Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2000-04-20
2002-01-01
Gaffin, Jeffrey (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S502000, C361S794000, C174S051000
Reexamination Certificate
active
06335865
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a printed wiring board having a structure for improving electromagnetic environmental compatibility (hereinafter abbreviated to EMC).
With a recent development of a digital technique, degree of integration of LSI (Large Scale Integrated Circuit) and density of a printed wiring board have been increased in recent years, and operating speed thereof has also been increased.
Such a high-speed digital circuit includes a digital signal containing many high-frequency components. Consequently, it is necessary to suppress radioactive noise due to unnecessary radiation for a printed wiring board having a digital circuit.
Furthermore, since resistance of the printed wiring board against external noise has become lower due to the increase in the density and operating speed of digital devices, it is necessary to take measures for improving noise resistance of a printed wiring board.
In order to improve EMC of such digital devices and circuit, a common mode choke conventionally has been mounted onto the printed wiring board.
In
FIG. 1
, a reference numeral
11
denotes a LSI. The LSI has circuit blocks CB
1
-CBn which are connected to pins
13
a
1
,
b
1
to
13
an, bn
for communication lines and a common E (earth or ground) pin
12
.
The pins
13
a
1
,
b
1
to
13
an, bn
for the communication lines are connected to common mode chokes
15
-
1
to
15
-
n
for preventing common mode noise via the communication lines
14
a
1
,
b
1
to
14
an, bn.
Capacitors
16
a
1
,
b
1
to
16
an, bn
having high-frequency characteristics are connected to portions of the communication lines between the common mode chokes
15
-
1
to
15
-
n
and terminals
17
a
1
,
b
1
to
17
an, bn
. On the other hand, the other terminals of the capacitors
16
a
1
,
b
1
to
16
an, bn
are connected to a solid E (earth) layer
32
illustrated in FIG.
2
.
Although a pair of communication lines
14
a
1
,
14
b
1
alone are shown in
FIG. 2
, similar common mode noise may occur in the other communication lines. Reference numeral Nab in the same drawing denotes common mode noise occurring in the E pin
12
. When the common mode noise Nab generates in the E pin
12
, common mode noise Na appears for the communication line
14
a
1
, while common mode noise Nb generates for the communication line
14
b
1
.
Under this circumstance, a common mode current Ia passing through the communication line
14
a
1
flows along a path which takes a round via the common mode choke
15
-
1
, capacitor
16
a
1
, solid E layer
32
and communication pin
13
a
1
. Thereby, the common mode current Ia generates magnetic flux &phgr;a.
In the meantime, a common mode current Ib passing through the communication line
14
b
1
flows along a path which takes a round via the common mode choke
15
-
1
, capacitor
16
b
1
, solid E layer
32
and communication pin
13
b
1
. Thereby, the common mode current Ib generates magnetic flux &phgr;b.
Since the units of magnetic flux a, b generate in the reverse directions to each other, a, b offset each other. In consequence, the common mode noises Na, Nb are attenuated with the result that levels of the common mode noises at the terminals
17
a
1
,
17
b
1
are lowered.
As described above, expensive common mode chokes must be used to suppress the occurrence of common mode noise of the digital circuit and to improve EMC in the related printed wiring board.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a printed wiring board which is capable of suppressing common mode noise without using expensive parts, such as, common mode chokes as EMC improving devices.
According to an aspect of the present invention, the printed wiring board capable of solving the above-mentioned problems has a laminate formed of a pattern-wired layer on which plural communication lines are print-wired, an insulating layer, and a grounding layer, the printed wiring board including slotted portions (groove portions) provided in the sections of the grounding layer which are positioned under two parallel-printwired communication lines, and capacitors provided between the slotted portions and external connecting terminals of the printed wiring board, and connected at one terminal thereof to the communication lines, and at the other terminal thereof to the grounding layer through a through hole provided in the insulating layer.
According to another aspect of the present invention, the width of each of the slotted portions of the first-described printed wiring board is determined on the basis of a distance between the two parallel-print-wired communication lines.
According to still another aspect of the present invention, each of the capacitors in the first-described printed wiring board may be formed of the pattern-wired layer, an insulator provided on the insulating layer and having a dielectric constant different from that of the insulating layer, and the grounding layer.
REFERENCES:
patent: 5488540 (1996-01-01), Hatta
patent: 5663870 (1997-09-01), Kerndlmaier
patent: 5847451 (1998-12-01), Ohtaki et al.
patent: 6111474 (2000-08-01), Nibe
Bui Hung
Foley & Lardner
Gaffin Jeffrey
NEC Corporation
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