JP2015082803A - Signal transmission line and transmission line design method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a signal transmission line and a transmission line design method that can restrain increase in transmission loss of a signal even if a transmission line in a backplane gets long.SOLUTION: A cross section size of a transmission line 2 inside a dielectric material 3 used in communication between two daughter cards 7 of a plurality of daughter cards 7 is determined on the basis of distance x between the two daughter cards 7. This can restrain increase in transmission loss of a signal even if the transmission line 2 in a backplane 1 gets long.

Description

  The present invention relates to a signal transmission line and a transmission line design method for realizing high-speed transmission lines in a backplane.

In recent years, the speed of digital transmission has been remarkably increased, and the realization of high-speed transmission is also required in backplane transmission.
Space saving, weight reduction, and high reliability can be achieved by connecting the substrates with a backplane rather than connecting the two substrates with a cable.

  Patent Document 1 below discloses a signal transmission line that realizes a high-speed transmission line in a backplane. In this signal transmission line, a tapered wiring, a wide wiring width, and a low characteristic impedance are disclosed. Combined with wiring.

JP 2006-245291 A (paragraph number [0016], FIG. 3)

  Since the conventional signal transmission line is configured as described above, it is possible to increase the speed of the transmission line in the backplane, but the transmission line in the backplane is a long wiring exceeding tens of centimeters. In this case, there is a problem that the transmission loss of the signal increases.

  The present invention has been made to solve the above-described problems, and provides a signal transmission line and a transmission line design method capable of suppressing an increase in signal transmission loss even when the transmission line in the backplane becomes long. For the purpose.

  A signal transmission line according to the present invention includes a backplane in which a transmission line that is a strip line is wired in a dielectric, and a line that is electrically connected to the transmission line that is wired in the dielectric of the backplane. A plurality of daughter cards, and the plurality of daughter cards have a function of communicating signals with other daughter cards through a transmission line wired in the dielectric of the backplane. Among them, the cross-sectional dimension of the transmission line in the dielectric used for communication between two daughter cards is determined based on the distance between the two daughter cards.

  According to the present invention, the cross-sectional dimension of the transmission line in the dielectric used for communication between two daughter cards among the plurality of daughter cards is determined based on the distance between the two daughter cards. Therefore, even if the transmission line in the backplane becomes longer, an increase in signal transmission loss can be suppressed.

1 is a perspective view showing a signal transmission line according to Embodiment 1 of the present invention. It is A-A 'sectional drawing of FIG. It is a block diagram which shows a part of communication apparatus to which the signal transmission line by Embodiment 1 of this invention is applied. It is explanatory drawing which shows the relationship between the line width w of the transmission line 2 in the backplane 1, and a passage characteristic. It is explanatory drawing which shows that the characteristic impedance of the transmission line from which transmission characteristics become the maximum differs with respect to the different line length of the transmission line. It is a flowchart which shows the transmission line design method by Embodiment 1 of this invention. It is explanatory drawing which shows the track | line width corresponding to the distance (track length) between two daughter cards.

Embodiment 1 FIG.
1 is a perspective view showing a signal transmission line according to Embodiment 1 of the present invention, and FIG. 2 is a cross-sectional view taken along line AA ′ of FIG.
1 and 2, a backplane 1 is a circuit board in which a transmission line 2 as a strip line is wired in a dielectric 3, and the dielectric 3 is sandwiched between ground conductors 4 and 5 from above and below.
The transmission line 2 which is a strip line has a line width w, a line thickness t, and the dielectric 3 has an electric body thickness b.
In FIG. 2, only one transmission line 2 is described for simplicity of explanation, but a plurality of transmission lines 2 are wired.
For example, when the daughter card 7a performs signal communication with each of the daughter cards 7b to 7d, at least the transmission line 2 connecting the daughter card 7a and the daughter card 7b, the transmission line 2 connecting the daughter card 7a and the daughter card 7c, A transmission line 2 connecting the daughter card 7a and the daughter card 7d is wired.

