JP2001211047A - Printed board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that unwanted radiation wave is strongly radiated with ease, depending on the size of a printed board in the electronic apparatus dealing with digital signal and to attenuate unwanted radiation wave to outside electronic apparatus absorbing effectively unwanted radiation wave. SOLUTION: A serial resonance circuit composed of a coil L and a condensor C on the component face of a multi-layer board is formed between a electric source (Vcc) pattern face and ground pattern face. A condensor capacitance C[F] and a coil inductance L[H] which satisfy an equation f=1/(2π√(L*C))[Hz] to synchronize with unwanted radiation wave frequency f=75*M[MHz] anticipated from the length of board M[m] are decided. As the result, the unwanted radiation wave near frequency f is effectively attenuated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to electronic devices such as digital circuits (e.g., devices using a microprocessor).
The present invention relates to a printed circuit board used for:

[0002]

2. Description of the Related Art In a conventional electronic apparatus, there are the following methods for reducing unnecessary radio waves employed on a printed circuit board. (1) A resistor is inserted in series with the output terminal of the output circuit.

When a resistor is connected in series to the output terminal of a digital rectangular wave, such as a circuit that outputs a sine wave output of a crystal oscillation circuit through a digital gate to a rectangular wave, the output waveform becomes round and becomes close to a sine wave. Therefore, it is known that there is an effect of attenuating harmonic components, which are unnecessary radiated radio wave components. (2) A bypass capacitor is inserted between the power supply pattern (Vcc) and the ground pattern.

It is known that high frequency components are attenuated when one or many capacitors are connected between a power supply pattern and a ground pattern. A so-called feedthrough capacitor has a structure in which a signal line passes through a dielectric, and allows a high frequency to be bypassed from an electrode from the dielectric to the ground. (3) As shown in FIG. 2, a noise filter as a component combining L and C, which is inserted into a power input portion of a printed circuit board, is commercially available and applied. Alternatively, a method is used in which these L and C are individually wired on a printed circuit board to form a filter on the printed circuit board. (4) A signal line that passes a core made of a magnetic material to attenuate high-frequency components.

In order to reduce unnecessary radiation of general high-frequency signals, the following filters (5) to (8) are used. The following filter is used in an output circuit of a signal of a radio wave transmitter, an input circuit of a radio wave receiver, or a halfway path of a feeder line (feeder cable or the like) connected in series. (5) High Pass Filter (HPF) With a circuit combining L and C, an HPF that efficiently passes frequencies above the cut-off frequency f and attenuates electric signals at frequencies below f can be configured. (6) Low Pass Filter (LPF) A circuit combining L and C efficiently passes frequencies below the cutoff frequency f. An LPF capable of attenuating an electric signal having a frequency of f or more can be configured. (7) Band Pass Filter (BPF) With a circuit combining L and C, a BPF that efficiently passes frequencies around the cutoff frequency f and attenuates electric signals at frequencies outside the band can be configured. (8) Trap Filter By connecting an LC series resonance circuit on a signal transmission line, a filter called a trap that attenuates an electric signal of a specific frequency of the LC series resonance circuit can be configured. A filter in which a plurality of LC resonance circuits having different resonance frequencies are connected is known as a distributed constant filter.

[0006]

SUMMARY OF THE INVENTION The above-mentioned prior art includes:
There are the following issues.

[0007] The technology according to the above (1) (2) (3) (4) alone
Since unnecessary radiation waves radiated from the printed circuit board cannot be sufficiently attenuated, there is a problem that external electronic devices may suffer from reception disturbance. The intensity of the frequency of the unnecessary radiated radio wave radiated from the printed circuit board has a correlation with the size of the printed circuit board, and the phenomenon that the wavelength of the radiated radio wave becomes larger when approaching the length of λ / 4 is experimentally observed. You can check.

[0008] The experimental results show that in a multilayer substrate, when one surface is allocated to ground and one surface is allocated to a power source, the entire substrate operates efficiently as an antenna on the same principle as a λ / 4 wavelength whip antenna. You can think. The radiation wave of the printed circuit board is generated from the ground pattern surface or the power supply pattern surface. It is well known as an electrical theory that the impedance of an LC series resonance circuit has a minimum at a resonance frequency.
It can also be confirmed experimentally.

Therefore, the ground pattern and the power pattern
If an LC series resonance circuit having a frequency corresponding to a wavelength close to the λ / 4 wavelength is connected between the two patterns, the LC resonance circuit can be efficiently used without the need for a frequency near the λ / 4 wavelength from the printed circuit board. By absorbing the radiated radio wave, the radiation of the unnecessary radio wave from the electronic device can be effectively reduced.

The techniques of (5), (6), (7), and (8) use techniques known to be used to reduce unnecessary radiation at the output of a transmitter circuit or to suppress unnecessary radio waves at a receiver input unit. It was raised. Since these are not used for reducing the radiation from the printed circuit board of the electronic device, they cannot be used alone for the purpose of reducing the unnecessary radiation of the printed circuit board.

[0011]

According to the present invention, the following means are provided to solve the above-mentioned problems. Multilayer board The printed board is composed of multilayer wiring patterns, one or more pattern planes are used as ground planes, and one or more pattern planes are used as power supply (Vcc) planes. (2) LC series resonance circuit The patterns on the ground plane and the power supply plane of the printed circuit board in (1) are connected by an LC series resonance circuit. The LC series resonance circuit is calculated by Equation 1.

