JPH0625028Y2 - Printed board for high frequency noise prevention - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] This invention can prevent the generation of high-frequency noise from a high-frequency noise prevention printed board, especially from the high-frequency current source mounted on itself and the reception of high-frequency noise from the outside. And a printed circuit board for preventing high frequency noise.

[Prior Art] In recent years, with the increase in electronic devices equipped with microcomputers in automobiles, high frequency noise current components generated from switching signals of clock pulses and power transistors are induced and radiated from electronic device casings and wire harnesses.
Other electronic devices and wireless devices, such as FM radios, radios,
There are problems that TVs, car phones, etc. are adversely affected, radio noise is generated, the device malfunctions, or the function stops.

Conventionally, as a countermeasure against clock noise from such a microcomputer, a method of preventing noise generation by using an element filter by a capacitor or a resistor or by making a clock pulse rise or fall has been used.

In addition, as a measure for suppressing high-frequency noise superimposed on a vehicle wire harness, the Japanese Patent Publication No.
The techniques described in JP-A-595962 and JP-A-52-147622 have been proposed.

That is, a noise trap wire of λ / 4 (where λ is the propagation wavelength of the noise current) is provided along the noise wire of the vehicle defogger heat wire or wire harness, and the high frequency noise current is controlled to an extremely small value in the middle of the noise wire. This reduces the influence of noise on other wires.

According to, for example, Japanese Patent Publication No. 57-59962 among the prior arts, as shown in FIG. 5, the noise wire 32 for connecting the vehicle-mounted battery and the defogger heating wire 30 includes:
A noise current i is generated over the entire length, and the first low impedance branch path 34 is connected to the noise wire 32 on which the noise current i is superposed to forcibly form a standing wave by the high frequency noise current, The second low-impedance branch 36 is connected to the position corresponding to the node of the standing wave so that the high-frequency noise current, which is a noise source, does not propagate to other wires extending near the electronic device. Then, these noise trap wires 34, 36
Are taped along the noise wire 32, and the noise current intensity can be reduced to such an extent that other wires are not affected.

[Problems to be Solved by the Invention] Conventional Problems However, all of the above-described measures against clock noise by element filters have limitations in terms of mounting and control, and noise trap wires provide wire harnesses. There is also a problem that taping the noise trap wire for each of these wires increases the number of man-hours.

For the above reasons, today, there is an increasing need to prevent electronic circuits such as microcomputers provided in in-vehicle electronic devices from being affected by strong electromagnetic fields from the outside due to broadcasting stations and high-power radios. For this reason, there has been an increasing demand for realizing a compact noise prevention device on a printed board of an on-vehicle electric device.

However, at the present time, a technique concerning high frequency noise prevention focusing on the circuit wiring pattern of the printed board has not been proposed yet.

The purpose of the present invention is to solve the above problems and to form a low impedance noise trap pattern on a printed circuit board and to form a ground pattern adjacent to the noise trap pattern on the same plane. It is an object of the present invention to provide a printed circuit board that prevents the influence of high frequency noise.

[Means and Actions for Solving Problems] In order to achieve the above object, the present invention has one end connected to a circuit wiring pattern side terminal of a printed circuit board on which various electronic components are mounted and the other end opened. A low impedance noise trap pattern having a length of λ / 4 + λ / 2 × n (λ is a propagation wavelength of a noise current, n = 0, 1, 2, ...) Is formed on the same plane as the noise trap pattern. It is characterized in that a ground pattern is formed adjacent to, to prevent the influence of high frequency noise.

With the above-described configuration, the high frequency component contained in the clock pulse emitted from the microcomputer is guided and radiated from the electronic device housing or the wire harness, and the FM radio, T
Although it may interfere with radio equipment such as V and car telephones, the high frequency noise trap pattern formed adjacently on the same plane as the circuit wiring pattern selectively selects the frequency region where the wavelength resonates at λ / 4. High frequency noise can be trapped by drawing in to the noise trap pattern side.

