U.S. patent application number 16/134811 was filed with the patent office on 2020-03-19 for bimodal impedance matching terminators.
The applicant listed for this patent is Apple Inc.. Invention is credited to Koussalya Balasubramanian, Venus Kumar, Jason W. Leung, Abhilash Rajagopal, Hao Shi, Gary S. Thomason.
Application Number | 20200089643 16/134811 |
Document ID | / |
Family ID | 69772495 |
Filed Date | 2020-03-19 |
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United States Patent
Application |
20200089643 |
Kind Code |
A1 |
Shi; Hao ; et al. |
March 19, 2020 |
Bimodal Impedance Matching Terminators
Abstract
A data network may include a data bus and network nodes. The
data bus may be a differential data bus having first and second
differential signal lines that convey differential signals between
the nodes. A bimodal impedance terminator may be coupled to the
first and second differential signal lines at one or both ends of
the data bus. The bimodal impedance terminator may include a first
resistor coupled between the first differential signal line and a
circuit node and a second resistor coupled between the second
differential signal line and the circuit node. A capacitor may be
coupled between the circuit node and ground. A third resistor may
be coupled between the circuit node and ground in series with the
capacitor. The bimodal impedance terminator may terminate both the
differential-mode impedance and the common-mode impedance of the
data bus to reduce signal reflections at the ends of the data
bus.
Inventors: |
Shi; Hao; (Mountain View,
CA) ; Thomason; Gary S.; (Boulder Creek, CA) ;
Rajagopal; Abhilash; (San Jose, CA) ; Leung; Jason
W.; (San Francisco, CA) ; Balasubramanian;
Koussalya; (Santa Clara, CA) ; Kumar; Venus;
(Pleasanton, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Family ID: |
69772495 |
Appl. No.: |
16/134811 |
Filed: |
September 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04L 25/0298 20130101;
G06F 13/4086 20130101; H01R 13/6464 20130101; H01R 13/646
20130101 |
International
Class: |
G06F 13/40 20060101
G06F013/40; H01R 13/646 20060101 H01R013/646; H04L 25/02 20060101
H04L025/02 |
Claims
1-8. (canceled)
9. A connector configured to be coupled to a differential pair of
signal lines that have a differential-mode impedance and a
common-mode impedance, the connector comprising: a bimodal
impedance terminator configured to terminate both the
differential-mode impedance and the common-mode impedance of the
differential pair of signal lines while the connector is coupled to
the differential pair of signal lines; a conductive shell that
defines an interior cavity; a grounding structure that couples the
conductive shell to a ground plane; a ground plate received within
the interior cavity and electrically coupled to the ground plane
through the conductive shell; and a dielectric substrate on the
ground plate, wherein the bimodal impedance terminator comprises
conductive traces on the dielectric substrate.
10. The connector defined in claim 9, further comprising: a first
conductive contact configured to be coupled to a first signal line
in the differential pair of signal lines; and a second conductive
contact configured to be coupled to a second signal line in the
differential pair of signal lines.
11. The connector defined in claim 10, the bimodal impedance
terminator comprising: a first resistor between a circuit node and
the first conductive contact; a second resistor between the circuit
node and the second conductive contact; a third resistor between
the circuit node and the grounded shield; and a capacitor between
the circuit node and the grounded shield in series with the third
resistor.
12. (canceled)
13. The connector defined in claim 11 wherein first, second, and
third openings are formed in the ground plate, the connector
further comprising: a conductive via coupled between the conductive
traces and the ground plate; a first conductive pin that extends
through the first opening; a second conductive pin that extends
through the second opening; and a third conductive pin that extends
through the third opening, wherein the first, second and third
conductive pins are coupled to the conductive traces, the first
conductive pin forms the first conductive contact, the second
conductive pin forms the second conductive contact, and the third
conductive pin is shorted to the ground plate by the conductive
via.
14. The connector defined in claim 11, further comprising: a
conductive catch bar mounted to the conductive shell within the
interior cavity, wherein the ground plate is affixed to the
conductive catch bar.
15. The connector defined in claim 11, wherein the grounding
structure comprises a support structure configured to hold the
connector at a fixed distance from the ground plane.
16. The connector defined in claim 10, further comprising: a third
conductive contact configured to be coupled to a network node; and
a fourth conductive contact configured to be coupled to the network
node, wherein the third conductive contact is coupled to the first
conductive contact and the fourth conductive contact is coupled to
the second conductive contact.
17. A data bus comprising: opposing first and second ends, wherein
the data bus is configured to convey differential signals between
at least two network stub nodes that are coupled to the
differential data bus between the first and second ends; first and
second differential signal lines configured to convey the
differential signals, the first and second differential signal
lines having a differential-mode impedance and a common-mode
impedance; a grounded shield defining an interior cavity; a
conductive catch bar within the interior cavity and coupled to the
grounded shield; a dielectric substrate within the interior and
mounted to the conductive catch bar; and an impedance terminating
circuit on the dielectric substrate and coupled to the first and
second differential signal lines at the first end of the data bus,
wherein the impedance terminating circuit is configured to
terminate both the differential-mode impedance and the common-mode
impedance and comprises: a first resistor coupled between the first
differential signal line and a circuit node; a second resistor
coupled between the second differential signal line and the circuit
node; a third resistor coupled between the circuit node and a
reference potential; and a capacitor coupled between the circuit
node and the reference potential in series with the third
resistor.
18. The data bus defined in claim 17, wherein the first and second
differential signal lines comprise a twisted pair of wires and the
data bus further comprises: a cable shield that surrounds the
twisted pair of wires and that is coupled to the reference
potential.
19. The data bus defined in claim 17, further comprising: a
dedicated ground wire coupled between the first and second ends of
the data bus, the dedicated ground wire being coupled to the
reference potential.
20. The data bus defined in claim 17, further comprising: an
additional impedance terminating circuit coupled to the first and
second differential signal lines at the second end of the data bus,
wherein the additional impedance terminating circuit is configured
to terminate both the differential-mode impedance and the
common-mode impedance and comprises: a fourth resistor coupled
between the first differential signal line and an additional
circuit node; a fifth resistor coupled between the second
differential signal line and the additional circuit node; a sixth
resistor coupled between the additional circuit node and the
reference potential; and an additional capacitor coupled between
the additional circuit node and the reference potential in series
with the sixth resistor.
21. (canceled)
22. (canceled)
23. An impedance terminator for a data bus having first and second
differential signal lines, the impedance terminator comprising: a
dielectric substrate having opposing first and second surfaces, a
conductive trace at the first surface, and an opening extending
from the first surface to the second surface; a first resistor on
the dielectric substrate and coupled between the first differential
signal line and a circuit node; a second resistor on the dielectric
substrate and coupled between the second differential signal line
and the circuit node; a capacitor on the dielectric substrate and
coupled between the circuit node and a ground; a third resistor
mounted to the first surface of the dielectric substrate and
coupled between the circuit node and the ground; a ground plate on
the second surface of the dielectric substrate; a conductive via
that extends through the dielectric substrate and that couples the
conductive trace to the ground plate; and a conductive pin that
extends through the opening and that is electrically coupled to the
conductive trace.
24. The impedance terminator of claim 23, wherein the third
resistor is coupled between the circuit node and the ground in
series with the capacitor.
25. The impedance terminator of claim 24, wherein the first
resistor has a first resistance, the second resistor has the first
resistance, and the third resistor has a second resistance greater
than the first resistance.
26. The impedance terminator of claim 25, wherein the first and
second differential signal lines exhibit a common-mode impedance
and a differential-mode impedance, the third resistance being
within 10% of the common-mode impedance minus one-quarter of the
differential-mode impedance.
27. The impedance terminator of claim 25, wherein the first and
second differential signal lines exhibit a common-mode impedance
and a differential-mode impedance, the third resistance being
within 10% of the common-mode impedance minus one-quarter of the
differential-mode impedance.
28. The impedance terminator of claim 27, wherein the first and
second resistances are each within 10% of one-half of the
differential-mode impedance.
29. The impedance terminator of claim 28, wherein the capacitor has
a capacitance between 1.0 nF and 10.0 nF.
30. The impedance terminator of claim 25 wherein the first and
second differential signal lines exhibit a common-mode impedance
and a differential-mode impedance, the impedance terminator being
configured to terminate both the common-mode impedance and the
differential-mode impedance of the first and second differential
signal lines.
