JP2003258586A - Noise suppression element and differential transmission circuit employing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a noise suppression element for suppressing occurrence of ringing noise and radiation noise and to provide a differential transmission circuit employing the same. <P>SOLUTION: The noise suppression element 1 includes: a core 2; first and second coils 3, 3' in pairs wound on the core 2, and is characterized in that a current flowing through the first and second coils 3, 3' produces magnetic fluxes in the same direction in the inside of the core 2 and resistors 4, 4' with the same resistance are connected between respective terminals of the first and second coils 3, 3'. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise suppression element for suppressing ringing noise and radiation noise and a differential transmission circuit using the same.

[0002]

2. Description of the Related Art In recent years, a differential transmission system has been used in a differential transmission system which has been put into practical use in the exchange of digital signals between a computer and its peripherals and between peripherals.

A conventional differential transmission circuit will be described with reference to FIGS. 11 to 13.

The differential transmission circuit has differential output terminals 28, 2
A differential driver circuit 29 having 8 ', a differential receiver circuit 31 having differential input terminals 30 and 30', and a transmission cable 32 connecting the differential driver circuit 29 and the differential receiver circuit 31. There is.

As shown in FIG. 12A, in the differential transmission circuit, the differential driver circuit 29 uses the input pulse signal Pin.
Is converted into a positive differential signal DRp and a negative differential signal DRn, which are output from the differential output terminals 28 and 28 ', respectively.
On the other hand, the differential receiver circuit 31 includes the differential driver circuit 29.
The differential input terminals 30 and 30 'respectively receive the positive differential signal DRp and the negative differential signal DRn from and output the output pulse signal Pout.

The differential driver circuit 29 and the differential receiver circuit 31 are connected via a transmission cable 32.

The same noise is generated in a pair of transmission lines forming such a differential transmission circuit. Therefore, when the positive differential signal DRp and the negative differential signal DRn are received by the differential receiver circuit 31, the difference between the positive differential signal DRp and the negative differential signal DRn is taken, so that the noise Are removed (cancelled). Therefore, the differential transmission circuit has a characteristic that it is excellent in noise resistance.

A differential impedance (impedance between lines) determined by factors such as the distance between the transmission lines and the width of the transmission line is generated between the pair of transmission lines constituting the transmission cable 32.

Positive differential signal DRp and negative differential signal D
Due to this differential impedance, Rn cannot be matched, and reflection occurs when it is received by the differential receiver circuit 31. Therefore, in the differential transmission circuit, between the connection end of the differential driver circuit 29 and the transmission cable 32,
Between the connection ends of the transmission cable 32 and the differential receiver circuit 31, terminating resistors 33 and 33 'having the same impedance as the differential impedance are connected to absorb reflection.

When the positive differential signal DRp and the negative differential signal DRn flowing in the transmission cable 32 are unbalanced, specifically, for example, as shown in FIG. When a phase difference occurs between DRp and the negative differential signal DRn, an unbalanced component as shown in FIG. 12C is generated. As a result, radiation noise is generated from the transmission line.
In order to reduce this radiation noise, normally, common mode choke coils 34 and 34 'are connected between the differential driver circuit 29 and the transmission cable 32 and between the differential receiver circuit 31 and the transmission cable 32 to radiate the radiation. We are trying to reduce noise. Common mode choke coils 34, 3
The reference numeral 4'constitutes two coils wound around a core so that magnetic fluxes in the same direction are generated inside the core.

[0011]

However, when the common mode choke coils 34 and 34 'are used in a differential transmission circuit, the difference caused by the resonance phenomenon generated between the common mode choke coils 34 and 34' and the transmission cable 32. As shown in FIG. 13, ringing noise occurs in the positive differential signal DRp and the negative differential signal DRn input to the dynamic receiver circuit 31 when the differential signal rises. As a result, there is a problem in that a receiver circuit connected to the differential transmission circuit malfunctions.

Further, the radiation noise radiated when a phase difference occurs between the positive differential signal DRp and the negative differential signal DRn causes a malfunction in other electronic equipment and is further reduced. There was a problem that I wanted to do.

Therefore, an object of the present invention is to provide a noise suppressing element for suppressing ringing noise and radiation noise, and a differential transmission circuit using the same.

