JPH10126190A - Filter circuit for emi - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce electromagnetic wave noise, leaking from the inside of an electronic device to a cable by using a band-pass filter having the same resonance frequency as any frequency component of an undesired signal. SOLUTION: A plurality of boards 2 on which electronic components such as an oscillator 3 are mounted are provided in the inside of a case 1 of a device 10, a connector 4 connecting to the boards 2 via signal lines is provided to part of the case 1, and a cable 5 is connected to the connector 4 for connection to other device 20. Power supply lines of each board 2 are connected to GND via a band pass filter 6, and signal lines from the boards 2 are connected to GND via a band-pass filter 7 at a duct 4 to configure the filter circuit for EMI(electromagnetic interference).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EMI filter circuit provided in an electronic device having an electronic component such as an oscillator, for reducing radiation of electromagnetic noise generated inside the device.

[0002]

2. Description of the Related Art In recent years, in electronic equipment, radiation of electromagnetic noise based on unnecessary signals using an oscillator or the like provided therein as a noise source has become a problem.
Measures have been taken in consideration of MI (Electromagnetic Noise Interference) measures.

As one of measures for preventing the emission of electromagnetic noise from electronic equipment, there is a method of wrapping the entire housing of the electronic equipment with a shielding material. For example, as shown in FIG. 2, in an electronic device including an oscillator 101 inside a housing 100,
A measure is taken to reduce the electromagnetic noise based on the oscillation of the oscillator 101 by forming a shield by applying a conductive material such as copper foil on the entire inner wall surface of the housing 100 and grounding a part of the shield part. Done.

However, even when the above-described shielded device is connected to another electronic device via a cable, noise leaks along the surface of the cable, and the cable becomes an antenna. Electromagnetic noise emission may occur. In order to prevent radiation of electromagnetic noise from such a cable, measures have been taken to shield the cable and ground the shield.

[0005]

However, the above-described radio noise reduction structure has the following problems.

As described above, even if the entire housing of the electronic device is shielded, electromagnetic noise leaks along the cable surface from the cable connection portion (duct portion). Electromagnetic noise leaked along the surface of this cable cannot be reduced sufficiently by simply shielding the cable and grounding it, depending on conditions (such as the type of noise and the relationship between impedances between devices via the cable). May act as an antenna to emit electromagnetic noise.

An object of the present invention is to provide a low-cost EMI filter circuit that can reduce electromagnetic wave noise leaking from inside an electronic device to a cable.

[0008]

In order to achieve the above object, an EMI filter circuit according to the present invention is provided in an electronic device to reduce electromagnetic noise generated inside the device.
A MI filter circuit, wherein a path through which the unnecessary signal serving as the electromagnetic noise propagates is grounded via a band-pass filter having the same resonance frequency as a frequency component of the unnecessary signal.

In the above case, the path through which the unnecessary signal is propagated may be either the signal line or the power supply line, or both. In this case, it is desirable that a connection portion between the signal line through which the unnecessary signal is propagated and a cable for connection to an external device be grounded via a band-pass filter.

Further, when the unnecessary signal has different frequency components, the band-pass filter may have a plurality of resonance frequencies corresponding to each frequency component of the unnecessary signal. May be grounded via a plurality of band-pass filters having resonance frequencies corresponding to the respective frequency components of the unnecessary signal.

According to the present invention as described above, the path through which the unnecessary signal is propagated is grounded via the band-pass filter having the same resonance frequency as the frequency component of the unnecessary signal. By consuming the resonance current, the electric energy of the unnecessary signal propagating through the path can be absorbed, and the electromagnetic noise can be reduced. Therefore, unlike the related art, the electromagnetic noise does not leak from the cable connecting portion (duct portion) along the surface of the cable, and the cable does not function as an antenna to emit electromagnetic noise.

[0012]

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the EMI filter circuit of the present invention.

In FIG. 1, a plurality of substrates 2 on which electronic components such as an oscillator 3 are mounted are provided inside a housing 1 of a device 10. The housing 1 is formed of, for example, a metal frame, and a part thereof is provided with a duct 4 connected to the substrate 2 via a signal line. The duct 4 is connected to another device 20. Cable 5 is connected.

