JP2019149675A - Active noise filter and active noise filter characteristic method - Google Patents

Abstract

To provide an active noise filter capable of suppressing common mode noise over a wide range and also to provide an active noise filter characteristic method.SOLUTION: In a noise suppressing system 1, an active noise filter 10 includes: a noise filter 11 for suppressing common mode noise in a first frequency band; and a noise filter 12 for suppressing the common mode noise in a second frequency band. The noise filters 11, 12 include: first and second size detection ferrite cores 11a, 12a; first and second size feedback ferrite cores 11b, 12b; and amplifier circuits 11c, 12c.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an active noise filter for suppressing common mode noise and a method for controlling the characteristics of an active noise filter.

  In a configuration in which a plurality of communication devices are connected by a power supply line, unnecessary conducted interference waves (for example, common mode noise) may be propagated to the power supply line provided outside the communication device. .

  It is known that common mode noise is generated due to a switching operation in an electronic device (for example, a power converter).

  As a measure for preventing this type of common mode noise, a ferrite core that does not require the power line to be cut is generally used.

  The ferrite core is a magnetic substance made of ferrite and has a donut-shaped annular shape.

  However, when only the ferrite core is used, there is a drawback that the effect of suppressing the common mode noise is small (for example, several [dB]).

  In order to cope with this drawback, there is known a technique for increasing the suppression effect of common mode noise by combining a feedback type amplifier circuit with a ferrite core.

  Specifically, two ferrite cores and a feedback amplifier circuit are combined, and the induced electromotive force (hereinafter referred to as counter electromotive force) obtained by negative feedback amplification by this feedback amplifier circuit is reduced in the direction of suppressing common mode noise. An active noise filter to be generated has been proposed (see, for example, Non-Patent Document 1).

  Hereinafter, a conventional active noise filter will be described with reference to FIG.

FIG. 14 is a diagram illustrating an overall configuration of an active noise filter 100 according to the related art.
The conventional active noise filter 100 includes a detection ferrite core 110, a feedback ferrite core 120, and a feedback amplifier circuit 130.

  As shown in the figure, the primary side coil and the secondary side are wound by winding the power wires (Sp1, Sp2) and the conductive wires (w1, w2) on both sides of the ferrite core (110, 120) (for detection and feedback). Each of the ferrite cores (110, 120) constitutes a transformer composed of the coils.

  Therefore, for example, in the detection ferrite core 110, the common mode noise Cn flowing through the primary side coil generates the induced electromotive force Va on the secondary side.

  Next, a feedback current I caused by the induced electromotive force Va is applied to the primary side coil of the feedback ferrite core 120 by the feedback amplifier circuit 130.

  Then, the counter electromotive force Vb is generated on the secondary side of the feedback ferrite core 120 in the direction of preventing the common mode noise Cn, and the common mode noise Cn can be reduced. Thereby, the active noise filter 100 which can suppress the large common mode noise Cn is realized.

Soichiro Yoshikawa, Akihiro Nishikata, Mahamd Fahan, Ken Okamoto, Kazuhiro Takaya, “Improvement of feedback common mode noise suppressor using ferrite core”, 2016 UEC, B-4-42, p.362 , 2016.

  As described above, in the conventional active noise filter 100, the effect of suppressing the common mode noise Cn is enhanced by combining the detection ferrite core 110, the feedback ferrite core 120, and the feedback amplifier circuit 130.

  In addition, by increasing the number of turns n of the power supply wire and the conductive wire wound on the primary side and the secondary side of the ferrite core, the effect of suppressing the common mode noise is increased and the frequency band that can suppress the common mode noise is widened. Is planned.

  However, in the active noise filter 100 in which the detection ferrite core 110 and the feedback ferrite core 120 have the same performance (for example, material, size, and shape), the frequency band in which the detection common mode noise Cn can be detected is Since the performance of the detection ferrite core 110 is limited, the frequency band in which the common mode noise Cn by the active noise filter 100 can be suppressed cannot be expanded beyond a certain level and is generated by the feedback ferrite core 120. There is a problem that the frequency band of the back electromotive force Vb is limited to the frequency band of the common mode noise Cn detected by the detection ferrite core 110.

  The present invention has been made in view of such a problem, and an object of the present invention is to provide an active noise filter capable of suppressing common mode noise in a wide band and a method for controlling the characteristics of the active noise filter.

  In order to achieve the above object, a first aspect of the present invention is to detect common mode noise in a first frequency band that is generated from a first electronic device and propagates through a first power line, and the common in the first frequency band is detected. A first detection ferrite core for inducing a first voltage due to mode noise; a first amplifier circuit for generating a first feedback current due to the first voltage induced by the first detection ferrite core; A first feedback ferrite core for inducing a first counter electromotive force that suppresses common mode noise in the first frequency band by the first feedback current from the first amplifier circuit; Propagating a second power line connected to the first power line of the first noise filter, detecting common mode noise in a second frequency band different from the first frequency band, and detecting the second frequency band A second detection ferrite core that induces a second voltage caused by common mode noise; and a second amplifier circuit that generates a second feedback current caused by the second voltage induced by the second detection ferrite core; A second feedback ferrite core for inducing a second counter electromotive force to suppress common mode noise in the second frequency band by a second feedback current from the second amplifier circuit; Is provided.

  In a second aspect, the first detection ferrite core and the first feedback ferrite core constituting the first noise filter are the second detection ferrite core and the second feedback ferrite core constituting the second noise filter. And at least one of material, shape, and size is different.

  In a third aspect, the active noise filter according to the first aspect or the second aspect is further disposed on the secondary side of the first detection ferrite core and propagates through the first power line. A first band-pass filter that cuts noise that amplifies the common mode noise and a second frequency band common mode noise that is disposed on the secondary side of the second detection ferrite core and propagates through the second power line. A second bandpass filter for cutting noise to be amplified.

  According to a fourth aspect, in the active noise filter according to the third aspect, the first band-pass filter and the second band-pass filter are a passive filter composed of resistance, capacitance, and inductance, or an amplifier circuit. It functions as an active filter composed of active elements.

  In the fifth aspect, the active noise filter according to the third aspect or the fourth aspect is further changed due to the magnitude of the common mode noise in the first frequency band, and the first detecting ferrite core A voltmeter for measuring the first voltage induced in the conducting wire wound around the secondary side, and a control unit for controlling the impedance value of the elements constituting the first amplifier circuit in order to reduce the first voltage And prepare.

