JP2003018224A - Difference signal transmission system and ic for use in transmission and reception of difference signal transmission - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress electromagnetic radiation and to enhance tolerance to noise with respect to difference signal transmission. SOLUTION: With respect to difference signal transmission, a means (common mode choke coil) which suppresses a common mode current flowing to a difference signal line is incorporated in an IC on the difference signal transmission side, and a common mode noise countermeasure means (center tap terminated parts) is incorporated in an IC on the difference signal reception side, and thus the signal line length between a driver on the difference signal transmission side and the means which suppresses the common mode current or between a receiver on the difference signal reception side and the common mode noise countermeasure means is shortened.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a differential signal transmission system and an IC used for transmission and reception in differential signal transmission.

[0002]

2. Description of the Related Art A method for transmitting a differential signal having a low voltage amplitude is used in high speed signal transmission. FIG. 9 shows a differential signal transmitting side IC 90, a differential signal receiving side IC 91, and a differential signal line 9.
2 is a diagram showing a general LVDS transmission mode composed of 2 and a terminating resistor 94. Normally, the drive on the differential signal transmission side is not ideally performed, and in other words, it is not a completely complementary signal.Therefore, cancellation on the forward and return paths of the differential signal line is not performed, and the common mode signal Was generated and unnecessary electromagnetic radiation was generated. Therefore, as shown in FIG. 10, conventionally, a common mode choke coil 1 which is a common mode filter for reducing a common mode signal is provided between signal lines immediately after a transmitting IC 100.
Measures to insert 03 are taken, or the accepting side I
A measure has been taken to insert a capacitor into the terminating resistor immediately before C to form the center tap termination 104. By doing so, the same current having different magnitudes only in the direction of the current is caused to flow through the pair of differential signal lines 102,
In the pair of transmission lines, the electromagnetic radiation from the differential signal line is suppressed by the canceling action of each other.

A mode in which one transmission line of two transmission lines for transmitting a differential signal is a forward path and the other transmission line is a return path is called a normal mode (or a differential mode). The mode in which the two transmission lines for transmission are on the outward path and the earth is on the return path is called the common mode. In the case of interfering voltage (noise), the common mode noise usually represents the voltage between the ground (earth), the housing or the signal reference and the point of interest of each conductor, etc. It means the voltage that appears between the virtual neutral point of the balanced pair and the ground.
Normal mode or differential mode
Noise means the voltage or the like appearing between the lines in a balanced pair cable.

[0004]

In the conventional technique shown in FIG. 9 or FIG. 10, in order to realize differential signal transmission in which unnecessary electromagnetic radiation is suppressed, the differential signal transmitting side IC 90 or 100 and the differential signal are transmitted. In addition to the IC 91 or 101 on the receiving side, two resistors and one capacitor required for the common mode choke coil 103 or the center tap termination 104 must be mounted on the printed wiring board, resulting in a large number of parts. Was a problem. For example, Japanese Patent Laid-Open No.
According to Japanese Patent Laid-Open No. 1-205118, an impedance matching unit that reduces the impedance at a differential driver output point to a predetermined impedance is provided in a differential signal line immediately after the LVDS output of an IC on the transmission side, and in series between a differential driver and a differential transmission line. A center tap termination is formed on the differential signal line that is inserted and has a predetermined impedance at the output point of the differential driver, and on the differential signal line immediately before the input to the reception side IC. Further, these common mode noise countermeasures are taken for all the plurality of LVDS transmission lines.

However, in the above-mentioned conventional method, the number of parts is remarkably increased and the space on the printed wiring board is taken up. The increase in the number of components in the layout design of printed wiring boards, which requires high-density mounting or miniaturization in recent years, hinders miniaturization, reduces the degree of freedom in board design, and eventually raises the manufacturing cost, which is a major problem. Has become.

