Filter circuit

Abstract

A filter circuit (1) is provided with: a magnetic material core (10) having a hollow hole through which a conductor wire can be inserted; windings (11, 12) wound around the magnetic material core through the hollow hole of the magnetic material core; and a variable impedance part (20) connected to the winding, the impedance of the variable impedance part (20) being variable in accordance with the current or voltage induced from the conductor wire to the winding.

Description

Technical Field

[0001] The present disclosure relates to filter circuits. Background Art

[0002] As a countermeasure against electromagnetic noise propagating in cables (conductor wires) connected to electrical and electronic equipment, a filter circuit is sometimes installed in the cable to suppress the propagation of electromagnetic noise. As this filter circuit, a cylindrical ferrite core that can be installed on the cable later is often used. For example, by passing the cable through the hollow part of the cylindrical ferrite core, the magnetic field from the cable is enhanced, the self-inductance of the cable is increased, and the cable becomes high impedance at high frequencies, thereby cutting off the propagation of electromagnetic noise to the cable.

[0003] However, the additional effect of the ferrite core, that is, the impedance characteristics of the ferrite core, is uniquely determined by physical constants such as the length of the ferrite core, the ratio of the inner diameter to the outer diameter of the tube, and the material properties of the ferrite. Therefore, the methods for obtaining arbitrary impedance characteristics are limited, and it is difficult to cope with cables of multiple types.

[0004] Therefore, for example, Patent Document 1 discloses a device having a structure for defining impedance characteristics by means other than the physical constants of a ferrite core. The noise attenuator of Patent Document 1 is constructed as follows: for a ferrite core installed in a cable that is the object of noise countermeasures, another winding is wound around the cylindrical portion of the ferrite core in a manner that penetrates the hollow portion, and a resistance component is installed in series in the middle of the winding. In addition, the resistance component can also be formed by a variable resistor. By constructing in this way, in an electronic device that is subject to electromagnetic noise interference, an optimal resistance value that can reduce and eliminate noise interference and improve the electromagnetic environment at the installation site can be selected.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: International Publication No. 2011 / 136232 Summary of the invention

[0008] Problem that the invention aims to solve

[0009] In the noise attenuator shown in Patent Document 1, when the optimal resistance value for reducing and removing noise interference is selected, the resistance value is often higher than the characteristic impedance of the cable. Therefore, impedance mismatch in signal transmission may occur at the portion where the ferrite core is installed in the cable. At this time, there is a problem that when the cable is used to transmit a transmission signal such as a digital communication signal or a periodic square wave clock signal, the waveform of the transmission signal is distorted or ringing occurs, resulting in degradation of signal transmission quality.

[0010] An object of the present disclosure is to provide a filter circuit capable of simultaneously suppressing the propagation of electromagnetic noise in a cable and suppressing the degradation of signal transmission quality.

[0011] Means used to solve problems

[0012] The filter circuit disclosed in the present invention comprises: a magnetic material core having a hollow hole through which a conductor wire can be inserted; a winding wound around the magnetic material core through the hollow hole of the magnetic material core; and a variable impedance part connected to the winding, the impedance of which can change according to the current or voltage induced from the conductor wire to the winding.

[0013] Effects of the Invention

[0014] According to the present disclosure, since it is configured as described above, it is possible to simultaneously achieve suppression of propagation of electromagnetic noise in the cable and suppression of degradation of signal transmission quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a diagram showing a configuration example of a filter circuit according to the first embodiment.

[0016] Figure 2 This is a diagram showing a configuration example of a variable impedance unit in the first embodiment.

[0017] Figure 3 This is a diagram showing the electrical connection of the filter circuit according to the first embodiment.

[0018] Figure 4 This is a diagram showing the electrical characteristics of the junction field effect transistor in the first embodiment. DETAILED DESCRIPTION

[0019] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0020] Implementation method 1.

[0021] Figure 1 1 is a diagram showing a configuration example of a filter circuit 1 according to Embodiment 1. Figure 1 As shown, the filter circuit 1 according to the first embodiment includes a magnetic material core 10 , a first winding 11 , a second winding 12 , and a variable impedance unit 20 .