  In a sixth aspect, in the active noise filter according to the fifth aspect, the first amplifier circuit includes a first element and a second element, and the control unit increases the impedance of the first element, and As a result, when it is determined by the voltmeter that the first voltage has increased, the impedance of the first element is decreased, or when it is determined by the voltmeter that the first voltage has decreased, The lowered first voltage is further lowered by lowering the impedance of the first element.

  In a seventh aspect, in the active noise filter according to the sixth aspect, the control unit decreases the impedance of the first element of the first amplifier circuit while increasing or decreasing the impedance of the first element. When it is determined that the voltage has increased again, the increase or decrease in the impedance of the first element is stopped.

  In an eighth aspect, the first element that constitutes the amplifier circuit according to the noise voltage that is generated by the detection ferrite core that detects the common mode noise that is generated from the electronic device that is the interference source and propagates through the power line. , And a characteristic control method of an active noise filter executed by a control device that sequentially controls the impedance of the second element, which is detected on the primary side of the detection ferrite core and is secondary to the detection ferrite core Monitoring the noise voltage according to the common mode noise induced in the signal, and increasing or decreasing the impedance of the first element of the amplifier circuit so that the noise voltage of the monitored common mode noise decreases. And the common obtained by increasing or decreasing the impedance of the first element As noise voltage mode noise is further reduced, and a possible increase or decrease the impedance of the second element of the amplifier circuit.

  According to the present invention, it is possible to realize an active noise filter and an active noise filter characteristic control method capable of suppressing common mode noise in a wide band.

The figure which showed the whole structure of the noise suppression system provided with the active noise filter which concerns on 1st Embodiment of this invention. The figure which showed each structure in the whole structure of the active noise filter which concerns on 1st Embodiment as a functional block. The graph which showed suppression of common mode noise Cn by the noise filter with which an active noise filter is provided. The figure which showed the whole block diagram of the active noise filter 10 which provided the single amplifier circuit with respect to the noise filter. The figure which showed the whole block diagram of the active noise filter 10 which provided the single amplifier circuit with respect to the noise filter. The figure which showed the insertion loss characteristic (S21 [dB] -frequency [Hz]) by an active noise filter. The figure which showed the whole structure of the noise suppression system provided with the active noise filter which concerns on 2nd Embodiment of this invention. The figure which showed each structure in the whole structure of the active noise filter which concerns on 2nd Embodiment as a functional block. The figure which showed the insertion loss characteristic (S21 [dB] -frequency [Hz]) by the active noise filter provided with the band pass filter. The figure which showed the whole structure of the noise filter which concerns on the 3rd Embodiment of this invention. The figure which showed the equivalent circuit of the noise filter. The figure which showed the equivalent circuit of the noise filter. The figure which showed the whole structure of the noise suppression system provided with the active noise filter which concerns on 4th Embodiment of this invention. The figure which showed in detail the circuit structure of the amplifier circuit and microcomputer in the noise filter of an active noise filter. The figure which showed each structure in the whole structure of an active noise filter as a functional block. The flowchart which showed the noise voltage monitoring process of the common mode noise implemented for every ferrite core for a detection provided in the noise filter of an active noise filter. The figure which showed the whole structure of the active noise filter which concerns on a prior art.

  Hereinafter, an active noise filter and an active noise filter characteristic control method according to embodiments of the present invention will be described with reference to the drawings.

1. First embodiment
FIG. 1 is a diagram illustrating an overall configuration of a noise suppression system 1 including an active noise filter 10 according to the first embodiment.

  The noise suppression system 1 includes an electronic device 20, an electronic device 30, and a noise filter 11 and a noise filter 12 provided between these electronic devices 20 and 30.

  Further, the noise filter 11 and the noise filter 12 constitute an active noise filter 10.

  The electronic device 20 generates common mode noise Cn. The common mode noise Cn propagates through the power supply lines (Sp1 to Sp5).

  When the power supply lines Sp1 to Sp5 are not distinguished from each other, they are simply referred to as the power supply lines Sp.

  The electronic device 30 is connected to the electronic device 20 through a power supply line Sp that relays the noise filter 11 and the noise filter 12.

  The active noise filter 10 suppresses common mode noise Cn propagating through the power supply line Sp.

  The active noise filter 10 includes a noise filter 11 and a noise filter 12 connected to the noise filter 11 through a power supply line Sp.

  Here, the noise filter 11 and the noise filter 12 suppress common mode noise Cn in different frequency bands.

  In the following, it is assumed that the common mode noise Cn in the first frequency band f1 is suppressed by the noise filter 11, and the common mode noise Cn in the second frequency band f2 is suppressed by the noise filter 12.

  Note that the number of noise filters included in the active noise filter 10 is not limited to two and may be more than that. Thereby, it is possible to suppress a wide frequency band by the number of noise filters.

  The noise filter 11 includes a detection ferrite core 11a, a feedback ferrite core 11b, and an amplifier circuit 11c, for example, having a first size.

  The detection ferrite core 11a has a power line Sp1 on the primary side and a conductive wire w1 wound on the secondary side to form a transformer having a primary coil and a secondary coil (not shown).

  The feedback ferrite core 11b has a conductor w2 on the primary side and a power supply line Sp2 on the secondary side to form a transformer having a primary coil and a secondary coil (not shown).

  The amplifier circuit 11c is configured by using, for example, a differential amplifier, and one end of a conducting wire w1 wound around the secondary side of the detection ferrite core 11a at the positive input terminal (hereinafter, non-inverting input terminal (+)). The other end of the lead wire w1 wound on the secondary side and the other end of the primary coil of the feedback ferrite core 11b are connected to the negative side input terminal (hereinafter referred to as the inverting input terminal (-)). The

  Furthermore, the output terminal OUT1 of the amplifier circuit 11c is connected to one end of a conducting wire w2 wound around the primary side of the feedback ferrite core 11b. Note that the other end of the lead wire w2 wound around the primary side of the feedback ferrite core 11b is not connected to the negative input terminal (hereinafter, the inverting input terminal (−)) of the amplifier circuit 11c, and is grounded (in FIG. 1). , Described as “G”).

  The amplifier circuit 11c configured as described above feeds a feedback current I1 corresponding to the potential difference supplied to the non-inverting input terminal (+) and the inverting input terminal (−) from the output terminal to the primary side of the feedback ferrite core 11b. It supplies to the end of the wound conducting wire w2.

  Further, the noise filter 12 is configured so that the size of the ferrite core (12a, 12b) constituting the (filter for detection, feedback) is larger than the ferrite core (11a, 11b) included in the noise filter 11 (for detection, feedback). Except for having a large size (second size), the same configuration as that of the noise filter 11 is adopted.

