U.S. patent application number 11/139315 was filed with the patent office on 2006-11-30 for differential measurement probe having a ground clip system for the probing tips.
Invention is credited to Paul G. Chastain, Mark W. Nightingale, Kei-Wean C. Yang.
Application Number | 20060267605 11/139315 |
Document ID | / |
Family ID | 36939238 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060267605 |
Kind Code |
A1 |
Yang; Kei-Wean C. ; et
al. |
November 30, 2006 |
Differential measurement probe having a ground clip system for the
probing tips
Abstract
A differential measurement probe has a ground clip system for
electrically coupling outer shielding conductors of differential
probing tips together. In one embodiment, the probing tips
independently move vertically relative to each other with the
ground clip system secured to each of the outer shielding
conductors of the probing tips. In a further embodiment, the
probing tips move both vertically and horizontally and the ground
clip system has a spring wire member that is secured to the probe.
The spring wire member is formed with various sections having
various angles to each other that allows one section to slidably
engage one of the outer shielding conductors on one of the probing
tips and another section to slidably engage the outer shielding
conductor of the other probing tip.
Inventors: |
Yang; Kei-Wean C.;
(Beaverton, OR) ; Nightingale; Mark W.;
(Washougal, WA) ; Chastain; Paul G.; (Portland,
OR) |
Correspondence
Address: |
WILLIAM K. BUCHER;TEKTRONIX, INC.
P O BOX 500 (50-LAW)
BEAVERTON
OR
97077-0001
US
|
Family ID: |
36939238 |
Appl. No.: |
11/139315 |
Filed: |
May 27, 2005 |
Current U.S.
Class: |
324/755.01 |
Current CPC
Class: |
G01R 1/06772 20130101;
G01R 1/06788 20130101 |
Class at
Publication: |
324/754 |
International
Class: |
G01R 31/02 20060101
G01R031/02 |
Claims
1. A differential measurement probe comprising: first and second
probing tip assemblies disposed within a housing with each of the
first and second probing tip assemblies having a probing tip
extending from one end of the housing with each probing tip having
a probing contact and an outer shielding conductor coupled to a
probe ground; a ground clip coupled between the outer shielding
conductors of the first and second probing tips of the first and
second probing tip assemblies adjacent to the probing contacts of
the first and second probing tips.
2. The differential measurement probe as recited in claim 1 wherein
each of the first and second probing tip assemblies further
comprises at least a first compressible element disposed within the
housing for allowing independent axial movement of the first and
second probing tip assemblies.
3. The differential measurement probe as recited in claim 1 further
comprising at least a first adjustment mechanism coupled to one of
the first and second probing tip assemblies for varying the
distance between the probing tips of the first and second probing
tip assemblies.
4. In a differential measurement probe having first and second
measurement probing tip extending from one end of the differential
measurement probe and laying in a common vertical plane with the
first and second measurement probing tips move axially and
laterally relative to each other, a ground clip system for
electrically coupling shielding conductors of the first and second
measurement probing tips together comprising: a circular spring
wire having a lateral section that transitions into a substantially
vertical section at one end and an angled section at the other end
with the angled section extending in the opposite direction from
the substantially vertical section and having an angle to the
lateral section, the lateral, vertical and angled sections of the
circular spring wire being in a common plane, and a protruding
section extending upward from the end of the angled section with
the protruding section having an acute angle to the common plane,
and a flattened wire section extending from the end of the
protruding section with the flattened section extending toward the
common plane and having an obtuse angle relative to the lateral
section of the circular spring wire and an acute angle relative to
the common plane; an angled bore formed in the end of the
differential measurement probe receiving the substantially vertical
section of the circular spring wire with the angle of the bore
extending toward the one of the first and second measurement
probing tips; and a protrusion having side surfaces extending
upward from the end of the differential measurement probe adjacent
to one of the measurement probing tips with the end of the lateral
section of the circular spring wire adjacent to the angled section
of the circular spring wire abutting the surface of the protrusion
facing the measurement probing tip such that the junction of the
angled section and the protruding section of the circular spring
wire engages one of the shielding conductors of the first and
second measurement probing tips and the flattened section of the
circular spring wire engages the shielding conductor of the other
of the first and second measurement probing tips.