31. The impedance terminator of claim 30, wherein the third
resistor has a resistance that is within 10% of the common-mode
impedance minus one-quarter of the differential-mode impedance.
32. The impedance terminator of claim 25, wherein the first and
second differential signal lines convey a differential signal at a
frequency, and wherein the first and second differential signal
lines exhibit, at the frequency, a differential-mode impedance and
a common-mode impedance, the common-mode impedance being greater
than the differential-mode impedance.
33. The impedance terminator of claim 25, wherein the first
resistor, the second resistor, and the capacitor are mounted to the
first surface of the dielectric substrate, the dielectric substrate
further comprising a first additional conductive trace coupled to
the first resistor, a second additional conductive trace coupled to
the second resistor, and first and second additional openings
extending from the first surface to the second surface.
34. The impedance terminator of claim 33, further comprising: a
first additional conductive pin that extends through the first
additional opening and that is electrically coupled to the first
additional conductive trace; and a second additional conductive pin
that extends through the second additional opening and that is
electrically coupled to the second additional conductive trace.
Description
FIELD
[0001] This relates generally to data networks including data
networks having differential data paths.
BACKGROUND
[0002] Data networks include a number of network nodes coupled
together over a data path such as a multi-point bus. In some
scenarios, data networks are implemented using differential data
paths. Differential data paths include a differential pair of
signal lines. The differential pair of signal lines conveys
differential signals between the network nodes. The differential
pair of signal lines is characterized by a differential-mode
impedance and a common-mode impedance.
[0003] If care is not taken, differential-mode impedance
discontinuities at the ends of the data path can reflect the
differential signals directly. Common-mode impedance
discontinuities at the ends of the data path can reflect
common-mode signals that are converted into differential noise and
introduce errors in data conveyed over the data path. Impedance
discontinuities thus leave the data path susceptible to external
interference.
SUMMARY
[0004] A system may include a data network and other components.
The data network may include network nodes and a data path such as
a multi-point bus. The data path may have first and second ends.
The network nodes may be coupled to the data path between the first
and second ends. The data path may be a differential data path
having first and second differential signal lines that convey
differential signals between the network nodes.
[0005] A bimodal impedance terminator may be coupled to the first
and second differential signal lines at one or both ends of the
data path. The bimodal impedance terminator may include a first
resistor coupled between the first differential signal line and a
circuit node and a second resistor coupled between the second
differential signal line and the circuit node. A capacitor may be
coupled between the circuit node and a reference potential such as
ground. A third resistor may be coupled between the circuit node
and ground in series with the capacitor. The bimodal impedance
terminator may terminate both the differential-mode impedance and
the common-mode impedance of the data path. In practical
differential lines with minor imbalances, terminating both the
differential-mode impedance and the common-mode impedance of the
data path serves to reduce or minimize signal reflections at the
ends of the data path and reduces or minimizes susceptibility of
the data path to external electromagnetic noise.
[0006] The bimodal impedance terminator may be integrated within a
connector that is configured to be coupled to (e.g., plugged into
or mounted to) the first and second differential signal lines. The
connector may have ground contacts that couple a cable shield or
dedicated ground wire for the data path to ground. If desired, the
connector may also couple a network node to the data path.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a schematic diagram of an illustrative system
having a network and other components in accordance with some
embodiments.
[0008] FIG. 2 is a diagram of an illustrative network having a
differential data path, network nodes, and bimodal impedance
terminators in accordance with some embodiments.
[0009] FIG. 3 is a circuit diagram of an illustrative bimodal
impedance terminator in accordance with some embodiments.
[0010] FIG. 4 is a plot of illustrative network performance (signal
reflection) as a function of frequency for a network having a
bimodal impedance terminator in accordance with some
embodiments.
[0011] FIG. 5 is a circuit diagram showing how an illustrative
bimodal impedance terminator may be integrated within a connector
having a grounded shield in accordance with some embodiments.
[0012] FIG. 6 is a diagram of an illustrative network having a
differential data path with a cable shield coupled between bimodal
impedance terminators in accordance with some embodiments.
[0013] FIG. 7 is a diagram of an illustrative network having a
differential data path with a dedicated ground wire coupled between
bimodal impedance terminators in accordance with some
embodiments.
[0014] FIG. 8 is a diagram of an illustrative network having an
unshielded differential data path coupled between bimodal impedance
terminators in accordance with some embodiments.
[0015] FIG. 9 is a perspective view showing how components may be
assembled to form an illustrative connector having an integrated
bimodal impedance terminator in accordance with some
embodiments.
[0016] FIG. 10 is a perspective view of an illustrative assembled
connector having an integrated bimodal impedance terminator in
accordance with some embodiments.
[0017] FIG. 11 is an illustrative equivalent circuit model of a
transmission-line pair with minor imbalances for a network that is
subject to common-mode electromagnetic excitations in accordance
with some embodiments.
[0018] FIG. 12 is a plot of illustrative network performance
(differential voltage) as a function of frequency for a network
under different impedance termination schemes in accordance with
some embodiments.
[0019] FIG. 13 is a plot of illustrative network performance
(differential voltage) as a function of frequency for a network
having a bimodal impedance terminator at only one end of the
network in accordance with some embodiments.
DETAILED DESCRIPTION
[0020] A system may include a data network and other components.
The data network may include a data path such as a multi-point bus
and two or more network nodes coupled to the data path. The network
nodes may include one or more electronic devices or other
electronic components. The data path may be a differential data
path that includes a differential pair of signal lines.
Differential signals may be conveyed between the network nodes over
the differential pair of signal lines.
[0021] The differential pair of signal lines may have opposing
first and second ends. Each of the network nodes may be coupled to
the differential pair of signal lines between the first and second
ends in a stub-node configuration. Impedance matching terminators
(sometimes referred to herein as impedance terminators) may be
coupled to the first and second ends to terminate the impedance of
the differential pair of signal lines and to thereby reduce or
minimize signal reflections at the first and second ends.
[0022] The impedance terminators may include circuitry for matching
both the differential-mode and the common-mode impedance of the
differential data path. Because the impedance terminators are
configured to match both the differential and common mode
impedances of the data path, the impedance terminators may
sometimes be referred to herein as bimodal impedance terminators,
bimodal impedance matching circuitry, or bimodal impedance matching
circuits.
[0023] An illustrative system that may include a network with a
differential data path and bimodal impedance terminators is shown
in FIG. 1. As shown in FIG. 1, system 10 may include a data network
such as network 12 and other components such as components 18.
System 10 may include one or more electronic devices (e.g., system
10 may be a desktop computer, laptop computer, network data center,
server farm, network in a campus, building, vehicle, etc.).
[0024] System 10 has communications paths such as one or more data
paths 14. System 10 may include two or more network nodes such as
nodes 16 coupled to data path 14. Data path 14 may, for example,
include parallel signal lines that form a data bus for network 14
and system 10. The parallel signal lines may include a differential
pair of signal lines for conveying differential signals between two
or more nodes 16 (e.g., data path 14 may be a multi-point
differential bus). The differential signals may be used to convey
communications data, control signals, sensor data, or any other
desired information between nodes 16. The signal lines of data path
14 may include conductive wires or other conductors formed within
one or more cables (e.g., Ethernet cables, coaxial cables, etc.),
conductive traces on flexible and/or rigid printed circuits, and/or
combinations of these structures. The signal lines may be arranged
in a twisted pair configuration if desired. Connectors may be used
to mechanically couple data path 14 to nodes 16 and/or to other
network components.
