Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2002-08-20
2004-09-21
Wamsley, Patrick (Department: 2819)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C338S308000
Reexamination Certificate
active
06794956
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to circuit substrates upon which electronic components are mounted. In particular, the present invention relates to a circuit substrate having thereon an equivalent resistance component, which is connected in series to an electronic component such as a capacitor, an inductor, or other suitable component.
2. Description of the Related Art
Previously, power supply circuits for supplying an operating voltage have been provided in computers and other electrical apparatuses. These power supply circuits have been implemented by circuit substrates in which a plurality of bypass capacitors (decoupling capacitors) for improving the operating stability and for speeding up the operating response are connected in parallel and mounted on the substrates. Low-capacitance laminated ceramic capacitors or large-capacitance electrolytic capacitors made from aluminum, tantalum, or other material are used as the bypass capacitors, according to the power supply capacity, the switching frequency, the circuit parameters smoothing coils used therewith, etc.
In recent years, in laminated ceramic capacitors, as a result of developments in thin-film forming technology and lamination technology of dielectrics and internal conductors, the capacitance of laminated ceramic capacitors and the capacitance of electrolytic capacitors have become approximately the same, and experiments have been carried out to replace electrolytic capacitors with laminated ceramic capacitors. However, when replacing electrolytic capacitors with laminated ceramic capacitors, since the impedance in the frequency range used with laminated ceramic capacitors is too small, disturbances occur in the output power waveform of the power supply circuits. This is due to step-shaped changes in the input voltage of, for example, a three-terminal regulator included in the power supply circuit, since the equivalent series resistance (ESR), described later, is too small.
Moreover, when using electrolytic capacitors, the impedance in the frequency range used is larger than that of laminated ceramic capacitors. However, since this impedance is larger, heat generation easily occurs, and furthermore, the smoothness of the power supply line tends to deteriorate.
Here, the relationship between the frequency used and the impedance in the power supply circuit will be described. The impedance at the power supply side as seen from the load side, that is to say, the combined impedance of the parallel circuit composed of the plurality of capacitors, becomes large at a specific frequency (parallel resonance frequency) due to a parallel resonance effect. The point at which this combined impedance becomes large is known as the anti-resonant point. The combined impedance at this anti-resonant point becomes larger as the equivalent series resistance (ESR) of the capacitor becomes smaller.
As described above, because the capacitance of laminated ceramic capacitors has increased in recent years, coupled with the fact that the equivalent series inductance (ESL) is smaller, laminated ceramic capacitors are being used to replace electrolytic capacitors such as tantalum capacitors. However, since the equivalent series resistance (ESR) in large-capacitance laminated ceramic capacitors is small, the impedance at the anti-resonant point is increased.
FIG. 1
is an equivalent circuit diagram including capacitors of, for example, a smoothing circuit mounted on a circuit substrate of the related art. On a circuit substrate B
1
in
FIG. 1
, a first capacitor
1
and a second capacitor
2
are connected in parallel. The capacitor
1
is defined by an electrostatic capacitance C
1
, an equivalent series resistance R
1
, and an equivalent series inductance L
1
. The capacitor
2
is defined by an electrostatic capacitance C
2
, an equivalent series resistance R
2
, and an equivalent series inductance L
2
. Furthermore, the circuit pattern on the circuit substrate has an equivalent inductance L, resistance R, and so on. Reference character S indicates a power supply voltage generating circuit which generates a power supply voltage. The power supply voltage generating circuit supplies a voltage to the smoothing circuit on the circuit substrate B
1
. Reference character T indicates a load to which the voltage from the power supply voltage generating circuit S is applied via the smoothing circuit. In
FIG. 1
, the power supply voltage generating circuit S is provided separately from the circuit substrate B
1
, however, the power supply voltage generating circuit S may be mounted on the circuit substrate B
1
.
FIG. 2
is a graph showing the relationship between the frequency and the impedance in the smoothing circuit (parallel capacitor circuit) shown in FIG.
1
. As shown by line a in
FIG. 2
, a peak impedance Z
1
is generated in this smoothing circuit at the parallel resonance frequency (anti-resonant point) F
1
.
Accordingly, setting the equivalent series resistance (ESR) of the capacitor to an appropriate value can be considered as one method to suppress the generation of such a peak impedance. In this case, since the necessary equivalent series resistance varies depending on the combined capacitors, it is necessary to arrange many equivalent series resistances so that they are suitable for all combinations. However, it is difficult to arrange this, if not almost impossible.
On the other hand, it is possible to set (regulate) the combined impedance at the anti-resonant point even when a chip resistor is mounted on the circuit substrate in series with the capacitor.
FIG. 3
is an equivalent circuit diagram including, for example, smoothing circuit capacitors and chip resistors, which are mounted on the above-described circuit substrate. A series circuit defined by the capacitor
1
and a chip resistor
3
and a series circuit defined by the capacitor
2
and a chip resistor
4
are connected in parallel on a circuit substrate B
2
in FIG.
3
. The capacitor
1
is defined by an electrostatic capacitance C
1
, an equivalent series resistance R
1
, and an equivalent series inductance L
1
, and the capacitor
2
is defined by an electrostatic capacitance C
2
, an equivalent series resistance R
2
, and an equivalent series inductance L
2
. The chip resistor
3
is defined by an equivalent resistance R
3
and an equivalent series inductance L
3
, and the chip resistor
4
is defined by an equivalent resistance R
4
and an equivalent series inductance L
4
. Furthermore, the circuit pattern on the circuit substrate B
2
includes an equivalent inductance L, resistance R, and so on. Moreover, reference character S indicates a power supply voltage generating circuit which generates a power supply voltage, which is then supplied to the smoothing circuit on the circuit substrate B
2
. Reference character T indicates a load to which the voltage from the power supply voltage generating circuit S is applied via the smoothing circuit. In
FIG. 3
, the power supply voltage generating circuit S is provided separately from the circuit substrate B
2
, however, the power supply voltage generating circuit S may also be mounted on the circuit substrate B
2
.
FIG. 4
is a graph showing the relationship between the frequency and the impedance in the smoothing circuit shown in FIG.
3
. The impedance of the smoothing circuit shown in
FIG. 3
varies with respect to frequency as shown by line b. From this graph, it is clear that the impedance variation indicated by line b is small compared with the impedance variation indicated by line a (the same as in FIG.
2
).
As can be understood from the structure of the circuit substrate according to the related art described above, even when a large-capacitance capacitor is used, it is possible to obtain a circuit in which the variation in impedance with respect to frequency is small, but, in this case, it is necessary to connect a resistance in series with the capacitor. However, when a chip resistor is mounted on the circuit substrate, since a series inductance component in th
Kitamura Hidekazu
Taniguchi Masaaki
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Wamsley Patrick
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