JP2001344299A - Wiring structure having branch point and method for forming wiring constitution having branch point - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wiring structure which can minimize a waveform disturbance due to reflection by approximately equalizing the electric delay times in wiring after branching in a wiring circuit constitution having a branch point. SOLUTION: First and second wiring lengths in the wiring from the branch point to second elements are determined by condition (L2+2×L3)<λe where λe is the effective wavelength determined by the operation frequency and the material of a printed circuit board. The branch point is set to the position of such point that distances from the branch point to respective second elements connected after the branching point may be equal to each other with respect to electric length. By this constitution, the electric delay times in the wiring after branching are approximately equal to each other even in the case that different parts are set after the branch point, and waveform disturbance due to reflection can be minimized, and thus a circuit free from disturbance of a voltage waveform in each element after branching is realized.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wiring structure having a branch point and a method of forming a wiring structure having a branch point. More specifically, the present invention relates to a wiring structure having a branch point and a method of forming a wiring configuration having a branch point, in which a wiring structure having a branch point can have substantially the same electrical delay time in each wiring after branching.

[0002]

2. Description of the Related Art When a wiring for a high-speed signal is formed on, for example, a printed circuit board, in a configuration having a branch, signal deterioration, signal reflection occurs in each wiring after branching, and a signal transmission error between wirings, that is, a delay amount. Differences and the like cause various problems in various signal processing using the branch wiring configuration.

[0003] Attempts to solve the above problems in branch wiring have been made in the past.
506 indicates that the wiring layer after branching has a characteristic impedance of 2;
A multi-layer substrate for high-speed signals, in which signal deterioration due to deterioration of transmission loss is prevented by controlling the dielectric thickness of the substrate so as to double the thickness, is disclosed. Also, Japanese Patent Application Laid-Open No. 10-5
No. 1147 discloses a configuration in which a cross portion formed by branching is made into a component so as not to increase the number of layers of the printed wiring board. Japanese Patent Application Laid-Open No. 11-163531 discloses a so-called equal-length wiring configuration in which the number of times of bending is equal in the bus wiring and the wiring lengths of the outer wiring and the inner wiring are equal to each other, thereby suppressing variations in transmission signal timing. An arrangement is disclosed.

[0004]

However, in the method of controlling the dielectric thickness of the substrate so that the characteristic impedance of the wiring layer after branching is doubled as in JP-A-6-326506, the wiring length after wiring is small. When the lengths are different or when the wiring length is long, there is a disadvantage that a delay error or a waveform distortion occurs at two or more input terminals.

[0005] Further, as disclosed in Japanese Patent Application Laid-Open No. Hei 10-51147, when a cross portion formed by branching is made into a component so as not to increase the number of layers of the printed wiring board, the same component cannot be used when many design changes are made. There are many disadvantages in that they are poor in versatility.

In a wiring method in which the number of times of bending is equal in the bus wiring and the wiring lengths of the outer wiring and the inner wiring are equal to each other as in Japanese Patent Application Laid-Open No. 11-163531, the delay times in the same part are the same. There is a disadvantage that a delay error occurs between different input components, and further, a waveform of a nearby component is disturbed by reflection from a distant component.

FIG. 9 shows a circuit having a configuration in which the wiring lengths after branching are equal. The wiring configuration shown in FIG.
CPU 102, SDRAM 10
3. A buffer 105 is provided adjacent to the DIMM 104 and the CPU 102. In this wiring configuration, realization of high-speed signal transmission is required between each element. The signal transmitted between the wirings includes, for example, a clock signal for setting processing timing in each element, an address signal used for reading data from and writing data to a memory, and the like.

In the wiring configuration having the branch point 101 shown in FIG. 9, the wiring length from the branch point 101 to the SDRAM 103 is a, the wiring length from the branch point 101 to the DIMM 104 is b, and a = b. I do. FIG. 10 shows the time change of the voltage waveform in each element measured by equalizing the wiring lengths a and b after branching in this way.