[0025] Nodes 16 may include portable electronic devices such as
laptop computers, cellular telephones, media players, wristwatch
devices, head-mounted equipment such as goggles or headphones,
larger electronic devices such as desktop computers, servers, line
cards on a network rack, computers embedded within computer
monitors, televisions, set-top boxes, gaming devices, computers
embedded within a kiosk, vehicle network(s), accessories such as
computer mice, keyboards, remote controls, or other accessories,
electronic components such as sensors (e.g., image sensors,
three-dimensional depth sensors, gaze tracking sensors, lidar
sensors, radar sensors, inertial/motion sensors such as
accelerometers, gyroscopes, or compasses, speedometers, odometers,
ambient light sensors, infrared sensors, solar cells, proximity
sensors, optical sensors, temperature sensors, magnetic sensors,
ultrasonic sensors, microphones, audio sensors, humidity sensors,
etc.), wireless communications circuitry (e.g., radio-frequency
transceivers, AM/FM radio receivers, satellite radio receivers,
satellite television receivers, satellite navigation receivers such
as Global Positioning System or Global Navigation Satellite System
receivers, wireless local area network transceivers, cellular
telephone transceivers, wireless personal area network transceivers
such as Bluetooth.RTM. transceivers, millimeter wave transceivers,
near-field communications transceivers, optical signal
transceivers, antennas, etc.), vehicle control components (e.g.,
steering control components, engine control components, cruise
(speed) control components, air flow control components, power
window motors, windshield wiper motors, brake control components,
seat adjustment components, etc.), output devices (e.g., display
components such as liquid crystal displays or light emitting diode
displays, lights such as status indicator lights, cabin lights, or
headlights, speaker components, haptic feedback and alert
components, etc.), wireless charging circuitry for wirelessly
charging portable electronic devices or other components in system
10, storage and processing circuits (e.g., processing circuitry
such as one or more microprocessors, signal processors,
microcontrollers, baseband processors, audio chips, and power
management units, memory such as non-volatile memory and volatile
memory, etc.), buttons, touch input devices, and/or other
components coupled to data path 14.
[0026] System 10 may include other components 18 that are not a
part of network 12. Other components 18 may include cosmetic
structures, engine structures, wheels, input-output devices (e.g.,
sensor circuitry, communications circuitry, output devices, and/or
input devices separate from network 12), and/or support structures
used in mechanically supporting some or all of the components of
system 10 such housing structures (e.g., conductive and/or
dielectric housing walls), chassis structures (e.g., a metal
chassis or frame for system 10), dashboard structures, windows,
furniture, etc. If desired, system 10 may include multiple separate
or interconnected networks 12. The example of FIG. 1 is merely
illustrative.
[0027] FIG. 2 is a diagram showing how nodes 16 of system 10 may be
coupled to data path 14. As shown in FIG. 2, data path 14
(sometimes referred to herein as data bus 14, communications bus
14, communications path 14, signal path 14, or bus 14) may include
differential signal lines 26H and 26L (e.g., a differential pair of
conductive lines). Nodes 16 may each be coupled to differential
signal line 26H over a corresponding signal path 28 and may each be
coupled to differential signal line 26L over a corresponding signal
path 30 (e.g., at locations between first end 21 and second end 23
of data path 14).
[0028] Differential signal lines 26H and 26L may convey
differential signals between nodes 16. The differential signals
include a first signal conveyed over differential signal line 26H
and a complementary second signal (e.g., a signal of equal and
opposite magnitude to the first signal at any given time) conveyed
over differential signal line 26L (e.g., the first and second
signals form a differential pair of signals). Differential signal
line 26H may sometimes be referred to herein as high signal line
26H whereas differential signal line 26L is sometimes referred to
herein as low signal line 26L.
[0029] In this way, any desired number of nodes 16 may be coupled
to differential signal lines 26H and 26L between ends 21 and 23 of
data path 14. If care is not taken, impedance discontinuities at
ends 21 and 23 of data path 14 can reflect the signals conveyed
over differential signal lines 26H and 26L. The reflected signals
may undesirably interfere with the operation of nodes 16 and can
introduce errors into the conveyed signals.
[0030] In order to reduce or minimize these impedance
discontinuities, data path 14 may include one or more impedance
termination circuits (impedance terminators) 20 such as first
termination circuit 20-1 and second termination circuit 20-2 of
FIG. 2. First termination circuit 20-1 may be coupled to (between)
differential signal lines 26H and 26L at end 21 whereas second
termination circuit 20-2 is coupled to (between) differential
signal lines 26H and 26L at end 23 of data path 14. In this way,
termination circuits 20-1 and 20-2 may form end nodes of network 12
whereas nodes 16 form stub nodes of network 12. Termination
circuits 20-1 and 20-2 may each be coupled to ground 32 and may be
configured to couple desired impedances between differential signal
lines 26H and 26L at ends 21 and 23 of data path 14. The impedances
may be selected to reduce or minimize impedance discontinuity and
thus signal reflection at ends 21 and 23 of data path 14.
[0031] In some scenarios, a single resistor such as a 120-ohm
resistor is coupled between the differential signal lines to
terminate each end of the data path. In other scenarios, a split
termination scheme is used in which a shunting capacitor is coupled
to one differential signal line through a first 60-ohm resistor and
to the other differential signal line through a second 60-ohm
resistor. In other implementations, resistors of other values can
be used. These arrangements may terminate the differential-mode
impedance of the differential signal lines, but are incapable of
terminating the common-mode impedance of the differential signal
lines. If care is not taken, remaining common-mode impedance
discontinuities will continue to reflect differential signals at
the ends of the data path. It may therefore be desirable to be able
to provide data path 14 with termination circuits that terminate
both the differential-mode impedance and the common-mode impedance
of differential signal lines 26H and 26L.
[0032] FIG. 3 is a circuit diagram of an impedance termination
circuit 20 having both differential-mode and common-mode
termination capabilities. As shown in FIG. 3, termination circuit
20 (e.g., termination circuit 20-1 or 20-2 of FIG. 2) may include a
capacitor such as capacitor 46 and first, second, and third
resistors such as resistors 44, 40, and 42. Capacitor 46 may be
coupled in series between ground 32 and first resistor 44. First
resistor 44 may be coupled in series between capacitor 46 and
circuit node 38. Second resistor 40 may be coupled in series
between circuit node 38 and terminal 36. Third resistor 42 may be
coupled in series between circuit node 38 and terminal 34. Terminal
34 may be coupled to differential signal line 26H whereas terminal
36 is coupled to differential signal line 26L (FIG. 2).
[0033] Capacitor 46 of FIG. 3 may have a capacitance C.sub.t.
Capacitance C.sub.t may be, for example, between 4.6 nF and 4.8 nF
(e.g., 4.7 nF), between 4.5 nF and 4.9 nF, between 4.0 nF and 5.0
nF, between 3.0 nF and 6.0 nF, between 1.0 nF and 10.0 nF, less
than 3.5 nF, or greater than 6.0 nF. Second resistor 40 and third
resistor 42 may both have resistance R.sub.t. Resistance R.sub.t
may be equal to one-half of the differential-mode impedance
Z.sub.diff of differential signal lines 26H and 26L. Resistance
R.sub.t may be approximately equal to this value if desired (e.g.,
within 20% of one-half of differential-mode impedance Z.sub.diff,
within 10% of one-half of differential-mode impedance Z.sub.diff,
etc.). As an example, resistance R.sub.t may be between 55 ohms and
65 ohms (e.g., 60 ohms in scenarios where Z.sub.diff is equal to
120 ohms), between 50 ohms and 70 ohms, between 45 ohms and 75
ohms, less than 45 ohms, or greater than 75 ohms.
[0034] First resistor 44 may have resistance R.sub.g. Resistance
R.sub.g may be equal to the difference between the common-mode
impedance Z.sub.comm of differential signal lines 26H and 26L and
one-quarter of differential-mode impedance Z.sub.diff (e.g.,
resistance R.sub.g may be set to Z.sub.comm-0.25*Z.sub.diff, where
"*" is the multiplication operator). Resistance R.sub.g may be
approximately equal to this value if desired (e.g., within 10-20%
of Z.sub.comm-0.25*Z.sub.diff, within 10% of
Z.sub.comm-0.25*Z.sub.diff, etc.). As an example, resistance
R.sub.g may be between 115 ohms and 125 ohms (e.g., 120 ohms),
between 110 ohms and 130 ohms, between 100 ohms and 140 ohms, less
than 100 ohms, between 140 ohms and 200 ohms, between 200 ohms and
300 ohms, between 230 ohms and 270 ohms (e.g., 250 ohms), or
greater than 270 ohms. The example of FIG. 3 is merely
illustrative. If desired, first resistor 44 may be coupled between
capacitor 46 and ground 32 (e.g., the locations of resistor 44 and
capacitor 46 in FIG. 3 may be swapped).
[0035] Resistor 40, resistor 42, and capacitor 46 may serve to
terminate the differential-mode impedance of differential signal
lines 26H and 26L. Coupling first resistor 44 in series between
circuit node 38 and ground 32 may serve to terminate the
common-mode impedance of differential signal lines 26H and 26L
(e.g., without compromising the differential-mode termination
provided by resistors 40 and 42). Because termination circuit 20 is
capable of terminating both the common-mode impedance and the
differential-mode impedance of differential signal lines 26L and
26H, termination circuit 20 may sometimes be referred to herein as
bimodal impedance terminator circuit 20, bimodal impedance
terminator 20, bimodal terminator 20, or bimodal terminator circuit
20.
[0036] Consider, for example, transmission line equivalent circuit
models of bimodal impedance terminator 20 when coupled to
differential signal lines 26L and 26H of FIG. 2. The transmission
line equivalent circuit models may include a differential-mode
equivalent circuit that models the differential-mode operation of
bimodal impedance terminator 20 and a common-mode equivalent
circuit that models the common-mode operation of bimodal impedance
terminator 20. A semi-infinite length positive transmission line is
used in the models to represent differential signal line 26H and a
semi-infinite length negative transmission line is used in the
models to represent differential signal line 26L.
[0037] In the differential-mode equivalent circuit, a resistance of
2*R.sub.t is coupled in series between terminal 34 (the positive
transmission line) and terminal 36 (the negative transmission
line). Resistance R.sub.g, capacitance C.sub.t, and ground 32 of
FIG. 3 are omitted from the differential-mode equivalent circuit.
In the common-mode equivalent circuit, a resistance of R.sub.t/2 is
coupled in series between circuit node 38 and terminal 34.
Resistance R.sub.g is coupled in series between circuit node 38 and
capacitance C.sub.t. Capacitance C.sub.t is coupled in series
between resistance R.sub.g and ground 32.
[0038] The positive and negative transmission lines in the
differential-mode and common-mode equivalent circuits exhibit a
per-unit-length self-capacitance C, a per-unit-length
mutual-capacitance C.sub.m, a per-unit-length self-inductance L,
and a per-unit-length mutual-inductance L.sub.m. The positive and
negative transmission lines in the differential-mode equivalent
circuit exhibit a differential-mode impedance of Z.sub.diff, given
by equation 1. The positive and negative transmission lines in the
common-mode equivalent circuit exhibit a common-mode impedance of
Z.sub.comm, given by equation 2.
Z.sub.diff=2*SQRT([L-L.sub.m]/[C+C.sub.m]) (1)
Z.sub.comm=0.5*SQRT([L+L.sub.m]/[C-C.sub.m]) (2)
[0039] In equations 1 and 2, SQRT( ) is the square-root operator
and "I" is the division operator. The common-mode equivalent
circuit can be used to derive the common-mode input impedance
Z.sub.in,c of bimodal impedance terminator 20, which is given by
equation 3.
Z.sub.in,c=(R.sub.t/2)+R.sub.g+1/(j*.omega.*C.sub.t) (3)
[0040] In equation 3, .omega. is the angular frequency of the
signals on the positive and negative transmission line conductors
and j is equal to SQRT(-1). The amount of signals that are
reflected at bimodal impedance terminator 20 back towards
differential signal lines 26H and 26L (e.g., back towards the
positive and negative transmission line conductors of the
equivalent circuit models) is characterized by reflection
coefficient .GAMMA..sub.C, as given by equation 4.
.GAMMA..sub.C=(Z.sub.in,c-Z.sub.comm)/(Z.sub.in,c+Z.sub.comm)
(4)
[0041] Reflection coefficient .GAMMA..sub.C is a complex number
having a magnitude |.GAMMA..sub.C|=SQRT(W.sup.2+Y.sup.2), where W
is the real part of reflection coefficient .GAMMA..sub.C and Y is
the imaginary part of reflection coefficient .GAMMA..sub.C.
Substituting equation (3) into equation (4), the magnitude
|.GAMMA..sub.C| of reflection coefficient .GAMMA..sub.C is given by
equation 5.
|.GAMMA..sub.C|=SQRT([|.omega..sup.2*C.sub.t.sup.2*(R.sub.t/2+R.sub.g-Z.-
sub.comm).sup.2+1]/[(.omega..sup.2*C.sub.t.sup.2*(R.sub.t/2+R.sub.g+Z.sub.-
comm).sup.2+1]) (5)
[0042] Assuming that common-mode impedance Z.sub.comm is greater
than R.sub.t/2, R.sub.g can be set equal to Z.sub.comm-R.sub.t/2.
This allows magnitude |.GAMMA..sub.C| of reflection coefficient
.GAMMA..sub.C to be simplified, as shown by equation 6.
|.GAMMA..sub.C|=SQRT(1/[.omega..sup.2*C.sub.t.sup.2*(2*Z.sub.comm).sup.2-
+1]) (6)
[0043] FIG. 4 is a plot of the magnitude of the reflection
coefficient at the end of differential signal lines 26H and 26L as
a function of frequency under different impedance termination
schemes. As shown in FIG. 4, frequency f is plotted on the X-axis
and the magnitude of the reflection coefficient is logarithmically
plotted on the Y-axis (e.g., where 20*LOG.sub.10 of the reflection
coefficient magnitude is plotted on the Y-axis).
[0044] Curve 45 represents the magnitude of the common mode
reflection coefficient in scenarios where a split termination
scheme is used (e.g., scenarios in which a shunting capacitor is
coupled to one differential signal line through a first R.sub.t
resistor and to the other differential signal line through a second
R.sub.t resistor without resistor 44 of FIG. 3). As shown by curve
45, a relatively high amount of signal reflection is present on the
differential signal lines, particularly at higher frequencies such
as frequencies over 100 kHz. This reflection is generated by the
presence of a common-mode impedance discontinuity at the end of
differential signal lines 26H and 26L (e.g., because the split
termination scheme is incapable of sufficiently terminating the
common-mode impedance of the signal lines). Curve 45 of FIG. 4 is
generated assuming that Z.sub.diff is 120-ohm, Z.sub.comm is
115-ohm, and C.sub.t is 4.7-nF, as an example.
[0045] Curve 47 represents magnitude |.GAMMA..sub.C| of common mode
reflection coefficient .GAMMA..sub.C in scenarios where bimodal
impedance terminator 20 of FIG. 3 is coupled to differential signal
lines 26H and 26L. Curve 47 may, for example, be generated using
equation 6. Because bimodal impedance terminator 20 sufficiently
terminates both the common-mode impedance and the differential-mode
impedance of differential signal lines 26H and 26L, there is
significantly less signal reflection on the differential signal
lines relative to the arrangement associated with curve 45,
particularly for frequencies over 100 kHz. In this way, bimodal
impedance terminator 20 may reduce or minimize signal reflections
on data path 14 (FIG. 1) across a wide range of frequencies. The
example of FIG. 4 is merely illustrative. In general, curves 45 and
47 may have other shapes (e.g., depending on the magnitude of
C.sub.t, R.sub.g, and R.sub.e).
[0046] Bimodal impedance terminator 20 may be integrated within
network 12 in any desired manner. In one suitable arrangement which
is sometimes described herein as an example, bimodal impedance
terminator 20 may be integrated within a connector (adapter) for
network 12. The connector may be coupled to (e.g., plugged into)
data path 14 so that differential signal lines 26H and 26L are
coupled to terminals 34 and 36 of bimodal impedance terminator 20
(FIG. 3), respectively, while also optionally coupling other
components such as additional cabling, additional segments of
differential signal lines 26H and 26L, additional nodes 16 (FIG.
2), and/or other components to data path 14.
[0047] FIG. 5 is a circuit diagram showing how bimodal impedance
terminator 20 may be integrated within a connector for network 12.
As shown in FIG. 5, bimodal impedance terminator 20 may be
integrated into a connector such as connector 48. Connector 48 may
include a first contact 52, a second contact 58, a third contact
60, and a fourth contact 64. Contacts 60, 52, 58, and 64 may be
used to convey differential signals between differential signal
lines 26H/26L (FIG. 2) and other portions of network 12 while
connector 48 is coupled to (e.g., connected or plugged into) data
path 14. Connector 48 can mate with or otherwise be attached
(affixed) to another connector that is coupled to ends 21 or 23 of
data path 14. Connector 48 may be removable from data path 14 if
desired.
