JP2018191039A - Mounting structure of common mode filter - Google Patents

Abstract

An object of the present invention is to provide a mounting structure of a common mode filter capable of removing common mode noise in a low frequency band generated in a clock signal line in high-speed data communication. A mounting structure of a common mode filter according to the present invention includes first and second common mode filters 2 and 4 and a plurality of coils built in each of the first and second common mode filters 2 and 4. 7 and 8, the clock signal line 1 connected to the first common mode filter 2, and the data signal line 3 connected to the second common mode filter 4 and independent of the clock signal line 1. The first common mode filter 2 and the second common mode filter 4 have different structures or use different materials. [Selection] Figure 1

Description

  The present invention relates to a small and thin common mode filter mounting structure used in various electronic devices such as digital devices, AV devices, and information communication terminals.

  In the conventional mounting structure of this type of common mode filter, the common mode filter is connected to each of the clock signal line and the data signal line.

  As a prior art document related to the invention of this application, for example, Patent Document 1 is known.

JP 2005-302810 A

  In high-speed data communication of a differential method such as HDMI (registered trademark), the data transfer speed is increasing rapidly. In the common mode filter used for such a data interface, it is necessary to reduce the loss so as not to deteriorate the differential signal to be accelerated.

  However, a common mode filter with a low loss with respect to such a differential mode reduces stray capacitance parasitic to the coil by reducing the number of turns of the coil or reducing the dielectric constant around the coil in order to reduce the loss of the coil. Although it is reduced, the self-resonance frequency of the inductor when operating as an inductor to remove common mode noise and shifting noise shifts to the high frequency side. Since the coil impedance tends to be low, noise in the low frequency region is difficult to remove.

  On the other hand, for example, in the case of HDMI (High-Definition Multimedia Interface), data is transferred at an ultra-high-speed transmission rate of about 6 Gbps. The clock frequency of the clock signal line running in parallel with the data signal line is 148 MHz. Since it is low, this harmonic often occurs as noise in a low frequency band of 1 GHz or less.

  As a result, in high-speed data communication, when the above-described low-loss common mode filter is simply connected to the clock signal line and the data signal line, the low-frequency common mode noise generated in the clock signal line cannot be removed. The problem arises.

  The present invention solves the above-described conventional problems, and removes low-frequency common mode noise generated in the clock signal line while maintaining the signal quality of the differential data line in the differential data communication interface which is increased in speed. It is an object to provide a mounting structure of a common mode filter that can be used.

The mounting structure of the common mode filter according to the first aspect includes first and second common mode filters, and a plurality of coils built in each of the first and second common mode filters. A clock signal line connected to one common mode filter, and a data signal line connected to the second common mode filter and independent of the clock signal line, the first common mode filter and the second common mode filter. Common mode filters have different structures or use different materials.

  In the mounting structure of the common mode filter according to the second aspect, in the first aspect, the resonance frequency in the frequency characteristic of the common mode noise attenuation amount of the first common mode filter is set as the resonance frequency of the second common mode filter. Lower than the frequency.

  In the mounting structure of the common mode filter according to the third aspect, in the first aspect, the cutoff frequency in the differential mode of the first common mode filter is lower than the cutoff frequency of the second common mode filter. did.

  In the mounting structure of the common mode filter according to the fourth aspect, in the first aspect, the dielectric constant around the coil formed in the first common mode filter is formed in the second common mode filter. It was made larger than the periphery of the coil.

  In the mounting structure of the common mode filter according to the fifth aspect, in the first aspect, the length of the coil formed in the first common mode filter is set to the length of the coil formed in the second common mode filter. It was longer than the length of the coil.

  In the mounting structure of the common mode filter according to the sixth aspect, in the third aspect, the data interface consisting of the clock signal line and the data signal line is HDMI (registered trademark), and the clock signal is cut with respect to the differential mode. The off frequency was 1 GHz or more.

  In the mounting structure of the common mode filter according to the seventh aspect, in the first aspect, a low-pass filter is used instead of the first common mode filter.

  In the mounting structure of the common mode filter according to the eighth aspect, in the first aspect, the group delay characteristic for the differential mode of the first common mode filter is substantially the same as the group delay characteristic of the second common mode filter. It was equal.

  In high-speed data communication, common mode noise in the low frequency band generated in the clock signal line can be removed.

The figure which shows the mounting structure of the common mode filter in one embodiment of this invention Cross section of the common mode filter Perspective view of the common mode filter The figure which shows the frequency characteristic of the attenuation amount of the common mode noise in the clock signal line and the data signal line in the mounting structure of the common mode filter The figure which shows the frequency characteristic of the insertion loss of the differential signal in the clock signal line and the data signal line in the mounting structure of the common mode filter

  FIG. 1 is a diagram showing a mounting structure of a common mode filter according to an embodiment of the present invention, FIG. 2 is a sectional view of the common mode filter, and FIG. 3 is a perspective view of the common mode filter.