  That is, the ferrite core (12a, 12b) constituting the noise filter 12 (for detection and feedback) functions as a transformer having a primary side coil and a secondary side coil (not shown).

  In the detection ferrite core 12a, the power line Sp3 is wound on the primary side, and the conductive wire w3 is wound on the secondary side.

  Here, the power supply line Sp3 wound on the primary side of the detection ferrite core 12a and the power supply line Sp2 wound on the secondary side of the feedback ferrite core 11b in the noise filter 11 are connected in series. Thus, the noise filter 12 and the noise filter 11 are connected.

  The feedback ferrite core 12b is wound with the lead wire w4 on the primary side and the power supply line Sp4 on the secondary side.

  The amplifier circuit 12c is configured by using, for example, a differential amplifier, and one end of a conducting wire w3 wound around the secondary side of the detection ferrite core 12a at a positive input terminal (hereinafter, non-inverting input terminal (+)). And the other end of the conducting wire w3 and the other end of the conducting wire w4 wound around the primary side of the feedback ferrite core 12b are connected to the negative side input terminal (hereinafter referred to as the inverting input terminal (−)). .

  Further, the output terminal OUT2 of the amplifier circuit 12c is connected to one end of a conducting wire w4 wound around the primary side of the feedback ferrite core 12b. Note that the other end of the lead wire w4 wound on the primary side of the feedback ferrite core 12b is not connected to the inverting input terminal (−) of the amplifier circuit 12c, and is grounded (described as “G” in FIG. 1). It may be configured.

  The amplifier circuit 12c configured as described above generates a feedback current I2 corresponding to the difference between the non-inverting input terminal (+) and the inverting input terminal (−) from the output terminal OUT2 to the primary side lead w4 of the feedback ferrite core 12b. To one end.

  The noise filter 11 and the noise filter 12 are configured to suppress different frequency bands. The detection ferrite core 11a and the feedback ferrite core 11b that constitute the noise filter 11, the detection ferrite core 12a that constitutes the noise filter 12, and Although the size of each ferrite core of the feedback ferrite core 12b is different, it is not limited to this.

  That is, at least one different material and shape may be employed for the detection ferrite core 11a and the feedback ferrite core 11b, and the detection ferrite core 12a and the feedback ferrite core 12b.

  In addition, since it is only necessary that the frequency bands that can be suppressed differ between the noise filters (11, 12), at least one of the size, shape, and material is between the detection ferrite core 11a and the detection ferrite core 12a. Any different configuration may be used.

Next, the function of each part constituting the active noise filter 10 shown in FIG. 1 will be described with reference to FIG.
FIG. 2 is a diagram showing each component in the overall configuration of the active noise filter 10 as a functional block. In this functional block diagram, the power supply line Sp (indicated as Sp1 to Sp5 in FIG. 2) through which the common mode noise Cn propagates is described outside the noise filter 11 and the noise filter 12.

  The detection ferrite core 11a has a function of detecting the common mode noise Cn in the first frequency band f1 among the common mode noise Cn propagating through the power line Sp.

  The amplifier circuit 11c has a function of supplying a feedback current I1 corresponding to the voltage of the common mode noise Cn detected by the detection ferrite core 11a (hereinafter, noise voltage VN) to the feedback ferrite core 11b.

  Due to the feedback current I1 from the amplifier circuit 11c, the feedback ferrite core 11b applies a counter electromotive force V1 (common mode noise Cn opposite to the propagation direction of the common mode noise Cn) to its secondary coil (not shown). A voltage V1) in the direction of suppression is induced.

  Thereby, the noise of the 1st frequency band f1 is suppressed among the common mode noise Cn which propagates the power supply line Sp.

  Further, the detection ferrite core 12a has a function of detecting the common mode noise Cn in the second frequency band f2 among the common mode noise Cn propagating through the power supply line Sp.

  The amplifier circuit 12c has a function of supplying a feedback current I2 corresponding to the noise voltage VN of the common mode noise Cn detected by the detection ferrite core 12a to the feedback ferrite core 12b.

  The feedback ferrite core 12b has a counter electromotive force V2 (a voltage V2 in a direction to suppress the common mode noise Cn) that is opposite to the propagation direction of the common mode noise Cn in the secondary coil by the feedback current I2 from the amplifier circuit 12c. ) Is induced.

  Thereby, the noise of the 2nd frequency band f2 is suppressed among the common mode noise Cn which propagates the power supply line Sp.

  As a result, in the common mode noise Cn, noise in the second frequency band f2 is suppressed in addition to noise in the first frequency band f1.

  The effect of suppressing the common mode noise Cn by the active noise filter 10 including the noise filter 11 and the noise filter 12 will be described with reference to FIG.

  FIG. 3 is a graph showing the insertion loss [S21 (dB)] on the vertical axis and the frequency [Hz] on the horizontal axis, and the effect of suppressing the common mode noise Cn by the active noise filter 10.

  The noise filter 11 has an insertion loss characteristic with a first center frequency fc1 and a first frequency bandwidth w1, and suppresses common mode noise Cn for the first frequency band f1.

  The noise filter 12 has insertion loss characteristics of the second center frequency fc2 and the second frequency bandwidth w2, and suppresses the common mode noise Cn in the second frequency band f2 different from the first frequency band f1.

  That is, by using the noise filter 11 and the noise filter 12 in the active noise filter 10, it is possible to obtain a noise filter having a wide bandwidth w3 in which the first frequency band f1 and the second frequency band f2 are overlapped.

  Therefore, the active noise filter 10 having the above configuration includes the noise filter 11 that suppresses the common mode noise Cn in the first frequency band f1 and the noise filter 12 that suppresses the common mode noise Cn in the second frequency band f2. The noise filter (11, 12) includes a first and second size detecting ferrite core (11a, 12a), a first and second size feedback ferrite core (11b, 12b), and an amplification. A power line Sp wound around the primary side of the detection ferrite core 12 a provided in the noise filter 12, and two of the feedback ferrite core 11 b in the noise filter 11. The noise filter 11 and the noise filter 12 are connected by connecting the power line Sp wound on the next side in series.

  According to the active noise filter 10 according to the first embodiment, the first frequency band f1 and the second frequency band f2 are superimposed using the noise filter 11 and the noise filter 12, and the common mode noise Cn is widened with a wide bandwidth w3. Can be suppressed.

  In addition, in 1st Embodiment, although the structure which provided the amplifier circuit 11c (12c) for each noise filter 11 (12) was employ | adopted, it is not restricted to this.

  For example, the structure which provided the single amplifier circuit with respect to the noise filter 11 and the noise filter 12 may be sufficient.

