these measures have not been sufficient, because they have respective problems that pbu time can not be appreciably reduced and that not only signal waveforms but also the lengths of delay time are different before and after the filter.
On the other hand, there have been the following problems in the electromagnetic control technologies in digital equipment and high-frequency equipment such as computers and others. By the way, the electromagnetic interference refers to a phenomenon in which high frequency signals circulating in such equipment are radiated from the lines of the equipment to the outside so as to interfere with the other equipment.
Conventional electromagnetic control technologies include a method that suppresses the radiation of disturbing waves by covering the lines radiating disturbing waves with electromagnetic energy absorbing materials such as a ferrite-containing rubber sheet. However, the amount of energy absorbed by such a sheet is only 2-4 dB, so that the sufficient suppression of disturbing waves has not been achieved when the radiation is strong.
Also, there are radiation suppression measures using magnetic resin compounds for circuit boards, but this method has been not practicable because of the substantially increased cost of the boards. Further, mosaic boards having the magnetic resin compounds limited only to the line portions requiring them has been manufactured in order to reduce cost, but such mosaic boards is not in practical use because the flexibility of board design is impaired remarkably.
SUMMARY OF THE INVENTION
It is therefore an object of the invention to provide a covering sheet permitting increased pbu of a signal line such as a signal bus for a computer with the smallest difference in signal waveforms and delay times on the line, a triplate line using the sheet, a signal bus for computers using the sheet, and a covering structure of electric circuits using the sheet.
Another object of the invention is to provide a covering sheet for permitting more effective prevention of electromagnetic interference, a triplate line using the sheet, a signal bus for a computer using the sheet, and a covering structure of electronic circuits using the sheet.
According to the present invention, a covering sheet includes at least one magnetic material layer made of a resin compound having an oxide magnetic material or a metal magnetic material mixed therein, a ground conductor layer laminated on one surface of the magnetic material layer, and a plurality of via holes for passing a conductor for grounding the ground conductor layer.
A target signal line or signal bus formed on a circuit board is covered with such a covering sheet, and one end of the conductor passing through via holes is connected to the ground conductor layer, and then the other end of the conducting unit is connected to a ground conductor of the circuit board, thereby a triplate line structure being constructed. This structure can increase the pbu of the signal line or signal bus. From an analysis of the mechanism of pulse transmission on lines, it is known that a leading cause of the distorting of pulse shapes is the components of higher order harmonics included in reflected negative pulses from branches and positive pulses from terminals in the signal line or signal bus. Therefore, when signals in the signal line or signal bus have the frequency components of the signals extended as near as possible to the resonance frequencies of the line, the delay time of the pulses can be reduced because the build up of pulses are made earlier and the lines can be stabilized by the suppression of resonance.
Further, such a triplate line structure can realize the absorption and shielding of unwanted signals at the same time, and thus can suppress the external radiation of unwanted signals from the signal line or signal bus, thereby permitting more effective measures against electromagnetic interference. Also, a large scale integrated circuit (LSI) and the like mounted on the circuit board are covered with the covering sheet and one end of conducting unit passing through via holes is connected to the ground conductor layer and, at the same time, the other end of the conducting unit is connected to a ground conductor of the circuit board, thereby a triplate line structure being constructed. Such a triplate line structure can suppress the external radiation of unwanted signals from this electronic circuit, thus permitting more effective measures against electromagnetic interference.
A plurality of conducting unit connected through the plurality of via holes to the ground conductor layer so as to ground the ground conductor layer are preferably provided.
Also, according to the present invention, a covering sheet includes a laminate consisting of at least one magnetic material layer made of a resin compound having an oxide magnetic material or a metal magnetic material mixed therein and at least one dielectric layer having a permittivity lower than that of the magnetic material layer, and a ground conductor layer laminated on one surface of the laminate.
A target signal line or signal bus formed on a circuit board is covered with such a covering sheet having a dielectric layer, and one end of the conducting unit passing through via holes is connected to the ground conductor layer, and, at the same time, the other end of the conducting unit is connected to a ground conductor of the circuit board, thereby a triplate line structure being constructed. This triplate line structure can increase the pbu of the signal line or signal bus and also make the characteristic impedance of the sheet-covered portion near to free space impedance, because the dielectric layer has a permittivity lower than that of the magnetic material layer, thereby permitting the suppression of changes in the characteristic impedance of the signal line or signal bus.
Further, such a triplate line structure can realize the absorption and shielding of unwanted signals at the same time, and thus can suppress the external radiation of unwanted signals from the signal line or signal bus, or electronic circuits, thereby permitting more effective measures against electromagnetic interference.
Preferably, the dielectric layer is adjacent to the ground conductor layer, or the magnetic material layer is adjacent to the ground conductor layer.
Furthermore, according to the present invention, a
Fujishiro Yoshikazu
Miura Taro
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Pascal Robert
Takaoka Dean
TDK Corporation
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