5. The ground clip system as recited in claim 4 wherein the
transition between the lateral and substantially vertical sections
of the circular spring wire further comprises an eighty-eight
degree angle.
6. The ground clip system as recited in claim 4 wherein the obtuse
angle between the lateral and angled sections of the circular
spring wire further comprises an angle in the range of ninety-two
and ninety-six degrees.
7. The ground clip system as recited in claim 4 wherein the angle
between the protruding section of the circular spring wire and the
plane of the lateral, vertical and angled sections of the circular
spring wire has a range of thirty-five to sixty-five degrees.
8. The ground clip system as recited in claim 4 wherein the
protruding section of the circular spring wire has an inside length
of 0.010 inches.
9. The ground clip system as recited in claim 4 wherein the
flattened section of the circular spring wire has a thickness in
the range of 0.004 inches to 0.007 inches.
10. The ground clip system as recited in claim 4 wherein the obtuse
angle of the flattened section of the circular spring wire to the
lateral section of the circular spring wire is in the range
ninety-two to ninety-five degrees.
11. The ground clip system as recited in claim 4 wherein the acute
angle of the flattened section of the circular spring wire to the
relative to the plane of the lateral, vertical and angled sections
of the circular spring wire lateral section of the circular spring
wire is in the range eight to fifteen degrees.
12. The ground clip system as recited in claim 4 wherein the angle
of the bore extending toward the common vertical plane of the first
and second measurement probing tips is twenty degrees.
13. In a differential measurement probe having first and second
measurement probing tip extending from one end of the differential
measurement probe and laying in a common vertical plane with the
first and second measurement probing tips move axially and
laterally relative to each other, a ground clip system for
electrically coupling shielding conductors of the first and second
measurement probing tips together comprising: a circular spring
wire having a lateral section that transitions into a substantially
vertical section at one end and an angled section at the other end
with the angled section extending in the opposite direction from
the substantially vertical section and having an angle to the
lateral section with the lateral section and the angled section
being in a common plane and the substantially vertical section
having an acute angle relative to the common plane, and a
protruding section extending upward from the end of the angled
section with the protruding section having an acute angle to the to
the common plane, and a flattened wire section extending from the
end of the protruding section with the flattened section extending
toward the common plane and having an obtuse angle relative to the
lateral section of the circular spring wire and an acute angle
relative to the lateral section plane; an bore formed in the end of
the differential measurement probe parallel to the common vertical
plane of the first and second measurement probing tips receiving
the substantially vertical section of the circular spring wire; and
a protrusion having side surfaces extending upward from the end of
the differential measurement probe adjacent to one of the
measurement probing tips with the end of the lateral section of the
circular spring wire adjacent to the angled section of the circular
spring wire abutting the surface of the protrusion facing the
measurement probing tip such that the junction of the angled
section and the protruding section of the circular spring wire
engages one of the shielding conductors of the first and second
measurement probing tips and the flattened section of the circular
spring wire engages the shielding conductor of the other of the
first and second measurement probing tips.
14. The ground clip system as recited in claim 13 wherein the acute
angle of the substantially vertical section of the circular spring
wire is at twenty degrees to the common plane.
15. In a differential measurement probe having first and second
measurement probing tip extending from one end of the differential
measurement probe and laying in a common vertical plane with the
first and second measurement probing tips move axially and
laterally relative to each other, a ground clip system for
electrically coupling shielding conductors of the first and second
measurement probing tips together comprising: a circular spring
wire having a lateral section that transitions into a substantially
vertical section at one end and an angled section at the other end
with the angled section extending in the opposite direction from
the substantially vertical section and having an angle to the
lateral section with the lateral section and the substantially
vertical section being in a common plane and the angled section
having an acute angle relative to the common plane, and a
protruding section extending upward from the end of the angled
section with the protruding section having an acute angle to the to
the common plane, and a flattened wire section extending from the
end of the protruding section with the flattened section extending
toward the common plane and having an obtuse angle relative to the
lateral section of the circular spring wire and an acute angle
relative to the lateral section plane; an bore formed in the end of
the differential measurement probe parallel to the common vertical
plane of the first and second measurement probing tips receiving
the substantially vertical section of the circular spring wire; and
a protrusion having side surfaces extending upward from the end of
the differential measurement probe adjacent to one of the
measurement probing tips with the end of the lateral section of the
circular spring wire adjacent to the angled section of the circular
spring wire abutting the surface of the protrusion facing the
measurement probing tip such that the junction of the angled
section and the protruding section of the circular spring wire
engages one of the shielding conductors of the first and second
measurement probing tips and the flattened section of the circular
spring wire engages the shielding conductor of the other of the
first and second measurement probing tips.