The horizontal axis in FIG. 10 is time (ns: nanosecond),
The vertical axis indicates the voltage (V: volt), and each of the three waveforms indicates the buffer 105, the SDRAM 103, and the DIMM1.
04 is voltage waveform data that changes with time and is measured in each element. Ideally, the SDRAM 103 and the DIMM 104 draw similar voltage waveforms following changes in the voltage waveform of the buffer 105. If such waveforms can be obtained, the SDRA
For example, data reading processing of the M103 and the DIMM 104 can be executed without malfunction.

However, the buffer 105, the SDRAM 103, and the DIM measured with the wiring lengths a and b after branching being equal.
As shown in FIG. 10, the voltage waveform measurement data of each element of the M104 is disturbed due to various reflected waves and the like, and it is difficult to transmit a stable electric signal.

The present invention has been made in view of the above-mentioned problems of the prior art. In a wiring structure having a branch point, waveform disturbance due to reflection is minimized, and different wirings connected via the branch point are provided. An object of the present invention is to provide a wiring structure having a branch point and a method of forming a wiring configuration having a branch point, which can reduce a delay error between input components. More specifically, among the wirings between the branch point and the plurality of second elements, the wiring lengths of the longest and second longest wires a and b are (a + 2 × b) <in relation to the effective wavelength. λ
Wiring that satisfies the relationship of e minimizes waveform disturbances due to reflections, and further reduces the delay error between different input components by equalizing the electrical length of each wiring after the branch point. And a wiring structure forming method having a branch point.

[0012]

SUMMARY OF THE INVENTION A first aspect of the present invention is as follows.
In a wiring structure having a branch point provided with a wiring pattern for branching an output of a first element and supplying a signal to a plurality of second elements, a longest of a plurality of distances from the branch point to each of the plurality of second elements is provided. The length of the wiring having the distance of b: the length of the wiring having the second longest distance: a, the frequency of the transmission signal in the wiring structure f, the inductance with respect to the reference potential per unit length of the wiring, and the capacitance, respectively. a branch point characterized by satisfying (a + 2 × b) <λe with respect to an effective wavelength λe calculated by the formula, λe = 1 / f × 1 / √lc, where l and c In the wiring structure having

Further, in one embodiment of the wiring structure having a branch point according to the present invention, the position of the branch point is such that the electrical lengths of a plurality of wirings from the branch point to the plurality of second elements are substantially equal. In this case, the electrical length NL is determined by NL = Lp / λe when the wiring length from the branch point to the second element is Lp.

Further, in one embodiment of the wiring structure having a branch point according to the present invention, the plurality of second elements are constituted by different elements.

Further, in one embodiment of the wiring structure having a branch point according to the present invention, the wiring lengths a and b are set as a = b, and the structure satisfies a = b <λe / 3. And

Further, in one embodiment of the wiring structure having a branch point according to the present invention, when the wiring length a satisfies a ≒ 0, b <λe / 2 is satisfied. .

According to a second aspect of the present invention, there is provided a method of forming a wiring structure having a branch point having a wiring pattern for branching an output of a first element and supplying a signal to a plurality of second elements. , A plurality of distances from the plurality of second elements to each of the plurality of second elements, a wiring length having the longest distance: b, a wiring length having the second longest distance: a, a frequency of a transmission signal in the wiring structure being f, When an inductance and a capacitance with respect to a reference potential per unit length of the wiring are 1 and c, respectively, the effective wavelength λe calculated by the formula, λe = 1 / f × 1 / √lc, is expressed by (a + 2 × b 3.) A method of forming a wiring configuration having a branch point, wherein the wiring length is set as a configuration satisfying <λe.

Further, in one embodiment of the wiring structure forming method having a branch point according to the present invention, the position of the branch point is
Set at a position where each electrical length in a plurality of wirings from the branch point to the plurality of second elements is substantially equal,
Here, the electrical length NL is characterized in that when the wiring length from the branch point to the second element is Lp, NL = Lp / λe.