[0048] For example, contact 52 may be coupled to differential
signal line 26H and contact 58 may be coupled to differential
signal line 26L of FIG. 2. If desired, contacts 60 and 64 may be
coupled to a given node 16 over respective signal paths 28 and 30
of FIG. 2 or may be left floating (i.e., without being in contact
with any other components). In scenarios where a given node 16 is
coupled to contacts 64 and 60, that node may convey differential
signals with the rest of network 12 through connector 48 and over
differential signal lines 26H and 26L. In this way, connector 48
may be used to both plug a corresponding node 16 into data path 14
and to terminate differential signal lines 26H and 26L, or may be
used to terminate differential signal lines 26H and 26L without
plugging any nodes into data path 14.
[0049] As shown in FIG. 5, connector 48 may include a grounded
shield 50 extending around a periphery of connector 48. Grounded
shield 50 may surround bimodal impedance terminator 20 in connector
48. Grounded shield 50 may be coupled to ground 32 (e.g., a
reference or ground potential of system 10 such as a metal chassis
or other ground plane structures). Grounded shield 50 may be formed
from a conductive housing or shell for connector 48, conductive
traces, sheet metal structures, and/or any other desired conductive
structures. Connector 48 may have a first ground contact 54 and a
second ground contact 62 coupled to grounded shield 50. Ground
contact 62 may be coupled to a ground terminal on a given node 16
and ground contact 54 may be coupled to a ground conductor in data
path 14 if desired (e.g., in scenarios where data path 14 includes
a cable shield or dedicated ground wire).
[0050] Terminal 34 of bimodal impedance terminator 20 may be
coupled to both contacts 64 and 52 of connector 48. Terminal 36 may
be coupled to both contacts 60 and 58 of connector 48. In this way,
terminals 34 and 36 of bimodal impedance terminator 20 may be
coupled to differential signal lines 26H and 26L when connector 48
is connected to data path 14. Capacitor 46 may be coupled to ground
32 via grounded shield 50. In the example of FIG. 5, capacitor 46
and ground contact 54 are both coupled to circuit node 56 on
grounded shield 50. This is merely illustrative and, if desired,
capacitor 46 may be coupled to other locations on grounded shield
50 or may be coupled to ground 32 separately from grounded shield
50. Contacts 52, 58, 60, and 64 may sometimes be referred to herein
as signal contacts, signal ports, signal terminals, input-output
(I/O) ports, I/O contacts, I/O terminals, ports, or terminals.
[0051] Contacts 52, 54, and 58 may be formed from male connector
structures (e.g., pins) that are configured to mate with female
connector structures on data path 14, may be formed from female
connector structures (e.g., pin receptacles) that are configured to
mate with male connector structures on data path 14, or may be
formed from other connector structures such as contact pads,
conductive adhesive, conductive springs, solder balls, welds,
conductive wire, sheet metal, and/or any other desired conductive
structures. Similarly, contacts 64, 62, and 60 may be formed from
male connector structures that are configured to mate with female
connector structures on a given node 16 or elsewhere in network 12,
may be formed from female connector structures that are configured
to mate with male connector structures on the given node 16 or
elsewhere in network 12, or may be formed from other connector
structures such as contact pads, conductive adhesive, conductive
springs, solder balls, welds, and/or any other desired conductive
structures.
[0052] Connector 48 may include attachment structures (e.g., clips,
adhesive, pins, alignment posts, sockets, fixtures, etc.) that
secure connector 48 to a mating connector on data path 14 or
elsewhere in network 12 (e.g., to ensure that connector 48 is
secured in place and a reliable electrical connection is
established between bimodal impedance terminator 20 and
differential signal lines 26H and 26L). The attachment structures
may also allow connector 48 to be detached from the mating
connector if desired. Grounded shield 50 may be omitted if desired
(e.g., circuit node 56 may be coupled to ground 32 over other
grounding structures).
[0053] Integrating bimodal impedance terminator 20 into a connector
for network 12 such as connector 48 of FIG. 5 may, for example,
serve to reduce the routing complexity of network 12, allow for
easy and inexpensive assembly of network 12, and/or allow bimodal
impedance terminator 20 to be easily moved to different locations
across network 12 over time (e.g., to ensure satisfactory
common-mode and differential-mode impedance termination as
additional nodes 16 are coupled to or de-coupled from data path 14
and/or as network 12 is upgraded, expanded, contracted, or
otherwise altered over time).
[0054] If desired, differential signal lines 26H and 26L of data
path 14 may be formed from a twisted pair of conductors (e.g., a
first wire that forms differential signal line 26H may be twisted
around a second wire that forms differential signal line 26L).
Forming differential signal lines 26H and 26L from a twisted pair
of conductors may serve to reduce or minimize electromagnetic
radiation by differential signal lines 26H and 26L, interference
from external sources onto differential signal lines 26H and 26L,
and/or electromagnetic crosstalk between differential signal lines
26H and 26L, as examples.
[0055] If desired, differential signal lines 26H and 26L may be
formed within a shielded cable to further isolate the differential
signal lines from external electromagnetic energy. The shielded
cable may include a shield structure that surrounds differential
signal lines 26H and 26L. The shield structure may
electromagnetically shield differential signal lines 26H and 26L
from electromagnetic noise and interference. The shield structure
may include, for example, a conductive braid or other outer
conductor that is wrapped around differential signal lines 26H and
26L.
[0056] FIG. 6 is a diagram showing how data path 14 may include two
connectors coupled together by a shielded cable. As shown in FIG.
6, data path 14 includes a first connector 48 such as connector 48A
at end 21 and a second connector 48 such as connector 48B at end
23. Bimodal impedance terminator 20 of FIG. 5 may be integrated
within first connector 48A (e.g., as bimodal impedance terminator
20-1 of FIG. 6) and may be integrated within second connector 48B
(e.g., as bimodal impedance terminator 20-2 of FIG. 6).
[0057] Connectors 48A and 48B in the example of FIG. 6 have been
coupled to (e.g., plugged into or mounted to) data path 14 such
that contact 52 of connectors 48A and 48B are coupled to
differential signal line 26H and such that contact 58 of connectors
48A and 48B are coupled to differential signal line 26L. Nodes 16
that are coupled to differential signal lines 26H and 26L between
connectors 48A and 48B may sometimes be referred to herein as
internal nodes 161 or stub nodes 161. Network 12 may include any
desired number of internal nodes 161.
[0058] Nodes 16 that are coupled to differential signal lines 26H
and 26L through a corresponding connector 48 may sometimes be
referred to herein as end nodes 16E. In the example of FIG. 6,
network 12 includes a first end node 16E-1 coupled to contacts 64
and 60 of connector 48A and a second end node 16E-2 coupled to
contacts 64 and 60 of connector 48B. End nodes 16E-1 and 16E-2 may
include connector structures that mate with the corresponding
connector 48 or may be coupled to connector 48 via intervening
cabling (e.g., end node 16E-1 may be coupled to a first connector
structure at a first end of a cable whereas a second connector
structure at a second end of the cable mates with connector 48A to
couple end node 16E-1 to contacts 64 and 60). End node 16E-1 and/or
end node 16E-2 may be omitted from network 12 if desired.
[0059] Data path 14 of FIG. 6 may include cable shield 66. Cable
shield 66 may, for example, include a conductive braid or other
outer conductor that surrounds differential signal lines 26H and
26L between connectors 48A and 48B. Cable shield 66 may be coupled
to ground contact 54 on connectors 48A and 48B (e.g., cable shield
66 may be coupled to ground 32 through grounded shield 50 on each
connector 48). Cable shield 66 may thereby be held at a ground
potential and may serve to isolate differential signal lines 26H
and 26L from external electromagnetic signals. Bimodal impedance
terminators 20-1 and 20-2 may terminate the common-mode and
differential-mode impedances of differential signal lines 26H and
26L while connectors 48A and 48B also serve to couple end nodes
16E-1 and 16E-2 to data path 14.