16. The ground clip system as recited in claim 15 wherein the acute
angle of the substantially vertical section of the circular spring
wire is at twenty degrees to the common plane.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention related generally to differential
measurement probes and more particularly to a differential
measurement probe having ground clip system for probing tips that
move axially and/or laterally relative to each other.
[0002] Differential measurement probe have first and second probing
tip extending from a probe body for acquiring differential signals
from a device under test or for acquiring a single signal with the
second probing tip connected to a ground node of the test device.
As the speed of electronic signal increases, inductive and
capacitive effects that were negligible at lower bandwidths become
increasing important. Inductive ground loops are one effect that
can limit the bandwidth of a differential measurement probe. As the
bandwidth of differential measurement probes approach 20 Ghz, there
is a need to reduce inductive ground loops as much as possible.
[0003] In a related application, the increasing speeds of
electronic signals has resulted in the need for transmission line
structures in printed circuit board (PCB) designs. To optimize high
performance PCB designs for high speed applications, smooth
transmission line structures are need to link communications
between components. Time domain reflectometry (TDR) probes launch a
rising or falling edge signal onto transmission line structures on
a printed circuit board and acquire the return signal from the
transmission line structures for determining parameters of the
transmission lines. For example, the verifying the integrity of a
transmission line structure can be determined using a TDR probe and
a sampling oscilloscope.
[0004] Although instruments for differential TDR measurements are
in existence, the limitations of commercially available TDR probes
has resulted in PCB manufacturers having to rely upon test
structures laid out on test coupons that are placed along the
periphery of the PCB flat for PCB transmission line impedance
control measurements. TDR data from the test coupon is used for
determining lot quality for accepting or rejecting the circuit
boards. This has lead to rejecting marginally good boards and
allowing marginally bad boards because the test coupon may be far
away from the actual transmission lines of interest. Correlation
studies between system speed and transmission line designs are
typically based on the test coupon results. Because of the
difficulty in controlling the laminate layer thicknesses, the
dielectric constant variations, metal line photo edge definitions
and the copper etching over large board areas, there is usually
sizable variations in the impedance of transmission lines depending
on the their board location. The non-uniformity between
transmission lines is typically on the order of ten percent. Due to
these problems, correlation studies for high performance
differential transmission lines to board impedance often requires
large quantities of samples to reveal the true relationship.
[0005] Another problem a user encounter when performing
differential TDR test is the need to provide a good ground for the
two differential signal lines. Typically when performing
differential signal measurements on a printed circuit board, a
coplanar probe pad arrangement is required. The general probe pad
arrangements are ground-signal-signal-ground (G-S-S-G) or a
ground-signal-ground-signal-ground (G-S-G-S-G). This is a very
restrictive requirement because the line spacing and line width of
differential pairs are of may different varieties depending on the
device pin pitch, PCB board materials, desired loss limit, and the
like. A differential TDR probe has to be able to accommodate these
different feature sizes.
[0006] An example of a TDR probe is the CP400-04, manufactured by
Candox System of Japan. The probe has a metal housing in which an
insulated signal conductor is disposed. The metal housing has a
threaded connector at one end for connecting a signal cable. The
other end of the housing has apertures for receiving spring action
pogo pins. One pogo pin is coupled to the insulated signal
conductor and the other pogo pins are connected to the metal
housing. The resulting probing tips have a GSG configuration with
2.5 millimeter center-to-center spacing between the pogo pins.