  4A and 4B are diagrams showing the entire configuration of the active noise filter 10 in which a single amplifier circuit 13 is provided for the noise filters (11, 12).

  FIG. 4A shows an active noise filter 10 including a detection ferrite core (11a, 12a) and a feedback ferrite core (11b, 12b) connected in parallel to the amplifier circuit 13.

  As shown in the figure, the detection ferrite cores (11a, 12a) are arranged on the left side with respect to the amplifier circuit 13, and the feedback ferrite cores (11b, 12b) are arranged on the right side.

  Specifically, power supply lines (Sp1, Sp2) connected in series are wound around the primary side of the detection ferrite cores (11a, 12a), and the detection ferrite cores (11a, 12a) are connected at the nodes N1 and N2. 12a), one end and the other end of the conducting wire w1 wound on the secondary side are connected in common, and one end and the other end of the conducting wire w1 are connected to the non-inverting input terminal (+) and the inverting input terminal (-) of the amplifier circuit 13, respectively. Connect.

  Further, with respect to the feedback ferrite core (11b, 12b), one end and the other end of the lead wire w2 wound around the primary side of the feedback ferrite core (11b, 12b) are commonly connected at the nodes N3 and N4, and the feedback is performed. The power supply lines (Sp3, Sp4) are wound around the secondary side of the ferrite core (11b, 12b).

  FIG. 4B is a diagram showing an active noise filter 10 in which a detection ferrite core (11a, 12a) and a feedback ferrite core (11b, 12b) are connected in series to the amplifier circuit 13.

  As in FIG. 4A, the detection ferrite cores (11a, 12a) are arranged on the left side of the amplifier circuit 13, and the feedback ferrite cores (11b, 12b) are arranged on the right side.

  Specifically, the power supply wires (Sp1, Sp2) and the conductive wire w1 wound around the primary side and the secondary side of the detection ferrite core (11a, 12a) are connected in series, and one end of the conductive wire w1 connected in series. And the other end are connected to the non-inverting input terminal (+) and the inverting input terminal (−) of the amplifier circuit 13.

  Further, similarly for the feedback ferrite core (11b, 12b), the lead wire w2 and the power supply line (Sp3, Sp4) wound around the primary side and the secondary side of the feedback ferrite core (11b, 12b) are respectively connected in series. .

  Note that the active noise filter 10 is configured such that the detection ferrite cores (11a, 12a) are connected in series as shown in FIG. 4B, while the feedback ferrite cores (11b, 12b) are connected in parallel as shown in FIG. 4A. May be adopted.

  Further, the active noise filter 10 is configured such that the detection ferrite cores (11a, 12a) are connected in parallel as shown in FIG. 4A, while the feedback ferrite cores (11b, 12b) are connected in series as shown in FIG. 4B. May be adopted.

  Even in the configuration of the active noise filter 10 shown in FIGS. 4A and 4B, the first frequency band f1 and the second frequency band f2 can be overlapped to suppress the common mode noise Cn with a wide bandwidth w3.

2. Second embodiment
Next, the active noise filter 10 according to the second embodiment will be described.
The active noise filter 10 according to the second embodiment is different from the first embodiment in that bandpass filters (BF1, BF2) are provided in front of the amplifier circuits (11c, 12c).

  Such a configuration is adopted in the first embodiment because the amplifier circuit (11c, 12c) and other elements in the noise filter (11, 12) included in the active noise filter 10 influence the common mode noise Cn. Depending on the frequency band, the phase of the back electromotive force (V1, V2) induced in the feedback ferrite core (11b, 12b) is in phase with the phase of the common mode noise Cn propagating through the power line Sp ( This is considered in view of the background that the common mode noise Cn may be amplified due to the fact that it is hereinafter referred to as “frequency characteristic deviation”.

  FIG. 5 is a graph showing how the insertion loss (S21 [dB]) becomes a positive value at the frequency f0 in the active noise filter 10 when no bandpass filter is provided.

  As shown in the figure, in the noise filters (11, 12) included in the active noise filter 10, the frequency loss is caused and the insertion loss [S21 (dB)] becomes a positive value at the frequency f0. As a result, the common mode noise Cn may be amplified.

  Note that the insertion loss (S21 [dB]) may be a positive value not only at the frequency f0 but also at a plurality of frequencies fn (n: natural number).

For this reason, in the second embodiment, the active noise filter 10 including the band-pass filters (BF1, BF2) that allow the insertion loss [S21 (dB)] of the common mode noise Cn to have a negative value is passed. Is adopted.
Hereinafter, a description will be given with reference to FIG.
In addition, about the structure same as the noise suppression system 1 which concerns on 1st Embodiment, the same code | symbol is attached | subjected and the description which concerns on the structure is abbreviate | omitted.

  FIG. 6 is a diagram illustrating an overall configuration of the noise suppression system 1 including the active noise filter 10 according to the second embodiment.

  As shown in the figure, the noise filters (11, 12) in the active noise filter 10 according to the second embodiment are upstream of the amplifier circuits (11c, 12c), and are secondary to the detection ferrite cores (11a, 12a). Band pass filters (BF1, BF2) provided between the conductive wires (w1, w2) wound on the side are provided.

  As an example, a resistance R, a capacitance C, and an inductance L are provided in the bandpass filters (BF1, BF2). In this case, the band pass filters (BF1, BF2) function as passive filters.

  The band pass filters (BF1, BF2) may be configured by using active elements such as an amplifier circuit. In this case, the band pass filters (BF1, BF2) function as active filters.

Next, the function of each part which comprises the active noise filter 10 which concerns on 2nd Embodiment is demonstrated using FIG. Note that the description of the same function as the active noise filter 10 according to the first embodiment is omitted.
FIG. 7 is a diagram showing each component in the overall configuration of the active noise filter 10 as a functional block. Here, the power supply line Sp (denoted as Sp1 to Sp5 in FIG. 7) through which the common mode noise Cn propagates is described outside the noise filter 11 and the noise filter 12.

  Further, the common mode noise Cn propagating to the power supply line Sp is classified into noise Cn1 (band noise Cn1: fine line to be suppressed in FIG. 7) and noise Cn2 (noise in a band to be amplified in FIG. 7: thick line). And divided.

  First, the detection ferrite core 11a has a function of detecting noise (Cn1, Cn2) in the first frequency band f1 among the common mode noise Cn propagating through the power supply line Sp.

  Here, when the noise Cn1 is detected by the detection ferrite core 11a, the noise Cn1 has a characteristic of inducing a counter electromotive force V1 having a phase opposite to the phase of the common mode noise Cn by the subsequent feedback ferrite core 11b. .