[0060] In another suitable arrangement, data path 14 may include a
dedicated ground wire. FIG. 7 is a diagram showing how data path 14
may include two connectors coupled together by a cable having a
dedicated ground wire such as dedicated ground wire 68. As shown in
FIG. 7, dedicated ground wire 68 is coupled between ground contact
54 on first connector 48A and ground contact 54 on second connector
48B. Ground contact 62 on first connector 48A may be coupled to a
ground port on end node 16E-1 and ground contact 62 on second
connector 48B may be coupled to a ground port on end node 16E-2. In
this way, the end node ground ports and dedicated ground wire 68
may be coupled to ground 32 (e.g., through grounded shield 50 of
connectors 48A and 48B) and may thereby be held at a ground
(reference) potential. Dedicated ground wire 68 may help the
differential pair of signal lines to exhibit a controlled,
constant-valued, common-mode impedance, which facilitates the
application of bimodal termination.
[0061] The example of FIG. 7 is merely illustrative. If desired,
one or both of end nodes 16E-1 and 16E-2 may be omitted.
Differential signal lines 26H/26L and dedicated ground wire 68 may
be surrounded by a cable shield such as cable shield 66 of FIG. 6
if desired. In another suitable arrangement, data path 14 may be
formed from an unshielded cable without a dedicated ground
wire.
[0062] FIG. 8 is a diagram showing how data path 14 may include two
connectors coupled together by an unshielded cable without a
dedicated ground wire. As shown in FIG. 8, connectors 48A and 48B
may be coupled together by differential signal lines 26H and 26L
without a cable shield such as cable shield 66 of FIG. 6 and
without a dedicated ground wire such as dedicated ground wire 68 of
FIG. 7. Grounded shield 50 of connector 48A may be coupled to
ground 32 (sometimes referred to herein as ground plane 32) via
grounding structures 72. Grounded shield 50 of connector 48B may be
coupled to ground plane 32 via grounding structures 74. Grounding
structures 72 and 74 may include conductive wires, metal housing
structures, sheet metal, conductive adhesive, welds, solder,
conductive contact pads, conductive traces on underlying
substrates, conductive springs, conductive bolts (e.g., ground
strap bolts), conductive pins, conductive screws, combinations of
these, and/or any other desired conductive interconnect structures.
Ground plane 32 may be a system ground for system 10 of FIG. 1
(e.g., a chassis or metal housing structures for system 10), as one
example.
[0063] In scenarios where data path 14 does not include a dedicated
ground wire or cable shield, resistance R.sub.G in bimodal
impedance terminators 20-1 and 20-2 (e.g., as shown in FIG. 5) may
be sensitive to the physical height of connectors 48 above the
ground plane 32. If desired, grounding structures 72 and 74 may
include support structures that hold (secure) connectors 48A and
48B at a fixed distance 76 from ground plane 70. The support
structures may include dielectric housing structures, metal housing
structures, clips, fasteners, plastic support structures, or any
desired combination of these and/or any other desired support
structures. Distance 76 may be selected to ensure that resistance
R.sub.G has a desired value and the support structures may ensure
that resistance R.sub.G and the common-mode impedance of data path
14 remains constant over time. This example is merely illustrative.
If desired, ground structures such as grounding structures 72 and
74 of FIG. 8 may be used to couple connectors 48A and 48B to ground
32 in scenarios where data path 14 includes dedicated ground wire
68 (FIG. 7) and/or cable shield 66 (FIG. 6).
[0064] FIG. 9 is a perspective view showing how different
components may be assembled to form connector 48 of FIG. 5 (e.g.,
one of connectors 48A or 48B of FIGS. 6-8). As shown in FIG. 9,
connector 48 may include a conductive (metal) shell 78. Conductive
shell 78 may form grounded shield 50 for connector 48 (FIG. 5). A
grounding structure such as ground strap bolt 80 may be coupled to
a given side of conductive shell 78. Ground strap bolt 80 may
couple conductive shell 78 to ground 32 (FIG. 5). For example,
ground strap bolt 80 may secure a conductive wire (e.g., a
conductive wire in grounding structures 72 or 74 of FIG. 8) to
conductive shell 78 to ensure that conductive shell 78 remains
reliably coupled to ground over time.
[0065] Conductive shell 78 may surround (define) an interior cavity
91. If desired, conductive shell 78 may include one or more
conductive ledges such as catch bars 90 within interior cavity 91.
A ground plate such as ground plate 82 may be lowered into interior
cavity 91 of conductive shell 78, as shown by arrow 112 of FIG. 9.
Catch bars 90 may catch ground plate 82 as the ground plate is
lowered into interior cavity 91 and may hold ground plate 82 in
place within conductive shell 78. Ground plate 82 may be secured to
catch bars 90 using conductive adhesive, solder, welds, and/or any
other desired interconnect structures. In this way, ground plate
82, catch bars 90, and conductive shell 78 may all be held together
at a ground potential.
[0066] A dielectric substrate such as a plastic substrate or
printed circuit board (not shown in FIG. 9 for the sake of clarity)
may be placed over ground plate 82. The dielectric substrate may
have opposing first and second lateral surfaces. The first surface
may be in contact with ground plate 82. Conductive traces used in
forming bimodal impedance terminator 20 (FIG. 5) may be formed on
the second surface of the dielectric substrate.
[0067] As shown in FIG. 9, the conductive traces may include a
first conductive trace 92, a second conductive trace 98, a first
ring-shaped conductive trace 96, a second ring-shaped conductive
trace 100, and a third ring-shaped conductive trace 94. Ring-shaped
conductive trace 100 may be electrically coupled to ground plate 82
over one or more conductive vias 102. Conductive vias 102 may, for
example, extend through the dielectric substrate placed over ground
plate 82. In this way, ring-shaped conductive trace 100 may be
coupled to ground (e.g., via conductive vias 102, ground plate 82,
catch bars 90, and conductive shell 78).
[0068] Ring-shaped conductive trace 96 may form terminal 36,
ring-shaped conductive trace 94 may form terminal 34, and
conductive trace 92 may form circuit node 38 of bimodal impedance
terminator 20 (FIG. 5). Resistor 42 may couple ring-shaped
conductive trace 96 to conductive trace 92. Resistor 40 may couple
ring-shaped conductive trace 94 to conductive trace 92. Resistor 44
may couple conductive trace 92 to conductive trace 98. Capacitor 46
may couple conductive trace 98 to ring-shaped conductive trace 100.
Resistor 42, resistor 40, resistor 44, and capacitor 46 may, for
example, be formed from surface-mount components mounted to the
surface of the underlying dielectric substrate formed on ground
plate 82.
[0069] Ground plate 82 may include holes or openings such as
openings 104, 106, and 108. Opening 104 may be aligned with the
center of ring-shaped conductive trace 96. Opening 106 may be
aligned with the center of ring-shaped conductive trace 100.
Opening 108 may be aligned with the center of ring-shaped
conductive trace 94. Conductive pins such as conductive pins 84,
86, and 88 may be placed within openings 108, 104, and 106, as
shown by arrow 110 of FIG. 9.
[0070] Conductive pins 84, 86, and 88 may each have first ends 116
with a first diameter and second ends 114 with a second diameter
greater than the first diameter. First ends 116 may pass through
openings 104, 106, and 108 whereas second ends 114 may be too large
to pass through ring-shaped conductive traces 96, 100, and 94. For
example, first end 116 of conductive pin 86 may pass through
ring-shaped conductive trace 96 and opening 104. Second end 114 of
conductive pin 86 may rest on ring-shaped conductive trace 96.
Conductive adhesive, solder, and/or welds may be used to
mechanically and galvanically connect second end 114 of conductive
pin 86 to ring-shaped conductive trace 96. In this way, end 116 of
conductive pin 86 may form contact 60 whereas end 114 of conductive
pin 86 forms contact 58 of connector 48 (FIG. 5).
[0071] Similarly, first end 116 of conductive pin 84 may pass
through ring-shaped conductive trace 94 and opening 108. Second end
114 of conductive pin 84 may rest against ring-shaped conductive
trace 94. Conductive adhesive, solder, and/or welds may be used to
mechanically and galvanically connect second end 114 of conductive
pin 84 to ring-shaped conductive trace 94. In this way, end 116 of
conductive pin 84 may form contact 64 whereas end 114 of conductive
pin 84 forms contact 52 of connector 48 (FIG. 5). In addition,
first end 116 of conductive pin 88 may pass through ring-shaped
conductive trace 100 and opening 106. Second end 114 of conductive
pin 88 may rest against ring-shaped conductive trace 100.