[0007] A further example is the A0131688 TDR Probe, manufactured
and sold by Inter-Continental Microwave, Santa Clara, Calif. The
TDR probe has a metallic housing with one end of the housing having
a threaded connector for connecting a signal cable. A substantially
rectangular member extends outward from below the connector and has
a threaded aperture for receiving a screw that secures the TDR
probe to the flat spring when the TDR probe is configured with a
similar probe for differential TDR applications. Below the
rectangular member is a circular portion that transitions into a
narrow rectangular probe tip member. The probe tip member has an
aperture that receives an RF pin and dielectric member. The RF pin
is electrically connected to a central signal contact of the
treaded connector. Additional apertures are formed in the narrow
rectangular probe tip member for receiving ground pogo pins. The
various apertures allow the ground pogo pins to be positioned at
various distances from the RF pin. The resulting probing tip has a
GSG configuration.
[0008] Two A0131688 TDR Probes are used to produce the A0134332
Differential TDR probe, manufactured and sold by Inter-Continental
Microwave, Santa Clara, Calif. The individual TDR probes that are
mounted to a flat spring using two screws. A variable spacing
adjustment clamp is position over the TDR probes adjacent to the
narrow rectangular probe tip members. The adjustment clamp has a
"U" shaped portion and a flat portion with the two portions being
secured together with screws. The two opposing sides of the "U"
shaped member have threaded apertures that receive adjustment cap
screws that extend through the sides of the "U" shaped member and
into interior space of the "U". Treaded apertures are formed in the
base of the "U" shaped member that intersect the threaded apertures
in the opposing sides of the "U" shaped member. Each threaded
aperture in the base receives a set screw that is tightened on the
adjustment cap screws.
[0009] Positioning of the RF pins are accomplished by loosening the
set screws on the adjustment cap screws and turning the adjustment
cap screws to move each TDR probes closer together or farther
apart. The flat spring to which the TDR probes are attached causes
outward pressure on the probes to force them against the adjustment
cap screws. The screws holding the TDR probes to the flat spring
may also be loosened to allow rotational movement of the probes.
When the RF tip and the ground pogo pins are positioned correctly,
the set screws and the flat spring screws are tightened.
[0010] U.S. Pat. No. 6,734,689 describes a measurement probe
providing signal control for an EOS/ESD protection control module.
The measurement probe has a spring loaded coaxial probe assembly
and a pressure sensor that work in combination to provide an
activation signal to the control module. The control module is
coupled to a TDR module in a sampling oscilloscope that provides
the rising or falling edge signal to the DUT and samples the return
signal from the DUT. The spring loaded coaxial cable assembly and
pressure sensor are disposed in a probe housing. The spring loaded
coaxial probe assembly has a semi-rigid coaxial cable with one end
forming a probing tip and the other end having a threaded
connector. A flexible coaxial cable is connected to the threaded
connector and to the control module. A ground probing tip is
disposed adjacent to the probing tip and is electrically coupled to
the outer shielding conductor of the semi-rigid coaxial cable. The
ground probing tip is a retractable, spring loaded probing tip that
is attached to a slotted collar that fits around outer shielding
conductor of the semi-rigid coaxial cable. The resulting probe has
a GS configuration.
[0011] What is needed is a differential measurement probe that
reduces inductive ground loops for achieving a 20 Ghz probe
bandwidth. Further, there is a need for a variable spacing
differential TDR probe that is not limited to existing
ground-signal-ground configurations. The variable spacing
differential TDR probe should be provided with a ground clip system
that couples the outer shielding conductors of the coaxial probing
tips together during all possible axial and lateral movements of
the coaxial probing tips.
SUMMARY OF THE INVENTION
[0012] Accordingly, the present invention is a differential
measurement probe having first and second probing tip assemblies
disposed within a housing. Each of the first and second probing tip
assemblies have a probing tip extending from one end of the housing
with each probing tip assembly having a probing contact and an
outer shielding conductor coupled to a probe ground. A ground clip
is coupled between the outer shielding conductors of the first and
second probing tips adjacent to the probing contacts of the first
and second probing tips.
