U.S. patent application number 14/745624 was filed with the patent office on 2015-12-24 for transmission of signals on multi-layer substrates with minimum interference.
The applicant listed for this patent is Blue Danube Systems, Inc.. Invention is credited to Robert C. Frye.
Application Number | 20150373837 14/745624 |
Document ID | / |
Family ID | 53541916 |
Filed Date | 2015-12-24 |
United States Patent
Application |
20150373837 |
Kind Code |
A1 |
Frye; Robert C. |
December 24, 2015 |
TRANSMISSION OF SIGNALS ON MULTI-LAYER SUBSTRATES WITH MINIMUM
INTERFERENCE
Abstract
A signal transmission system including first and second
transmission lines laid out side by side on a planar surface over a
length L, each transmission line including a first conducting path
and a second conducting path and each transmission line including a
plurality of crossover structures at each of which the first and
second conducting paths of that transmission line cross over each
other to reverse the position of the two conducting paths relative
to each other, wherein the plurality of crossover structures on the
two transmission lines are arranged over the length L of the two
transmission lines such that each of the first and second
conducting paths of the first transmission line is a nearest
neighbor of each of the first and second conducting paths of the
second transmission line over distances that are substantially the
same.
Inventors: |
Frye; Robert C.;
(Piscataway, NJ) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Blue Danube Systems, Inc. |
Warren |
NJ |
US |
|
|
Family ID: |
53541916 |
Appl. No.: |
14/745624 |
Filed: |
June 22, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62015604 |
Jun 23, 2014 |
|
|
|
Current U.S.
Class: |
333/4 ;
333/5 |
Current CPC
Class: |
H05K 1/0228 20130101;
H01P 3/081 20130101; H01P 3/02 20130101; H05K 1/0242 20130101; H01P
5/028 20130101; H01P 3/026 20130101 |
International
Class: |
H05K 1/02 20060101
H05K001/02; H01P 3/02 20060101 H01P003/02 |
Claims
1. A signal transmission system comprising first and second
transmission lines laid out side by side on a planar surface over a
length L, each transmission line comprising a first conducting path
and a second conducting path and each transmission line comprising
a plurality of crossover structures at each of which the first and
second conducting paths of that transmission line cross over each
other to reverse the position of the two conducting paths relative
to each other, wherein the plurality of crossover structures on the
two transmission lines are arranged over the length L of the two
transmission lines such that each of the first and second
conducting paths of the first transmission line is a nearest
neighbor of each of the first and second conducting paths of the
second transmission line over distances that are substantially the
same.
2. The signal transmission system of claim 1, wherein the plurality
of crossover structures on the two transmission lines are arranged
over the length L of the two transmission lines such that each of
the first and second conducting paths of the first transmission
line is a nearest neighbor of each of the first and second
conducting paths of the second transmission line over distances
that are equal.
3. The signal transmission system of claim 1, wherein the distance
over which each conducting path of the first transmission line is a
nearest neighbor of a conducting path of the second transmission
lines is equal to L/4.
4. The signal transmission system of claim 1, further comprising a
substrate defining said planar surface.
5. The signal transmission system of claim 1, wherein the first and
second transmission lines are differential transmission lines.
6. The signal transmission system of claim 1, wherein the plurality
of crossover structures on the first transmission line are
staggered relative to the plurality of crossover structures on the
second transmission line.
7. The signal transmission system of claim 1, wherein each
crossover structure of the plurality of crossover structures on the
first and second transmission lines comprises an in-plane crossover
and an out-of-plane crossover.
8. The signal transmission system of claim 7, wherein the
out-of-plane crossover has two vertical, electrically conductive
structures to transition to and from a conductive path located in a
plane that is either above or below the planar surface.
9. The signal transmission system of claim 8, wherein each of the
two electrically conducive structures comprises an electrically
conductive via.