[0022] like Figure 1 As shown, the magnetic core 10 is formed in a cylindrical shape. In addition, a hollow hole is formed in the magnetic core 10, and the first winding 11 and the second winding 12 and a conductor wire (not shown) to be a target of noise countermeasures can be inserted through the hollow hole.

[0023] The first winding 11 and the second winding 12 are wound around the magnetic material core 10 through the hollow hole formed in the magnetic material core 10. In addition, both ends (ends 11a and 11b) of the first winding 11 and both ends (ends 12a and 12b) of the second winding 12 are connected to the variable impedance unit 20, respectively.

[0024] The variable impedance unit 20 is connected to both ends (ends 11a and 11b) of the first winding 11 and both ends (ends 12a and 12b) of the second winding 12. The variable impedance unit 20 is configured so that when a transmission signal such as a digital communication signal or a periodic square wave clock signal is transmitted in the cable, the impedance can be changed according to the current or voltage induced from the cable to the first winding 11 and the second winding 12.

[0025] Figure 2 2 is a diagram showing a configuration example of the variable impedance unit 20 in the first embodiment. Figure 2 As shown, the variable impedance unit 20 is configured to include an element 21 , a peripheral circuit 22 , a winding connection terminal 23 , and a winding connection terminal 24 .

[0026] The element 21 has the following characteristics: when a transmission signal such as a digital communication signal or a periodic square wave clock signal is transmitted in the cable, the impedance can be adaptively changed according to the current or voltage induced from the cable to the first winding 11 and the second winding 12. The element 21 is, for example, a junction field-effect transistor (JFET), which is one of the field effect transistors.

[0027] The peripheral circuit 22 is a circuit for electrically connecting the element 21 to the winding connection terminal 23 and the winding connection terminal 24. The peripheral circuit 22 is configured to include, for example, a resistor 25 and a conductor wiring 26 (see Figure 3 ).

[0028] The winding connection terminal 23 is a terminal connected to the end portions 11a and 11b of the first winding 11. Figure 2 As shown, for example, two winding connection terminals 23 are provided at the corners of the peripheral circuit 22 .

[0029] The winding connection terminal 24 is a terminal connected to the end portions 12a and 12b of the second winding 12. Figure 2 As shown, for example, two winding connection terminals 24 are provided at corners of the peripheral circuit 22 at locations different from the locations where the winding connection terminals 23 are provided.

[0030] In addition, the number of winding connection terminals corresponding to the number of windings may be provided in the peripheral circuit 22. For example, in the first embodiment, two windings are used, and therefore, four winding connection terminals are provided accordingly.

[0031] Next, the electrical connection of the filter circuit 1 according to the first embodiment will be described. Figure 3 1 is a diagram showing electrical connections of the filter circuit 1 according to Embodiment 1. Here, a case where two windings (a first winding 11 and a second winding 12) are used and an N-channel junction field effect transistor is used as the element 21 of the variable impedance unit 20 is described as an example.

[0032] The end portions 11 a and 11 b of the first winding 11 are connected to the two winding connection terminals 23 , respectively.

[0033] In addition, one of the two winding connection terminals 23 (for example, the one connected to the end 11a of the first winding 11) is connected to the drain terminal of the junction field effect transistor 21 via the conductor wiring 26 and the resistor 25. In addition, the other of the two winding connection terminals 23 (for example, the one connected to the end 11b of the first winding 11) is connected to the source terminal of the junction field effect transistor 21 via the conductor wiring 26 and the resistor 25.

[0034] In addition, the two winding connection terminals 23, that is, the drain terminal and the source terminal of the junction field effect transistor 21 are also connected to each other via the conductor wiring 26 and the resistor 25. As a result, the potential difference generated in the first winding 11 is applied as a voltage between the drain terminal and the source terminal of the junction field effect transistor 21. Hereinafter, this voltage is also referred to as "drain-source voltage".

[0035] The two winding connection terminals 24 are connected to the end portions 12 a and 12 b of the second winding 12 , respectively.