Further, in one embodiment of the method for forming a wiring structure having a branch point according to the present invention, the wiring lengths a and b are set to a
= B, and a = b <λe / 3.

Further, in one embodiment of the method for forming a wiring structure having a branch point according to the present invention, the wiring length a is a ≒.
When 0, b <λe / 2 is satisfied.

[0021]

According to the present invention, the pattern wiring of the high-speed signal having the branch point formed on the printed circuit board is the total of the longest two (a, b) of the wiring between the branch point and the plurality of second elements. This is a printed wiring board for wiring the first and second elements such that the wiring length (a + b) satisfies (a + 2 × b) <λe. However, λe is the effective wavelength determined from the operating frequency of this signal and the wiring structure. λe = 1 / f × 1 / √lcf
Is a signal frequency, and l and c are an inductance and an electric capacity with respect to a reference potential per unit length of each wiring. At this time, the branch point is determined to be the midpoint of the electrical length of the longest total of the two wiring lengths among the wiring between the branch point after the branch and the plurality of second elements, and the wiring before the branch is determined. I do. At this time, the electrical length is calculated from the propagation delay time, the operating frequency, and the wiring length obtained from L (inductive) and C (capacitive) per unit length of the wiring pattern, and the electrical length of the module component having the wiring pattern is calculated. In this case, the electrical length of this portion is also included in the total length of the two longest wires among the wires between the branch point after the branch and the plurality of second elements.

In the printed circuit board formed according to the wiring structure having the branch point and the wiring configuration forming method of the present invention, since the electrical length from the branch point to the input terminal of each input component is equal, the signal delay error is extremely small. Further, since the wiring length between the farthest ends after the branching is set to satisfy the condition of a + 2 × b <λe with respect to the effective wavelength λe determined by the operating frequency of the signal, waveform disturbance due to reflection is extremely small.

[0023]

[Embodiment 1] An embodiment of a wiring structure having a branch point and a method of forming a wiring structure having a branch point according to the present invention will be described with reference to the drawings. First, a wiring configuration having a branch point according to the first embodiment of the present invention will be described with reference to FIG.

FIG. 2 shows an example of a wiring structure having a branch point provided with a wiring pattern for branching the output of the first element and supplying signals to a plurality of second elements.
Three resistors 302 and three transmission lines 310, 320, 33
0, and a circuit having a configuration including the second elements P and 303 and the second elements Q and 304. Each of the second elements P and 303 and the second elements Q and 304 is connected to each of the transmission lines 320 and 330 after the branch point 350.
Here, the three transmission lines 310, 320, and 330 correspond to the pattern wiring on the printed wiring board, and are arranged among the elements according to the arrangement positions of the component having the output element, the component having the input element, and the component having the input element group. , The respective wiring length L
1, L2 and L3.

In the wiring configuration having such a branch point 350, in the present invention, the length of the wiring between the branch point and the plurality of second elements after branching is defined as follows. Of the wiring lengths between the branch point and the plurality of second elements after the branch, the longest two wiring lengths are L2 and L3, respectively, and the longer wiring is L3. At this time, the pattern wiring determined by the operating frequency and the material of the printed wiring board is set to have a length satisfying the condition of (L2 + 2 × L3) <λe with respect to the effective wavelength: λe.

In FIG. 2, since only two second elements are connected to the branch point 350, the longest two of the wiring lengths between the branch point and the plurality of second elements after the branch are formed. The wiring lengths correspond to L2 and L3 shown in FIG. 2, respectively. In addition to the configuration example shown in FIG.
In the case where the above-described second elements are connected, the length of the wiring between the branch point and the plurality of second elements after the branch is L
, L3, L4, L5..., The longest two wiring lengths are selected from the plurality of wiring lengths,
In the case of 2, L3, the wiring length satisfying the condition of (L2 + 2 × L3) <λe is set based on the effective wavelength: λe determined by the operating frequency and the material of the printed wiring board.