[0013] On one embodiment of the differential measurement probe,
each of the probing tip assemblies has at least a first
compressible element disposed within the housing for allowing
independent axial movement of the first and second probing tip
assemblies. In a further embodiment, the differential measurement
probe has at least a first adjustment mechanism coupled to one of
the first and second probing tip assemblies for varying the
distance between the probing tips of the first and second probing
tip assemblies.
[0014] In a further embodiment, a ground clip system electrically
couples the shielding conductors of first and second measurement
probing tips together in a differential measurement probe. The
measurement probing tip extend from one end of the differential
measurement probe and lay in a common vertical plane with the first
and second measurement probing tips move axially and laterally
relative to each other. The ground clip system has a circular
spring wire having a lateral section that transitions into a
vertical section at one end and an angled section at the other end.
The angled section extends in the opposite direction from the
vertical section and has an obtuse angle to the lateral section. In
a first embodiment, the lateral, vertical and angled sections of
the circular spring wire are in the same plane. A protruding
section extends upward from the end of the angled section with the
protruding section having an acute angle to the to the plane of the
lateral, vertical and angled sections. A flattened wire section
extends from the end of the protruding section with the flattened
section extending toward the plane of the lateral, vertical and
angled sections of the circular spring wire. The flattened section
has an obtuse angle relative to the lateral section of the circular
spring wire and an acute angle relative to the plane of the
lateral, vertical and angled sections of the circular spring
wire.
[0015] An angled bore is formed in the end of the differential
measurement probe and receives the vertical section of the circular
spring wire. The angle of the bore extends toward the common
vertical plane of the first and second measurement probing tips. A
protrusion having side surfaces extends upward from the end of the
differential measurement probe adjacent to one of the measurement
probing tips. The end of the lateral section of the circular spring
wire adjacent to the angled section of the circular spring wire
abuts the surface of the protrusion facing the measurement probing
tip. The junction of the angled section and the protruding section
of the circular spring wire engages one of the shielding conductors
of the first and second measurement probing tips and the flattened
portion of the circular spring wire engages the shielding conductor
of the other of the first and second measurement probing tips.
[0016] In the preferred embodiment, the transition between the
lateral and vertical sections of the circular spring wire is
substantially ninety degree. The obtuse angle between the lateral
and angled sections of the circular spring wire has a range of
ninety-two and ninety-six degrees. The angle between the protruding
section of the circular spring wire and the plane of the lateral,
vertical and angled sections of the circular spring wire has a
range of thirty-five to sixty-five degrees. The protruding section
of the circular spring wire has an inside length of 0.010 inches.
The flattened section of the circular spring wire has a thickness
in the range of 0.004 inches to 0.007 inches. The obtuse angle of
the flattened section of the circular spring wire to the lateral
section of the circular spring wire is in the range ninety-two to
ninety-five degrees. The acute angle of the flattened section of
the circular spring wire to the relative to the plane of the
lateral, vertical and angled sections of the circular spring wire
lateral section of the circular spring wire is in the range eight
to fifteen degrees. The angle of the bore extending toward the
common vertical plane of the first and second measurement probing
tips is twenty degrees.
[0017] In a further embodiment of the invention, the lateral
section defines a plane and at least one of the vertical section
and the angled section of the circular spring wire is at an acute
angle to the lateral section plane. The bore formed in the end of
the differential measurement probe is parallel to the common
vertical plane of the first and second measurement probing tips and
receives the vertical section of the circular spring wire. In one
implementation, the acute angle of the vertical section of the
circular spring wire is at twenty degrees to the lateral section
plane. In another implementation, the acute angle of the angled
section of the circular spring wire is at twenty degrees to the
lateral section plane. In a further embodiment, the vertical
section of the circular spring wire and the angled section of the
circular spring wire are angled to the lateral section plane with
the total angle of the vertical section of the circular spring wire
and the angled section of the circular spring wire being at twenty
degrees to the lateral section plane.
[0018] The objects, advantages and novel features of the present
invention are apparent from the following detailed description when
read in conjunction with appended claims and attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a perspective view of a differential measurement
probe having a ground clip system according to the present
invention.
[0020] FIG. 2 is a partially exploded perspective view of the
differential measurement probe having a ground clip system
according to the present invention.
[0021] FIG. 3 is a perspective view of a differential TDR
measurement probe having a ground clip system according to the
present invention.