[0036] One of the two winding connection terminals 24 (for example, the one connected to the end 12a of the second winding 12) is connected to the gate terminal of the junction field effect transistor 21 via the conductor wiring 26 and the resistor 25. In addition, the other of the two winding connection terminals 24 (for example, the one connected to the end 12b of the second winding 12) is connected to the source terminal of the junction field effect transistor 21 and the other of the two winding connection terminals 23 via the conductor wiring 26 and the resistor 25. As a result, the potential difference generated in the second winding 12 is applied as a voltage between the gate terminal and the source terminal of the junction field effect transistor 21. Hereinafter, this voltage is also referred to as "gate-source voltage".

[0037] Next, an operation example and effects of the filter circuit 1 according to the first embodiment will be described.

[0038] First, the user installs the filter circuit 1 on the cable that is the object of the noise countermeasure. Specifically, the user inserts the cable through the hollow hole of the magnetic material core 10. In addition, the cable is previously assigned the role of transmitting a transmission signal such as a digital communication signal or a periodic square wave clock signal, and not only electromagnetic noise but also the transmission signal is transmitted in the cable.

[0039] Here, when the voltage or current related to the electromagnetic noise or the transmission signal increases, the magnetic field generated from the cable is enhanced in the magnetic material core 10. As a result, a potential difference corresponding to the number of turns of the first winding 11 is generated not only in the first winding 11 wound on the magnetic material core 10, but also in the second winding 12. Therefore, the drain-source voltage and the gate-source voltage are applied to the junction field effect transistor 21.

[0040] here, Figure 4 The electrical characteristics of the junction field effect transistor 21 in the first embodiment are shown. Figure 4 It is the electrical characteristic of a common N-channel junction field effect transistor. Figure 4 In FIG. 1 , the horizontal axis shows the drain-source voltage applied to the junction field effect transistor 21 , and the vertical axis shows the current flowing between the drain terminal and the source terminal of the junction field effect transistor 21 (hereinafter, also simply referred to as “drain current”).

[0041] like Figure 4 As shown, in the junction field effect transistor 21 of the first embodiment, a drain current corresponding to the applied drain-source voltage flows. For example, in the junction field effect transistor 21, when the applied drain-source voltage is increased from 0V, the drain current also increases. However, when the applied drain-source voltage is increased from Figure 4 When the dashed-dotted area shown in FIG. 1 is on the right side, the drain current does not increase even if the drain-source voltage is increased. Figure 4 In FIG. 1 , the area on the left side of the one-dot chain line is called a resistance area, and the area on the right side is called a saturation area.

[0042] Here, in the junction field effect transistor 21, if it is the resistance area on the left side of the single-dot chain line, the value of the drain current can be changed according to the value of the applied drain-source voltage. That is, in the junction field effect transistor 21, if the ratio of the value of the applied drain-source voltage to the value of the drain current is considered as the resistance between the drain terminal and the source terminal (hereinafter also referred to as "drain-source resistance"), then by changing the applied drain-source voltage, the value of the drain-source resistance can be changed within the range of the resistance area.

[0043] In addition, if Figure 4 As shown, the characteristic curve of the drain current can also be changed according to the value of the gate-source voltage applied to the junction field effect transistor 21.

[0044] For example, if the gate-source voltage applied to the junction field effect transistor 21 is 0V, the characteristic curve of the drain current becomes a track as shown by reference numeral 401, and as the gate-source voltage decreases from 0V, the characteristic curve of the drain current changes to tracks as shown by reference numerals 402, 403, and 404. That is, in Embodiment 1, by changing the value of the gate-source voltage applied to the junction field effect transistor 21, the ratio of the value of the drain-source voltage to the value of the drain current, that is, the value of the drain-source resistance, can also be changed within the range of the resistance region. In addition, Figure 4 Reference numeral 405 shows the value of the drain-source resistance when the characteristic curve of the drain current follows the trajectory shown by reference numeral 404 .