In the case where a branch can be made at the midpoint of the total length of the two longest wires among the wires between the branch point and the plurality of second elements, L2 = L3, so the condition (L2 + 2 × L3) is satisfied.
<Λe is L2 = L3 <λe / 3.

In the printed wiring board and the wiring method according to the present invention, the arrangement position of the component having the input element and the component having the input element group are determined so that the wiring satisfies the above conditions. At this time, it is desirable that the wiring be formed as the shortest wiring satisfying the above conditions. The measured value of the wiring length is the Manhattan length obtained from the position of the input pin of the component having the input element and the input pin of the component having the input terminal group, that is, the case where the wiring is squared on the X axis and the Y axis. Use length.

For example, in the configuration of FIG. 2, the impedance of each wiring: Z ₀ and the length Ln are as follows: L1: Z ₀ = 75Ω, 110 mm L2: Z ₀ = 60Ω, 40 mm L3: Z ₀ = 60Ω, 40 mm Is set to

A specific method for setting the wiring length will be described. An example in which the operating frequency on the circuit is 100 MHz will be described. In this case, the cycle: T becomes T = 10 ns. Hereinafter, R, L, per unit length of the pattern wiring,
C is described assuming two modes.

As a first example, R, L, and C per unit length of the pattern wiring are R = 6.741e-3 and L, respectively.
= 4.47e-10, C = 7.836e-14, the wiring length setting process will be described. In this case, the characteristic impedance is Z ₀ = √L / C = 75Ω, and the signal propagation speed is v = 1 / √LC = 0.1689 mm / pS.
In the case of the first example, the wiring length of one effective wavelength is obtained as follows. One effective wavelength is λe = T × v, λ
e = 10 nS × 0.1689 mm / pS = 16.89c
m, and the wiring length of one effective wavelength in the first example is 16.8.
9 cm.

The arrangement processing of each element in this case will be described. The wiring length of one effective wavelength is 16.89 cm. At this time, the SDRA of FIG.
Consider a configuration in which M and DIMM are connected after a branch point. FIG. 1 shows an example of a circuit configuration in which elements are arranged according to the above condition: (L2 + 2 × L3) <λe.

The wiring configuration shown in FIG. 1 has a branch point 401, and the CPU 402, SDRAM 403, D
A buffer 405 is provided adjacent to the IMM 404 and the CPU 402, and the elements are the same as those in the configuration in FIG. In this wiring configuration, a clock signal,
Alternatively, a high-speed signal such as an address signal used for reading data from and writing data to the memory is transmitted.

In the configuration shown in FIG. 1, the wiring length between the elements is determined according to the above condition of the present invention: (L2 + 2 × L3) <λe. In the configuration of FIG. 1, among the wirings after the branch point 401, the configuration is such that the branch can be made at the middle point of the total wiring length of the longest two wirings, so that the condition (L2 + 2 × L3) <λe
Is applied as L2 = L3 <λe / 3. In this case, as shown in the figure, if the wiring length from the branch point 401 to the SDRAM 403 is a and the wiring length from the branch point 401 to the DIMM 404 is b, a (L2) = b (L3), that is, a = b < The wiring length can be set as λe / 3.

Λe = 10 nS × 0.1689 mm / pS
= 16.89 cm, λe / 3 is 5.63 cm
Becomes From the condition L2 = L3 <λe / 3 in the case of equal-length wiring, the distance from the branch point 401 of the input pin of the component having the input element and the input pin of the component having the input element group is 2 × λe / 3 in Manhattan length. = 11.26 cm or less. In this way, the maximum distance from the branch point of the second element to be connected after the branch point to the second element is set. That is, a = b <11.26 cm.