  On the other hand, when the noise Cn2 is detected by the detection ferrite core 11a, the noise Cn2 has a characteristic of inducing a counter electromotive force V1 having the same phase as that of the common mode noise Cn by the feedback ferrite core 11b.

  Therefore, the bandpass filter BF1 has a function of passing the noise Cn1 and cutting the noise Cn2.

  As a result, only the noise Cn1 that induces the counter electromotive force V1 having the opposite phase to the phase of the common mode noise Cn in the first frequency band f1 passes through the band pass filter BF1. That is, only noise that can make the insertion loss [S21 (dB)] of the common mode noise Cn negative passes through the band-pass filter BF1.

  As described above, the noise filter 11 according to the second embodiment cuts the noise Cn2 that induces the counter electromotive force V1 having the same phase as that of the common mode noise Cn in the first frequency band f1 to thereby reduce the common mode. It has a function of preventing the insertion loss [S21 (dB)] of the noise Cn from becoming a positive value.

  Thereafter, similar to the noise filter 11, the common mode noise Cn is suppressed by the noise filter 12. That is, the common mode noise Cn in the second frequency band f2 is suppressed without setting the insertion loss [S21 (dB)] of the common mode noise Cn to a positive value in the second frequency band f2.

  Specifically, the noise Cn1 is passed through the noise (Cn1, Cn2) in the second frequency band f2 detected by the detection ferrite core 12a by the bandpass filter BF2, and the noise Cn2 is cut.

  Thus, the noise filter 12 according to the second embodiment cuts the noise Cn2 that induces the counter electromotive force V2 having the same phase as the phase of the common mode noise Cn in the second frequency band f2. It has a function of preventing the insertion loss [S21 (dB)] of the common mode noise Cn from becoming a positive value.

  Therefore, according to the active noise filter 10 having the above-described configuration, only the noise Cn1 that can induce the counter electromotive force (V1, V2) that suppresses the common mode noise Cn is provided in front of the amplifier circuits (11c, 12c). Band-pass filters (BF1, BF2) to be passed are provided.

  According to the active noise filter 10 according to the second embodiment, the insertion loss (S21 [dB]) becomes a positive value at the frequency f0 due to the deviation of the frequency characteristics, and as a result, the common that propagates through the power line Sp. The phenomenon that the mode noise Cn is amplified can be prevented.

  This is because of the back electromotive force induced in the feedback ferrite core 11b by the noise Cn2 included in the common mode noise Cn depending on the frequency band of the common mode noise Cn due to the influence of the amplifier circuit (11c, 12c) or the like. V1 and V2) are in phase with the phase of the common mode noise Cn. By cutting this with the band-pass filters (BF1 and BF2), the first frequency band f1 and the second frequency band f2 This is because the common mode noise Cn can be suppressed.

  FIG. 8 shows the effect of suppressing the insertion loss (S21 [dB]) at the frequency f0. FIG. 8 is a diagram showing insertion loss characteristics (S21 [dB] −frequency [Hz]) by the active noise filter 10.

  As shown in the figure, it is possible to prevent the insertion loss [S21 (dB)] from becoming a positive value within the bandwidth w3.

  As shown in FIG. 5, when the frequency f0 is located on the high frequency side when viewed from the noise filter 11, the bandpass filter BF1 may be a low-pass filter LPF composed of, for example, a capacitance and an inductance.

3. Third embodiment
Next, the active noise filter 10 according to the third embodiment will be described. In the active noise filter 10 according to the third embodiment, a part of the self-inductance L of the secondary coil wound around the detection ferrite core 11a is used as the inductance L constituting the low-pass filter (LPF1, LPF2). Different from the second embodiment.

  9A to 9C are diagrams showing the noise filter 11 (12) according to the third embodiment.

  Here, FIG. 9A is a diagram showing an overall configuration of the noise filter 11 (12), and FIGS. 9B and 9C are diagrams showing an equivalent circuit of the noise filter 11 (12).

  As shown in FIG. 9A, the capacitance C is arranged at both ends of the conducting wire w1 wound around the secondary side of the detection ferrite core 11a (12a).

  Here, as shown in FIG. 9B, a part of the self-inductance L (L2a, L2b) of the secondary coil wound around the detection ferrite core 11a (12a) (denoted as L2b in FIG. 9) As shown in 9C, the low pass filters LPF (LPF1, LPF2) function as inductances.

  Note that a part of the self-inductance L of the secondary coil wound around the detection ferrite core 11a (12a) (denoted as L2a in FIG. 9B) is 1 wound around the primary side of the detection ferrite core 11a. The secondary coil functions as a self-inductance L1a and a transformer.

  In this configuration, the voltage Va ′ is induced in the secondary coil.

  Therefore, in the detecting ferrite core 11a (12a) shown in FIG. 9C, the voltage source Va ′, the amplifier circuits (11c, 12c), and the low-pass filter LPF (here, the capacitance C and the inductance L2b) provided therebetween. Are formed as a low-pass filter LPF).

  The active noise filter 10 having the above configuration includes a configuration in which the capacitance C is arranged at both ends of the conducting wire w1 wound around the secondary side of the detection ferrite core 11a (12a) constituting the noise filter 11 (12).

  According to this, in addition to the capacitance C, the low-pass filter LPF that can suppress the high frequency side of the common mode noise Cn without intentionally arranging the inductance L on the secondary side of the detection ferrite core 11a (12a). Can be formed.

  That is, as shown in FIG. 5, the insertion loss (positive value) on the high frequency side when viewed from the insertion loss characteristic (S21 [dB]) by the noise filter 11 can be cut by the low-pass filter LPF. it can.

4). Fourth embodiment
Next, the active noise filter 10 according to the fourth embodiment will be described with reference to FIGS.
In the active noise filter 10 according to the fourth embodiment, the impedance (Z1 to Z4) of each element e (hereinafter referred to as element e1 to element e4) constituting the amplifier circuit (11c, 12c) is variable, and the common mode is set. It is provided with a configuration for controlling the insertion loss characteristic (for example, the shape of the S21 [dB] -frequency [Hz] characteristic curve shown in FIG. 3) of the noise filter (11, 12) according to the magnitude of the noise Cn. Different from the first to third embodiments.

  Such a configuration is adopted, for example, in the first embodiment, in the frequency band (for example, bandwidth w3) in which the common mode noise Cn is suppressed by the noise filters (11, 12), the insertion loss characteristic (S21 [ In view of the background that, for example, sufficient suppression may not be desired depending on the magnitude of the common mode noise Cn.