[0045] In addition, for example, the characteristic adjustment factor can be adjusted by changing at least one of the type of the junction field effect transistor 21 used, the number of turns of the first winding 11 and the second winding 12, the type of the first winding 11 and the second winding 12, the type of the conductor wiring 26 included in the peripheral circuit 22, and the constant of the resistor 25 included in the peripheral circuit 22 (hereinafter, these are also referred to as "characteristic adjustment factors"). Figure 4 The electrical characteristics of the junction field effect transistor 21 are shown. The variation range when the drain-source resistance value is varied as described above can be appropriately designed by making the above-described adjustments, for example, according to the purpose for which the filter circuit 1 is used.

[0046] Therefore, in the filter circuit 1 of the first embodiment, by utilizing this effect, when the voltage or current related to the transmission signal and electromagnetic noise flowing in the cable increases or decreases, the value of the drain-source resistance of the junction field effect transistor 21 can be changed according to the voltage induced in the first winding 11 and the second winding 12. Therefore, in the filter circuit 1 of the first embodiment, when the voltage or current related to the transmission signal and electromagnetic noise increases or decreases, the resistance value between the two winding connection terminals 23 can be changed in the variable impedance unit 20.

[0047] For example, the user pre-adjusts the above-mentioned characteristic adjustment element so that the drain-source resistance of the junction field effect transistor 21 becomes as small as possible when the voltage or current related to the transmission signal flowing in the cable becomes larger or when the voltage or current related to the electromagnetic noise flowing in the cable becomes smaller. On the other hand, the user pre-adjusts the above-mentioned characteristic adjustment element so that the drain-source resistance of the junction field effect transistor 21 becomes as large as possible when the voltage or current related to the transmission signal flowing in the cable becomes smaller or when the voltage or current related to the electromagnetic noise flowing in the cable becomes larger.

[0048] Therefore, in the filter circuit 1 of embodiment 1, when the voltage or current related to the transmission signal flowing in the cable increases or the voltage or current related to the electromagnetic noise flowing in the cable decreases, the drain-source resistance of the junction field effect transistor 21 decreases, and the impedance of the cable electromagnetically coupled through the magnetic material core 10 becomes low, thereby suppressing the distortion or ringing of the waveform of the transmission signal.

[0049] Furthermore, in the filter circuit 1 of embodiment 1, in addition to the above-mentioned effects, when the voltage or current associated with the transmission signal flowing in the cable becomes smaller or when the voltage or current associated with the electromagnetic noise flowing in the cable becomes larger, the drain-source resistance of the junction field effect transistor 21 becomes larger, and the impedance of the cable electromagnetically coupled through the magnetic material core 10 becomes higher, thereby being able to suppress the propagation of electromagnetic noise of a level lower than the level (intensity) of the transmission signal in the cable.

[0050] Therefore, in Embodiment 1, by installing the filter circuit 1 configured as described above on a cable through which a transmission signal such as a digital communication signal or a clock signal flows, it is possible to suppress not only the distortion or ringing of the waveform of the transmission signal, but also the propagation of electromagnetic noise in the cable. As a result, in Embodiment 1, the effect of suppressing the propagation of electromagnetic noise in a system using a cable equipped with the filter circuit 1 can be improved, and the signal transmission quality of the transmission signal can be improved.

[0051] In addition, in the above description, an example is described in which the winding connection terminals 23 and 24 are provided at the corners of the peripheral circuit 22. However, the location where the winding connection terminals 23 and 24 are provided is not limited to the corners of the peripheral circuit 22. For example, they may be provided at any location of the peripheral circuit 22 according to the winding method of the first winding 11 and the second winding 12 with respect to the magnetic material core 10, etc.

[0052] In addition, in the above description, an example is described in which the filter circuit 1 includes two windings (the first winding 11 and the second winding 12). However, the filter circuit 1 is not limited to this, and may include three or more windings. In this case, the peripheral circuit 22 may be configured to include winding connection terminals of a number corresponding to the number of windings.

[0053] For example, when the filter circuit 1 includes a third winding in addition to the first winding 11 and the second winding 12, the peripheral circuit 22 is configured to include a total of six winding connection terminals. In addition, the six winding connection terminals are connected to any one of the drain terminal, the gate terminal, and the source terminal of the junction field effect transistor 21 via the conductor wiring 26 and the resistor 25 as described above. Thus, in the first embodiment, the magnitude of the drain-source voltage and the gate-source voltage applied to the junction field effect transistor 21 can be adjusted, and as a result, the value of the drain-source resistance can be adjusted.