[0014]

The present invention employs the following means for solving the above problems. (1) In a noise suppression element, a core and a pair of first and second coils wound around the core are provided, and the same is provided inside the core by a current flowing through the first and second coils. Directional magnetic flux is generated, and resistors having the same resistance value are connected between the respective ends of the first and second coils. (2) In the noise suppression element described in (1), the resistance value of the resistor is 100Ω or more and 3 kΩ or less. (3) In a differential transmission circuit, the first and second noise suppression elements according to claim 1 and a first differential output terminal for outputting a positive differential signal and a negative differential signal are provided. A differential driver circuit having a second differential output terminal for outputting, a first differential input terminal for inputting a positive differential signal and a second differential input terminal for inputting a negative differential signal A differential transmission circuit comprising a differential receiver circuit having: and a transmission cable composed of a pair of transmission lines, wherein the first differential output terminal and one end of the first coil of the first noise suppression element And connecting the other end of the first coil of the first noise suppression element and the input end of one transmission line of the transmission cable, and the output end of one transmission line of the transmission cable and the first end of the transmission cable. The first coil of the second noise suppression element is connected to one end of While connecting the other end of the first coil of the second noise suppression element and the first differential input terminal, of the second differential output terminal and the second coil of the first noise suppression element One end is connected, the other end of the second coil of the first noise suppressing element is connected to the input end of the other transmission line of the transmission cable, and the output end of the other transmission line of the transmission cable is connected. Connecting one end of the second coil of the second noise suppression element, and connecting the other end of the second coil of the second noise suppression element and the second differential input terminal.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) A noise suppressing element according to the present invention will be described with reference to FIGS.

FIG. 1 is a diagram showing a conceptual configuration of the noise suppressing element of the present invention.

The noise suppressing element 1 comprises a core 2, coils 3, 3 ', and resistors 4, 4'. The pair of coils 3 and 3 ′ are, as shown in FIG. 1 (a) and FIG. 1 (b),
It is wound around the surface of the core 2 so that a magnetic flux (arrow) in the same direction is generated inside the core 2 by the current flowing through the coil. Further, resistors 4 and 4'having the same resistance value are connected between the winding start end and the winding end of each of the coils 3 and 3 '.

Next, the specific structure of the noise suppressing element is shown in FIG.
And it demonstrates using FIG.

The noise suppressing element 1 comprises a laminated body 5 in which the coils 3 and 3'and the resistors 4 and 4'are integrally laminated, and a pair of cores 26 and 26 '.

The laminate 5 is obtained by stacking a plurality of sheets 7 to 14 each having an electrode pattern printed on the surface of a green sheet 6 formed by using ferrite magnetic powder and a binder, and sintering the laminate integrally. Is formed by.

The sheets 7 to 14 have the same shape, and a hole 15 is formed in the center of each of the sheets 7 to 14 so as to overlap each other.

No conductor pattern is formed on the surface of the first sheet 7.

On the front surface of the second sheet 8 (hereinafter referred to as S1 side), the left end side of the drawing (hereinafter, referred to as S1 side).
First lead line 16 extending from the S2 side) to the center
Is provided. A first connecting portion 17 and a second connecting portion 18 are provided at the central portion of the first lead wire 16 and on the right end side in the drawing (hereinafter referred to as the S3 side). On the surface of the third sheet 9, the first resistance pattern 19 is provided on the S1 side.
Is provided.

The end T of the first resistance pattern 19 on the S2 side
A first through hole 20 is formed in the first electrode 1, and a conductor paste (not shown) is embedded therein. A second through hole 21 is formed between the first resistance pattern 19 and the hole 15, and a conductor paste (not shown) is embedded therein. A third connecting portion 22 is provided at the end T2 of the first resistance pattern 19 on the S3 side. The end T1 of the first resistance pattern 19 is electrically connected to the first connecting portion 17 via the first through hole 20.

A first coil pattern 23 is formed on the surface of the fourth sheet 10 so as to surround the holes 15 in the clockwise direction. A third through hole 24 is formed in the end portion T3 of the first coil pattern 23 on the S3 side, and a conductor paste (not shown) is embedded therein. In addition, the fourth through hole 25 is provided at the central end portion T4 of the first coil pattern 23.
Are formed and a conductor paste (not shown) is embedded. The end portion T3 of the first coil pattern 23 is electrically connected to the third connecting portion 22 via the third through hole 24. Further, the end portion T4 of the first coil pattern 23 is electrically connected to the second connecting portion 18 via the second through hole 21 and the fourth through hole 25.

