JP2002083920A - Circuit board for reducing power supply voltage fluctuation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that a voltage drop occurring in a wiring due to its impedance due to a high frequency current on a feed wiring of a semicon ductor element is suppressed by a bypass capacitor but, if the wiring is long between a semiconductor electric power source terminal and the bypass capaci tor, this capacitor cannot effectively suppress the potential fluctuation at the semiconductor element power source terminal. SOLUTION: A series resonance circuit is connected in parallel to a wiring between a semiconductor element power source terminal and a bypass capacitor, and the resonance frequency of this circuit is set to the frequency of a major component among high frequency components of a potential fluctuation. This reduces the wiring impedance to a very low value at this frequency, and hence the bypass capacitor can effectively suppress the potential fluctuation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit board on which a semiconductor element used for an electronic device is mounted, and more particularly to a circuit board for suppressing a potential change of a power supply terminal of a semiconductor element.

[0002]

2. Description of the Related Art Conventionally, a bypass capacitor has been used to suppress a potential change at a power supply terminal of a semiconductor device. However, in order to use the bypass capacitor effectively, it is necessary to shorten the distance between the semiconductor element power supply terminal and the bypass capacitor, and as disclosed in JP-A-3-254150, a chip capacitor is provided on the semiconductor chip. For example, a method of mounting the device has been considered.

[0003]

When the semiconductor element is switched, a high-frequency current flows through a power supply wiring to the semiconductor element due to a through current. When this high-frequency current flows, a voltage drop occurs due to the impedance of the power supply wiring, and the potential of the semiconductor element power supply terminal fluctuates. If this potential fluctuation is superimposed on the output and exceeds the allowable range of the input of the next stage, a malfunction will occur.

[0004] A bypass capacitor is used to suppress the potential fluctuation of the power supply terminal of the semiconductor element. In order to suppress the potential fluctuation of the semiconductor element power supply terminal by supplying the electric charge from the bypass capacitor, it is necessary to shorten the wiring between the bypass capacitor and the semiconductor element power supply terminal. If the length increases, the impedance of the wiring increases, so that the effect of the bypass capacitor is lost, and the potential fluctuation of the power supply terminal of the semiconductor element increases.

However, when the number of pins of the semiconductor element is increased or the mounting area is reduced, the wiring between the semiconductor power supply terminal and the bypass capacitor cannot be shortened. There is a problem that it is difficult to effectively suppress the potential fluctuation of the element power supply terminal by the bypass capacitor, and even if the wiring between the semiconductor element power supply terminal and the bypass capacitor becomes long, the potential fluctuation of the semiconductor element power supply terminal is effectively prevented. There was a problem of suppression.

[0006]

In order to solve the above-mentioned problems, it is only necessary to reduce the impedance of the wiring between the power supply terminal of the semiconductor element and the bypass capacitor even with the same wiring length.

According to the present invention, a series resonance circuit 1 having a resonance frequency having a large frequency of a high-frequency component due to a potential change of a power supply terminal of a semiconductor element is connected to a wiring between a power supply terminal of a semiconductor element 6 and a bypass capacitor 4 as shown in FIG. The problem is to be solved by connecting them in parallel.

By connecting the series resonance circuits in parallel, the impedance of the wiring at the resonance frequency has a very small value, and the voltage drop due to the high-frequency current component at that frequency can be reduced. Thus, the fluctuation of the potential of the semiconductor element power supply terminal can be effectively suppressed by the bypass capacitor.

Furthermore, by connecting a plurality of series resonance circuits in parallel, it is possible to cope with a plurality of frequency components.

When actually mounting, a series resonance circuit is formed using the capacitance and the inductance. For example, since the capacitor element has a series equivalent inductance, the capacitor element itself is a series resonance circuit. What is necessary is just to mount the capacitor element having the target resonance frequency on the wiring pattern.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to embodiments.

FIG. 2 shows a circuit used in the embodiment. The circuit board uses a four-layer board with an interlayer thickness of 0.4 mm, and the wiring between the bypass capacitor 9 and the semiconductor element power terminals 11 and 12 is 2 m wide.
m and length 10 mm. For the semiconductor device, 74AC541 (SOP) 10 used for the bus buffer is used, and 10
Clock 14 with 50% duty ratio of MHz was given. A capacitance of 10 pF was connected as the dummy load 13. As the bypass capacitor 9, a 1608 type chip capacitor having a capacitance of 0.1 μF was used.

The series resonance circuit 8 connected in parallel to the wiring between the power supply terminal of the semiconductor element and the bypass capacitor has a series connection of three lead-type ceramic capacitors 19 connected in parallel as shown in the circuit diagram of FIG. A resonant circuit was used. The impedance between the terminals 17-18 of this circuit has a frequency characteristic as shown in FIG.

As a comparative example, when the series resonance circuit was not connected, the waveform of the potential fluctuation between the semiconductor element power supply terminals 11 and 12 was as shown in FIG. 5, and the width 20 of the potential fluctuation was 781 mV.

In the present embodiment in which a series resonance circuit is connected, the waveform is as shown in FIG. 6, and the potential fluctuation width 21 is 455 mV. Therefore, there is an effect that the width of the potential fluctuation is reduced by 40% as compared with the comparative example.

In this embodiment, a lead type ceramic capacitor is used for the series resonance circuit. However, a chip capacitor may be used, or a series resonance circuit may be formed by a capacitor and an inductor. Further, a capacitance formed by a pattern, an inductance formed by a pattern, or the like may be used. Further, these may be combined to form a series resonance circuit.

[0017]

As described above, by connecting the series resonance circuit in parallel to the wiring between the power supply terminal of the semiconductor element and the bypass capacitor, the impedance of the wiring at a selective frequency can be made very small. In addition, the fluctuation in the potential of the semiconductor element power supply terminal can be effectively reduced by the bypass capacitor. Further, even if the wiring between the semiconductor power supply terminal and the bypass capacitor becomes long, the potential fluctuation can be effectively suppressed by the bypass capacitor.

[Brief description of the drawings]

FIG. 1 is a circuit diagram illustrating the present invention.

FIG. 2 is a circuit diagram showing a circuit used in the embodiment.

FIG. 3 is a circuit diagram of a series resonance circuit used in the embodiment.

FIG. 4 is a frequency characteristic diagram of impedance of a series resonance circuit used in an example.

FIG. 5 is a potential fluctuation waveform diagram of a comparative example.

FIG. 6 is a potential fluctuation waveform diagram of the embodiment.

[Explanation of symbols]

1 ... series resonance circuit, 2 ... capacitance, 3 ... inductance, 4 ... bypass capacitor, 5 ... wiring impedance, 6 ... semiconductor element, 7 ... power supply, 8 ... series resonance circuit, 9 ... bypass capacitor, 10 ... semiconductor element 74AC541 ( SOP), 11,1
2 ... Semiconductor element power supply terminal, 13 ... Pseudo load, 14 ... Clock signal, 15 ... Capacitance, 16 ... Equivalent inductance,
17, 18… Terminal, 19… Lead type ceramic capacitor, 20… Comparative potential fluctuation width, 21… Example potential fluctuation width.

Claims (1)

[Claims] 1. A circuit board on which a semiconductor element is mounted, wherein at least one or more series resonance circuits are connected in parallel to a wiring between a bypass capacitor connected to the semiconductor element power supply terminal.