10. The signal transmission system of claim 7, wherein the
plurality of crossover structures in the first transmission line
are constructed such that the first conducting path of the first
transmission line has an equal number of in-plane crossovers and
out-of-plane crossovers.
11. The signal transmission system of claim 10, wherein the
plurality of crossover structures in the first transmission line
are constructed such that the second conducting path of the first
transmission line has an equal number of in-plane crossovers and
out-of-plane crossovers.
12. The signal transmission system of claim 11, wherein the
plurality of crossover structures in the second transmission line
are constructed such that the first conducting path of the second
transmission line has an equal number of in-plane crossovers and
out-of-plane crossovers.
13. The signal transmission system of claim 12, wherein the
plurality of crossover structures in the second transmission line
are constructed such that the second conducting path of the second
transmission line has an equal number of in-plane crossovers and
out-of-plane crossovers.
14. The signal transmission system of claim 1, wherein the first
and second transmission lines are designed to carry signals having
a wavelength and wherein distances between crossover structures in
each transmission line are shorter than L/4.
15. The signal transmission system of claim 1, further comprising
an integrated circuit wherein the first and second transmission
lines are fabricated within the integrated circuit.
Description
[0001] This application claims the benefit under 35 U.S.C.
.sctn.119(e) of Provisional Application Serial No. 62/015,604 filed
Jun. 23, 2014, entitled "Method for Transmission and Coupling of
Signals on Multi-Layer Boards with Minimum Interference," the
entire contents of which are incorporated herein by reference.
TECHNICAL FIELD
[0002] The described inventions generally relate to high frequency
signal distribution on Printed Circuits Boards (PCBs) and other
multi-layer substrates so as to preserve signal integrity in the
presence of line cross coupling.
BACKGROUND OF THE INVENTION
[0003] High frequency signal transmission is most commonly
point-to-point. Power is generated at a source (the transmitter),
and delivered to a load (the receiver) via a transmission line. In
such cases, the receiver usually includes a terminating resistance
that is equal to the characteristic impedance of the transmission
line. The transmitted signal power is dissipated in this
resistance, and no signal reflection occurs from the receiver.
[0004] Complex systems may comprise multiple distribution lines of
the above type. In such systems, any signal coupled between the
lines is a source of interference.
SUMMARY
[0005] The embodiments described herein employ a method for
distributing two or more differential signal transmission lines in
planar technologies such as PCBs. The transmission lines are
arranged in such a way as to have balanced opposing regions of
mutual coupling, resulting in minimal net coupling for lines in
physical proximity.
[0006] In general, in one aspect, the invention features a signal
transmission system including first and second transmission lines
laid out side by side on a planar surface over a length L, each
transmission line including a first conducting path and a second
conducting path and each transmission line including a plurality of
crossover structures at each of which the first and second
conducting paths of that transmission line cross over each other to
reverse the position of the two conducting paths relative to each
other, wherein the plurality of crossover structures on the two
transmission lines are arranged over the length L of the two
transmission lines such that each of the first and second
conducting paths of the first transmission line is a nearest
neighbor of each of the first and second conducting paths of the
second transmission line over distances that are substantially the
same.
[0007] Other embodiments may include one or more of the following
features. The plurality of crossover structures on the two
transmission lines are arranged over the length L of the two
transmission lines such that each of the first and second
conducting paths of the first transmission line is a nearest
neighbor of each of the first and second conducting paths of the
second transmission line over distances that are equal. The
distance over which each conducting path of the first transmission
line is a nearest neighbor of a conducting path of the second
transmission lines is equal to L/4. The signal transmission system
also includes a substrate defining the planar surface. The first
and second transmission lines are differential transmission lines.