  FIG. 10 is a diagram illustrating an overall configuration of the noise suppression system 1 including the active noise filter 10 according to the fourth embodiment.

  Hereinafter, the same code | symbol is attached | subjected about the structure same as the noise suppression system 1 which concerns on 1st Embodiment, and the description which concerns on the structure is abbreviate | omitted.

  As shown in FIG. 10, the active noise filter 10 according to the fourth embodiment further includes a microcomputer (MC1, MC2) and an AC voltmeter (Vac1, Vac2) for each noise filter (11, 12), and an amplifier circuit. (11c, 12c) is variable (hereinafter referred to as a variable amplifier circuit).

  First, in the noise filter 11, the AC voltmeter Vac1 is provided between the conductors w1 wound around the secondary side of the detection ferrite core 11a. The AC voltmeter Vac1 measures a noise voltage VN (here, the AC voltage Vac between the conductors w1) and outputs a DC voltage Vdc1 corresponding to the AC voltage Vac.

  The variable amplifier circuit 11c includes, for example, an element e such as a resistance R, an inductance L, a capacitance C, a varicap VC, and a differential amplifier circuit (not shown), and an impedance Z of the element e and the differential amplifier circuit. The configuration can be made variable by an external control signal.

  Furthermore, the microcomputer MC1 outputs a control signal to the variable amplifier circuit 11c based on the DC voltage Vdc1 from the AC voltmeter Vac1.

  The AC voltmeter Vac2 and the microcomputer MC2 in the noise filter 12 are also arranged in the same manner as the noise filter 11. That is, the AC voltmeter Vac2 is provided between the conducting wires w3 wound on the secondary side of the detection ferrite core 12a, and the microcomputer MC2 controls the amplification circuit 12c based on the DC voltage Vdc2 from the AC voltmeter Vac2. Is output.

  FIG. 11 is a diagram showing in detail the circuit configurations of the amplifier circuits (11c, 12c) and the microcomputers (MC1, MC2) in the noise filters (11, 12) of the active noise filter 10.

  Since the amplifier circuit 11c and the amplifier circuit 12c included in the noise filter 11 and the noise filter 12 and the microcomputer MC1 and the microcomputer MC2 have the same configuration and function, in the description using FIG. 11, the amplifier circuit 11c in the noise filter 11 is used. Attention is focused on the microcomputer MC1 corresponding thereto.

  As illustrated in FIG. 11, the amplifier circuit 11 c includes, for example, an element e4 (amplifier AMP) in addition to the elements e1 to e3 including a resistance R, an inductance L, a capacitance C, a varicap VC, and the like. .

  The microcomputer MC1 includes a control unit (hereinafter referred to as CPU) 41A that functions as a computer.

  A memory 41B, an input unit 41C, and an output unit 41D are connected to the CPU 41A.

  The memory 41B includes a program data area 41b1 for storing data of the noise voltage monitoring processing program PRG and a work area AREA 41b2.

  That is, the CPU 41A, in accordance with the noise voltage monitoring processing program PRG stored in advance in the memory 41B, enters the amplifier circuit 11c based on the DC voltage Vdc1 from the AC voltmeter Vac1 input from the input unit 41C and stored in the work area AREA 41b2. Control signals (for example, “L” level and “H” level voltages) for controlling the values of the impedances Z1 to Z4 of the elements e1 to e4 in the order of the elements e1, e2, e3, and e4. Output from the output unit 41D.

  The input unit 41C supplies the DC voltage Vdc1 from the AC voltmeter Vac1 to the CPU 41A, and the output unit 41D outputs a control signal to the amplifier circuit 11c.

Next, the function of the above configuration will be described.
FIG. 12 is a diagram showing each component in the active noise filter 10 as a functional block.

  Hereinafter, the same components as those of the active noise filter 10 according to the first embodiment are denoted by the same reference numerals, and descriptions of the functions of the components are omitted.

  In the configuration as shown in FIG. 12, the AC voltmeter Vac1 monitors the AC voltage Vac of the common mode noise Cn detected by the detection ferrite core 11a, and the DC voltage Vdc proportional to the magnitude of the monitored AC voltage Vac. Is supplied to the microcomputer MC1.

  Further, the microcomputer MC1 outputs a control signal for controlling the impedance values (Z1 to Z4) of the elements (e1 to e4) in the amplifier circuit 11c according to the magnitude of the DC voltage Vdc1 from the AC voltmeter Vac1. And has a function of optimizing the impedance (Z1 to Z4).

  Specifically, the microcomputer MC1 reduces or increases, for example, the value of the impedance Z1 of the element e1 in the amplifier circuit 11c so that the DC voltage Vdc1 from the AC voltmeter Vac1 increases when the DC voltage Vdc1 increases. Is output, the insertion loss characteristic (S21 [dB] −frequency [Hz]) of the active noise filter 10 is controlled.

  This is because when the impedance Z1 is lowered according to the frequency component or voltage level of the common mode noise Cn, the voltage of the common mode noise Cn decreases, and conversely the voltage increases. It is.

  Therefore, the microcomputer MC1 first increases the value of the impedance Z1, and determines whether the voltage of the common mode noise Cn increases or decreases.

  As a result of the determination, if the suppression effect by the noise filter 11 decreases and the voltage of the common mode noise Cn increases, a control signal is output so that the value of the impedance Z1 becomes a minimum value to reduce this, while the noise filter If the suppression effect by 12 increases and the voltage of the common mode noise Cn decreases, the value of the impedance Z1 is increased as it is and a control signal is output so that the value of the impedance Z1 becomes the maximum value.

  However, when the voltage of the common mode noise Cn, which has been reduced so far, starts increasing again in the process of decreasing the value of the impedance Z1, the impedance Z1 is controlled (increased or decreased) during the increase. To stop.

  When the microcomputer MC1 performs the above-described control performed on the impedance Z1 of the element e1 in the same manner for each of the elements e2 to e4, the second control in the noise filter 12 by the microcomputer MC2 is performed. The insertion loss characteristic (S21 [dB] −frequency [Hz]) of the frequency band f2 is controlled.

  That is, as with the noise filter 11, control is performed on the amplifier circuit 12 c (element e <b> 1 to element e <b> 4) by the microcomputer MC <b> 2 provided in the noise filter 12.

  That is, the microcomputer MC2 controls the impedances Z1 to Z4 of the elements e1 to e4 in the amplifier circuit 12c according to the magnitude of the DC voltage Vdc2 from the AC voltmeter Vac2.