In addition, such an increase in the number of parts increases the loop formed by the forward path and the return path of the signal current between the driver and the transmission line in the IC on the transmission side on the transmission side, and as a result, from that portion. It is supposed to increase electromagnetic radiation. In addition, one of the differential signal outputs of the driver 107 of the transmission side IC passes through the differential signal line and the terminating resistor to the other differential signal line, and reaches the other differential signal output of the transmission side IC driver 107. The pattern to the input pin of the receiver 108 of the receiving side IC, which is a pattern branched from the signal path, has a high input impedance of the receiving side IC. Weaken.

From the viewpoint of noise resistance, L
In the VDS differential signal transmission system, the output impedance of the output driver is high, and the signal line length portion between the means for suppressing the common mode current that does not become a signal line having the specified impedance is not affected by noise from the outside. It can be said to be the part that is easily affected (unbalanced). In the design for differential signal transmission, these signal line lengths should be shortened as much as possible to suppress electromagnetic radiation and enhance noise resistance, but the increase in the number of components makes this difficult.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress unnecessary electromagnetic radiation on the transmission side in differential signal transmission, enhance noise resistance, and receive signals. On the side, it is to provide a differential signal transmission method for improving noise resistance and an IC used for transmission and reception in differential signal transmission.

[0009]

In order to achieve such an object, the present invention provides a differential signal transmission system according to a first aspect of the present invention, which is a differential signal transmission method. The means for suppressing the common mode current flowing in the lines is built in the differential signal transmitting side IC, and the common mode noise countermeasure means is built in the differential signal receiving side IC, whereby the driver on the differential signal transmitting side and the common mode It is characterized in that the signal line length between the means for suppressing the current or between the receiver on the differential signal receiving side and the common mode noise countermeasure means is shortened.

The invention described in claim 2 is the same as claim 1.
5. The differential signal transmission method according to claim 1, wherein the differential signal transmission side IC has a common mode choke coil arranged between an output lead pin of the IC package and an IC chip having the driver, The output signal is output to the output pin of the IC package through the common mode choke coil.

The invention described in claim 3 is the same as claim 1.
5. The differential signal transmission method according to claim 1, wherein the differential signal receiving IC has a center tap termination component between an input lead pin, a ground pin, and an IC chip having the receiver in the IC package. It is characterized by being arranged.

The invention according to claim 4 is the same as claim 1.
5. The differential signal transmission system according to claim 1, wherein the center tap termination component includes a resistor having the same impedance value and one capacitor, and both ends of the series connection of the two resistors are the respective lines of the differential signal. And the capacitor is connected to an intermediate point of the series connection, and the other end of the capacitor is connected to the ground pin.

According to a fifth aspect of the present invention, there is provided a differential signal transmitting side IC, wherein the transmitting side IC used for differential signal transmission suppresses a common mode current between differential signal lines. It is characterized by having a built-in.

According to a sixth aspect of the present invention, there is provided a differential signal receiving side IC, wherein the receiving side IC used for differential signal transmission suppresses a common mode current between differential signal lines. It is characterized by having a built-in.

The invention according to claim 7 is the same as claim 5
5. The differential signal transmitting side IC according to claim 1, wherein the differential signal transmitting side IC is connected between an output lead pin of a package of the IC and an IC chip having the driver.
A choke coil is arranged so that the output signal of the driver is output to the output pin of the IC package through the common mode choke coil.

The invention according to claim 8 is the same as claim 6
5. The differential signal receiving side IC according to claim 1, wherein the differential signal receiving side IC is a center tap termination component between an input lead pin, a ground pin, and an IC chip having the receiver in the IC package. Is arranged.

The invention described in claim 9 is the same as that of claim 6.
5. The differential signal receiving IC according to claim 1, wherein the center tap termination component includes a resistor having the same impedance value and one capacitor, and the two ends of the series connection of the two resistors respectively correspond to the differential signal. The capacitor is connected to a line, the capacitor is connected to an intermediate point of the series connection, and the other end of the capacitor is connected to a ground pin.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 illustrates the concept of a differential signal transmission system according to the first embodiment of the present invention, or the configuration of a transmission side IC. The differential signal transmission of the present invention is performed by the differential signal transmitting side IC 10 and the differential signal receiving side IC 1.
1, a differential signal line 12 including a pattern or a cable, a connector, etc. on a printed wiring board that connects them, and a terminating resistor 14. In this differential signal transmission, the common mode choke coil built-in differential signal transmitting side IC 10 is used to prevent the common mode signal current from flowing through the differential signal line 12, and unnecessary due to the common mode signal current. It suppresses the radiation of various electromagnetic waves.

Further, the common mode choke coil 1
3 is arranged immediately after the differential signal driver 17 on the transmitting side to shorten the length of the signal line between the differential signal driver 17 on the transmission side and the driver having a high output impedance value in terms of impedance, and a loop formed by this signal line. Has reduced the size of.

This is because the differential signal line 12 shown in FIG.
As a matter of course, it is necessary to reduce the common mode signal current to a signal in which the influence of stray capacitance from the output part of the differential signal transmitting side driver to the common mode choke coil is reduced, and This has the effect of bringing the output signal and the signal on the differential signal line closer together. This reduces the common mode signal current of the driver's differential output current itself, which causes a reduction of high frequency electromagnetic radiation. In other words, the small stray capacitance in this portion is used as a load to reduce the signal current flowing in the driver.

Reducing the loop formed in the signal line reduces the electromagnetic radiation radiated from that portion in proportion to its smallness.

In summary, it can be said that the choke coil in such a use reduces both the common mode signal current flowing in the driver of the transmitter IC and the common mode signal current flowing in the signal line, thus reducing electromagnetic radiation.

Also, the common mode choke coil is I
The differential signal transmission side IC 10 with a built-in common mode choke coil built in C realizes the reduction of the common mode signal flowing in the differential signal transmission line in the IC package, thereby reducing the number of parts on the printed wiring board. It has the feature that it can be reduced and the space on the printed wiring board can be secured.

In the first embodiment shown in FIG. 1,
It is possible to suppress electromagnetic radiation due to generation of a common mode signal as compared with the configuration of the conventional differential signal transmission shown in FIG. 9, and further, compared with the configuration shown in FIG. 10, the number of parts mounted on the printed wiring board. Can be reduced.

First, a method of arranging the common mode choke coil in the differential signal output IC package will be described. FIG. 2 is a diagram showing an example in which a common mode choke coil is arranged in the differential signal output IC. IC chip 2 that constitutes a driver on the ceramic substrate 21
An SMD type common mode choke coil 23 having an arbitrary frequency characteristic is arranged between 0 and the differential signal output lead pin 22 and connected by a bonding wire 24,
Cover with the IC package 25.

FIG. 3 and FIG. 4 describe the circuit configuration and overview of the common mode choke coil. The two input terminals 31 and the two output terminals are respectively connected to the inductors 33 and 34.
It is characterized in that the inductor 33 and the inductor 34 are magnetically coupled to each other and act as a low-impedance resistor for a differential current flowing between the two lines and a high-impedance resistor for a common mode current.

As the common mode choke coil applicable to the present invention, there is an SMD type winding type or laminated type common mode choke coil. Currently 1.6
It is possible to use a device having a square size of 1 mm and a height of about 1 mm.

This common mode choke coil built-in I
The differential signal transmission method using C10 makes it possible to suppress the common mode current flowing between the differential signal lines without increasing the number of parts on the printed wiring board.

The above-mentioned differential signal transmission system reduces the common mode current between two differential signal lines to reduce the common mode current as compared with the transmission system shown in FIG. 9 which is an example of the conventional differential signal transmission. It suppresses unnecessary electromagnetic radiation generated as noise. Further, since the common mode noise countermeasure component is formed in the differential signal transmission side IC, unnecessary electromagnetic wave radiation can be suppressed more effectively without taking up space on the printed wiring board.

(Second Embodiment) FIG. 5 illustrates the concept of the differential signal transmission system of the present invention or the configuration of a receiving side IC. The differential signal transmission of the present invention is formed by a differential signal transmitting side IC 50, a differential signal receiving side IC 51, and a differential signal line 52 such as a pattern or a cable or a connector on a printed wiring board connecting them. In this differential signal transmission, the differential signal receiving side I with a built-in center tap termination component
C51 is used to prevent unnecessary electromagnetic waves from being radiated by causing signal currents of the same magnitude to flow through the pairs of differential signal lines 52 only in different directions.