The plurality of crossover structures on the first transmission
line are staggered relative to the plurality of crossover
structures on the second transmission line. Each crossover
structure of the plurality of crossover structures on the first and
second transmission lines includes an in-plane crossover and an
out-of-plane crossover. The out-of-plane crossover has two
vertical, electrically conductive structures to transition to and
from a conductive path located in a plane that is either above or
below the planar surface. Each of the two electrically conducive
structures includes an electrically conductive via. The plurality
of crossover structures in the first transmission line are
constructed such that the first conducting path of the first
transmission line has an equal number of in-plane crossovers and
out-of-plane crossovers. The plurality of crossover structures in
the first transmission line are constructed such that the second
conducting path of the first transmission line has an equal number
of in-plane crossovers and out-of-plane crossovers. The plurality
of crossover structures in the second transmission line are
constructed such that the first conducting path of the second
transmission line has an equal number of in-plane crossovers and
out-of-plane crossovers. The plurality of crossover structures in
the second transmission line are constructed such that the second
conducting path of the second transmission line has an equal number
of in-plane crossovers and out-of-plane crossovers. The first and
second transmission lines are designed to carry signals having a
wavelength .lamda. and wherein distances between crossover
structures in each transmission line are shorter than 214. The
signal transmission system also includes an integrated circuit
wherein the first and second transmission lines are fabricated
within the integrated circuit.
[0008] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 shows a layout of two transmission lines using
multiple crossovers.
[0010] FIG. 2 shows multiple different crossover structures for use
in multi-layer planar technologies.
[0011] FIG. 3 shows a sequence of line sections formed by multiple
crossover structures in two parallel transmission lines.
DETAILED DESCRIPTION
[0012] A common technique for minimizing the electromagnetic
coupling between different transmission lines is to form a shielded
enclosure by surrounding each of the lines with a conductor.
Additionally, coupling can generally be reduced by increasing the
physical distance between the lines. In applications where the use
of these techniques is not feasible or is undesirable, an
alternative technique, described herein, can be applied.
[0013] A method that can be employed in planar technologies such as
PCBs or multi-layer ICs is shown in FIG. 1. In this diagram, four
conducting lines 1-4 are formed into two differential lines, one
line consisting of the pair 1-2 and the other consisting of the
pair 3-4. When placed in proximity, mutual electromagnetic coupling
will occur between these two pairs of lines, determined by their
proximity to each other and by the physical length of the region of
interaction. Within a particular differential transmission line,
the current flow (indicated by arrows) in the pair of conducting
lines at any position along the line is substantially equal in
magnitude but opposite in direction. (The actual direction of
current flow alternates with time and location, so the diagram in
FIG. 1 may be considered to represent the configuration at an
instant in time.)
[0014] If, as shown in FIG. 1, crossover structures 50 are
provided, the positions of the two conducting lines in the
differential pair are swapped at those crossover structures to
reverse their positions relative to each other. The result, as
shown in the diagram, is to make alternating regions of clockwise
and counter-clockwise current flow, shown as unshaded and shaded
regions, respectively. This results in a reversal of both the
electric and magnetic field distribution emanating from the lines,
and consequently a change in sign of the electromagnetic coupling
between the two pairs.
[0015] Electromagnetic coupling between uniform transmission lines
accrues on a per-unit-length basis. FIG. 1 shows one such interval
40 in which electrical coupling may occur. Similarly, coupling will
occur in the interval 41. However, by a suitable arrangement of the
conductors and choice of the interval lengths, the coupling in
interval 41 may nearly cancel that in interval 40, resulting in a
significant reduction in net coupling. The most obvious
arrangement, as suggested by the figure, is the one in which the
physical structures in intervals 40 and 41 have mirror symmetry and
consequently the same magnitude of coupling per unit length.
However, because of the crossover structure in one of the
conducting pairs, the polarity is switched, resulting in a change
in sign of the coupling. In a regular structure this pattern can be
repeated. However, it is not strictly necessary to use a regular
pattern. The basic principle is the local cancellation of accrued
coupling by the use of the crossover structure to change the
polarity.
[0016] In finite frequency applications, it is not generally
possible to achieve perfect cancellation using this method because
the signals propagate at finite speed in the transmission lines.
Consequently, the coupling in the two intervals 40 and 41 will
differ by some phase, making their cancellation imperfect. However,
if the distance between the intervals is short compared with the
signal wavelength, significant reduction in coupling may be
achieved by using this method.
[0017] The crossover structure is formed by two crossovers, an
in-plane line crossover and an out-of-plane line crossover. The
in-plane line crossover is formed by a line that jogs over within
the plane on which the conductor lines are formed. To implement the
out-of-plane line crossover in multi-layer planar technologies it
is necessary to make vertical transitions in one of the lines so
that it passes over or under the other line. Thus, the crossover
section of the line is formed in a different plane. The
out-of-plane crossovers are shown in FIG. 2 in which vertical
connecting conducting thru-vias 51 are indicated by the small
circles. Especially in PCB technologies where the dielectric
thickness may be comparable to the signal line cross-sectional
dimensions, the vertical transition and crossing line structure
form a half-loop that may generate a significant component of
lateral electromagnetic field coupling to the adjacent line. This
creates an added source of coupling that can be cancelled using the
same principle of polarity reversal.
[0018] FIG. 2 shows an example interval 42 consisting of a
crossover structure adjacent to a pair of lines. This structure is
paired with the structure in interval 43 which is identical except
for the reversal in polarity of the upper differential lines.
Because of this polarity reversal and the symmetry of their
structures, the coupling in these two intervals, except for the
phase shift mentioned above, will cancel. Similarly, coupling
cancellation is obtained in intervals 44 and 45, 46 and 47, and 48
and 49.
[0019] The sections shown in FIG. 2 represent the eight possible
combinations (four different types of crossover structure and two
different polarities). These sections may be combined sequentially
to form a transmitting structure with minimal mutual coupling. FIG.
3 shows an example of a sequence of 16 line sections. In this
sequence there are eight crossover structures in the bottom
transmission line and eight in the top. The crossover structures in
the bottom line are implemented from one each of the eight
structures shown in FIG. 2. Consequently, coupling that may occur
from any one of these sections is approximately cancelled by
coupling of opposite sign in one of the others. The crossover
structures in the top line are similarly implemented, using rotated
sections to place the crossover in the upper line.
[0020] Note that the crossover structures are staggered, i.e., they
are not next to each other. There's nothing that prohibits one from
placing crossovers in the two adjacent transmission lines next to
each, but doing so would not do anything to reduce the coupling
between the two lines. If two crossover structures are adjacent,
both lines flip, so there is no net change in the sign of the
coupling.
[0021] The particular sequence shown in FIG. 3 is only one example
of a large number of possible sequences. With reference to FIG. 2
it can be seen, for example, that the section 42 can be exchanged
with section 48 without changing the connectivity, section 43 with
49, etc.
[0022] Another consideration for the crossover structures in PCB
technologies is the signal path length. In differential
transmission lines using cross-over structures as shown in FIG. 6,
the line passing through the vertical transition is longer than the
line that does not, unless some other compensating design feature
is added. This difference in length causes added delay in the
longer line, and can cause undesirable timing skew in a
differential transmission line. The overall sequence of sections
shown in FIG. 3 has an equal number of vertical transitions for all
four of the lines to avoid this. This is true of all sequences that
use the eight basic structures in both lines.
[0023] In line structures having regular line-to-line separations,
a general condition for cancellation is that the length of the
intervals intended to cancel each other be the same in a pair-wise
fashion. However, it is not necessary for all intervals in the
overall structure to be the same. In an arrangement like the one
shown in FIG. 2, it may be desirable to make all of the intervals
and all of the crossover structures the same, since this
facilitates design and analysis, but it is not strictly necessary.
Also note that a regular structure, like the one shown in FIG. 3,
can be repeated indefinitely to form long sections of lines having
minimal mutual electrical coupling. Other regular structures and
even irregular structures can be devised based on the same concept
of cancellation through polarity reversal.