That is, an antinode of the standing wave of the high frequency current is formed at the extraction point of the noise trap pattern, and the noise is absorbed by the electrostatic coupling with the ground pattern formed adjacently on the same plane as the noise trap pattern. And the reverse induction to the electronic circuit element can be prevented.

[Embodiment] A preferred embodiment of the present invention will be described below with reference to the drawings.

1 (a) and 1 (b) show an embodiment of a printed circuit board for preventing high frequency noise according to the present invention. In the figure,
A printed circuit board 14 on which an electronic component such as the microcomputer 10 and a connector 12 for connecting to the outside is mounted is housed in a conductive case 16.
Is grounded (18).

Here, a feature of the present invention is that one end is connected to the circuit wiring pattern side terminal of a printed circuit board on which various electronic components are mounted and the other end is opened, and the length is λ / 4 + λ / 2 × n (λ Is a low-impedance noise trap pattern having a noise current propagation wavelength, n = 0, 1, 2, ..., And a ground pattern is formed adjacent to the noise trap pattern on the same plane. Is.

That is, in this embodiment, the microcomputer 1
0 clock terminal 10-1 and connector 12 terminal 12-
1 is connected by a circuit wiring pattern 20,
A low impedance noise trap pattern 22 is formed adjacent to the circuit wiring pattern 20 on the same plane. The noise trap pattern 22 is formed of copper foil or the like similar to the circuit wiring pattern 20, has one end connected to the connector terminal 12-1 and the other end open, and its length is equal to that of the noise current. When the propagation wavelength is λ, λ / 4 + λ / 2 × n (λ is the propagation wavelength of the noise current, n = 0, 1, 2, ...).

In the case where the noise trap pattern 22 is formed in this way, in the extraction portion of the noise trap pattern 22,
Comparing the impedance of the noise trap pattern 22 side with the impedance of the wire harness side including the connector 12,
The impedance on the side of the wire harness is extremely large, while the impedance on the side of the noise trap pattern 22 is extremely small. Therefore, the high frequency current mostly flows to the side of the noise trap pattern and hardly flows to the side of the wire harness. It is possible to effectively prevent generation of high-frequency clock noise included in the clock pulse signal such as the outside.

The length of the noise trap pattern 22 is practically λ / 4 when n = 0, and for example, F of 76 to 90 MHz is used.
75 cm for M band, 30 cm for 200 MHz TV band, 15 cm for 430 MHz amateur radio band, and 7.5 cm for 800 MHz car phone.

Further, the present invention is characterized in that the ground pattern 24 is formed adjacent to the noise trap pattern 22 on the same plane.

That is, with respect to clock noise or the like from the microcomputer 10, high-frequency noise is trapped by the noise trap pattern 22, and an antinode of the standing wave of the high-frequency current is formed at the extraction point of the connector terminal 12-1. High frequency noise is absorbed by electrostatic coupling with the ground pattern 24 formed adjacently on the same plane.

Therefore, as shown in FIG. 1B, if the ground pattern 24 is grounded by the cable 26 in the vicinity of the extraction point (12-1) near the antinode of the standing wave, the filter effect becomes extremely large. The smaller the gap between the earth pattern 24 and the noise trap pattern 22, the stronger the electrostatic coupling and the greater the noise prevention effect.
It is formed with a gap of m.

Further, since the noise current flows mainly on the surface due to the skin effect of the high frequency current, the noise pattern 2
As for the film thickness of 2 and the ground pattern 24, the copper foil thickness of the normal circuit wiring pattern 20 (for example, 25 μm) is sufficient,
It is known that the larger the width of the ground pattern 24, the better the filter effect.

When the conductive case 16 of the present embodiment is made of a non-conductive material such as plastic, the ground pattern 24 is formed adjacent to the noise trap pattern 22 on the same plane to achieve an extremely effective filtering action. Be seen.

