Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1998-11-02
2001-03-06
Kincaid, Kristine (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S301200, C361S301100, C361S311000
Reexamination Certificate
active
06198619
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a capacitor network of which line patterns are formed on both sides on a printed circuit board.
2. Description of the Related Art
A capacitor network typical in the related art comprises a plurality of component capacitors interconnected such that the capacitance (composite capacitance) of the capacitor network can be reduced. Each component capacitor is formed from a pair of metallic foil layers on opposite sides of a printed circuit board.
FIG. 11
shows the equivalent circuit of a typical capacitor network
500
as described above. The component capacitors C
60
to C
65
of this capacitor network
500
are formed from two metallic foil layers on opposite sides of a printed circuit board, and are connected in series. The capacitance of this capacitor network
500
is the sum of the capacitance of each component capacitor C
60
to C
65
. As a result, the capacitance of the capacitor network
500
can be reduced by an amount equal to the capacitance of the last capacitor C
65
in this example by cutting the lines at points P
50
and P
51
to isolate the capacitor C
65
from the network. The capacitance of the capacitor network
500
can be further reduced by an amount equal to the capacitance of capacitor C
64
, for example, by similarly cutting the lines at points P
52
and P
53
.
It will be clear that the capacitance of this capacitor network
500
can only be adjusted downward by electrically isolating a number of component capacitors from the network. This creates the problem of not being able to optimally adjust the capacitance of the capacitor network
500
in certain cases.
Consider, for example, a contactless IC card in which an LC resonance circuit containing a capacitor network
500
as a circuit element is used as an antenna, and the capacitance of the capacitor network
500
is set to the capacitance (the “optimum capacitance” below) providing the greatest read/write distance to the reader/writer. The optimum capacitance is determined in this case by actually adjusting (reducing) the capacitance of the capacitor network
500
while measuring the read/write distance to the reader/writer.
The value of this optimum capacitance is the capacitance at which the resonance frequency of the LC resonance circuit of the contactless IC card matches the operating frequency of the reader/writer. With the above-noted method of setting the optimum capacitance, however, it is not possible to predict at what point the capacitance of the capacitor network
500
will be closest to the optimum capacitance. As described above, the capacitance of the capacitor network
500
can only be reduced in increments equal to the capacitance of the component capacitors. The capacitance of the capacitor network
500
is therefore always set to the last-adjusted value, that is, to the capacitance at which the network capacitance is less than the optimum capacitance or the capacitance resulting in a short circuiter read/write distance. It should be noted that while it is possible to increase the capacitance of the capacitor network
500
in such cases, this requires reconnecting the cut lines, a complicated and costly task.
For some applications a variable capacitor component can be mounted on the circuit board in place of a capacitor network
500
, but these components are typically thick, large, and expensive. Such capacitor components also cannot be used on certain products having specific thickness limitations, including credit-card-size contactless IC cards with an ISO-standard 0.76 mm thickness limit.
It is noted that Japan Unexamined Patent Publication (kokai) S62-233913 (1987-233913) teaches a capacitor whereby the capacitance distributed to the front and back of the circuit board through through-holes is controlled using the circuit board thickness. The problem with this design, however, is that once the thickness of the circuit board is fixed, the capacitance of the capacitor cannot be changed. The above-described problem is therefore not resolved.
There is therefore a need for a capacitor network of simple configuration whereby the composite capacitance of the capacitor network can be easily increased and decreased.
SUMMARY OF THE INVENTION
To address the above-described need, an object of the present invention is to provide a capacitor network whereby the composite network capacitance can be increased or decreased.
More specifically, a capacitor network having a plurality of component capacitors formed from two metallic foil layers on opposite sides of a printed circuit board interconnected by lines disposed on both sides of said printed circuit board comprises at least one series circuit section and at least one parallel circuit section. The series circuit section comprises two or more component capacitor circuits, each comprising at least one component capacitor, connected in series. The parallel circuit section comprises two or more parallel-connected component capacitor circuits, each comprising at least one component capacitor.
The capacitance of the capacitor network thus comprised can be increased by short circuiting component capacitors connected in series, and can be decreased by cutting component capacitors connected in parallel from the circuit.
Corresponding lines on the front and back sides of the printed circuit board are preferably disposed to non-overlapping positions. As a result, line capacitance can also be eliminated.
Furthermore, of the two metallic foil layers used to form the component capacitors of the series circuit section, one or both of the foils is preferably a plastically deformable, conductive material that can be caused to contact the other metallic foil layer disposed at the corresponding position on the opposite side of the printed circuit board by inserting a needle. When thus comprised, a needle can be inserted to easily short circuit a component capacitor.
The component capacitors connected in series are also preferably formed with different capacitances. This makes it possible to adjust the network capacitance more precisely.
A capacitor network according to the present invention further preferably comprises at least one short circuiting line for short circuiting a series connected component capacitor. When thus comprised, the short circuiting line can be cut to reduce the capacitance of the capacitor network.
A further capacitor network according to the present invention preferably comprises a series-parallel circuit in which two or more parallel circuits of two or more component capacitor circuits connected in parallel are series connected. This enables fine adjustment of the capacitance.
Yet a further capacitor network according to the present invention comprises two or more series-parallel circuits connected in parallel where each series-parallel circuit comprises two or more parallel circuits of two or more component capacitor circuits connected in parallel. This configuration enables even more precise capacitance adjustment.
Note that network capacitance can be set with yet greater precision by changing the number of parallel connected component capacitors in each series parallel circuit.
Further preferably, each component capacitor series connected by the lines comprises a means enabling contact with the metallic foil on the back side of the printed circuit board from the front of the printed circuit board. This makes it possible to effectively short circuit a component capacitor using a test probe, for example, to increase the capacitor network capacitance without actually short circuiting the component capacitor. This functionality can be used during adjustment to easily determine whether the capacitance of the capacitor network should be increased or decreased.
The capacitance of the capacitor network can also be finely adjusted by cutting a number of parallel-connected component capacitors from the capacitor network lines, and short circuiting a number of series-connected component capacitors. The capacitance can also be increased by short circuiting rem
Kincaid Kristine
Mitsubishi Denki & Kabushiki Kaisha
Thomas Eric
LandOfFree
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