[0022] FIG. 4 is a partially exploded view of the differential TDR
measurement probe having a ground clip system according to the
present invention.
[0023] FIG. 5 is close-up perspective view of the front end of the
differential TDR measurement probe having a ground clip system
according to the present invention.
[0024] FIG. 6 is a side view and a plan view of the spring wire
member of the ground clip system according to the present
invention
[0025] FIG. 7 is a simplified end view of the probing tip
assemblies and a portion of the ground clip system according to the
present invention.
[0026] FIGS. 8A and 8B are side views of alternative configurations
of the spring wire member in the ground clip system according to
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0027] Referring to FIG. 1, there is a perspective view of a
differential measurement probe 10 having a ground clip system 12
coupled to outer shielding conductors 14, 16 of probing tips 18,
20. Each probing tip 18, 20 has a probing contact 22, 24 centrally
disposed in the probing tip 18, 20. The probing tips 18, 20 extend
outward from a housing 26. The differential measurement probe 10
may be part of a measurement probing system such as described in
co-pending U.S. patent application Ser. No. ______, filed
concurrently herewith and incorporated by reference. The
measurement probing system includes a probe body electrically
coupled to a measurement test instrument, such as an oscilloscope
or the like, via a coaxial cable. The coaxial cable also contains
power and signal lines that provide electrical power to active
circuitry in the probe body and communication signals to and from
the probe body for controlling the active circuitry. Two coaxial
cables extends from the probe body through an inverted strain
relief and is coupled to a differential measurement probe 10. The
probing tips 18, 20 are part of first and second probing tip
assemblies 28, 30 disposed in the housing 26 as best shown by the
partially exploded perspective view of FIG. 2.
[0028] The housing 26 has first and second housing members 32, 34
formed of an insulating material, such as ABS plastic,
polycarbonate, or the like. The probing tip assemblies 28, 30 may
be formed from flexible semi-rigid coaxial cables 36, 38, such as
manufactured and sold by Tensolite, Corp., St. Augustine, Fla.,
under the trade name Semi-Flex@. The Semi-Flex has a central signal
conductor and an tightly braised outer shielding conductor formed
of an electrically conductive material that is covered with an
insulating material 40. A portion of the outer insulating material
40 is removed from the cables 36, 38 and the exposed braided
portions of the outer shielding conductors are dipped in a liquid
solder. The solder flows into the braids and stiffen those portions
of the cables to form an unbending semi-rigid coaxial cables 44,
46. The unbending semi-rigid coaxial cables 44, 46 forms the
probing tip assemblies 28, 30 with the solid outer shielding
conductors forming the outer shielding conductors 14, 16 of the
probing tip assemblies 28, 30. The probing contacts 22, 24 of the
probing tips 18, 20 are preferably secured to respective resistive
elements 48, 49 that are electrically coupled to the center signal
conductors of the semi-rigid coaxial cables 44, 46. In a further
embodiment, the semi-rigid coaxial cables 44, 46 may traditional
semi-rigid coaxial cables having solid outer shielding conductors.
The outer shielding conductors 14, 16 of the semi-rigid coaxial
cables are coupled to electrical ground through the electrical
circuitry of the probe body.
[0029] The first and second probing tip assemblies 28, 30 have
first compression springs 50, 52 positioned on the respective
semi-rigid coaxial cables 44, 46. One end of each of the first
compression springs 50, 52 are fixedly positioned on the semi-rigid
coaxial cables 44, 46. In one implementation, the spring ends abut
respective retention plates 54 that are secured to the outer
shielding conductors 14, 16 of the semi-rigid coaxial cable 44, 46.
The opposing side of the retention plate 54 abuts a transverse wall
56 in the housing 26. The other ends of the first compression
springs 50, 52 abut a transverse wall 58 such that the first
compression springs 50, 52 are compressed between the transverse
walls 56 and 58.