Sheets 11-14 are sheets 7-10
Is formed similarly to.

The sheets 7 to 14 are superposed and sintered together.

After that, the end of the first coil 3, the end of the first resistor 4, the end of the second coil 3 ', and the second resistor 4 exposed on the surface of the laminate 5 are exposed. On each of the '
Side electrodes 27, 27 'are provided.

The pair of U-shaped cores 26, 26 ′ has one leg 26 in the through hole 15 provided in the center of the laminated body 5.
It is attached to the laminated body 5 by inserting a. In addition,
The leg portions 26a, 26a 'of the pair of cores 26, 26' have their front end surfaces superposed on each other to form a closed magnetic circuit.

In the noise suppressing element, a resistor having the same resistance value may be connected by soldering between the winding start end and the winding end of each pair of the existing common mode choke coils.

(Embodiment 2) A differential transmission circuit using the noise suppressing element 1 described in Embodiment 1 will be described with reference to FIGS.
It will be described based on. The difference from the differential transmission circuit described in the conventional example is that instead of the conventional choke coil,
The differential transmission circuit of the present invention is characterized in that a noise suppressing element is used. Therefore, the same numbers are used for the same configurations as the conventional example, and the description is omitted.

A characteristic difference between a differential transmission circuit using the noise suppressing element 1 of the present invention and a conventional differential transmission circuit using a choke coil will be described.

In the conventional differential transmission circuit, as shown in FIG. 13, ringing noise having a maximum amplitude value of A1 and an oscillation time of T1 occurs, but in the differential transmission circuit using the noise suppressing element 1 of the present invention, As shown in FIG. 5, the vibration time is from T1 to T
It was confirmed that the value was shortened to 2 and the maximum amplitude value was reduced from A1 to A2.

However, in reality, as shown in FIG. 12B, there is a phase difference between the positive differential signal DRp and the negative differential signal DRn.

Here, the definition of the vibration time of ringing noise and the improvement rate of the maximum amplitude value is defined as follows. Ringing noise vibration time improvement rate (%) = {(T1-T2) / T1} x 100 Ringing noise maximum amplitude improvement rate (%) = {(A1-A2) / A1} x 100 Shown in FIG. In the characteristic curve of the improvement rate, the oscillation time of the ringing noise and the improvement rate of the maximum amplitude value are plotted on the vertical axis, and the resistance value of the resistor used as the noise suppression element is plotted on the horizontal axis. The characteristic curve shows the improvement rate of the vibration time of the ringing noise, and the characteristic curve shows the improvement rate of the maximum amplitude value of the ringing noise.

When the resistance value is 100 to 3000Ω,
An improvement rate of 5% or more was obtained for any of the characteristic curves. This can be said to be a level at which it can be empirically recognized that a waveform shaping effect can be obtained for ringing noise.

Next, the change in the frequency characteristic of the radiation noise level when the resistance value in the range of 100 to 3000 Ω was used was examined.

For the measurement of the change in the frequency characteristic of the radiated noise level, a noise suppressing element in which a resistor having a resistance value of 500Ω, 1 kΩ and 2 kΩ is connected to both ends of a coil having an inductance of 4.2 μH is used. To 150 kH
It was performed by changing between z and 1 GHz.

In the measurement, a reference (comparison standard) was a state in which a resistor was not connected to both ends of a coil having an inductance of 4.2 μH. 7 to 9 show spectrum curves of the radiation noise level when the resistors of the respective resistance values are connected, and FIG. 10 shows spectrum curves of the radiation noise level when the resistors are not connected.

The spectrum curve of FIG. 10 and FIGS.
Comparing the spectrum curves of (1) When the resistor of 500Ω is connected, the center frequency 10
Around -20MHz and center frequency 100-200M
There is a tendency for the radiated noise level to improve near Hz,
(2) When a 1 kΩ resistor is connected, there is a tendency of improvement in the vicinity of the center frequency of 100 to 200 MHz indicated by a circle, and (3) When a 2 kΩ resistor is connected,
An improvement tendency is seen in the vicinity of the center frequency 10 to 20 MHz indicated by the mark.

As a result, by connecting the resistors 4 and 4'to the common mode choke coil and selecting the resistance value, the radiation noise in the required frequency band could be further reduced.

[0042]

In the noise suppressing element of the present invention, the resistors having the same resistance value are connected to both ends of each of the pair of coils.
As a result, the waveform shaping effect of the differential transmission signal is significantly enhanced, and the noise removal effect is enhanced.

