Electricity: measuring and testing – Magnetic – Magnetometers
Reexamination Certificate
2000-09-20
2002-05-28
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Magnetic
Magnetometers
C343S841000
Reexamination Certificate
active
06396264
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a high-frequency circuit including a stripline, and more particularly to a stripline structure with an enhanced shielding capability for suppressing ambient electromagnetic noise and electromagnetic interference such as crosstalk, and a magnetic field detector incorporating such a stripline structure.
2. Description of the Related Art
High-frequency circuits tend to cause characteristic degradation because of electromagnetic wave interference between a plurality of circuit components and transmission lines that interconnect the circuit components. Therefore, various efforts have been made to provide electromagnetic shields in high-frequency circuits that are liable to radiate unwanted electromagnetic waves or suffer external electromagnetic waves by using metal casings and metal patterns on printed-circuit boards.
In order to increase the shieldability of transmission paths, microstrip lines having metal strips exposed on the surface layer may be changed to triplate striplines which have a metal strip as an inner layer sandwiched between upper and lower ground layers. The triplate striplines are less susceptible to at least direct electromagnetic radiations from mounted circuit components and external electromagnetic waves, and contribute to minimizing overall circuit characteristic deterioration.
However, even triplate striplines fail to provide a complete shielding capability as they suffer crosstalk between adjacent striplines in the same layer. According to one solution, as shown in
FIG. 1
of the accompanying drawings, upper and lower ground layers
2002
are electrically connected to each other by vias
2003
on opposite sides of an inner conductor
2001
in surrounding relationship to the inner conductor
2001
. These vias are provided in a plurality in the direction of the transmission path for increased isolation from an adjacent stripline.
Although triplate striplines are less advantageous than microstrip lines in terms of the mounting of circuit components, it is effective to apply highly shielded triplate striplines if spaced circuit components reed to be interconnected over a relatively long distance. Consequently, it is advisable to use microstrip lines in the vicinity of mounted circuits and use triplate striplines to interconnect circuit components over a relatively long distance.
For connecting a high-frequency circuit module which comprises a multilayer circuit board to another spaced high-frequency circuit module which comprises a multilayer circuit board, it is often customary to use highly shielded transmission paths such as coaxial lines between transmission and reception terminals of those high-frequency circuit modules.
FIG. 2
of the accompanying drawings shows a simplest way of connecting a coaxial line to a stripline on a multilayer circuit board.
As shown in
FIG. 2
, a triplate stripline
2103
has an inner conductor
2101
sandwiched between two ground patterns
2102
in a multilayer circuit board
2100
. The inner conductor
2101
is electrically connected through a via
2104
to a pad
2106
of certain area on an uppermost layer
2105
. The pad
2106
is electrically joined to a central conductor
2108
of a coaxial line
2107
by a solder body
2109
or the like. The ground layers
2102
are electrically connected through vias
2110
to a pad
2111
on the uppermost layer
2105
, which is electrically joined to an outer conductor
2112
of the coaxial line
2107
by a solder body
2113
or the like.
An application for patent has been filed for a shielded-loop magnetic field detector using such a triplate stripline (see Japanese patent application No. 10-346030).
FIG. 3
of the accompanying drawings shows the disclosed shielded-loop magnetic field detector using a triplate stripline.
As shown in
FIG. 3
, an inner conductor
2202
is disposed on an unexposed layer of a multilayer circuit board
2201
which comprises at least three layers, and upper and lower ground patterns
2203
are disposed above and below the inner conductor
2202
with insulators interposed therebetween, thus providing a triplate stripline
2204
. An insulator may be disposed on the upper surface of the upper ground pattern, or the lower surface of the lower ground pattern, or both for the purpose of increasing the mechanical strength of the multilayer circuit board
2201
.
On each of the ground patterns
2203
, the stripline
2204
includes a lead
2205
extending as a straight portion from the left end and a loop
2206
bent at a right angle into a square shape on a right-hand side of the lead
2205
. The loop
2206
has a terminal end
2207
short-circuited to the ground pattern
2203
of the stripline
2204
. The loop
2206
has a gap
2208
defined in the right end thereof, and includes a square loop opening
2209
defined therein.
The inner conductor
2202
has a portion positioned at first half portions
2210
of the loops
2206
, extending across the gaps
2208
, and electrically connected through a via
2211
to the ground patterns
2203
at second half portions
2212
of the loops
2206
.
With the above structure, an output produced by a magnetic field that crosses the loop openings
2209
is propagated as a stripline mode to the left ends of the leads
2205
.
Since the inner conductor of the triplate stripline is sandwiched between the upper and lower ground layers, as described above, the inner conductor is highly shielded vertically by the ground layers, but not horizontally because it is open horizontally. Even if the triplate stripline is used to interconnect circuit components, therefore, it fails to provide a complete electromagnetic shield. It has heretofore been considered to be effective to employ wide upper and lower ground layers in order to increase the shielded capability of the inner conductor.
As shown in
FIG. 1
, the upper and lower ground patterns are electrically connected to each other by the vias on opposite sides of the inner conductor in surrounding relationship to the inner conductor to increase isolation from an adjacent stripline for thereby solving, to a certain extent, the problem of crosstalk between adjacent striplines in the same layer. However, if the electromagnetic field is disturbed in the vicinity of the vias, then electromagnetic interference occurs between the adjacent striplines, and hence the isolation from the adjacent stripline is not necessarily sufficient.
As shown in
FIG. 2
, if the stripline and the coaxial line are connected to each other, then since the central conductor
2108
of the coaxial line is exposed, it is likely to be affected by the electromagnetic field generated by nearby circuit components and interconnections. Furthermore, if the board and the coaxial line are stressed by an external action, then the sold bodies and metal patterns tend to be peeled off, resulting in poor electric connections.
If a printed-circuit board is positioned on the right-hand side of the conventional shielded-loop magnetic field detector using a triplate stripline as shown in
FIG. 3 and a
magnetic field near the PCB interconnections is to be detected by the magnetic field detector, then since the electromagnetic field near the PCB where a number of circuit components are mounted and connected by highly dense interconnections is not uniform, but highly disturbed, it is difficult for the shielded-loop magnetic field detector that is positioned in the disturbed electromagnetic field to detect only the desired magnetic field.
Furthermore, as described above, the inner conductor sandwiched between the upper and lower ground patterns is highly shielded vertically by the ground layers, but not horizontally because it is open horizontally. If there is a disturbed electromagnetic field near a printed-circuit board, the magnetic field detector tends to detect the unwanted electromagnetic field other than the desired magnetic field, and hence suffers poor measurement accuracy.
SUMMARY OF THE INVENTION
It is therefore an object of the present inve
Masuda Norio
Tamaki Naoya
Lefkowitz Edward
McGinn & Gibb PLLC
Zaveri Subhash
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