As shown in FIG. 1, the common mode filter mounting structure according to the embodiment of the present invention includes a clock signal line 1 to which a first common mode filter 2 is connected, and is independent from the clock signal line 1. A second common mode filter 4 is connected to the data signal line 3.

  A second common mode filter 4 is formed for each of the three data signal lines 3. The data signal line 3 is not necessarily limited to three.

  The transmission lines of the clock signal line 1 and the data signal line 3 each have a pair of transmission lines, and between the transmission side IC 5 and the reception side IC 6 in the HDMI (registered trademark) interface used for high-speed communication. It is connected.

  As shown in FIGS. 2 and 3, the first and second common mode filters 2 and 4 include first and second coils 7 and 8 that are magnetically coupled to each other and the first and second coils, respectively. 7 and 8 and a first to fourth external electrodes 10a, 10b, 10c, and 10d connected to both ends of the first and second coils 7 and 8, respectively.

  The first to fourth external electrodes 10a, 10b, 10c, and 10d are connected to two transmission lines of the clock signal line 1 or the data signal line 3, respectively.

  Further, the periphery of the first and second coils 7 and 8 is covered with a nonmagnetic material 11, and the dielectric constant of the nonmagnetic material 11 in the first common mode filter 2 is determined by the second common mode filter 4. It is larger than the dielectric constant of the nonmagnetic material 11 in FIG. The dielectric constant is changed by changing the material of the nonmagnetic material 11.

  Therefore, when common mode noise enters, the resonance frequency of the common mode noise attenuation amount of the first common mode filter 2 becomes lower than the resonance frequency of the second common mode filter 4, and the first common mode filter 2 The cutoff frequency of the mode filter 2 is lower than the cutoff frequency for the differential mode of the second common mode filter 4.

  The lengths of the first and second coils 7 and 8 in the first common mode filter 2 are longer than the lengths of the first and second coils 7 and 8 in the second common mode filter 4. The resonance frequency in the frequency characteristic of the common mode noise attenuation amount of the first common mode filter 2 may be lower than the resonance frequency of the second common mode filter 4.

  The lengths of the first and second coils 7 and 8 are changed, for example, by changing the number of turns.

  The plurality of second common mode filters 4 connected to the data signal line 3 all have the same dielectric constant, and the lengths of the first and second coils 7 and 8 are also the same.

  At this time, the cutoff frequency of the clock signal is set to 1 GHz or more. In HDMI (registered trademark), it is necessary to perform a TDR (Time Domain Reflectometry) test in the same differential mode as that of the data signal line 3 even on the clock signal line 1. Accordingly, it is necessary to satisfy that the characteristic impedance of the differential mode is within the HDMI (registered trademark) standard. By ensuring a cutoff frequency of 1 GHz or more in the differential mode, the differential mode can be used in the TDR test. Characteristic impedance matching can be ensured.

  Here, the cut-off frequency is a frequency at which the insertion loss in the differential mode is attenuated by 3 dB.

  Note that a low-pass filter may be used instead of the first common mode filter 2 connected to the clock signal line 1. All noises in the common mode, differential mode, and normal mode that occur in the clock signal line 1 that is equal to or higher than the cutoff frequency of the low-pass filter can be removed.

  Further, the group delay characteristic of the first common mode filter 2 with respect to the differential mode may be substantially equal to the group delay characteristic of the second common mode filter 4. There is no timing shift in the waveform after the output of the differential signal by the first common mode filter 2 and the second common mode filter 4.

  The group delay characteristic in the differential mode is a characteristic related to the transit time from the input to the output of the differential signal input to the common mode filter.

  There are various interfaces in the high-speed transmission system in the differential mode, but when a clock recovery circuit is essential on the receiving device side for connection between devices such as HDMI (registered trademark), the clock signal line 1 and The group delays in the differential mode of the common mode noise filter of the data signal line 3 need not be the same.

  However, when the clock recovery circuit is not mounted on the receiving side for in-device connection like MIPI, it is necessary to make the group delay characteristics of the differential mode the same.

  Since the group delay characteristic of the differential mode depends on the length of the built-in coil and the dielectric constant around the coil, the first and second coils in the first common mode filter 2 and the second common mode filter 4 It is necessary to adjust the lengths of 7 and 8 and the dielectric constant around the coil.