  Specifically, the microcomputer MC2 first outputs a control signal for increasing, for example, the value of the impedance Z1 of the element e1 in the amplifier circuit 12c so as to decrease the DC voltage Vdc2 from the AC voltmeter Vac2. As a result, it is determined whether the DC voltage Vdc2 increases or decreases.

  As a result of the determination, if the suppression effect by the noise filter 12 decreases and the voltage of the common mode noise Cn increases, a control signal is output so that the value of the impedance Z1 becomes the minimum value, while the suppression by the noise filter 12 is performed. If the effect increases and the voltage of the common mode noise Cn decreases, a control signal is output so that the value of the impedance Z1 becomes the maximum value.

  However, when the voltage of the common mode noise Cn, which has been reduced so far, starts to increase again in the process of decreasing the value of the impedance Z1, control (increase or decrease) of the impedance Z1 is performed during the increase. Stop.

  As described above, the control of the impedances (Z1 to Z4) is performed in the order of the noise filter 11 and the noise filter 12 without performing the above-described control on the noise filter 11 and the noise filter 12 in parallel. 11c and 12c), if the values of the impedances (Z1 to Z4) of the elements e1 to e4 are controlled in parallel, the increase / decrease of the common mode noise Cn is caused by the change of the impedance Z of the element e. This is because it cannot be determined.

  In the active noise filter 10 configured as described above, the CPU 41A controls the operation of each unit in accordance with instructions described in the noise voltage monitoring processing program PRG, and the software and hardware cooperate to operate as follows. The noise voltage monitoring function is realized as described in the explanation of the operation.

  Next, the operation of the active noise filter 10 configured as described above will be described.

  FIG. 13 shows noise voltage monitoring of common mode noise Cn performed for each of the detection ferrite cores (11a, 12a,..., Na) provided in the noise filters (11, 12,..., N) of the active noise filter 10. It is a flowchart which shows a process.

  Here, it is assumed that the amplifier circuits (11c, 12c,..., Nc) included in the noise filters (11, 12,..., N) include elements e1 to en, respectively.

  First, when the CPU 41A receives the noise voltage VN (DC voltage Vdc1) of the common mode noise Cn induced on the secondary side of the detection ferrite core 11a from the AC voltmeter Vac1, first, the CPU 41A first detects the element e1 in the amplifier circuit 11c. A control signal is output to the element e1 so that the impedance Z1 increases (step S1).

  For example, when the element e1 is a varicap VC, the capacitance value is changed by applying a voltage according to the control signal to the varicap.

  Next, it is determined whether or not the noise voltage VN of the common mode noise Cn has increased (step S2).

  As a result, when the noise voltage VN of the common mode noise Cn rises (step S2, YES), the impedance Z1 of the element e1 is lowered to the minimum value (step S3).

  When the noise voltage VN of the common mode noise Cn, which has been reduced until then, increases while the value of the impedance Z1 is decreasing, the control for the element e1 is stopped during the increase. In the middle, the value of the impedance Z1 is fixed (step S3).

  On the other hand, if the noise voltage VN of the common mode noise Cn has decreased as a result of step S2 (step S2, NO), the impedance Z1 of the element e1 is increased as it is to the maximum value (step S4).

  If the noise voltage VN of the common mode noise Cn, which has been decreased, starts to increase again while increasing the value of the impedance Z1, control is performed on the element e1 during the increase. Stop and fix the value of impedance Z1 (step S4).

Next, the control shifts to the impedance Z2 of the element e2. Specifically, the control performed on the element e1 is similarly performed on the element e2 (steps S5 to S8).
That is, first, a voltage control signal is output to the element e2 so that the impedance Z2 of the element e2 increases (step S5).

  Next, it is determined whether or not the noise voltage VN of the common mode noise Cn has increased (step S6).

  As a result, when the noise voltage VN of the common mode noise Cn increases (YES in step S6), the impedance Z2 of the element e2 is decreased to the minimum value (step S7).

  If the noise voltage VN of the common mode noise Cn, which has been reduced until then, starts to increase again in the process of decreasing the value of the impedance Z2, the control of the impedance Z2 for the element e2 in the middle of the increase Is stopped and the value of the impedance Z2 is fixed (step S7).

  On the other hand, when the noise voltage VN of the common mode noise Cn decreases as a result of step S6 (step S6, NO), the impedance Z2 of the element e2 is increased to the maximum value as it is (step S8).

  Then, when the noise voltage VN of the common mode noise Cn that has been reduced in the process of increasing the value of the impedance Z2 starts to increase, the control of the impedance Z2 for the element e2 is controlled in the middle of the increase. Stop and fix the value of the impedance Z2 (step S9).

The above processing is performed up to the element en (steps S9 to S12), and the impedance Z of each element e1 to en is optimized.
Thereby, since the impedance control of each element e1 to en included in the noise filter 11 is completed, the same impedance control is executed in the order of the noise filter 12, ..., the noise filter n (step S1 to step S12).

  Finally, when the impedance control for the noise filter n is completed, the impedance control for the noise filter 11 is performed again to further reduce the impedance Z of each element e1 to en for each noise filter (11, 12,..., N). Is optimized (steps S1 to S12).

  Although the noise voltage monitoring process of the common mode noise Cn when the amplifier circuit 11c (12c) is provided for each noise filter 11 (12) has been described, a single amplifier circuit is used as shown in FIGS. 4A and 4B. When 13 is provided, for example, the process from step S1 to step S12 may be performed for the element e1 to element en included in the amplifier circuit 13.

  Therefore, according to the active noise filter 10 having the above configuration, the common detected by the primary side of the detection ferrite core (11a, 12a) and measured by the AC voltmeter (Vac1, Vac2) on the secondary side thereof. According to the magnitude of the noise voltage VN of the mode noise Cn, the impedances (Z1 to Zn) of the elements (elements e1 to en) constituting the amplifier circuit (11c, 12c) are sequentially changed by the microcomputer (MC1, MC2). Control.

  Specifically, the microcomputer (MC1, MC2) increases the impedance Z1 of the element e1, for example, determines whether the noise voltage VN of the common mode noise Cn increases or decreases, and the result of the determination If the noise voltage VN rises, the impedance Z1 of the element e1 is lowered to the minimum value, or when the noise voltage VN rises again while the impedance Z1 is lowered, The value of impedance Z1 is fixed.

  On the other hand, if the noise voltage VN decreases as a result of the determination, the impedance Z1 of the element e1 is increased to the maximum value as it is, or when the noise voltage VN increases in the middle of increasing the impedance Z1, In the middle of the increase, the value of the impedance Z1 is fixed, and then the same process is performed on the element e2.

