JP2016165081A - Noise filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a noise filter capable of flexibly corresponding to a resonance frequency and effectively reducing a noise in the resonance frequency, even when a resonance frequency is changed, the resonance frequency being caused by a floating capacitance due to a differential transmission cable and a common mode inductance of a common mode choke coil.SOLUTION: A noise filter 1 includes: a common mode choke coil 10 having a first coil 101 and a second coil 102; a first LC series resistance circuit 21 connected between one end of the first coil 101 and the ground; and a second LC series resistance circuit 22 connected between one end of the second coil 102 and the ground. Constants of coils 213, 224 and capacitors 211, 222 configuring the first LC series resonance circuit 21 and the second LC series resonance circuit 22 are set according to the resonance frequency of the resonance caused by a common mode inductance of the common mode choke coil 10 and a floating capacitance 51 formed between a differential transmission cable 50 and the ground.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a noise filter, and more particularly to a noise filter using a common mode choke coil.

  Conventionally, for example, a common mode choke coil has been used to remove common mode noise on a pair of differential transmission lines for transmitting signals. Here, Patent Document 1 discloses a common mode noise filter including a common mode choke coil connected to a differential transmission line and an LC series resonance circuit connected between each differential transmission line and the ground. Has been.

  According to this common mode noise filter, the LC series resonance circuit can cause series resonance between the ground in a specific band, so that the attenuation of common mode noise and differential mode noise is increased in the specific resonance frequency band. be able to.

JP 2014-53765 A

  However, in the above-described common mode noise filter of Patent Document 1, the resonance frequency of resonance that can be caused by the common mode noise filter (common mode choke coil) being interposed is different from the resonance frequency of the LC series resonance circuit. In such a case, a large current flows through the differential transmission line at a resonance frequency of resonance that may occur when the common mode noise filter is interposed, which may increase noise.

  In particular, for example, by changing the routing of a cable (differential transmission cable) connecting a plurality of controllers (between communication ICs), the stray capacitance formed between the cable and the ground changes, and the floating When the resonance frequency of resonance due to the capacitance and the common mode inductance of the common mode choke coil changes, the common mode noise filter of Patent Document 1 cannot reduce noise corresponding to the change of the resonance frequency. .

  The present invention has been made to solve the above problems, and can flexibly cope with a change in resonance resonance frequency due to stray capacitance due to a differential transmission cable and common mode inductance of a common mode choke coil. An object of the present invention is to provide a noise filter capable of effectively reducing noise at the resonance frequency.

  The noise filter according to the present invention includes a common mode choke coil having a pair of first and second coils, a first resonance circuit connected between one end of the first coil and the ground, and one end of the second coil. And a second resonance circuit connected between the first resonance circuit and the ground, the resonance frequencies of the first resonance circuit and the second resonance circuit are connected to the common mode inductance of the common mode choke coil and the common mode choke coil. It is characterized in that it is set in accordance with the resonance frequency of resonance caused by the stray capacitance formed between the differential transmission cable and the ground.

  According to the noise filter of the present invention, the resonance frequency of the first resonance circuit and the second resonance circuit is such that the common mode inductance of the common mode choke coil, the differential transmission cable connected to the common mode choke coil, and the ground Is set in accordance with the resonance frequency of resonance caused by stray capacitance formed between the two. Therefore, the first resonance circuit and the second resonance circuit also resonate at the resonance frequency of resonance caused by the stray capacitance due to the differential transmission cable and the common mode inductance of the common mode choke coil, and the first resonance circuit and the second resonance circuit. Impedance decreases. Therefore, a large current flowing in the differential transmission cable at the resonance frequency is caused to flow (dropped) to the ground through the first resonance circuit and the second resonance circuit, thereby preventing a large current from flowing in the differential transmission cable. The As a result, even if the resonance frequency of the resonance due to the stray capacitance due to the differential transmission cable and the common mode inductance of the common mode choke coil changes, it is possible to respond flexibly and effectively reduce noise at the resonance frequency. It becomes.

  In the noise filter according to the present invention, each of the first resonance circuit and the second resonance circuit is preferably an LC series resonance circuit having a coil and a capacitor connected in series to the coil.

  If it does in this way, each of the 1st resonance circuit and the 2nd resonance circuit can be constituted using LC series resonance circuit which has a coil and a capacitor connected in series to the coil.

  In the noise filter according to the present invention, the constants of the coil and the capacitor constituting each of the first resonance circuit and the second resonance circuit are the common mode inductance of the common mode choke coil and the differential transmission connected to the common mode choke coil. It is preferable to set according to the resonance frequency of the resonance caused by the stray capacitance formed between the cable and the ground.

  In this way, by adjusting the constants of the coils and capacitors constituting the first resonance circuit and the second resonance circuit, respectively, the resonance frequencies of the first resonance circuit and the second resonance circuit are set to the common mode choke coil. The resonance frequency of resonance due to the common mode inductance and the stray capacitance formed between the differential transmission cable connected to the common mode choke coil and the ground.

  In the noise filter according to the present invention, the common mode choke coil is interposed between the CAN transceiver constituting the communication network of the vehicle and the differential transmission cable, and the resonance frequencies of the first resonance circuit and the second resonance circuit, respectively. Is preferably set in accordance with the resonance frequency of resonance due to the common mode inductance of the common mode choke coil and the stray capacitance formed between the differential transmission cable and the vehicle ground.

  In this way, it is possible to effectively reduce noise in a circuit including a CAN (Controller / Car Area Network) transceiver and a differential transmission cable connected to the CAN transceiver, which is mounted on the vehicle. In particular, even when the resonance frequency changes depending on how the differential transmission cables are arranged, it is possible to respond flexibly.

  In the noise filter according to the present invention, one end of the first coil and one end of the second coil are connected to a pair of differential transmission cables, and the other end of the first coil and the other end of the second coil are each CAN. Preferably, it is connected to a transceiver.

  In this way, since the first resonance circuit and the second resonance circuit are connected between the common mode coke coil and the differential transmission cable, noise can be reduced more effectively.

  In the noise filter according to the present invention, the resonance frequency of each of the first resonance circuit and the second resonance circuit is measured, the common mode inductance of the common mode choke coil, and the differential transmission cable connected to the common mode choke coil It is preferable to set according to the measured value of the resonance frequency of resonance caused by the stray capacitance formed between the ground and the ground.

  In this case, the resonance frequencies of the first resonance circuit and the second resonance circuit are set based on the actually measured resonance frequencies of the resonance due to the stray capacitance due to the differential transmission cable and the common mode inductance of the common mode choke coil. Is done. Therefore, even if the resonant frequency of resonance due to the stray capacitance due to the differential transmission cable and the common mode inductance of the common mode choke coil changes, it is possible to flexibly and appropriately take measures against noise.

  According to the present invention, even if the resonance frequency of the resonance due to the stray capacitance due to the differential transmission cable and the common mode inductance of the common mode choke coil changes, it is possible to respond flexibly and effectively reduce noise at the resonance frequency. It becomes possible.

It is a circuit diagram which shows the structure of the noise filter which concerns on embodiment. It is a figure showing an example at the time of applying a noise filter concerning an embodiment to a CAN bus. It is a graph which shows the measurement result of the radiation noise at the time of using the common mode choke coil which does not have LC series resonance circuit. It is a graph which shows the measurement result of the radiation noise at the time of using the noise filter which concerns on embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals are used for the same or corresponding parts. Moreover, in each figure, the same code | symbol is attached | subjected to the same element and the overlapping description is abbreviate | omitted.

  First, the configuration of the noise filter 1 according to the embodiment will be described using FIG. 1 and FIG. 2 together. FIG. 1 is a circuit diagram showing the configuration of the noise filter 1. FIG. 2 is a diagram illustrating an example (example) when the noise filter 1 is applied to a CAN bus.