Conductive adhesive, solder, and/or welds may be used to
mechanically and galvanically connect second end 114 of conductive
pin 88 to ring-shaped conductive trace 100. In this way, end 116 of
conductive pin 88 may form ground contact 62 whereas end 114 of
conductive pin 88 forms ground contact 54 of connector 48 (FIG.
5).
[0072] In the example of FIG. 9, ends 114 of conductive pins 84,
86, and 88 include female connector structures that are configured
to receive mating male connector structures on data path 14. At the
same time, ends 116 of conductive pins 84, 86, and 88 include male
connector structures that are configured to be received within
mating female connector structures on data path 14 (or on one of
end nodes 16E-1 or 16E-2 as shown in FIGS. 6-8). This is merely
illustrative. Male connector structures may be located at end 114
of conductive pins 84, 86, and 88, female connector structures may
be located at end 116 of conductive pins 84, 86, and 88, male
connector structures may be located at both ends of conductive pins
84, 86, and 88, female connector structures may be located at both
ends of conductive pins 84, 86, and 88, or other connector
structures may be used if desired. Ring-shaped conductive traces
96, 100, and 94 need not have a ring shape and may, in general,
have any other desired shapes.
[0073] FIG. 10 is a perspective view showing an assembled connector
48 (e.g., after mounting ground plate 82 to catch bars 90 and
mounting conductive pins 84, 86, and 88 to ring-shaped conductive
traces 94, 96, and 100, respectively). As shown in FIG. 10, the
components of bimodal impedance terminator 20 are integrated within
connector 48 and mounted within interior cavity 91 of conductive
shell 78. Side 120 of connector 48 may be mounted to a
corresponding (mating) connector on differential signal lines 26H
and 26L. Side 118 of connector 48 may be mounted to a corresponding
(mating) connector on a given one of end nodes 16E-1 and 16E-2 or
to a corresponding connector on a cable that is coupled to a given
one of end nodes 16E-1 and 16E-2 (FIGS. 6-8). Side 118 of connector
48 need not be coupled to a corresponding node 16 if desired. The
example of FIGS. 9 and 10 is merely illustrative. In general,
connector 48 may have any desired form factor and bimodal impedance
terminator 20 may be integrated within connector 48 in any desired
manner.
[0074] Forming bimodal impedance terminator 20 within one or both
of connectors 48A and 48B may optimize the immunity of data path 14
to common-mode electromagnetic excitations. Consider, for example,
a transmission line equivalent circuit model of a simplest-case
network 12 that is provided with only two internal nodes 161 and
that is subject to a common-mode external electromagnetic
disturbance.
[0075] FIG. 11 is a diagram of an illustrative transmission line
equivalent circuit model 130 for network 12 when provided with only
two internal nodes 161, two impedance terminators, and a
common-mode external electromagnetic disturbance. As shown in FIG.
11, differential signal line 26H of data path 14 (FIGS. 2 and 6-8)
is modeled by transmission line 132 whereas differential signal
line 26L is modeled by transmission line 134. Transmission lines
132 and 134 each have a length (e.g., along the X-axis of FIG. 11)
that is equal to |l.sub.1+l.sub.2|.
[0076] Common-mode voltage sources 136 are coupled to transmission
lines 132 and 134 and inject a common-mode voltage V.sub.S at
location X=0 along the length of the transmission lines.
Common-mode voltage V.sub.S may simulate a common-mode external
electromagnetic disturbance on data path 14. Transmission lines 132
and 134 in model 130 each exhibit minor imbalances in
per-unit-length inductance and capacitance. For example,
transmission lines 132 and 134 may each exhibit per-unit-length
self-capacitance C, per-unit-length mutual-capacitance C.sub.M,
per-unit-length capacitance imbalance of .DELTA.C, per-unit-length
self-inductance L, per-unit-length mutual-inductance L.sub.M, and
per-unit-length inductance imbalance .DELTA.L. The ratio of
per-unit-length capacitance imbalance .DELTA.C to per-unit-length
self-capacitance C (e.g., .DELTA.C/C) and the ratio of
per-unit-length inductance imbalance .DELTA.L to per-unit-length
self-inductance L (e.g., .DELTA.L/L) may each be on the order of
10.sup.-3 or smaller. If transmission lines 132 and 134 are
perfectly balanced, per-unit-length capacitance imbalance of
.DELTA.C and per-unit-length inductance imbalance of .DELTA.L are
each equal to zero, and the differential-mode voltages and current
are all equal to zero.
[0077] Model 130 includes two impedance terminator equivalent
circuits 138 and 140 at opposing ends of transmission lines 132 and
134. Impedance terminator equivalent circuit 138 includes impedance
Z.sub.a coupled between transmission line 132 and circuit node 142,
impedance Z.sub.a coupled between transmission line 134 and circuit
node 142, and impedance Z.sub.b,1 coupled between circuit node 142
and ground 32. Impedance terminator equivalent circuit 140 includes
impedance Z.sub.a coupled between transmission line 132 and circuit
node 144, impedance Z.sub.a coupled between transmission line 134
and circuit node 144, and impedance Z.sub.b,2 coupled between
circuit node 144 and ground 32.
[0078] Assuming that the transmission lines are not perfectly
balanced, the modal conversion factor .zeta. of model 130 is given
by equation 7.
.zeta.=0.5*MAX{|.xi.-.eta.|,|.xi.+.eta.|} (7)
[0079] In equation 7, MAX{ } is the maximum value operator that
outputs the greater of its inputs |.xi.-.eta.| and |.xi.+.eta.|,
.xi. is a transmission line ratio defined by equation 8, and .eta.
is a transmission line ratio defined by equation 9.
.xi.=(C*.DELTA.L-L*.DELTA.C)/(C*L.sub.M-L*C.sub.M) (8)
.eta.=(C.sub.M*.DELTA.L-L.sub.M.DELTA.C)/(C*L.sub.M-L*C.sub.M)
(9)
[0080] The differential voltage .DELTA.V(-l.sub.1) at left end 154
of model 130 (e.g., between circuit nodes 146 and 148 of FIG. 10)
is approximated by equation 10 and the differential voltage
.DELTA.V(l.sub.2) at right end 156 of model 130 (e.g., between
circuit nodes 150 and 152) is approximated by equation 11.
.DELTA.V(-l.sub.1).apprxeq..zeta.*|[1-.GAMMA..sub.e,2*exp(-2*j*.beta.*l.-
sub.2)]*[1+.GAMMA..sub.e,1]|*V.sub.s/.DELTA..sub.e (10)
.DELTA.V(l.sub.2).apprxeq.|[1-.GAMMA..sub.e,1*exp(-2*j*.beta.*l.sub.1)]*-
[1+.GAMMA..sub.e,2]|*V.sub.s/.DELTA..sub.e (11)
[0081] In equations 10 and 11, exp( ) is the exponential operator
(e.g., Euler's number raised to the power of the argument of exp(
)), .GAMMA..sub.e,2 is the reflection coefficient of transmission
lines 132 and 134 at location X=l.sub.2, defined by equation 12,
.GAMMA..sub.e,1 is the reflection coefficient of transmission lines
132 and 134 at location X=-l.sub.1, defined by equation 13, .beta.
is the common-mode propagation constant of model 130, given by
equation 12, and .DELTA..sub.e is a denominator factor, defined by
equation 15. Common-mode propagation constant .beta. may sometimes
referred to as even-mode propagation constant .beta..
.GAMMA..sub.e,1=(Z.sub.a+2*Z.sub.b,1-2*Z.sub.comm)/(Z.sub.a+2*Z.sub.b,1+-
2*Z.sub.comm) (12)
.delta..sub.e,2=(Z.sub.a+2*Z.sub.b,2-2*Z.sub.comm)/(Z.sub.a+2*Z.sub.b,2+-
2*Z.sub.comm) (13)
.beta.=.omega.*SQRT([L+L.sub.M]*[C-C.sub.M]) (14)
.DELTA..sub.c=1-.GAMMA..sub.e,1*F.sub.e,2*exp(-2*j*.beta.*[l.sub.1+l.sub-
.2]) (15)
[0082] In equations 12-15, Z.sub.comm is the common-mode impedance
of the transmission lines (e.g., as given by equation 2) and w is
the angular frequency of signals on the transmission lines. As one
example (e.g., in a scenario where data path 14 is implemented
using an Ethernet cable), L.apprxeq.9.86854*10.sup.-7 (H/m),
L.sub.M.apprxeq.7.29226*10.sup.-7 (H/m),
.DELTA.L.apprxeq.2.0*10.sup.-10 (H/M), C.apprxeq.3.94471*10.sup.-11
(F/m), C.sub.M.apprxeq.3.25842*10.sup.-11 (F/m), and
.DELTA.C.apprxeq.1.9*10.sup.-14 (F/m), Z.sub.diff.apprxeq.119.6
ohms, and Z.sub.comm.apprxeq.250 ohms. This example is merely
illustrative and, in general, the differential signal lines may
have any desired inductive and capacitive characteristics (e.g., as
determined by the characteristics and arrangement of the cabling
used to implement data path 14).