Further, in the differential transmission circuit using the noise suppressing element of the present invention, the ringing noise of the signal waveform can be suppressed, so that the malfunction of the circuit can be prevented. Further, since the radiation noise can be reduced, the influence on other electronic devices can be reduced.

[Brief description of drawings]

FIG. 1 is a diagram showing a conceptual configuration of a noise suppression element of the present invention.

FIG. 2 is a configuration diagram of a noise suppression element in which a coil and a resistor of the present invention are integrally formed.

FIG. 3 is a block exploded view of the noise suppression element of the present invention.

FIG. 4 is a configuration diagram of a differential transmission circuit using the noise suppression element of the present invention.

FIG. 5 is a diagram illustrating ringing noise on a differential signal in the differential transmission circuit of the present invention.

FIG. 6 is a diagram showing a change in frequency of an oscillation time of ringing noise and an improvement rate of a maximum amplitude value in the differential transmission circuit of the present invention.

FIG. 7 is a radiation noise characteristic diagram of the noise suppressing element of the present invention when the parallel resistance is 500Ω.

FIG. 8 is a radiation noise characteristic diagram of the noise suppressing element of the present invention when the parallel resistance is 1 kΩ.

FIG. 9 is a radiation noise characteristic diagram of the noise suppressing element of the present invention when the parallel resistance is 2 kΩ.

FIG. 10 is a radiation noise characteristic diagram in the case where the parallel resistance of the conventional noise suppression element is 0Ω.

FIG. 11 is a configuration diagram of a conventional differential transmission circuit.

FIG. 12 is a diagram illustrating a conventional differential transmission signal.

FIG. 13 is a diagram illustrating ringing noise on a differential signal in a conventional differential transmission circuit.

[Explanation of symbols]

1 noise suppression element 2, 26, 26 'core 3, 3' coil 4, 4'resistor 5 laminated body 6 green sheet 7, 8, 9, 10, 11, 12, 13, 14 sheet 15 printed with an electrode pattern Hole 16 First lead wire 17 First connection portion 18 Second connection portion 19 First resistance pattern 20 First through hole 21 Second through hole 22 Third connection portion 23 First coil pattern 24 Third through hole 25 Fourth through hole 26a, 26a 'Leg portion 27, 27' Side electrode 28, 28 'Differential output terminal 29 Differential driver circuit 30, 30' Differential input terminal 31 Differential receiver circuit 32 Transmission cable 33, 33 'Termination resistor 34, 34' Common mode choke coil

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Toru Harada             2-10-10 Tenjin Stock Exchange, Nagaokakyo City, Kyoto Prefecture             Inside the company Murata Manufacturing F-term (reference) 5E070 AA01 AB01 BA14                 5J024 CA06 DA21 EA08 FA02 KA01                       KA05

Claims (3)

[Claims] 1. A magnetic flux having a core and a pair of first and second coils wound around the core, the magnetic flux flowing in the core in the same direction by a current flowing through the first and second coils. And a resistor having the same resistance value is connected between the respective ends of the first and second coils. 2. The resistance value of the resistor is 100Ω or more, 3
The noise suppressing element according to claim 1, wherein the noise suppressing element is set to be kΩ or less. 3. The first and second noise suppression elements according to claim 1 or 2, a first differential output terminal for outputting a positive differential signal and a second differential output terminal for outputting a negative differential signal. Differential driver circuit having a differential output terminal and a differential input terminal for inputting a positive differential signal and a second differential input terminal for inputting a negative differential signal. A receiver circuit, a differential transmission circuit comprising a transmission cable consisting of a pair of transmission lines, connecting the first differential output terminal and one end of the first coil of the first noise suppression element, The other end of the first coil of the first noise suppression element is connected to the input end of one transmission line of the transmission cable, and the output end of one transmission line of the transmission cable and the second noise suppression The second noise suppressing element is connected to one end of the first coil of the element. Connecting the other end of the first coil and the first differential input terminal, and connecting the second differential output terminal and one end of the second coil of the first noise suppressing element. , The other end of the second coil of the first noise suppression element and the input end of the other transmission line of the transmission cable are connected, and the output end of the other transmission line of the transmission cable and the second noise Differential transmission characterized in that one end of the second coil of the suppression element is connected, and the other end of the second coil of the second noise suppression element is connected to the second differential input terminal. circuit.