Next, the setting position of the branch point, that is, the setting of the distance between the branch point and the plurality of second elements will be described. The electrical length as an electrical characteristic value of the wiring derived from each value of the wiring length such as a and b shown in FIG. 1 and the effective wavelength: λe:
NL is defined. The electrical length NL is defined as NL = Ln / λe, where Ln is the wiring length. In the configuration of FIG. 1, the electrical length from the branch point 401 to the SDRAM 403 is a / λe, and the electrical length from the branch point 401 to the DIMM 404 is
The electrical length up to is b / λe.

The branch point includes a plurality of second nodes connected after the branch point.
Elements (SDRAM 403, DIMM 40 in FIG. 1)
4) The input pin of the component having the input element and the position of the point where the distance from the branch point to the input pin of the component having the input element group is equal in electrical length are set. Wiring is performed from the branch point set in this way to the output pin of the component having the first element (the CPU 402 in FIG. 1) which is the output element. Various components such as a resistor can be connected between the first element and the branch point. In this way, the position of the branch point is set, and the wiring configuration is determined.

The wiring configuration shown in FIG. 1 is such that a = b <λe / 3, and the branch point is set to have the same electrical length from the branch point to each second element. FIG. 3 shows a time change of a voltage waveform in each element in this circuit configuration.

The horizontal axis of FIG. 3 is time (ns: nanosecond), and the vertical axis is voltage (V: volt). Each of the three waveforms is a buffer 405, an SDRAM 403, and a DIMM 40.
4 is voltage waveform data that changes with time and is measured in each element. As described above, ideally, the SDRAMs 403 and D
This is a mode in which the IMM 404 draws a similar voltage waveform. FIG.
According to the wiring method of the present invention, a substantially ideal voltage waveform can be obtained in a wiring configuration satisfying the above conditions as shown in FIG. With such a waveform, for example, data reading processing of the SDRAM 403 and the DIMM 404 can be executed without malfunction according to the operating frequency of the CPU 402.

Next, as a second example, R = 6.527e-
3, L = 4.187e-10, C = 1.166e-13
A description will be given of the wiring configuration determination process in the case of (1). At this time, the characteristic impedance is Z ₀ = √L / C = 60Ω, and the signal propagation speed is v = 1 / √LC = 0.143 mm / pS
Becomes In this case, one effective wavelength is λe = T × v,
e = 10 nS × 0.143 mm / pS = 14.3 cm, and the wiring length for one effective wavelength is 14.3 cm.

The wiring length for one effective wavelength is 14.3 cm, and λe / 3 = 4.77 cm. Based on the condition L2 = L3 <λe / 3 for equal length wiring, the distance from the branch point to the input pin of the component having the input element and the input pin of the component having the input element group is 2 × λe / manhattan length. 3
= 9.54 cm or less. In this way, the maximum distance from the branch point to the second element is obtained. As in the first example, the position of the branch point is determined by a plurality of second elements (SDRAM 40 in FIG. 1) connected after the branch point.
(3, DIMM 404) is set at a position where the distance from the branch point to the input pin of the component having the input element and the input pin of the component having the input element group is equal in electrical length.

As described above, according to the wiring method of the present invention, the first and second wiring lengths among the wiring lengths from the branch point to the second element are determined by the operating frequency and the effective wavelength determined by the material of the printed wiring board. : Based on λe, condition (L2 + 2 × L3) <
λe, and the position of the branch point is set to a position where the distance from the branch point to each of the second elements is equal in electrical length. According to this wiring configuration determination method, even when different components are installed after the branch point, the electrical delay times of the wiring after the branch almost match, and the waveform disturbance due to reflection can be minimized. As shown in the figure, a circuit without disturbance in the voltage waveform in each element after branching is realized.

Next, a description will be given of a wiring configuration determination process in the case where a component having an input terminal group, which is a second element connected after the branch point, further includes some input elements. An input element group having several input elements therein includes, for example, a module device in which a plurality of components having input elements are mounted. FIG. 4 shows a circuit configuration example. FIG. 4 shows one first element 301, one resistor 302, three transmission lines 310, 320, 330, and a second element group 60.
A circuit having a configuration including a second element P, 601, a second element R, 602, and a second element Q, 304 in 0,
The second element P, 601, the second element R, 602, and the second element
Each of the elements Q and 304 is connected to each of the transmission lines 320 and 330 after the branch point 350. The wiring lengths L1, L2, L3 are the same as in the configuration of FIG.
In the configuration of FIG. 4, there is a wiring length Lm between the second elements P and 601 and the second elements R and 602.

In such a case, it is necessary to consider L2 + L3 + Lm as the total wiring length after the branch point 350. At this time, when there are a plurality of wirings inside the second element, Lm having the longest electrical length is selected. The signal transmitted from the output element is reflected at each input element and goes to another input element, but the above-mentioned conditional expression is applied to the total wiring length after the branch, that is, L2 + L3 + Lm. That is, in this case, (L3 + 2 × (L2 + L
m)) The wiring configuration satisfies the condition of <λe.

By adopting a wiring configuration that satisfies the above equation, even if there is signal reflection between the elements on the wiring, the signal at one input terminal viewed from the branch point has a total reflected waveform. Since the wavelength is less than the wavelength, there is no large disturbance in the original waveform. Therefore, a good waveform is obtained in each input element.

[Embodiment 2] In the above description, only two wirings are formed after the branch point. However, the wiring configuration determination processing when there are three or more wirings after the branch point will be described. A second embodiment of the present invention will be described below.

FIG. 5 shows an example of a circuit configuration when the number of branch wirings is three. FIG. 5 shows one first element 701, one resistor 702, and four transmission lines 710, 720, 73.
0, 740, the second element S, 703, and the second element T, 70
4 and a circuit having a second element U, 705. Each of the second element S, 703, the second element T, 704, and the second element U, 705 is a transmission line after the branch point 750. 720, 730, and 740, respectively. Here, the four transmission lines 710 to 740 correspond to the pattern wiring on the printed wiring board, and each of the four transmission lines 710 to 740 is arranged between the elements according to the arrangement position of the component having the output element, the component having the input element, and the component having the input element group. It has a certain wiring length L1, L2, L3, L4.

In the wiring configuration having such a branch point 750, of the wiring between the branch point 750 after the branching and the plurality of second elements, the longest total wiring length is determined by the operating frequency and the printed wiring. It is set based on the effective wavelength λe determined by the material of the plate. When the longest one of L2, L3, and L4 is L3, and the next longest wiring is L2, (L2 + 2
× L3) The arrangement position of the component having the input element and the component having the input element group is determined so that the length satisfies the condition of <λe. In FIG. 5, an example in which three branch wirings are provided after the branch point 750 has been described. However, even when there are four or more branch wirings, the longest wiring and the second longest wiring length among them (L2 + 2 × L3) The setting is made so as to satisfy the condition of <λe. As in the first embodiment, the position of the branch point is determined by a plurality of second elements connected after the branch point (the second element in FIG. 5).
Positions of the input pins of the elements S, 703, the second elements T, 704, and the second elements U, 705) and the points at which the distance from the branch point to the input pin of the component having the input element group becomes equal in electrical length. Set to.

Specifically, in the configuration of FIG. 5, the impedance of each wiring: Z ₀ and the length Ln are: L1: Z ₀ = 75Ω, 110 mm L2: Z ₀ = 60Ω, 40 mm L3: Z ₀ = 60Ω, 40 mm L4: Z ₀ = 60Ω, set as 40 mm.

FIG. 6 shows the time change of the voltage waveform in each element in the circuit configuration set as described above. The horizontal axis in FIG. 6 is time (ns: nanosecond), the vertical axis is voltage (V: volt), and the waveforms are the first element 701 and the second element, respectively.
This is voltage waveform data that changes with time and is measured in the elements S and 703, the second elements T and 704, and the second elements U and 705. According to the wiring method of the present invention, as shown in FIG. 6, when the wiring configuration satisfies the above-described conditions, the voltage waveform in each element changes uniformly, and the waveform disturbance is suppressed. Is obtained.