  The noise filter 1 includes a common mode choke coil 10 having a pair of a first coil 101 and a second coil 102, a first LC series resonance circuit 21 connected between one end of the first coil 101 and the ground, and a second A second LC series resonance circuit 22 connected between one end of the coil 102 and the ground is provided. In addition, as the common mode choke coil 10, for example, a well-known winding type common mode choke coil or a laminated common mode choke coil can be suitably used.

  Each of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 is an LC series resonance circuit having coils 213 and 224 and capacitors 211 and 222 connected in series to the coils 213 and 224. More specifically, the first LC series resonance circuit 21 is an LC series resonance circuit including a third coil 213 and a first capacitor 211 connected in series with the third coil 213. Similarly, the second LC series resonance circuit 22 is an LC series resonance circuit having a fourth coil 224 and a second capacitor 222 connected in series with the fourth coil 224.

  The resonance frequencies of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 are the common mode inductance of the common mode choke coil 10, one end of the common mode choke coil 10, that is, one end of the first coil 101 and the second resonance frequency. It is set in accordance with the resonance frequency of LC resonance by a pair of differential transmission cables 50 connected to one end of the coil 102 and the stray capacitance 51 formed between the grounds.

  That is, the constants (values) of the third coil 213 and the first capacitor 211 constituting the first LC series resonance circuit 21 and the constants (values) of the fourth coil 224 and the second capacitor 222 constituting the second LC series resonance circuit 22. Is the resonance frequency of LC resonance due to the common mode inductance of the common mode choke coil 10 and the stray capacitance 51 formed between the pair of differential transmission cables 50 connected to the common mode choke coil 10 and the ground. They are set together (to match).

  At that time, the resonance frequency of each of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 is obtained by actually measuring the common mode inductance of the common mode choke coil 10, the pair of differential transmission cables 50, and the ground. It is set in accordance with the resonance frequency (measured value) of the LC resonance caused by the stray capacitance 51 formed therebetween.

Here, if the value of the resonance frequency f ₀ is obtained by measurement, the constants (inductance L and capacitance C) of the third coil 213 and the first capacitor 211 constituting the first LC series resonance circuit 21, and the second LC Constants (inductance L and capacitance C) of the fourth coil 224 and the second capacitor 222 constituting the series resonance circuit 22 can be set based on the following equation (1).
f ₀ = 1 / 2π√LC (1)

  By the way, the noise filter 1 according to the present embodiment can be suitably applied to, for example, a vehicle-mounted CAN (Controller Area Network) bus constituting a vehicle communication network. Here, an example (example) when the noise filter 1 is applied to an in-vehicle CAN bus is shown in FIG. In this case, the other end of the first coil 101 and the other end of the second coil 102 constituting the common mode choke coil 10 are connected to the CAN transceiver 30. That is, the noise filter 1 is interposed between the CAN transceiver 30 and the pair of differential transmission cables 50.

  In this case, the resonance frequency of each of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 includes the common mode inductance of the common mode choke coil 10, the pair of differential transmission cables 50, and the vehicle ground (vehicle body). Are set in accordance with the resonance frequency of the LC resonance caused by the stray capacitance 51 formed between the two.

  With this configuration, according to this embodiment (or example), the common mode inductance of the common mode choke coil 10 and the stray capacitance formed between the pair of differential transmission cables 50 and the ground. 51, the first LC series resonance circuit 21 and the second LC series resonance circuit 22 also resonate, and the impedance of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 decreases. Therefore, a large current flowing in the differential transmission cable 50 at the resonance frequency is caused to flow (drop) to the ground through the first LC series resonance circuit 21 and the second LC series resonance circuit 22, thereby causing a large current in the differential transmission cable 50. Is prevented from flowing.

  Therefore, in order to confirm the noise reduction effect of the noise filter 1 according to the present embodiment, radiation noise was measured using a CAN evaluation board. Subsequently, the noise reduction effect of the noise filter 1 according to the present embodiment will be described with reference to FIGS.

  The measurement system shown in FIG. 2 described above was used for measurement of radiation noise. That is, as described above, FT-CAN (Fault Tolerant CAN) for in-vehicle use is used as an interface of the differential transmission line. Then, a 50 kHz pulse signal is input from the signal generator to the CAN transceiver 30 corresponding to FT-CAN, and the radiated noise in a state where the CAN signal output at that time is transmitted to the pair of differential transmission cables 50 is detected. It was measured. In this case, the pair of differential transmission cables 50 serve as antennas to radiate noise.

  Noise measurement was performed using an anechoic chamber, and radiated noise was measured in a measurement environment (conditions) based on CISPR25, which is an emission standard for in-vehicle devices. That is, the differential transmission cable 50 was lifted 5 cm from the grounded copper plate of the measurement system, and the tip was an open end. Further, for the common mode choke coil 10, “DLW43SH510XK2” manufactured by Murata Manufacturing Co., Ltd. was used.

  The measurement results of radiation noise are shown in FIGS. Here, the horizontal axis of FIGS. 3 and 4 is the frequency (MHz), and the vertical axis is the noise level (dBμV / m). FIG. 3 also shows a case of a short circuit, that is, a case where neither the common mode choke coil 10 nor the noise filter 1 of the present embodiment is connected (Comparative Example 1), and no LC series resonance circuits 21 and 22. The measurement result of the radiation noise when only the common mode choke coil 10 is applied (Comparative Example 2) is shown. On the other hand, FIG. 4 shows measurement results of radiation noise in the case of the short circuit and when the noise filter 1 according to the present embodiment is applied.

  In FIG. 3, the measurement result in the case of the short circuit (Comparative Example 1) is indicated by a thick gray line, and only the common mode choke coil 10 having no LC series resonance circuits 21 and 22 is applied (Comparative Example 2). The measurement results are shown by black thin lines. On the other hand, in FIG. 4, the measurement result in the case of the short circuit (Comparative Example 1) is shown by a gray thick line, and the measurement result when the noise filter 1 according to the present embodiment is applied is shown by a black thin line.

  As shown in FIG. 3, when only the common mode choke coil 10 that does not have the LC series resonance circuits 21 and 22 is applied (Comparative Example 2), the short circuit (that is, the common mode choke coil 10 is also the noise filter 1). The noise level in the vicinity of 3 MHz, which is the resonance frequency, was higher compared to (Comparative Example 1).

  On the other hand, as shown in FIG. 4, when the noise filter 1 according to this embodiment is applied, only the common mode choke coil 10 that does not have the LC series resonance circuits 21 and 22 described above is applied. Compared with the case (Comparative Example 2), it was confirmed that the noise level in the vicinity of the resonance frequency of 3 MHz can be reduced by about 28 dB.

  As described above in detail, according to the present embodiment, the resonance frequencies of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 are equal to the common mode inductance of the common mode choke coil 10 and the common mode choke coil. 10 is set in accordance with the resonance frequency of the LC resonance caused by the pair of differential transmission cables 50 connected to 10 and the stray capacitance 51 formed between the ground. Therefore, the first LC series resonance circuit 21 and the second LC series resonance circuit 22 also resonate at the resonance frequency of resonance caused by the stray capacitance due to the differential transmission cable 50 and the common mode inductance of the common mode choke coil 10, and the first LC series resonance occurs. The impedances of the resonance circuit 21 and the second LC series resonance circuit 22 are lowered. Therefore, a large current flowing in the differential transmission cable 50 at the resonance frequency is caused to flow (drop) to the ground through the first LC series resonance circuit 21 and the second LC series resonance circuit 22, thereby causing a large current in the differential transmission cable 50. Is prevented from flowing. As a result, even if the resonance frequency of the resonance due to the stray capacitance due to the differential transmission cable 50 and the common mode inductance of the common mode choke coil 10 changes, it is possible to respond flexibly and effectively reduce noise at the resonance frequency. It becomes possible.

  Further, according to the present embodiment, by adjusting the constants (inductance L and capacitance C) of the coils 213 and 224 and the capacitors 211 and 222 constituting the first LC series resonance circuit 21 and the second LC series resonance circuit 22, respectively. The resonance frequency of each of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 is set to the common mode inductance of the common mode choke coil 10, the stray capacitance 51 formed between the pair of differential transmission cables 50 and the ground. It can be matched (matched) with the resonance frequency of LC resonance.