[0024] The coupling between the two differential transmission lines
is electromagnetic--i.e., it depends on both electric fields
(arising from voltages) and magnetic fields (arising from
currents). In a transmission line, the voltage and current are
linearly related by the characteristic impedance. Coupling is
similarly related and is linked to both types of fields. In a
differential line, the currents in the two conductors are of equal
magnitude but run in opposite directions and the voltages along the
lines are of equal magnitude but of opposite signs. So, a possibly
more useful way to think of the coupling between the two
transmission lines is that the proximity component is the same on
either side of the crossover, but both magnetic and electric fields
have flipped signs. Thus, net coupling per unit length on one side
of the coupler structure is of equal magnitude but opposite sign to
coupling on the other side.
[0025] Notice that the crossover structures on the two transmission
lines are arranged over a length L of the two transmission lines
such that each of the conducting paths of the first transmission
line is a nearest neighbor of each of the conducting paths of the
second transmission line over distances that are equal or
approximately equal. (It is approximate because the crossovers are
discrete structures that are separated by finite distances.) In
other words, the distance over which the various combinations of
conducting paths are nearest neighbors is equal to or approximately
equal to L/4.
[0026] The transmission lines that are described herein are
differential. One important characteristic of differential lines is
that the two conducting lines that form the pair need to be
balanced. The most convenient way to achieve balance is to take
advantage of symmetry. In the examples that are illustrated, the
number of times a conductor crosses over out-of-plane is equal to
the number of times it crosses in-plane, so the same is true of the
other conductor in the pair. This symmetry maintains balance. For
the arrangement involving two pairs, it is also important for both
differential lines in the pair to have identical transmission
characteristics. So the symmetry of the arrangement guarantees this
as well. That's why the number and type of crossover structures is
the same for all four of the conductors.
[0027] So, as one moves along the two transmission lines counting
the total number of crossover structures in each line, the total
number of crossover structures on one line is always approximately
equal to the total number of crossover structures on the other
line. The equality is approximate because the crossover structures
are staggered, so as one moves along the two lines the count of
crossover structures in one line will increase while the count in
the other line remains the same--so the count in the two lines is
not necessarily equal depending on where you are on the line. But
as one moves further along the lines, the count in both lines will
become equal again as crossover structures are encountered in the
other line. In other words, the crossover structures are roughly
equally distributed along both lines.
[0028] In addition, in each transmission line, the number of
out-of-plane crossovers along one conducting path is equal to the
number of out-of-plane crossovers along the other conducting path.
This guarantees that the actual lengths of the two conducting lines
are equal.
[0029] At 1 GHz the wavelength of a signal is about six inches.
Generally, the crossovers need to be inserted an intervals small
compared with one quarter wavelength, which would be 1.5 inches.
So, crossovers at half-inch intervals is a reasonable choice,
though larger or smaller intervals could also be used. Furthermore,
at higher or lower frequencies the intervals could be
proportionally smaller or larger.
[0030] The technology described herein has particular applicability
to multi-point signal generation networks and low cost antenna
arrays such as those described in U.S. Pat. No. 8,259,884 and U.S.
Pat. No. 8,611,959, respectively, the contents of which are
incorporated herein in their entirety. For example, referring to
FIG. 5 in that '884 patent, there is shown two tree-networks, one
of which carries a first carrier signal and the second of which
carries a second carrier signal. At various places the branch of
one tree network runs alongside (e.g. "parallel") to a
corresponding branch of the other tree network. For that pair of
branches, one carries the first carrier signal in one direction and
the other branch carries the second carrier signal in the other
direction. Along the length of the dual parallel transmission
lines, there are number of Arrival-Time-Averaging Circuits (ATACs),
each with one input connect to one of the transmission lines and a
second input connected to the other transmission line. Those
parallel transmission lines can be laid out using the concepts
described herein to reduce interference that one line causes in the
other.
[0031] Other embodiments are within the following claims.
* * * * *