[Third Embodiment] Next, as a third embodiment, a description will be given of a wiring configuration determining process when there is a large difference in the lengths of a plurality of wirings after a branch point.

FIG. 7 shows one first element 901, one resistor 902, and three transmission lines 910, 920, and 930.
This is a circuit having a configuration having the second element P, 903 and the second element Q, 904, and the second element P, 903 and the second element
Each of the elements Q and 904 is connected to each of the transmission lines 920 and 930 after the branch point 950. Here, the three transmission lines 910, 920, and 930 correspond to pattern wiring on a printed wiring board, and include components having output elements,
Depending on the arrangement position of the component having the input element and the component having the input element group, certain wiring lengths L1 and L
2, L3.

In the example shown in FIG. 7, when the branch point 950 is extremely biased to one side, it is assumed that L2 is short and L2 ≒ 0.
At this time, the conditional expression described in the first embodiment: (L2 + 2
× L3) <λe can be rewritten as follows. That is, (2 × L3) <λe, and L3 <λe / 2.

At this time, R, L, and C per unit length of the pattern wiring are R = 6.527e-3 and L = L, respectively.
4.187e-10, C = 1.166e-13,
The characteristic impedance is Z ₀ = √L / C = 60Ω, and the signal propagation speed is v = 1 / √LC = 0.143 mm / pS. In this case, one effective wavelength is λe = T × v, and λe =
10 nS × 0.143 mm / pS = 14.3 cm, and L3 <λe / 2 = 7.15 cm.

FIG. 8 shows waveforms when L3 = 7 cm and L2 = 0.1 cm. The horizontal axis of FIG. 8 is time (ns: nanosecond), the vertical axis is voltage (V: volt), and the waveforms are respectively the first element 901, the second elements P and 903, and the second elements Q and 904. Is voltage waveform data that changes with time and is measured in FIG. As shown in FIG. 8, in the case of a wiring configuration satisfying the above-described conditions according to the wiring method of the present invention, the voltage waveform in each element changes uniformly, and a substantially ideal voltage waveform in which waveform disturbance is suppressed is obtained. can get.

The present invention has been described in detail with reference to the specific embodiments. However, it is obvious that those skilled in the art can modify or substitute the embodiment without departing from the spirit of the present invention. That is, the present invention has been disclosed by way of example, and should not be construed as limiting. In order to determine the gist of the present invention, the claims described at the beginning should be considered.

[0057]

As described above, according to the wiring structure having a branch point and the method of forming a wiring structure having a branch point of the present invention, the first and second wiring lengths from the branch point to the second element are obtained. Based on the operating wavelength and the effective wavelength λe determined by the material of the printed wiring board, the condition (L
2 + 2 × L3) <λe, and the position of the branch point is set to a position where the distance from the branch point to each of the second elements is equal to the electrical length. Even if the device is installed, the electrical delay time in the wiring after branching is almost the same, and the waveform disturbance due to reflection can be minimized, realizing a circuit without voltage waveform disturbance in each element after branching Is done.

[Brief description of the drawings]

FIG. 1 is a diagram showing a component arrangement and a schematic wiring in a wiring structure having a branch point according to the present invention.

FIG. 2 is a diagram illustrating a wiring length setting process in a wiring structure having a branch point according to the present invention.

3 is a diagram showing an analysis result of a voltage waveform in the wiring structure having a branch point according to the present invention shown in FIG. 1;

FIG. 4 shows a wiring structure having a branch point according to the present invention.
FIG. 4 is a diagram illustrating a configuration having a wiring length Lm in a second element.

FIG. 5 is a diagram illustrating a configuration having three wirings after a branch point as a second embodiment of the wiring structure having a branch point according to the present invention.