The connectors 6a to 6d are connecting parts for connecting the daughter cards 7a to 7d to the backplane 1.
The daughter cards 7a to 7d have lines that are electrically connected to the transmission line 2 in the backplane 1 via connectors 6a to 6d.
The daughter cards 7a to 7d have a function of communicating signals with other daughter cards through the transmission line 2 in the backplane 1.

FIG. 3 is a block diagram showing a part of a communication apparatus to which the signal transmission line according to Embodiment 1 of the present invention is applied.
FIG. 3 shows an example in which two daughter cards 7 are connected to one backplane 1.
The transmission circuit 11 is a circuit that transmits a signal to be communicated. Reference numeral 12 denotes an output impedance of the transmission circuit 11, which is connected to the transmission end line 13.
The receiving circuit 14 is a circuit that receives a signal transmitted from the transmitting circuit 11, 15 is a terminating resistor, and 16 is a receiving end line.
The transmission circuit 11, the output impedance 12, and the transmission end line 13 are configured on one daughter card 7 (for example, the daughter card 7a) in FIG. 1, and the reception circuit 14, the termination resistor 15, and the reception end. The track 16 is also configured on one daughter card 7 (for example, daughter card 7b) in FIG.
The transmission line 17 corresponds to the transmission line 2 in the backplane 1 of FIG.
The connector 18 corresponds to the connector 6 in the backplane 1 of FIG.

Next, the operation will be described.
The transmission line 2 in the backplane 1 is wired in a dielectric 3, and the dielectric 3 is sandwiched between ground conductors 4 and 5 from above and below.
For example, when the daughter card 7a and the daughter card 7b transmit and receive signals, the lines in the daughter cards 7a and 7b are connected by the connectors 6a and 6b (in the example of FIG. 3, the transmission end line 13 and the reception end line 16 correspond). However, in the state electrically connected with the transmission line 2 in the back plane 1 which connects the daughter card 7a and the daughter card 7b, a signal is transmitted / received through the transmission line 2.
Similarly, for example, when the daughter card 7a and the daughter card 7d transmit and receive signals, the connectors 6a and 6d cause the lines in the daughter cards 7a and 7d to be transmitted in the backplane 1 connecting the daughter card 7a and the daughter card 7d. Signals are transmitted and received through the transmission line 2 while being electrically connected to the line 2.

Here, a design method of the transmission line 2 in the backplane 1 will be described.
In the example of FIG. 2, the line width of the transmission line 2 which is a strip line is w, the line thickness of the transmission line 2 is t, and the electric body thickness of the dielectric 3 is b. The value of the wiring width w, which is a design value that is generally easy to change, is considered with the line thickness t of 2 and the electrical thickness b of the dielectric 3 as constant values.

For example, when the daughter card 7a transmits a signal to the daughter card 7d, when the characteristic impedance of the daughter cards 7a and 7d is Z ₀ and the characteristic impedance Z of the transmission line 2 in the backplane 1, the characteristic impedance mismatch ( Since multiple reflection due to Z ₀ ≠ Z) occurs, it is necessary to comprehensively consider the multiple reflection and transmission loss, and to determine the wiring width w from the characteristic impedance Z that provides the best transmission characteristics.

The longer the distance between the two daughter cards 7, the longer the line length of the transmission line 2 used for communication between the two daughter cards 7, and the resistance value increases. When the resistance value of the transmission line 2 increases, the signal transmission loss in the transmission line 2 increases.
Therefore, the longer the distance between the two daughter cards 7, the wider the line width w of the transmission line 2 used for communication between the two daughter cards 7, and the resistance value of the transmission line 2 is reduced. 2 to reduce signal transmission loss.
However, if the line width w of the transmission line 2 is too large, multiple reflection due to mismatch (Z ₀ ≠ Z) between the characteristic impedance Z ₀ of the daughter card 7 and the characteristic impedance Z of the transmission line 2 in the backplane 1. Will occur.