  According to this, the noise voltage VN of the common mode noise Cn rises in the frequency band (for example, bandwidth w3) in which the common mode noise Cn is suppressed by the noise filter (11, 12), and the noise filter (11, 12). ), The noise loss VN detected by the detection ferrite core (11a, 12a) is monitored by the microcomputer (MC1, MC2) while the insertion loss characteristic (S21 [dB] − Frequency [Hz]) can be controlled to achieve optimum characteristics. Therefore, not only the suppression band of the common mode noise Cn by the noise filter (11, 12) is widened to the bandwidth w3, but also sufficient suppression is achieved even when the common mode noise Cn increases in the suppression band w3. Can do.

  Further, even when the frequency band of the common mode noise Cn changes each time, by repeating the processing from step S1 to step S12 for the noise filter (11, 12), the common mode noise Cn is changed to the common mode noise Cn. The optimum impedance Z of the suitable element e can be set.

  When the element e1 is a varicap, the value of the capacitance is changed by applying a voltage corresponding to the control signal to the element e1, but the method of making the impedance Z1 of the element e1 variable is not limited thereto. I can't. That is, for example, if the element e1 is a trimmer capacitor whose capacitance can be changed by rotating the dial, a configuration in which the dial can be rotated by a control signal from the microcomputer (MC1, MC2) is adopted. May be.

  In the first to fourth embodiments, attention is paid to the suppression of the common mode noise Cn. However, the present invention is not limited to this and can be applied to the suppression of the differential mode noise.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the invention when it is practiced. Further, the embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. For example, even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment or some constituent requirements are combined in different forms, the problems described in the column of the problem to be solved by the invention are not solved. When the effects described in the column “Effects of the Invention” can be obtained, a configuration in which these constituent requirements are deleted or combined can be extracted as an invention.

1 ... Noise suppression system, 10, 100 ... Active noise filter,
11, 12 ... Noise filter, Sp1-Sp5 ... Power line,
11a, 12a, 110 ... ferrite core for detection,
11b, 12b, 120 ... feedback ferrite core, 130 ... feedback type amplifier circuit,
11c, 12c, 13 ... amplification circuit, 20 ... electronic device, 30 ... electronic device,
41A ... Control unit (CPU), 41B ... Memory, 41C ... Input unit, 41D ... Output unit,
41b1 ... Noise voltage monitoring processing program PRG,
AREA 41b2 ... work area, BF1, BF2 ... band pass filter,
Cn1, Cn2 ... noise, OUT1 ... output terminal, OUT2 ... output terminal,
Cn: common mode noise, I1, I2: feedback current,
L1a ... self inductance, MC1, MC2 ... microcomputer, e1-e4 ... element,
V1, V2 ... counter electromotive force, Vac1, Vac2 ... AC voltmeter,
Vdc1, Vdc2 ... DC voltage, VN ... noise voltage,
Z1-Z4 ... impedance, f0 ... frequency,
f1, f2 ... frequency band, fc1 ... first center frequency, fc2 ... second center frequency,
w1 ... 1st frequency bandwidth, w2 ... 2nd frequency bandwidth, w3 ... bandwidth.

Claims (8)

First detection ferrite that detects common mode noise in the first frequency band that is generated from the first electronic device and propagates through the first power supply line, and induces a first voltage caused by the common mode noise in the first frequency band A first amplifying circuit that generates a first feedback current caused by the first voltage induced by the first detecting ferrite core; and the first feedback current from the first amplifying circuit causes the first amplifying circuit to A first feedback ferrite core for inducing a first counter electromotive force that suppresses common mode noise in one frequency band; and
A common mode noise of a second frequency band different from the first frequency band, which propagates through a second power line connected to the first power line of the first noise filter, is detected, and a common of the second frequency band is detected. A second detection ferrite core for inducing a second voltage caused by mode noise; a second amplifier circuit for generating a second feedback current caused by the second voltage induced by the second detection ferrite core; A second feedback filter including a second feedback ferrite core for inducing a second counter electromotive force that suppresses common mode noise in the second frequency band by a second feedback current from the second amplifier circuit; Active noise filter provided.   The first detection ferrite core and the first feedback ferrite core are different from the second detection ferrite core and the second feedback ferrite core in at least one of material, shape, and size. Active noise filter as described. A first bandpass filter disposed on the secondary side of the first detection ferrite core and configured to cut noise that amplifies common mode noise in a first frequency band propagating through the first power line;
A second band-pass filter disposed on the secondary side of the second detection ferrite core for cutting noise that amplifies common mode noise in a second frequency band propagating through the second power line;
The active noise filter according to claim 1, further comprising: The first bandpass filter and the second bandpass filter are:
4. The active noise filter according to claim 3, wherein the active noise filter functions as a passive filter composed of resistance, capacitance and inductance, or an active filter composed of active elements such as an amplifier circuit. A voltmeter that changes due to the magnitude of the common mode noise in the first frequency band, and that measures the first voltage induced in the conducting wire wound around the secondary side of the first detection ferrite core;
A control unit for controlling the impedance value of an element constituting the first amplifier circuit in order to reduce the first voltage;
The active noise filter according to claim 3 or 4, further comprising: The first amplifier circuit includes a first element and a second element,
The control unit increases the impedance of the first element, and as a result,
When the voltmeter determines that the first voltage has increased, the impedance of the first element is reduced, or when the voltmeter determines that the first voltage has decreased, the first voltage is directly unchanged. The active noise filter according to claim 5, wherein the reduced first voltage is further reduced by reducing the impedance of one element.   When the control unit determines that the first voltage that has been decreased increases again during the increase or decrease in the impedance of the first element of the first amplifier circuit, the control unit determines the impedance of the first element. The active noise filter according to claim 6, wherein the increase or decrease is stopped. The first element and the second element that constitute the amplifier circuit according to the noise voltage that is generated by the detection ferrite core that detects the common mode noise that is generated from the electronic device that is the interference source and propagates through the power line. An active noise filter characteristic control method executed by a control device for sequentially controlling impedance,
Monitoring the noise voltage according to the common mode noise detected on the primary side of the detection ferrite core and induced on the secondary side of the detection ferrite core;
Increasing or decreasing the impedance of the first element of the amplifier circuit such that the monitored noise voltage of the common mode noise decreases;
Increasing or decreasing the impedance of the second element of the amplifier circuit such that the noise voltage of the common mode noise obtained by increasing or decreasing the impedance of the first element is further decreased; An active noise filter characteristic control method comprising: