JP2008153386A - Digital signal transmission substrate, and computer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a digital signal transmission substrate in which skew is reduced in a high transfer rate, and to provide a computer into which the substrate is incorporated. <P>SOLUTION: The digital signal transmission substrate, equipped with a dielectric substrate having a first and second principal surfaces, a first conductor provided on the first principal surface of the dielectric substrate, a second conductor provided on the principal surface of the dielectric substrate, a grounding conductor provided on the principal surface of the dielectric substrate, a plurality of island type conductor units arranged so as to be neighbored to the first conductor and a connecting conductor for connecting at least either one of the plurality of island-type conductor units to the first conductor while the island type conductor units connected through the connecting conductor constitute a capacitive stub, is provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a digital signal transmission board and a computer incorporating the same.

  The data transfer speed between a host represented by a personal computer and a storage device such as a hard disk is becoming higher. In the conventional parallel transfer method, a transfer rate of 133 MB / s or more is difficult, and a serial transfer method is promising for realizing a higher transfer rate.

  For example, a magnetic disk drive (hereinafter referred to as HDD) having a serial ATA (AT Attachment) interface is connected to a host via a serial ATA bus. In the serial transfer method, a transfer rate of 3 Gbps (corresponding to about 380 MB / s) is also possible.

  In order to realize such a high transfer rate, a differential transmission method such as LVDS (Low Voltage Differential Signal) which is a differential signal having a low logic amplitude of 400 mV or less is used. In this case, skew (delay time difference) between differential signals occurs if there are non-uniform characteristics of the drivers and receivers that are integrated into the IC, or differences in the pair line lengths.

In the case of transmitting a plurality of signals using a printed circuit board on which a plurality of signal lines are arranged, there is a technology disclosure example of a printed circuit board that can reduce the skew while minimizing the influence of the reflection characteristics of the through holes (Patent Document 1). .
JP 2004-165200 A

  The present invention provides a digital signal transmission board with reduced skew at a high transfer rate and a computer incorporating the same.

  According to one aspect of the present invention, a dielectric substrate having first and second main surfaces, a first conductor provided on the first main surface of the dielectric substrate, and the dielectric substrate A second conductor provided on the first main surface; a ground conductor provided on the second main surface of the dielectric substrate; and a plurality of islands disposed in proximity to the first conductor. And a connecting conductor connecting at least one of the plurality of island-shaped conductor portions and the first conductor, and the island-shaped conductor portion connected by the connecting conductor constitutes a capacitive stub A digital signal transmission board is provided.

  According to another aspect of the present invention, the digital signal transmission board includes a driver that transmits a signal and a receiver that receives the signal, and the signal from the driver is provided on the wiring board. A computer apparatus is provided that is output to the receiver through the first and second transmission lines.

  According to the present invention, a digital signal transmission board having a reduced skew at a high transfer speed and a computer incorporating the same are provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1A and 1B show a digital signal transmission board 5 according to a specific example of the present invention, in which FIG. 1A is a schematic plan view and FIG. 1B is a schematic cross-sectional view along the line AA. In order to transmit a high-speed differential signal such as 3 Gbps constituting the serial ATA transfer system, a microstrip line using a glass epoxy substrate or the like is used. Further, such a microstrip line is also used for a plurality of bus lines for transmitting a plurality of high-speed signals such as a clock signal, not a differential signal. Such a microstrip line includes an upper conductor 10 and a GND conductor 20 that sandwich a dielectric 16 of a glass epoxy substrate. Similarly, the upper conductor 12 and the GND conductor 20 sandwich the dielectric 16.

If the dielectric thickness is 0.1 mm by using a glass epoxy substrate, the characteristic impedance Z ₀ can be 50Ω when the width of the upper conductors 10 and 12 is 0.18 mm. Further, for example, a multilayer wiring board in which one upper conductor is disposed in the dielectric 16 is possible. In the case of standard FR4 PCB material, the relative dielectric constant is in the range of 4 to 4.5.

  In FIG. 1, a positive differential signal is transmitted to one microstrip line, and a negative differential signal is transmitted to the other stripline. That is, the output signal from the driver and the input signal to the receiver are transmitted by the microstrip line. In order to transmit a digital high-speed signal like serial ATA, it is preferable that the logic amplitude is as low as 200 to 400 mV. However, since the low-voltage single-ended signal has low noise resistance, it is improved by using LVDS which is a differential signal.