Here, FIG. 4 is an explanatory diagram showing the relationship between the line width w of the transmission line 2 and the pass characteristics in the backplane 1.
FIG. 5 is an explanatory diagram showing that the characteristic impedance of the transmission line having the maximum passing characteristic differs with respect to the different line lengths of the transmission line 2.
As can be seen from FIG. 4, when the line width w of the transmission line 2 is increased, the resistance value of the transmission line 2 is reduced and the passing characteristics are improved. However, if the line width w of the transmission line 2 is increased too much, Multiple reflections due to impedance mismatch (Z ₀ ≠ Z) occur, and pass characteristics are degraded.

FIG. 6 is a flowchart showing a transmission line design method according to Embodiment 1 of the present invention.
FIG. 7 is an explanatory diagram showing a line width w corresponding to a distance x (line length) between two daughter cards 7.
The transmission line design method will be described below with reference to FIG.
First, the line width w corresponding to the distance x (line length) between the two daughter cards 7 is calculated (step ST1 in FIG. 6).
As shown in FIG. 7, the longer the distance x (line length) between the two daughter cards 7, the wider the line width w is calculated.

式（１）において、Ｓ_２１は通過特性、Ｔ_１（ｗ）は図３の送信端線路１３から伝送線路１７への透過係数、Ｔ_２（ｗ）は図３の伝送線路１７から受信端線路１６への透過係数である。
また、α_ｃ（ｗ）は図３の伝送線路１７の導体損失、α_ｄは図３の伝送線路１７の誘電損失、ｘは図３の伝送線路１７の線路長である。
この実施の形態１では、式（１）において、所望の線路長ｘ対して、通過特性Ｓ_２１が最も大きくなる線路幅ｗを決定する。
ただし、式（１）は、あくまでも簡易式であり、線路幅ｗの算出精度を高める必要がある場合には、シミュレータを使用する。 Here, the following formula (1) shows the correspondence between the distance x (line length) between the two daughter cards 7 and the line width w.

In Expression (1), S ₂₁ is a pass characteristic, T ₁ (w) is a transmission coefficient from the transmission end line 13 to the transmission line 17 in FIG. 3, and T ₂ (w) is a transmission end line from the transmission line 17 in FIG. 16 is the transmission coefficient.
Α _c (w) is the conductor loss of the transmission line 17 in FIG. 3, α _d is the dielectric loss of the transmission line 17 in FIG. 3, and x is the line length of the transmission line 17 in FIG.
In the first embodiment, in formula (1), for the desired line length x, passing characteristic S ₂₁ to determine the most larger line width w.
However, Expression (1) is a simple expression to the last, and a simulator is used when it is necessary to increase the calculation accuracy of the line width w.

Next, the line width w corresponding to the distance x between the two daughter card 7, passing characteristic _{S 21} is maximized line width _{w pass · max} (in FIG. 4, line width pass characteristic _{S 21} is maximized) comparing (step ST2), the line width w corresponding to the distance x is shorter than the line width _{w pass · max} which pass characteristic _{S 21} is maximized _{(w <w pass · max),} between two daughter card 7 The line width of the transmission line 2 used for the communication is determined as the line width w corresponding to the distance x between the two daughter cards 7 (the line width w calculated by the expression (1)) (step ST3).
On the other hand, the line width w corresponding to the distance x, passing characteristic _{S 21} is longer than the line width _{w pass · max} which maximizes _{(w ≧ w pass · max)} , used for communication between the two daughter card 7 transmits the line width of the line 2, passing characteristic _{S 21} to determine the line width _{w pass · max} which maximizes (step ST4).

  As apparent from the above, according to the first embodiment, the cross-sectional dimension of the transmission line 2 used for communication between the two daughter cards 7 among the plurality of daughter cards 7 is between the two daughter cards 7. Since it is configured so as to be determined based on the distance x, even if the transmission line 2 in the backplane 1 becomes longer, there is an effect that an increase in signal transmission loss can be suppressed.

Embodiment 2. FIG.
In the first embodiment, the line width w of the transmission line 2 is determined with the line thickness t of the transmission line 2 and the electric body thickness b of the dielectric 3 as constant values. The line thickness t of the transmission line 2 may be determined by setting w and the electric body thickness b of the dielectric 3 to constant values, and the same effect as in the first embodiment can be obtained.
In this case, as the distance x between the two daughter cards 7 is longer, the line thickness t of the transmission line 2 used for communication between the two daughter cards is increased as in the case where the wiring width w of the transmission line 2 is determined. To do.
However, if the line thickness t of the transmission line 2 is made too thick, the characteristic impedance Z ₀ in the daughter card 7 and the transmission in the back plane 1 are the same as when the line width w of the transmission line 2 is made too wide. Multiple reflections due to mismatch (Z ₀ ≠ Z) with the characteristic impedance Z of the line 2 occur.

式（２）において、Ｓ_２１は通過特性、Ｔ_１（ｔ）は図３の送信端線路１３から伝送線路１７への透過係数、Ｔ_２（ｔ）は図３の伝送線路１７から受信端線路１６からへの透過係数である。
また、α_ｃ（ｔ）は図３の伝送線路１７の導体損失、α_ｄは図３の伝送線路１７の誘電損失、ｘは図１の伝送線路１７の線路長である。
この実施の形態２では、式（２）において、所望の線路長ｘ対して、通過特性Ｓ_２１が最も大きくなる線路厚ｔを決定する。
ただし、式（２）は、あくまでも簡易式であり、線路厚ｔの算出精度を高める必要がある場合には、シミュレータを使用する。 Therefore, in the second embodiment, first, the line thickness t corresponding to the distance x between the two daughter cards 7 is calculated.
Here, the following equation (2) shows the correspondence between the distance x (line length) between the two daughter cards 7 and the line thickness t.

In Expression (2), S ₂₁ is a pass characteristic, T ₁ (t) is a transmission coefficient from the transmission end line 13 to the transmission line 17 in FIG. 3, and T ₂ (t) is a transmission end line from the transmission line 17 in FIG. The transmission coefficient from 16 to.
Α _c (t) is the conductor loss of the transmission line 17 in FIG. 3, α _d is the dielectric loss of the transmission line 17 in FIG. 3, and x is the line length of the transmission line 17 in FIG.
In the second embodiment, in formula (2), for the desired line length x, passing characteristic S ₂₁ to determine the most larger line thickness t.
However, Expression (2) is a simple expression to the last, and a simulator is used when it is necessary to increase the calculation accuracy of the line thickness t.

Next, the line thickness t corresponding to the distance x between the two daughter card 7, compares the line thickness t _{pass · max} which pass characteristic S ₂₁ is maximized, the distance corresponding to the x line thickness t is, pass characteristics if thinner than the line thickness _{t pass · max} where S ₂₁ is maximized _{(t <t pass · max)} , the line thickness of the transmission line 2 for use in communication between the two daughter card 7, between two daughter card 7 The line thickness t corresponding to the distance x (the line thickness calculated by the equation (2)) is determined.
On the other hand, line thickness t corresponding to the distance x is used for communication between it thicker than the line thickness _{t pass · max} which pass characteristic _{S 21} is maximized _{(t ≧ t pass · max)} , 2 single daughter card 7 the line thickness of the transmission line 2, passing characteristic _{S 21} to determine the line thickness _{t pass · max} of maximum.

Embodiment 3 FIG.
In the first and second embodiments, the transmission line 2 wired to the backplane 1 is a strip line (a line wired in the dielectric 3). However, the transmission line 2 wired to the backplane 1 is wired to the backplane 1. The transmission line 2 may be a microstrip line (a line wired on the dielectric 3).
Also in this case, among the plurality of daughter cards 7, the cross-sectional dimension of the transmission line 2 used for communication between the two daughter cards 7 is determined based on the distance between the two daughter cards 7. Unlike the first and second embodiments, the longer the distance between the two daughter cards 7, the smaller the value of the line width w of the transmission line 2 used for communication between the two daughter cards 7.

The reason why the line width w of the transmission line 2 used for communication between the two daughter cards 7 is reduced as the distance between the two daughter cards 7 increases is that when the transmission line 2 is a microstrip line, the transmission line 2 This is because the dielectric loss is not constant as in the case of a strip line, and when the wiring width w is widened, the ratio of the dielectric loss increases due to the reduction of the conductor loss.
Even when the transmission line 2 is a microstrip line, the optimum value of the line width w exists as in the case of the stripline.

  In the first to third embodiments, the transmission line 2 is a strip line or a microstrip line. However, the transmission line 2 may be a single-ended signal line or a differential signal line. There may be.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 1 Backplane, 2 Transmission line (strip line), 3 Dielectric, 4,5 Ground conductor, 6a-6d connector, 7a-7d Daughter card, 11 Transmission circuit, 12 Output impedance of transmission circuit, 13 Transmission end line, 14 Receiving circuit, 15 termination resistor, 16 receiving end line, 17 transmission line, 18 connector.

Claims (9)

A backplane in which a transmission line, which is a strip line, is wired in a dielectric;
A plurality of daughter cards having transmission lines wired in the dielectric of the backplane and lines electrically connected;
The plurality of daughter cards have a function of communicating signals with other daughter cards through a transmission line wired in the dielectric of the backplane,
A signal in which a cross-sectional dimension of a transmission line in the dielectric used for communication between two daughter cards among the plurality of daughter cards is determined based on a distance between the two daughter cards. Transmission line.   2. The signal according to claim 1, wherein the longer the distance between the two daughter cards, the wider the line width of the transmission line in the dielectric used for communication between the two daughter cards. Transmission line. When the line width corresponding to the distance between the two daughter cards is shorter than the line width that maximizes the pass characteristic, the line width of the transmission line in the dielectric used for communication between the two daughter cards is 2 The line width corresponding to the distance between the two daughter cards is determined,
When the line width corresponding to the distance between the two daughter cards is longer than the line width at which the passing characteristic is maximized, the line width of the transmission line in the dielectric used for communication between the two daughter cards is The signal transmission line according to claim 1, wherein the line width is determined to have a maximum characteristic.   2. The signal according to claim 1, wherein the longer the distance between the two daughter cards, the thicker the line thickness of the transmission line in the dielectric used for communication between the two daughter cards. Transmission line. When the line thickness corresponding to the distance between the two daughter cards is thinner than the line thickness that maximizes the pass characteristic, the line thickness of the transmission line in the dielectric used for communication between the two daughter cards is 2 The line thickness corresponding to the distance between the two daughter cards is determined,
When the line thickness corresponding to the distance between the two daughter cards is thicker than the line thickness that maximizes the pass characteristic, the line thickness of the transmission line in the dielectric used for communication between the two daughter cards is The signal transmission line according to claim 1, wherein the line thickness is determined to have a maximum characteristic. A backplane in which a transmission line that is a microstrip line is wired on a dielectric;
A plurality of daughter cards having transmission lines wired on the dielectric of the backplane and lines electrically connected;
The plurality of daughter cards have a function of communicating signals with other daughter cards through the transmission line,
Of the plurality of daughter cards, a cross-sectional dimension of a transmission line on the dielectric used for communication between two daughter cards is determined based on a distance between the two daughter cards. Signal transmission line.   The line width of the transmission line on the dielectric used for communication between the two daughter cards is determined to be narrower as the distance between the two daughter cards is longer. Signal transmission line.   The backplane transmission line used for communication between the two daughter cards is a single-ended signal line or a differential signal line. The signal transmission line described.   Of the transmission lines wired in or on the dielectric of the backplane, the cross-sectional dimensions of the transmission lines used for communication between the two daughter cards are determined based on the distance between the two daughter cards. Transmission line design method.

Images