  As described above, in the mounting structure of the common mode noise filter according to the embodiment of the present invention, the clock signal line 1 connected to the first common mode filter 2 and the second common mode filter 4 are connected. The clock signal line 1 and the independent data signal line 3 are provided, and the first common mode filter 2 and the second common mode filter 4 are configured such that the dielectric constant of the nonmagnetic material 11 is different, or the coil 7, The length of 8 is different.

  As a result, the resonance frequency in the frequency characteristic of the common mode noise attenuation amount of the first common mode filter 2 can be made lower than the resonance frequency of the second common mode filter 4, so that the low frequency generated in the clock signal line 1 can be reduced. The effect that the common mode noise of a frequency band can be removed is acquired.

  In addition, since the cutoff frequency of the differential mode of the first common mode filter 2 can be made lower than the cutoff frequency of the second common mode filter 4, the differential in the high frequency region of the clock signal line 1 is possible. Mode and normal mode noise can also be removed.

  Here, FIG. 4 is a diagram showing frequency characteristics of the attenuation amount of the common mode noise in the clock signal line and the data signal line in the mounting structure of the common mode filter according to the embodiment of the present invention.

  As is clear from FIG. 4, the common mode filter in the clock signal line 1 can remove common mode noise in a lower frequency band than the data signal line 3.

FIG. 5 is a diagram showing frequency characteristics of differential mode insertion loss in the clock signal line and the data signal line in the common mode filter mounting structure according to the embodiment of the present invention.

  As is apparent from FIG. 5, the common mode filter in the clock signal line 1 has a lower cutoff frequency in the differential mode than the data signal line 3.

  In the above embodiment, the first and second common mode filters 2 and 4 are each provided with a pair of first and second coils 7 and 8, but two or more sets of the first common mode filters 2 and 4 are provided. Alternatively, an array type having the second coils 7 and 8 may be used.

  Moreover, what provided the magnetic core which penetrates a coil inside the coil of the 1st, 2nd common mode filter 2 and 4 may be used. In this case, even if the length of the coil is short, the magnetic core can increase the impedance of the first and second coils 7 and 8 incorporated when the inductor operates against common mode noise.

  A ground electrode may be formed on the first common mode filter 2 connected to the clock signal line 1. When common mode noise enters due to stray capacitance components between the ground electrode and the first and second coils 7 and 8, an action of bypassing the common mode noise to the ground occurs in the high frequency region. Common mode noise can be reduced over a wide frequency band.

  Further, when the common mode noise generation from the clock signal line 1 is largely dominant as compared with the common mode noise from the data signal line 3, the first common mode filter 2 is connected only to the clock signal line 1. The second common mode filter 4 may not be connected to the data signal line 3.

  The mounting structure of the common mode filter according to the present invention has an effect of removing common mode noise in the low frequency band generated in the clock signal line in high-speed data communication, and in particular, digital equipment and AV equipment. It is useful in a small and thin common mode filter used for information communication terminals and the like.

DESCRIPTION OF SYMBOLS 1 Clock signal line 2 1st common mode filter 3 Data signal line 4 2nd common mode filter 7, 8 1st, 2nd coil

Claims (8)

A clock signal line having first and second common mode filters and a plurality of coils built in each of the first and second common mode filters, and connected to the first common mode filter; The first common mode filter and the second common mode filter are connected to the second common mode filter and include a data signal line independent from the clock signal line, and the first common mode filter and the second common mode filter have different structures or different materials. Mounting structure of common mode filter using The mounting structure of the common mode filter according to claim 1, wherein a resonance frequency in a frequency characteristic of a common mode noise attenuation amount of the first common mode filter is lower than a resonance frequency of the second common mode filter. The mounting structure for a common mode filter according to claim 1, wherein a cutoff frequency for the differential mode of the first common mode filter is lower than a cutoff frequency of the second common mode filter. The mounting of the common mode noise filter according to claim 1, wherein a dielectric constant around the coil formed in the first common mode filter is larger than that around the coil formed in the second common mode filter. Construction. The mounting structure of the common mode noise filter according to claim 1, wherein a length of the coil formed in the first common mode filter is longer than a length of the coil formed in the second common mode filter. 4. The common mode filter mounting structure according to claim 3, wherein a data interface including the clock signal line and the data signal line is HDMI (registered trademark), and a cutoff frequency for the differential mode of the clock signal is 1 GHz or more. The common mode filter mounting structure according to claim 1, wherein a low pass filter is used instead of the first common mode filter. The common mode filter mounting structure according to claim 1, wherein a group delay characteristic of the first common mode filter with respect to a differential mode is substantially equal to a group delay characteristic of the second common mode filter.