Further, the center tap termination component 54 is
By arranging just before the receiver on the differential signal receiving side, the differential signal appearing at both ends of the series resistance of the terminating component is transmitted from the both ends to the receiver through the shortened signal line.
The signal line from both ends of the terminating component to the receiver is different from the low impedance line to the terminator, and the input impedance of the receiver is high, and therefore the resistance to external noise is also weak. Shortening the signal line length of this portion has the effect of increasing the noise resistance of this portion. Further, shortening the signal line length in this portion is also effective in transmitting the signal appearing between both ends of the terminator to the receiver without causing waveform distortion.

Further, the capacitor connected to the middle point of the terminating resistor in which two resistors having the same resistance value are connected in series is connected to the signal ground at the other end, so that a differential signal is obtained with respect to the high frequency signal component. It has a function of equalizing the loads on the signal grounds of the signal lines. This is
The signal currents flowing through the differential signal lines, at least the high-frequency component currents, have the same magnitude except that the directions are different, so that the electromagnetic waves emitted from the pair of differential signal lines cancel each other. Further, since it is insulated from the ground by a capacitor, it has an effect that unnecessary DC components other than signal components do not flow in the differential signal line.

Further, with respect to the common mode noise component applied to the differential signal line from the outside, the impedance between the respective grounds of the differential signal pair is made equal, and the differential mode noise signal is not given to the receiver. Also has.

Here, the center tap termination component 54 is
Chip resistance between 10Ω and 200Ω, capacitor is 1
It is a chip capacitor with a capacity of 00 pF or more.

The center-tap termination component built-in differential signal reception side IC 51 in which the center-tap termination component 54 is built in the IC realizes the common mode noise countermeasure in the differential signal transmission in the package of the reception IC. At the same time, the number of parts is reduced and the space on the printed wiring board can be secured.

The above-described differential signal transmission method suppresses unnecessary radiation noise due to common mode noise and suppresses external radiation noise from the method shown in FIG. 9 or 10 which is an example of conventional differential signal transmission. The resistance to common mode noise can be improved, and the number of components mounted on the printed wiring board can be reduced as compared with FIG.

The center of the differential signal input IC package
A method of arranging the tap ends will be described with reference to FIG.

Between the two input lead pins 61, the ground pin 62 and the IC chip 60 on the ceramic substrate 67, the chip resistors 63 and 64 and the chip capacitor 65 are provided.
Are connected by a bonding wire 66 to form a center tap termination, and the IC package 68 is covered. The connection of the chip resistor and chip capacitor to form the center tap termination will be described in detail with reference to FIG. Two
A chip resistor 63 and a chip resistor 64 are connected in series to the input lead pin 61 of the book by a bonding wire 66-1 and a bonding wire 66-2, and the other electrodes of the chip resistor 63 and the chip resistor 64 are bonded to each other. Chip with wire 66-4 and bonding wire 66-5
Connect to capacitor 65. The other electrode of the chip capacitor 65 is bonded to the ground pin 62.
Connect with wire 66-3. The chip resistors 63 and 64 are connected to the IC chip 60 by bonding wires 66-6 and 66-7 from the electrodes on the side connected to the input lead pins 61.

By the differential signal transmission method using the IC 52 with a built-in center tap termination component having the above-mentioned configuration, the differential signal transmitted through the differential signal line is faithfully reproduced by the receiving IC.
Can be received by the receiver without increasing the number of components on the printed wiring board.

In the above differential signal transmission system, the current due to noise that jumps into the two differential signal lines from the outside is
By flowing to ground between equal resistance values and a common capacitor, an in-phase voltage equal to the two differential inputs is generated across the series termination resistor, but the same phase voltage across the series termination resistor is generated. The voltage can be transmitted to the receiver without distortion, and the common mode
Effectively eliminating noise does not take up space on the printed wiring board and unnecessary electromagnetic radiation can be suppressed.

(Third Embodiment) Next, the differential signal transmitting IC with a built-in common mode choke coil used in the first embodiment and the center tap termination component built-in difference used in the second embodiment. The concept of the differential signal transmission system using both the moving signal reception side ICs will be described with reference to FIG. In the differential signal transmission of the present invention, the differential signal transmitting IC 80 with a built-in common-mode choke coil, the differential signal receiving IC 81 with a built-in center tap termination, and the pattern or cable, connector, etc. on the printed wiring board connecting them are different. Motion signal line 82
Is formed by.

Since the common mode choke coil 83 functions to reduce the common mode current component contained in the differential signal, the differential signal transmitting IC 100 as shown in FIG.
Is arranged immediately after, and reduces the common mode current output from the differential signal transmitting side IC 100, and is used as a measure for reducing electromagnetic radiation. The common-mode choke coil 83 is built in the IC, and the built-in common-mode choke coil built-in differential signal transmission side IC 80 realizes common mode noise countermeasures for differential signal transmission in the IC package, reducing the number of parts. The feature is that the space on the printed wiring board is secured.

The center tap termination component 84 is arranged immediately before the IC 101 on the differential signal receiving side as shown in FIG. 10, and is used as a countermeasure against common mode noise that jumps into the differential signal line from the circuit. The center-tap termination component built-in IC 81 has a center-tap termination component built-in differential signal transmission side IC 81 that implements common mode noise countermeasures in differential signal transmission in an IC package, reducing the number of components. The feature is that the space on the printed wiring board is secured.

Therefore, unnecessary radiation noise due to common mode noise can be suppressed more than in the case of FIG. 9 which is an example of conventional differential signal transmission, and further, compared with FIG. 10, components mounted on a printed wiring board. It is possible to reduce the score. Furthermore, the effect of suppressing common mode noise is greater than that of either the first embodiment or the second embodiment.

The above-mentioned differential signal transmission system reduces the common mode current between the two differential signal lines and secures a current path for the return current that cancels the common mode current.
By canceling the common mode current with the return current, unnecessary electromagnetic radiation due to the signal current generated in the common mode is suppressed. Further, since the common mode noise countermeasure component is formed in the differential signal transmitting side IC or the differential signal receiving side IC, unnecessary electromagnetic radiation can be suppressed without taking up space on the printed wiring board. The differential signal transmission system of the third embodiment has a greater effect of suppressing common mode noise in a broad sense than either the first embodiment or the second embodiment.

[0047]

According to the first embodiment of the present application, a measure against common mode noise that reduces the common mode current between two differential signal lines without utilizing the space on the printed wiring board. By forming the common mode choke coil, which is a component, inside the differential signal transmission side IC, it becomes possible to provide a differential signal transmission system in which unnecessary electromagnetic radiation generated as common mode noise is suppressed.

According to the second embodiment of the present application,
A center that secures a current path for the common mode noise current generated between two differential signal lines without using the space on the printed wiring board and prevents the common mode noise current from becoming differential noise. -By forming the tap termination component in the differential signal receiving IC, it becomes possible to provide a differential signal transmission system in which the influence of common mode noise is reduced.

According to the third embodiment of the present application,
A common mode choke coil, which is a common mode noise countermeasure component that reduces the common mode current between two differential signal lines without using the space on the printed wiring board, is installed in the IC on the differential signal transmission side. Further, by forming a center tap termination component, which is a common mode noise suppression component, in the IC on the differential signal receiving side, respectively, a common sense mode in a broader sense than in either the first embodiment or the second embodiment is formed. By suppressing noise, it is possible to further suppress unnecessary electromagnetic radiation generated as common mode noise and to provide a differential signal transmission method having high noise resistance.

[Brief description of drawings]

FIG. 1 is a diagram showing a concept of differential signal transmission using a differential signal transmission side IC having a common mode choke coil built in the IC.

FIG. 2 is a diagram showing a configuration of a differential signal transmission side IC having a common mode choke coil inside an IC package.