[0054] In the above description, an example is described in which the element 21 of the variable impedance unit 20 is composed of an N-channel junction field effect transistor. However, the element 21 of the variable impedance unit 20 is not limited to this, and may be composed of a P-channel junction field effect transistor, for example. In this case, Figure 4 The drain current in the electrical characteristics shown decreases as the gate-source voltage applied to the element 21 increases from 0 V. That is, Figure 4 The characteristic curve of the drain current in the illustrated electrical characteristics changes to the loci indicated by reference numerals 402 , 403 , and 404 as the gate-source voltage applied to the element 21 increases from 0 V.

[0055] In the above description, an example is described in which the element 21 of the variable impedance unit 20 is composed of a junction field effect transistor. However, the element 21 of the variable impedance unit 20 is not limited thereto, and may be composed of, for example, a bipolar transistor, a metal-oxide-semiconductor field-effect transistor (MOSFET), or an insulated gate bipolar transistor (IGBT).

[0056] In the above description, an example is described in which the element 21 of the variable impedance section 20 is composed of an N-channel junction field effect transistor and the filter circuit 1 includes two windings (the first winding 11 and the second winding 12). However, when the element 21 of the variable impedance section 20 is composed of an N-channel or P-channel junction field effect transistor, the filter circuit 1 may be configured to omit the second winding 12 and include one winding (the first winding 11).

[0057] In this case, since no gate-source voltage is applied to the element 21 (junction field effect transistor), the user follows Figure 4 The characteristic curve of the drain current shown by reference numeral 401 can be obtained by changing the value of the drain-source resistance.

[0058] For example, the user pre-adjusts the factors after excluding the factors related to the second winding 12 from the above-mentioned characteristic adjustment factors so that the drain-source resistance of the junction field effect transistor 21 becomes as small as possible when the voltage or current related to the transmission signal flowing in the cable becomes larger or the voltage or current related to the electromagnetic noise flowing in the cable becomes smaller. On the other hand, the user pre-adjusts the factors after excluding the factors related to the second winding 12 from the above-mentioned characteristic adjustment factors so that the drain-source resistance of the junction field effect transistor 21 becomes as large as possible when the voltage or current related to the transmission signal flowing in the cable becomes smaller or the voltage or current related to the electromagnetic noise flowing in the cable becomes larger.

[0059] However, in this case, as described above, if the filter circuit 1 is constructed to include two windings (the first winding 11 and the second winding 12) and a gate-source voltage is applied to the element 21, the user can more flexibly change the value of the drain-source resistance, which is preferred.

[0060] On the other hand, when the element 21 of the variable impedance section 20 is composed of other than a junction field effect transistor (for example, when a gate-source voltage or a gate-source current needs to be applied to the element 21 in order to operate the element 21), the filter circuit 1 may be configured to include two windings (a first winding 11 and a second winding 12). In this case, the magnitude of the current or voltage applied to the gate-source of the element 21 is controlled by the current or voltage induced in the second winding 12, thereby controlling the magnitude of the drain current flowing through the element 21.

[0061] As described above, according to the first embodiment, the filter circuit 1 includes: a magnetic material core 10 having a hollow hole through which a conductor line can be inserted; windings 11 and 12 wound around the magnetic material core 10 through the hollow hole of the magnetic material core 10; and a variable impedance unit 20 connected to the windings 11 and 12, the impedance of which can be changed according to the current or voltage induced from the conductor line to the winding. Thus, the filter circuit 1 of the first embodiment can simultaneously suppress the propagation of electromagnetic noise in the cable and suppress the degradation of signal transmission quality.

[0062] Furthermore, the variable impedance unit 20 includes: an element 21 having a characteristic that impedance can be adaptively changed according to the current or voltage induced from the conductor line to the windings 11 and 12; a conductor wiring 26 connecting the element 21 to both ends of the windings 11 and 12; and a resistor 25 connected to the conductor wiring 26, and the impedance of the variable impedance unit 20 changes according to at least one of the type of the element 21, the number of turns of the windings 11 and 12, the type of the windings 11 and 12, the type of the conductor wiring 26, and the constant of the resistor 25. Thus, the filter circuit 1 of the first embodiment can appropriately adjust the impedance of the cable, and can easily achieve both the suppression of the propagation of electromagnetic noise in the cable and the suppression of the degradation of the signal transmission quality.