  Further, the upper conductor 10 of one signal line in FIG. 1 includes three stubs 30. In this case, the three stubs 30 are spaced apart by an equal interval of 5 mm, but need not be limited to an equal interval, an interval of 5 mm, and the number of stubs of three. The stub 30 has a rectangular shape of 0.4 mm × 0.6 mm, but is not limited to this shape and size.

  The stub 30 functions as a capacitor. 2A and 2B are diagrams for explaining the operation of the stub. FIGS. 2A and 2B are schematic plan views, and FIG. 2C is an equivalent circuit diagram. In FIG. 2A, an island-like conductor 32 is provided in advance along the upper conductor 10 by patterning. When the skew between the plus signal and the minus signal is large, a metal foil 34 such as copper is bonded to the upper conductor 12 with solder or the like. It can be adjusted in a short time while comparing the plus / minus signals with an oscilloscope or the like so that the skew of the two signals is reduced.

  After the adjustment, for example, two stubs 30 as illustrated in FIG. 2B are arranged. In this case, the striped stub 30 having a length L can be considered as a microstrip line having an open end. An open-ended microstrip line is capacitive when L is shorter than a quarter wavelength. Here, since L is sufficiently shorter than the quarter wavelength, it can be considered that lumped constant capacitors C1 and C2 are arranged as illustrated in FIG.

  Further, it can be considered that inductance is between C1 and C2. The equivalent circuit of FIG. 2B can be considered as a delay circuit by the capacitance of C1 and C2 and the equivalent inductance determined by the distance between C1 and C2. That is, it can be seen that the delay time can be adjusted by changing the shape, position, and interval of the stub 30.

  Here, the definition and specification of the skew in the serial ATAII will be described. Skew is a difference in delay time between plus / minus differential signals caused by non-uniform driver and receiver characteristics, line length differences due to differences in package pin assignments, and the like. In designing, consideration is given to avoiding such unbalance of differential signals. However, the higher the speed, the greater the influence of deviation from the design value, such as bonding wire length, transmission line bending, and transmission line termination mismatch, and skew adjustment becomes necessary.

  3A and 3B are schematic diagrams for explaining the definition of skew. FIG. 3A is a minimal-skew, FIG. 3B is a late-skew, and FIG. 3C is an early skew. Represents an early-skew. FIGS. 3B and 3C show a state in which the delay time between the plus signal and the minus signal becomes large and the skew becomes large. In the specification of the serial ATAII, Tx Differential skew needs to be smaller than 20 ps.

  4A and 4B are graphs for explaining a change in the delay time due to the stub 30. FIG. 4A shows a case where the skew adjustment is performed by the stub, and FIG. 4B shows a case where the skew adjustment by the stub is not performed. . The vertical axis represents delay time (ps), and the horizontal axis represents frequency (GHz). That is, FIG. 4A shows a case where the upper conductor 10 having three stubs 30 of FIG. 1 is provided and skew adjustment is performed. In the frequency range up to 9.3 GHz, the delay time is 366.5 to This indicates that the adjustment is within the range of 373 ps.

  On the other hand, FIG. 4B shows the case of the upper conductor 12 having no stub shown in FIG. 1 and no skew adjustment. In this case, in the frequency range up to 10 GHz, the delay time is linearly changed from 357.5 to 358.7 ps by about 2 ps. Although it is necessary to adjust the Tx Differential skew of the serial ATAII specification described in FIG. 3 to be smaller than 20 ps, it is difficult without the skew adjustment of FIG. On the other hand, in FIG. 3A, the delay time of about 9 to 14 ps can be changed as compared with FIG. As a result, the delay time can be easily adjusted within the serial ATAII specification.

  In the above specific example, the differential signal transmission of the serial ATA transfer method has been described. However, the present invention is not limited to this. That is, this example can also be used to adjust the skew between a plurality of signal lines that transmit a high-speed data signal including a high-speed clock pulse.

  FIG. 5 shows a modified example. FIG. 5A is a schematic plan view when the patterned island-shaped conductor 32 is larger than FIG. 2A, and FIG. 5B is a stub after soldering with a metal foil. 30. When the island pattern 32 is large, the equivalent capacitors C1 and C2 become large, and the delay time can be changed more greatly. Further, as shown in FIG. 5B, the delay time can be finely adjusted by changing the adhesion positions S1, S2, and S3 of the metal foil without changing the pattern of the island pattern 32. In this way, the adjustment range of the delay time can be further increased, and for example, it can be easily adapted to the serial ATAII specification.

  FIG. 6 is a schematic plan view showing the skew adjustment unit 6 according to the comparative example. In the comparative example, as the skew adjusting means, the lengths of the two upper conductors 10 and 12 are changed as shown in FIG. If the skew after the actual measurement exceeds the adjustment range at the time of design, it is necessary to cut or add a pattern. For example, when the skew adjustment is impossible only by the bent portion 40 of the upper conductor 10 in FIG. 6A, after cutting a part as shown in FIG. Install and adjust.

  However, partial cutting of the wiring board is not easy, and the addition of the line length may be difficult with a limited board shape, and the reproducibility of characteristics is not sufficient. On the other hand, in this specific example, the line is not cut and the pattern is provided in advance, so that the adjustment is easy and the connection can be made reliably.

Next, a personal computer including a driver 50, a receiver, and the like and including a differential signal transmission line will be described.
FIG. 7 is a block diagram for explaining a configuration of a part that transmits a differential signal, in particular, in a personal computer provided with the digital signal transmission board 5 according to an embodiment of the present invention. A high-speed signal from the driver 50 provided in the host 20 represented by the personal computer and connected to the personal computer body passes through the digital signal transmission board 5 coupling capacitor 57 and reaches the SATA connector 60.

  A differential signal is input to the HDD 70 via the cable 64 connected to the STAT connector 60. Similarly, a differential signal from the HDD 70 is input to a receiver (not shown) through a cable, an input terminal (not shown), a digital signal transmission board, and the like. In this way, the host 20 and the HDD 70 are connected by the serial ATA bus, and 3 Gbps high-speed differential signals are transmitted and received.

    FIG. 8 is a schematic plan view of a printed circuit board 56 incorporated in a computer according to a specific example of the present invention. The center of the printed circuit board 56 is an IC mounting area. The driver 50 and the receiver are one-chip ICs. In this figure, three drivers (T0, T1, T2) and three receivers (R0, R1, R2) are integrated.

  Since the driver and receiver transmit and receive differential signals, the transmission lines make a pair. The digital signal transmission board 5 is connected to a transmission line on the printed board 56, respectively. The digital signal transmission board 5 may be incorporated in the pattern of the printed board 56, but is not limited to this and may be externally attached. As a result, the skew between the differential signals is reduced, and a personal computer having a function of connecting the host 20 and the HDD 70 by the serial ATA transfer method becomes possible.

  The embodiments of the present invention have been described above with reference to the drawings. However, the present invention is not limited to these. For example, regarding a substrate material, a microstrip line, a stub, a digital signal transmission substrate, etc. that constitute a wiring substrate, even if a person skilled in the art makes a design change, it is within the scope of the present invention without departing from the gist of the present invention. Is included.

It is a schematic diagram of a digital signal transmission board according to a specific example of the present invention. It is a schematic diagram showing the effect | action of the skew adjustment by a stub. It is a graph showing the definition of skew. It is a graph showing the adjustment range of skew. It is a schematic diagram of the digital signal transmission board | substrate concerning the modification of this invention. It is a schematic diagram of the digital signal transmission board | substrate concerning a comparative example. It is a block diagram of a computer incorporating a digital signal transmission board according to a specific example of the present invention. It is a schematic plan view of the printed circuit board concerning the example of this invention.

Explanation of symbols

  5 Digital signal transmission board, 10, 12 Upper conductor, 16 Dielectric, 20 GND conductor, 30 Stub, 32 Island conductor, 50 Driver, 56 Printed board

Claims (4)

A dielectric substrate having first and second major surfaces;
A first conductor provided on the first main surface of the dielectric substrate;
A second conductor provided on the first main surface of the dielectric substrate;
A ground conductor provided on the second main surface of the dielectric substrate;
A plurality of island-shaped conductor portions disposed in proximity to the first conductor;
A connection conductor connecting at least one of the plurality of island-shaped conductor portions and the first conductor;
With
The digital signal transmission board according to claim 1, wherein the island-like conductor portions connected by the connection conductor constitute a capacitive stub.   The width of the connection conductor viewed in a direction parallel to the extending direction of the first conductor is larger than the width of the island-shaped conductor portion viewed in a direction parallel to the extending direction of the first conductor. 2. The digital signal transmission board according to claim 1, wherein the digital signal transmission board is small.   The digital signal transmission board according to claim 1, wherein the first and second transmission lines transmit a differential signal. A digital signal transmission board according to any one of claims 1 to 3,
A driver that sends a signal;
A receiver for receiving the signal;
With
A signal from the driver is output to the receiver through first and second transmission lines provided on the wiring board.

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