[0030] The first and second probing tip assemblies 28, 30 have
second compressive springs 60, 62 positioned on the semi-rigid
coaxial cables 44, 46. One end of each of the second compression
springs 60, 62 abut respective pressure plates 64 having bores 66
there through for positioning the pressure plates 64 around the
semi-rigid coaxial cable 44, 46. The pressure plates 64 are free to
move along the semi-rigid coaxial cables 44, 46. The pressure
plates 64 abut a transverse wall 68. The other ends of the second
compression springs 60, 62 abut a transverse wall 70 such that the
second compression springs 60, 62 are compressed between the
transverse walls 68, 70. Actuators 72 are fixedly positioned on the
outer shielding conductors 14 of the semi-rigid coaxial cables 44,
46 with the actuators having protrusions 74 extending toward the
pressure plates 64. The protrusions 74 of the actuators 72 pass
through apertures 76 formed in the transverse wall 68 and engage
the pressure plates 64 during movement of the housing 26 relative
to the probing tip assemblies 28, 30. The first and second
compressible springs 50, 52, 60, 62 allow independent axial
movement of the probing tip assemblies 28, 30 within the housing 26
during use.
[0031] The ground clip system 12 may be formed of a flexible
braided copper 80 that is plated with silver. The silver plated
braided copper 80 is secured to the outer shielding conductors 14,
16 of probing tips 18, 20 using solder, electrically conductive
epoxy or the like. The silver plated braided copper 80 has
sufficient length and flexibility to allow the maximum travel of
the independently movable probing tip assemblies 28, 30 within the
housing 26.
[0032] Referring to FIG. 3, there is shown a perspective view of a
differential TDR measurement probe 100 incorporating the ground
clip system 102. The TDR measurement prob 100 has a housing 104 in
which are disposed first and second probing tip assemblies to be
described in greater detail below. The housing 104 is preferably
elongate with a predominate rectangular cross-section and made of
first and second member 114 116. The housing 104 is formed of an
insulating material, such as ABS plastic, polycarbonate, or the
like. Extending from one end of the housing 104 are probing tips
106, 108. Extending from the far end of the housing are coaxial
threaded connectors 110, 112 that are coupled to flexible coaxial
cables (not shown). The coaxial cables connect the differential TDR
measurement probe 100 to first and second control modules (not
shown) providing electrical overstress (EOS) and electrostatic
discharge (ESD) protection. The first and second control modules
couple the signals from the differential TDR measurement probe 100
to a TDR sampling module in a sampling oscilloscope (not
shown).
[0033] Referring to FIG. 4, the housing member 114 has first and
second channels 118, 120 for receiving the first and second coaxial
probe assemblies 122, 124. Each of the coaxial probe assemblies
122, 124 has a semi-rigid coaxial cable 126 having a central signal
conductor 128 and an outer shielding conductor 130. The central
signal conductors 128 extend outward past the outer shielding
conductors 130 at one end to form the probing tips 106, 108. The
semi-rigid coaxial cables 126 have curved portions 132 at the
probing tip ends 106, 108 that transitions to straight portions at
the probing tips 106, 108. The coaxial threaded connectors 110, 112
are attached to the other ends of the semi-rigid coaxial cables
126. The threaded portions of the coaxial threaded connectors 110,
112 are coupled to the outer shielding conductors 130 and the
central signal conductors 128 are coupled to respective central
conductors axially disposed within the coaxial threaded connectors
110, 112. The outer shielding conductors 130 of the semi-rigid
coaxial cables 126 are capable of being coupled to electrical
ground through the flexible coaxial connectors 110, 112 being
coupled to the flexible coaxial cables that are connected to the
first and second control modules in the sampling oscilloscope.
Attachment plates 134 are attached to the outer shielding
conductors 130 adjacent to the coaxial threaded connectors 110,
112. Abutting the attachment plates 134 on the side away from the
coaxial threaded connectors 110, 112 are anti-rotation block 136,
138. Each anti-rotation block 136, 138 has a channel 140 formed
therein that accepts one of the semi-rigid coaxial cables 26. The
anti-rotation blocks 136, 138 have threaded apertures that receive
threaded screws passing through apertures formed in the attachment
plates 134 for securing the anti-rotation blocks 136, 138 to the
attachment plates 134.