FIG. 3 is a diagram showing a circuit of a common mode choke coil.

FIG. 4 is a diagram showing an overview of a common mode choke coil.

FIG. 5 is a diagram showing the concept of differential signal transmission using a differential signal receiving side IC having a center tap termination built in the IC.

FIG. 6 is a diagram showing the configuration of a differential signal reception side IC having a center tap termination component inside the IC package.

7 is a diagram showing a configuration of a center tap termination component built in the differential signal receiving side IC shown in FIG.

FIG. 8 is a diagram showing a concept of differential signal transmission using a differential signal transmitting side IC having a common mode choke coil inside the IC and a differential signal receiving side IC having a center tap termination inside the IC. Is.

FIG. 9 is a diagram showing a differential signal transmission system that does not take measures against common mode noise in the related art.

FIG. 10 is a diagram showing a differential signal transmission system in which a countermeasure against common mode noise in the related art is taken outside a transceiver IC.

[Explanation of symbols]

10, 50, 80, 90, 100 Transmission side IC 11, 51, 81, 91, 101 Reception side IC 12, 52, 82, 92, 102 Differential signal line 13, 23, 83, 103 Common mode choke coil 14 , 94 Terminating resistors 15, 55, 85, 95, 105 Transmission side printed circuit board 16, 56, 86, 96, 106 Reception side printed circuit board 17, 87, 97 Driver 18, 88, 98 Receiver 20 IC chip 21, 67 Ceramics substrate 22 Output Lead Pins 24, 66 Bonding Wires 25, 68 IC Package 31 Input Terminal 32 Output Terminals 33, 34 Inductors 54, 84, 104 Center Tap Termination Parts 61 Input Lead Pins 62 Ground Pins 63, 64 Chip Resistor 65 Chip capacitor

Claims (9)

[Claims] 1. In differential signal transmission, a means for suppressing a common mode current flowing through a differential signal line is built in a differential signal transmission side IC, and a common mode noise countermeasure means is built in a differential signal reception side IC, As a result, between the driver on the differential signal transmitting side and the means for suppressing the common mode current, or the receiver on the differential signal receiving side and the common mode
A differential signal transmission method characterized in that the signal line length between the noise suppression means is shortened. 2. The differential signal transmission side IC has a common mode choke coil disposed between an output lead pin of a package of the IC and an IC chip having the driver, and an output signal of the driver is the common mode. The differential signal transmission system according to claim 1, wherein the signal is output to an output pin of the IC package via a choke coil. 3. The differential signal receiving IC has a center tap termination component arranged between an input lead pin, a ground pin, and an IC chip having the receiver in the IC package. The differential signal transmission system according to claim 1. 4. The center tap termination component includes a resistor having the same impedance value and one capacitor, and
Both ends of a series connection of two resistors are connected to respective lines of the differential signal, the capacitor is connected to an intermediate point of the series connection, and the other end of the capacitor is connected to a ground pin. Claim 1 characterized by the above.
Differential signal transmission method described in. 5. A differential signal transmitting side IC used in differential signal transmitting, comprising means for suppressing a common mode current between differential signal lines. 6. A differential signal receiving side IC used for differential signal transmission, comprising means for suppressing a common mode current between differential signal lines. 7. The differential signal transmission side IC has a common mode choke coil arranged between an output lead pin of a package of the IC and an IC chip having the driver, and the output signal of the driver is the common mode. The differential signal transmitting side IC according to claim 5, wherein the IC is output to an output pin of the IC package via a choke coil. 8. The differential signal receiving side IC has a center tap termination component arranged between an input lead pin, a ground pin, and an IC chip having the receiver in the IC package. The differential signal reception side IC according to claim 6. 9. The center tap termination component includes a resistor having the same impedance value and one capacitor, and
Both ends of a series connection of two resistors are connected to respective lines of the differential signal, the capacitor is connected to an intermediate point of the series connection, and the other end of the capacitor is connected to a ground pin. 7. The method according to claim 6, wherein
The differential signal reception side IC according to item 1.