  At that time, according to the present embodiment, based on the actually measured actual value of the resonance frequency of the resonance caused by the stray capacitance by the differential transmission cable 50 and the common mode inductance of the common mode choke coil 10. The resonance frequency of each of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 is set. Therefore, for example, even if the stray capacitance 51 changes due to the handling of the differential transmission cable 50 and the resonance frequency of resonance due to the stray capacitance 51 due to the differential transmission cable 50 and the common mode inductance of the common mode choke coil 10 changes. It becomes possible to take noise countermeasures flexibly and appropriately.

  Further, according to the present embodiment (example), it is possible to effectively reduce noise of a circuit including the CAN transceiver 30 mounted on the vehicle and the pair of differential transmission cables 50 connected to the CAN transceiver 30. Can do. In particular, even if the stray capacitance 51 formed between the ground (vehicle body) of the vehicle changes depending on how the differential transmission cable 50 is arranged and the resonance frequency changes, it is possible to respond flexibly. Can do. According to the present embodiment, noise can be reduced particularly effectively in a system such as FT-CAN that has a high characteristic impedance of the signal system and is difficult to obtain the effect of the common mode choke coil alone.

  Although the embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the case where the present invention is applied to an in-vehicle CAN bus has been described as an example. However, the scope of application of the present invention is not limited to an in-vehicle CAN bus, and for example, a CAN bus used in an industrial machine. The present invention can also be suitably applied to communication lines and the like.

  In the above embodiment, the LC series resonance circuit is used as the resonance circuit, but other types of resonance circuits may be used. Each of the first LC series resonance circuit 21 and the second LC series resonance circuit 22 may be connected to the other end side of the common mode choke coil 10 (first coil 101, second coil 102).

DESCRIPTION OF SYMBOLS 1 Noise filter 10 Common mode choke coil 101 1st coil 102 2nd coil 21 1st LC series resonance circuit 22 2nd LC series resonance circuit 213 3rd coil 224 4th coil 211 1st capacitor 222 2nd capacitor 30 CAN transceiver 50 Differential Transmission cable 51 Floating capacitance

Claims (6)

A common mode choke coil having a pair of first and second coils;
A first resonant circuit connected between one end of the first coil and the ground;
A second resonance circuit connected between one end of the second coil and the ground,
The resonance frequencies of the first resonance circuit and the second resonance circuit are the common mode inductance of the common mode choke coil, and the stray capacitance formed between the differential transmission cable connected to the common mode choke coil and the ground. A noise filter characterized by being set according to a resonance frequency of resonance caused by.   2. The noise filter according to claim 1, wherein each of the first resonance circuit and the second resonance circuit is an LC series resonance circuit including a coil and a capacitor connected in series to the coil.   The constants of the coil and the capacitor constituting each of the first resonance circuit and the second resonance circuit are a common mode inductance of the common mode choke coil, a differential transmission cable connected to the common mode choke coil, and a ground. The noise filter according to claim 2, wherein the noise filter is set in accordance with a resonance frequency of resonance caused by a stray capacitance formed therebetween. The common mode choke coil is interposed between a CAN transceiver constituting a vehicle communication network and the differential transmission cable,
The resonance frequency of each of the first resonance circuit and the second resonance circuit is a resonance resonance caused by a common mode inductance of the common mode choke coil and a stray capacitance formed between the differential transmission cable and a vehicle ground. The noise filter according to claim 1, wherein the noise filter is set according to a frequency. One end of the first coil and one end of the second coil are connected to a pair of the differential transmission cables,
The noise filter according to claim 4, wherein the other end of the first coil and the other end of the second coil are connected to the CAN transceiver. The resonance frequency of each of the first resonance circuit and the second resonance circuit is measured between the common mode inductance of the common mode choke coil and the differential transmission cable connected to the common mode choke coil and the ground. The noise filter according to claim 1, wherein the noise filter is set in accordance with an actual measurement value of a resonance frequency of resonance caused by a stray capacitance formed in the filter.

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