FIG. 6 is a diagram showing an analysis result of a voltage waveform in the wiring structure having a branch point according to the present invention shown in FIG. 5;

FIG. 7 is a diagram illustrating a configuration having a wiring portion having a short wiring length after a branch point as a third embodiment of the wiring structure having a branch point according to the present invention.

8 is a diagram showing an analysis result of a voltage waveform in the wiring structure having a branch point according to the present invention shown in FIG. 7;

FIG. 9 is a diagram schematically illustrating component arrangement and wiring in a conventional circuit configuration having a branch point.

FIG. 10 is a diagram showing an analysis result of a voltage waveform in the conventional circuit configuration having a branch point shown in FIG.

[Explanation of symbols]

 101 branch point 102 CPU 103 SDRAM 104 DIMM 105 buffer 301 first element 302 resistor 303, 304 second element 310, 320, 330 transmission line 350 branch point 401 branch point 402 CPU 403 SDRAM 404 DIMM 405 buffer 600 second element group 601 , 602 Second element 701 First element 702 Resistance 703, 704, 705 Second element 710, 720, 730, 740 Transmission line 750 Branch point 901 First element 902 Resistance 903, 904 Second element 910, 920, 930 Transmission line 950 junction

Claims (9)

[Claims] 1. A wiring structure having a branch point provided with a wiring pattern for branching an output of a first element and supplying a signal to a plurality of second elements, wherein a plurality of branching points from the branch point to each of the plurality of second elements are provided. , The wiring length having the longest distance: b, the wiring length having the second longest distance: a, the frequency of the transmission signal in the wiring structure being f, the inductance with respect to the reference potential per unit length of the wiring. , Λe = 1 / f ×
A wiring structure having a branch point, wherein (a + 2 × b) <λe is satisfied with respect to an effective wavelength λe calculated by 1 / √lc. 2. The wiring structure having the branch point, wherein the position of the branch point is set to a position at which each electrical length in a plurality of wirings from the branch point to the plurality of second elements is substantially equal. 2. The branching point according to claim 1, wherein the electrical length NL is determined by NL = Lp / λe, where Lp is the wiring length from the branching point to the second element. Wiring structure having. 3. The wiring structure having a branch point according to claim 1, wherein in the wiring structure having the branch point, the plurality of second elements are constituted by different elements. 4. The wiring structure having the branch point, wherein the wiring lengths a and b are set as a = b, and a = b <λe / 3 is satisfied. 3. A wiring structure having a branch point according to any one of the above items 3. 5. The wiring structure having the branch point, wherein when the wiring length a satisfies a ≒ 0, b <λe / 2 is satisfied. A wiring structure having a branch point according to any one of the above. 6. A method for forming a wiring structure having a branch point provided with a wiring pattern for branching an output of a first element and supplying a signal to a plurality of second elements, wherein: from a branch point to each of the plurality of second elements. Of the plurality of distances, the wiring length having the longest distance: b, the wiring length having the second longest distance: a, the frequency of the transmission signal in the wiring structure being f, the reference potential per unit length of the wiring Λe = 1 / f ×
A wiring configuration forming method having a branch point, wherein a wiring length is set as a configuration satisfying (a + 2 × b) <λe with respect to an effective wavelength λe calculated by 1 / √lc. 7. A method of forming a wiring structure having a branch point, wherein the position of the branch point is set to a position at which respective electrical lengths of a plurality of wirings from the branch point to the plurality of second elements are substantially equal. 7. The wiring having a branch point according to claim 6, wherein the electrical length NL is determined by NL = Lp / λe, where Lp is a wiring length from the branch point to the second element. Configuration forming method. 8. The method for forming a wiring structure having a branch point, wherein the wiring lengths a and b are set as a = b, and a = b <λe / 3 is satisfied. 8. A method for forming a wiring configuration having a branch point according to 6 or 7. 9. The method for forming a wiring structure having a branch point, wherein the wiring length a satisfies b <λe / 2 when a ≒ 0. 8. The method for forming a wiring configuration having a branch point according to 7.