Substrate size (length) = M (m), λ = 4
* M [m], f = 300 / λ [MHz] ｆ f = 300 / (4 * M)
= 75 * M [MHz]

[0013]

[Formula 1] f = 1 / (2π√ (L * C)) [Hz] L: Inductance of coil (H), C: Capacitance of capacitor (F) The combination of L and C is the frequency of the unnecessary radio wave to be attenuated. f
, An infinite number of combinations occur, but by fixing either value, one value can be obtained.

When the coil L has a fixed inductance, C is a trimmer type capacitor having a variable capacitance,
The tuning frequency is adjusted by changing the capacitance of the capacitor so that unnecessary radiation is minimized.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. The numbers in parentheses correspond to the site numbers in FIG.

FIG. 1 shows the configuration of the present invention.

This embodiment shows an example of a printed circuit board of length M [m] having a wiring board 2 on the front and back sides and a ground plane 4 and a power supply (Vcc) plane 5 on the inner layer of the multilayer board 1. . The capacitor 6 (C) and the coil 7 (L) are connected and wired to the board component surface 2 with a series pattern 8, one terminal of C is connected to the ground plane 4 of the inner layer, and one terminal of L is connected to the power supply (Vcc ) Plane 5 and the power supply (Vcc) plane pattern 4 and the ground plane pattern 5
During this period, an LC series resonance circuit is formed.

The LC resonance circuit is surrounded by a magnetic material 9 for preventing radiation of leaked radio waves, further shielded by a metal case 10, and soldered to the metal case 10 on a ground pattern on the wiring surface 2. 11 and 12, the shielding effect and the bypass effect of the unnecessary radiation wave are enhanced. The capacitor 6 is of a trimmer type having a variable capacitance, and can be adjusted by an adjustment driver 13 to rotate the trimmer to minimize unnecessary radiation waves.

[0019]

[Equation 2] f * λ = c where (c is the speed of light and c = 30 0000
000 [m / s]), λ = 1 wavelength [m]} Equation 2 represents the frequency f [Hz] of the electromagnetic wave and the wavelength as physical laws.
It is known as a relational expression between λ [m] and light speed c [m / s].

From the length M [m] of the printed circuit board, a tuning frequency as an electric antenna having the printed circuit board of 1/4 wavelength can be obtained. From an experiment, it has been confirmed from a printed circuit board having a length of M [m] that radio wave radiation having a frequency having a length of 1/4 wavelength becomes the strongest.

[0021]

[Formula 3] M = λ / 4 From formulas 2 and 3

[0022]

Equation 4 f = c / λ = c / (4 * M) = 75 * M [MHz] Equation 4 is obtained.

From equation (4), the frequency of a radio wave that is easily radiated from the printed circuit board can be obtained. On the other hand, the frequency f of the series LC resonance circuit is

[0024]

[Formula 5] f = 1 / (2π√ (L * C)) [Hz] It is known that L [H] is determined by the inductance of the coil, and C [F] is determined by the reactance of the capacitor.

Here, in the present invention, first, the frequency f at which the radiation from the printed circuit board is maximized is obtained from Equation 4 and
The values of L and C satisfying Expression 5 which is equivalent to the above are calculated, and a printed circuit board having the LC series resonance circuit obtained in this way is configured.

According to the present invention, the multilayer printed circuit board having this configuration allows the LC series resonance circuit to absorb radio waves radiated as an antenna of the board itself, thereby effectively attenuating unnecessary radiated radio waves around the frequency f. Can be done.

[0027]

According to the present invention, it is possible to effectively attenuate unnecessary radiated radio waves related to the size inherent to a substrate, such as a digital circuit, in which unnecessary radiated high frequency components are easily generated. In addition, this LC series resonance circuit
It is possible to tune to absorb unnecessary frequencies at the intensity that is a problem in the radio regulatory standards,
By connecting a plurality of LC resonance circuits in parallel, a circuit called a distributed constant filter can be configured to attenuate the radiation of unnecessary radio waves of a plurality of frequencies.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing the overall configuration of the present invention.

FIG. 2 is a schematic diagram illustrating a configuration of a conventional noise filter.

[Explanation of symbols]

1: multilayer printed circuit board, 2: component surface and wiring pattern surface of multilayer substrate, 3: wiring pattern surface of inner layer of multilayer substrate, 4: ground (GND) surface of multilayer substrate, 5: power supply (Vcc) surface of multilayer substrate,
6: Variable capacitance (trimmer type) capacitor Capacitance C
[F], 7: Coil inductance L [H], 8: Connection pattern of LC resonance circuit, 9: Shield by magnetic material, 10: Shield by metal case, 11, 12: Solder joint, 13: Adjustment driver.

Claims (1)

[Claims] In order to absorb unnecessary radiation waves radiated from a printed circuit board, a resonance frequency calculated from the size of the printed circuit board is matched between a power supply pattern of the multilayer printed circuit board and a ground pattern. A printed circuit board on which a series resonance circuit composed of a coil and a capacitor is mounted, and the length M (m) of the multilayer printed circuit board, the resonance frequency f as an electric antenna is f * λ = c where c Is the speed of light c = about 30000000 [m /
s]), λ = 1 wavelength [m]｝, and since the size of the printed circuit board resonates as a λ / 4 wavelength whip antenna, M = λ / 4∴f = 300 / λ = 75 * M [MHz] The resonance frequency is obtained by connecting a coil and a capacitor in series between the power supply (Vcc) pattern and the ground pattern.
f is calculated as f = 1 / (2π√ (L * C)) [Hz], and f = 75 * M [MHz].
A printed circuit board comprising an LC resonance circuit by selecting L and C.