The EMI filter circuit of the present embodiment uses a band-pass filter having the same resonance frequency as the frequency component of the unnecessary signal that becomes electromagnetic noise, and absorbs the electric energy related to the unnecessary signal (frequency component) to generate electromagnetic noise. In this case, the power supply line and the signal line of the device 10 are provided. That is, the power supply line of each substrate 2 is commonly grounded to GND via the band-pass filter 6, and the substrate 2
Is grounded to GND via a band-pass filter 7 in the duct unit 4.

In the EMI filter circuit configured as described above, when the electromagnetic wave noise propagating through the power supply line is generated by an unnecessary signal of the frequency component f1, the bandpass having the same resonance frequency as the frequency component f1 is used. The filter 6 is used. With this configuration, the resonance current is consumed by the resistance in the band-pass filter 6, and the electric energy of the unnecessary signal of the frequency component f1 can be attenuated. As a result, electromagnetic wave noise propagating through the power supply line is reduced.

Similarly, when the electromagnetic noise propagating through the signal line is generated by an unnecessary signal of the frequency component f2, the band-pass filter 7 having the same resonance frequency as the frequency component f2 is used. With such a configuration, the electrical energy of the unnecessary signal of the frequency component f2 can be attenuated by the bandpass filter 7, and the electromagnetic wave noise propagating through the signal line is reduced.

As described above, the electromagnetic wave noise that propagates through the signal line and the power supply line is absorbed by the EMI filter circuit, so that the electromagnetic wave noise that leaks along the surface of the cable is reduced, and the electromagnetic wave noise from the cable 5 is reduced. Radiation is reduced.

When there are a plurality of frequency components of the unnecessary signal, a plurality of band-pass filters corresponding to each frequency component are used, or a band-pass filter having a plurality of resonance frequencies corresponding to the frequency components is used. Used.

In the above description, the EMI filter circuit is constituted by the band-pass filter. However, the present invention is not limited to this. For example, the EMI filter circuit has a resonance frequency and has the same frequency component as the resonance frequency during resonance. If you can absorb the electrical energy of unwanted signals with
Any one may be used.

Although the EMI filter is provided in the device 10, in a system connected to the external device 20 by the cable 5, if electromagnetic noise is generated inside the device 20, Similarly, it is desirable to provide the EMI filter of the present invention.

[0022]

According to the present invention constructed as described above, electromagnetic wave noise transmitted from the cable connection portion (duct portion) to the surface of the cable and leaking can be reduced. Radiation can be prevented.

Further, by using the EMI filter circuit of the present invention, for example, effective EMI for an electronic device to satisfy the standards of the FCC (Federal Communications Commission) and VDE (German Institute of Electrical Engineers) can be obtained. Countermeasures can be taken at low cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of an EMI filter circuit of the present invention.

FIG. 2 is a configuration diagram illustrating an example of a shielding of a housing of an electronic device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Substrate 3 Oscillator 4 Duct part 5 Cable 6,7 Bandpass filter 10,20 Equipment

Claims (5)

[Claims] 1. An EMI filter circuit provided in an electronic device for reducing electromagnetic wave noise generated inside the device, wherein a path through which the unnecessary signal serving as the electromagnetic wave noise propagates is defined by a frequency component of the unnecessary signal. An EMI filter circuit, which is grounded via a band-pass filter having the same resonance frequency. 2. The EMI filter circuit according to claim 1, wherein a path through which the unnecessary signal propagates is one or both of a signal line and a power supply line.
Filter circuit. 3. The EMI filter circuit according to claim 2, wherein a connection portion between the signal line through which the unnecessary signal is propagated and a cable for connection to an external device is grounded via a band-pass filter. An EMI filter circuit, comprising: 4. The EMI filter circuit according to claim 1, wherein the unnecessary signal has different frequency components, and the bandpass filter has a plurality of resonance frequencies corresponding to each frequency component of the unnecessary signal. EM characterized by the following:
Filter circuit for I. 5. The EMI filter circuit according to claim 1, wherein the unnecessary signal has a different frequency component, and a path through which the unnecessary signal propagates is a resonance path corresponding to each frequency component of the unnecessary signal. An EMI filter circuit grounded via a plurality of bandpass filters having frequencies.