[0063] In addition, the element 21 is a junction field effect transistor, the winding includes a first winding 11, one end 11a of the first winding 11 is connected to the drain terminal of the junction field effect transistor, and the other end 11b of the first winding 11 is connected to the source terminal of the junction field effect transistor, and the impedance of the variable impedance unit 20 is equivalent to the ratio of the voltage generated between the drain and source of the junction field effect transistor and the current flowing between the drain and source of the junction field effect transistor when the current or voltage is induced from the conductor line to the first winding 11. Thus, the filter circuit 1 of the first embodiment can achieve the suppression of the propagation of electromagnetic noise in the cable and the suppression of the degradation of signal transmission quality at the same time with a simple structure.

[0064] Furthermore, the winding includes a second winding 12, one end 12a of the second winding 12 is connected to the gate terminal of the junction field effect transistor, and the other end 12b of the second winding 12 is connected to the source terminal of the junction field effect transistor, and the impedance of the variable impedance unit 20 changes according to the voltage generated between the gate and the source of the junction field effect transistor when a current or voltage is induced from the conductor line to the second winding 12. Thus, the filter circuit 1 of the first embodiment can flexibly adjust the impedance of the cable, and can easily achieve both the suppression of the propagation of electromagnetic noise in the cable and the suppression of the degradation of the signal transmission quality.

[0065] In addition, the present disclosure can modify arbitrary components of each embodiment, or can omit arbitrary components in each embodiment.

[0066] Industrial Applicability

[0067] The present disclosure can simultaneously suppress the propagation of electromagnetic noise in a cable and suppress the degradation of signal transmission quality, and is suitable for use in a filter circuit.

[0068] Description of Reference Numerals

[0069] 1 filter circuit, 10 magnetic material core, 11 first winding, 11a end, 11b end, 12 second winding, 12a end, 12b end, 20 variable impedance part, 21 element (junction field effect transistor), 22 peripheral circuit, 23 winding connection terminal, 24 winding connection terminal, 25 resistor, 26 conductor wiring, 401 to 404 characteristic curves of drain current, 405 value of drain-source resistance.

Claims

1. A filter circuit, wherein: The filter circuit comprises: A magnetic material core having a hollow hole through which a conductor wire can be inserted; a winding passing through a hollow hole of the magnetic material core and wound around the magnetic material core; and A variable impedance unit is connected to the winding, and the impedance of the variable impedance unit can be changed according to the current or voltage induced from the conductor line to the winding.

2. The filter circuit according to claim 1, characterized in that: The variable impedance unit comprises: an element having a characteristic that impedance can be adaptively changed according to a current or a voltage induced from the conductor line to the winding; Conductor wiring connecting the element to both ends of the winding; as well as a resistor connected with the conductor wiring, The impedance of the variable impedance unit changes according to at least one of the type of the element, the number of turns of the winding, the type of the winding, the type of the conductor wiring, and the constant of the resistor.

3. The filter circuit according to claim 2, characterized in that: The element is a junction field effect transistor, The winding comprises a first winding, One end of the first winding is connected to the drain terminal of the junction field effect transistor. The other end of the first winding is connected to the source terminal of the junction field effect transistor. The impedance of the variable impedance section corresponds to a ratio of a voltage generated between a drain and a source of the junction field effect transistor and a current flowing between a drain and a source of the junction field effect transistor when a current or a voltage is induced from the conductor line to the first winding.

4. The filter circuit according to claim 3, characterized in that: The winding includes a second winding, One end of the second winding is connected to the gate terminal of the junction field effect transistor. The other end of the second winding is connected to the source terminal of the junction field effect transistor. The impedance of the variable impedance section changes according to a voltage generated between a gate and a source of the junction field effect transistor when a current or a voltage is induced from the conductor line to the second winding.

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