As described above, high-frequency components such as clock pulses generated from the microcomputer are normally transmitted through the wiring harness from the connector terminal through the circuit wiring pattern, and go out to the outside to interfere with radio equipment such as FM radio, TV, and car telephone. However, according to this embodiment, the noise trap pattern 22 connected to the connector terminal 12-1 selectively draws the frequency region resonating at λ / 4 to the noise trap pattern 22 side, and Noise is prevented by electrostatic coupling with the ground pattern 24.

That is, according to the embodiment of the present invention, the ground pattern 2
Since it is possible to suppress the secondary radiation of the high frequency noise trapped in the noise trap pattern 22 by 4 and to protect it by the low impedance ground pattern 24 by capacitive coupling, as shown in FIG.
Compared with the conventional printed board, the filter effect is increased by about 3 to 13 dB, and the noise level can be further reduced.

In addition, the ECU (Electronic C
It is possible not only to prevent the generation of high-frequency noise from the high-frequency current generation source such as an ontrol unit), but also to external EMI (Electro Magnetic Interface).
It is an abbreviation of e and includes vehicle noise and external noise caused by broadcast waves).

Further, according to the embodiment of the present invention, it is possible to form a noise trap pattern and an earth pattern in the same manner as a normal circuit wiring pattern in the process of manufacturing a printed circuit board. It is possible to perform high-frequency noise prevention practically at low cost without requiring a noise prevention filter or the like.

FIG. 3 shows an embodiment in which a ground pattern is formed around the noise trap pattern.

That is, the ground pattern 124 is formed around the noise trap pattern 122 so as to surround the noise trap pattern 122, and the ground pattern 124 is grounded by the cable 126.

According to this embodiment, the shield effect can be further improved by 2 to 3 dB as compared with the embodiment of FIG.

FIG. 4 shows an embodiment in which a noise trap pattern and a ground pattern are formed along the connector terminal.

That is, the noise trap pattern 222 is formed along each terminal 112-1 of the connector 112, and the connector terminal 224 and the noise trap pattern 22 are formed.
A ground pattern 124 is formed between the two.

According to this embodiment, for example, the secondary coupling of high frequency noise to the other connector terminals 112-2, 112-5 other than the connector terminal 112-1 connected to the clock terminal of the microcomputer is connected to the ground pattern 224. Therefore, the filter effect is improved by 4 to 5 dB as a whole as compared with the first embodiment.

[Advantages of the Invention] As described above, the present invention forms a low impedance noise trap pattern on a printed circuit board and a ground pattern adjacent to the noise trap pattern on the same plane. High frequency noise can be effectively prevented without using a noise prevention filter or the like.

[Brief description of drawings]

FIG. 1 is an explanatory view of an embodiment of a printed board for preventing high frequency noise according to the present invention, FIG. 2 is a view showing a filter effect according to an embodiment of the present invention, and FIG. 3 is a ground pattern formed around a noise trap pattern. FIG. 4 is a view showing an embodiment in which a noise trap pattern and an earth pattern are formed along a connector terminal, and FIG. 5 is a conventional example for preventing high-frequency noise superimposed on a vehicle wire harness. FIG. 10 ... Microcomputer 12 ... Connector 14 ... Printed circuit board 16 ... Conductive case 20 ... Circuit wiring pattern 22, 122, 222 ... Noise trap pattern 24, 124, 224 ... Ground pattern

Claims (1)

[Scope of utility model registration request] 1. A circuit wiring pattern side terminal of a printed circuit board on which various electronic components are mounted, one end of which is connected and the other end of which is open to have a length of λ / 4 + λ / 2 × n (where λ is a propagation of a noise current). High-frequency noise prevention characterized by forming a low-impedance noise trap pattern having a wavelength of n = 0, 1, 2, ..., And forming a ground pattern adjacent to the noise trap pattern on the same plane. Printed board.