[0083] At conditions where .DELTA..sub.e approaches zero,
differential voltages .DELTA.V(-l.sub.1) and .DELTA.V(l.sub.2) will
peak (e.g., as shown by equations 10 and 11). However, as shown by
equations 10, 11, and 15, if one or both of the reflection
coefficients .delta..sub.e,1 and .GAMMA..sub.e,2 drop to zero,
peaks in differential voltages .DELTA.V(-l.sub.1) and
.DELTA.V(l.sub.2) will vanish. As described above (e.g., as shown
by equation 6), terminating data path 14 using one or more bimodal
impedance terminators 20 will greatly reduce the magnitude of the
reflection coefficients, thereby reducing or minimizing any peaks
in differential voltages .DELTA.V(-l.sub.1) and
.DELTA.V(l.sub.2).
[0084] Consider one example in which impedance Z.sub.a of model 130
is set to 0.5*Z.sub.diff (e.g., where Z.sub.diff is the
differential mode impedance given by equation 1) and the same
termination scheme is used at both ends 154 and 156 of model 130
(e.g., ends 21 and 23 of data path 14, respectively, as shown in
FIGS. 2 and 6-8). In this example, in scenarios where a single
120-ohm resistor is coupled between the transmission lines,
impedance Z.sub.b in model 130 approaches infinity. This infinite
impedance leaves the differential signal lines very vulnerable to
external common-mode excitations and interference. In scenarios
where a split termination scheme is used (e.g., where a shunting
capacitance C.sub.t is coupled to one differential signal line
through a first 60-ohm resistor and to the other differential
signal line through a second 60-ohm resistor without resistor
R.sub.g of FIG. 5), impedance Z.sub.b approaches
1/(j*.omega.*C.sub.t). This may reduce common-mode noise by as much
as 30 dB over scenarios where impedance Z.sub.b approaches
infinity. In scenarios where bimodal impedance terminator 20 is
used, impedance Z.sub.b approaches R.sub.g+1/(j*.omega.*C.sub.t).
This may further reduce noise by 10 dB or greater over scenarios
where a split termination scheme is used.
[0085] FIG. 12 shows graphs of the differential voltage at the ends
of the data path 14 under different impedance termination schemes.
In this example, the same impedance termination scheme is used at
both ends of data path 14. As shown in FIG. 12, graph 158
illustrates the differential voltage (e.g., as generated using
equation 10) as a function of frequency f at left end 154 of
transmission lines 132 and 134 in model 130 of FIG. 11 (e.g., at
end 21 of differential signal lines 26H and 26L of FIGS. 2 and
6-8). Graph 160 illustrates the differential voltage (e.g., as
generated using equation 11) as a function of frequency f at right
end 156 of transmission lines 132 and 134 in model 130 of FIG. 11
(e.g., at end 23 of differential signal lines 26H and 26L in FIGS.
2 and 6-8).
[0086] Curve 162 of graphs 158 and 160 plots the differential
voltage in scenarios where a single 120-ohm resistor is coupled
between the differential signal lines. The infinite common-mode
impedance in this scenario may cause excessive signal reflections
at both ends of the data path and may leave the data path
susceptible to external common-mode noise. This noise may generate
relatively large signal peaks 168 in the differential voltage,
which can generate an excessive number of errors in the data
conveyed over the data path.
[0087] Dark curve 164 of graphs 158 and 160 plots the differential
voltage in scenarios where a split termination scheme is used
(e.g., where a shunting capacitance C.sub.t is coupled to one
differential signal line through a first 60-ohm resistor and to the
other differential signal line through a second 60-ohm resistor
without resistor R.sub.g of FIG. 5). Using a split termination
scheme may reduce the common-mode impedance discontinuity and thus
signal reflection at the ends of the data path relative to the
arrangement associated with curve 162. However, the data path may
still be susceptible to common-mode noise, as shown by peaks 170.
While peaks 170 are smaller than peaks 168 (e.g., by as much as 40
dB), this noise can still introduce an excessive number of errors
in the data conveyed over the data path.
[0088] Dotted curve 166 of graphs 158 and 160 plots the
differential voltage in scenarios where bimodal impedance
terminator 20 is coupled to both ends of the data path (e.g., where
bimodal impedance terminator 20-1 is coupled to end 21 and bimodal
impedance terminator 20-2 is coupled to end 23 of data path 14 as
shown in FIGS. 2 and 6-8). Bimodal impedance terminators 20-1 and
20-2 may terminate the common-mode impedance of the data path and
may thereby reduce or minimize signal reflection at both ends of
the data path (e.g., bimodal impedance terminators 20-1 and 20-2
may reduce reflection coefficients .GAMMA..sub.e,1 and
.GAMMA..sub.e,2 to zero). This may serve to reduce or minimize
peaks in the differential voltage. As shown by dotted curve 166,
any peaks in the differential voltage are smaller than the peaks in
dark curve 164 (e.g., by 10 dB or greater). This differential
voltage peak reduction may reduce or eliminate common-mode noise
from the data path, thereby mitigating any common-mode
noise-related errors in the data conveyed over the data path.
[0089] The example of FIG. 12 is merely illustrative. In general,
curves 164, 166, and 162 may have other shapes. If desired, data
path 14 may include a bimodal impedance terminator at only one end
while still exhibiting satisfactory common-mode performance.
[0090] FIG. 13 shows graphs of the differential voltage at the ends
of the data path 14 when bimodal impedance terminator 20 is only
coupled to a single end of the data path. As shown in FIG. 13,
graph 172 illustrates the differential voltage (e.g., as generated
using equation 10) as a function of frequency f at left end 154 of
transmission lines 132 and 134 in model 130 of FIG. 11 (e.g., at
end 21 of differential signal lines 26H and 26L of FIGS. 2 and
6-8). Graph 174 illustrates the differential voltage (e.g., as
generated using equation 11) as a function of frequency fat right
end 156 of transmission lines 132 and 134 in model 130 of FIG. 11
(e.g., at end 23 of differential signal lines 26H and 26L in FIGS.
2 and 6-8).
[0091] Curve 176 of graphs 172 and 174 plots the differential
voltage in scenarios where a bimodal impedance terminator 20 is
only coupled to left end 21 of differential signal lines 26H and
26L of FIGS. 2 and 6-8. Curve 178 of graphs 172 and 174 plots the
differential voltage in scenarios where a bimodal impedance
terminator 20 is only coupled to right end 23 of differential
signal lines 26H and 26L of FIGS. 2 and 6-8. A single 120-ohm
resistor or any other desired termination scheme may be used to
terminate the end of data path 14 opposite to the bimodal impedance
terminator.
[0092] As shown by curves 176 and 178, bimodal impedance terminator
20 will still reduce peaks in differential voltage when coupled to
only a single end of the data path relative to scenarios where a
single 120-ohm resistor is used to terminate both ends (e.g., as
shown by curve 162 of FIG. 12). Bimodal impedance terminator 20 may
reduce the peaks in differential voltage to approximately the
magnitude of peaks 170 associated with curve 164 of FIG. 12 or, at
some frequencies, may reduce the peaks in differential voltage to
even smaller than the magnitude of peaks 170. In other words,
bimodal impedance terminator 20 may still reduce or minimize signal
reflection and common-mode noise relative to other termination
schemes, even when only a single bimodal impedance terminator 20 is
coupled to data path 14. The example of FIG. 13 is merely
illustrative. In general, curves 176 and 178 may have other
shapes.
[0093] The foregoing is merely illustrative and various
modifications can be made to the described embodiments. The
foregoing embodiments may be implemented individually or in any
combination.
* * * * *