[0034] The first and second coaxial probe assemblies 122, 124 have
first compressive elements 146, 148 in the form of compression
springs 150 positioned on the semi-rigid coaxial cables 126. One
end of the compression springs 150 are preferably held in place on
the semi-rigid coaxial cables 126 by a compression spring retention
members 152 secured to outer shielding conductors 130 of the
semi-rigid coaxial cables 126. The other ends of the compression
springs 150 are free to move along the semi-rigid coaxial cables
126. A pressure plate 154 in the form of a washer is preferably
positioned adjacent to each of the free ends of the compression
springs 150 for engaging the rearward end walls 156, 158 of the
channels 118, 120. The first and second coaxial probe assemblies
122, 124 have respective second compressive elements 160, 162 in
the form of compression springs disposed within pogo pins 164, 166,
168. The compression springs are partially compressed in the pogo
pins 164, 166, 168 by the movable electrical contacts 170, 172, 174
of the pogo pins.
[0035] The first coaxial probe assembly 122 has a first pressure
sensor 180 that includes first and second electrically conductive
contacts 182 and 184. The first electrically conductive contact 182
is positioned on the semi-rigid coaxial cable 126 and the second
electrically conductive contact 184 is positioned in the housing
member 1114. The electrically conductive contact 182 preferably
takes the form of a rectangular shaped retention block 186 having a
curved slot 188. The curved portion 132 of the semi-rigid coaxial
cable 126 of the first coaxial probe assembly 122 is disposed in
the curves slot 188 of the retention block 186 and makes electrical
contact with the retention block 186. The retention block 186 is
preferably made of an electrically conductive material, such as
copper, brass, or the like, that is plated with gold. The second
electrically conductive contact 184 is the pogo pin 164 of the
second compressive element 160 of the first coaxial probe assembly
122.
[0036] The second coaxial probe assembly 124 has a second pressure
sensor 190 that includes first and second electrically conductive
contacts 192 and 194. The first electrically conductive contact 192
is positioned on a rectangular shaped retention block 196 having a
curved slot 198. The curved portion 132 of the semi-rigid coaxial
cable 126 of the second coaxial probe assembly 124 is disposed in
the curves slot 198 of the retention block 196 and makes electrical
contact with the retention block 196. The retention block 196 is
preferably made of an electrically conductive material, such as
copper, brass, or the like, that is plated with gold. An
electrically insulating material 200 is disposed between the
electrically conductive contact 192 and the retention block 196 to
electrically isolate the contact 192 from the coaxial probe
assembly 126. The second electrically conductive contact 194 of the
second pressure sensor 190 is the two pogo pins 166, 168 of the
second compressive element 162 of the second coaxial probe assembly
124.
[0037] The differential TDR measurement probe 100 has an adjustment
mechanism 210 that moves the first coaxial probe assembly 122
relative to the second coaxial probe assembly 124 which, in turn,
varies the spacing between the probing tips 106, 108. The
adjustment mechanism has a carrier 212 closely receiving the
retention block 186 of the first coaxial probe assembly 122. The
carrier 212 is preferably a "U" shaped member having a threaded
aperture formed therein for receiving a threaded cap screw 214
having a cap head 216 and the threaded shank 218. The threaded cap
screw 214 is inserted in a bore 220 of the housing member 114 with
the threaded shank 218 extending into a recess 222 of the channel
118 and screwing into the carrier 212. The cap head 216 of the cap
screw 214 sits in a recess formed in the outer surface of the
housing member 114. A cap plate 224 fits over this recess and is
held in place with a screw 226 that is screwed into the housing
member 114. The cap plate 224 closely captures the cap head 216
between the housing member 114 and the cap plate 224 so that there
is no axial movement of the cap head 216 in the recess.
[0038] The retention block 186 frictionally fits in the "U" shaped
carrier 212 so that there is no lateral play of the retention block
186 in the carrier 212. The carrier 212 is positioned in a recess
230 of the channels 118 of the housing member 114 and moves
laterally across the recess 230 in response to the turning of the
cap screw 214. Turning the cap screw 214 clockwise generates
pressure to the bottom surface of the cap head 216 by the housing
member 114 causing the carrier 212 to move outward towards the side
of the housing member 114. Turning the cap screw 214 counter
clockwise generates pressure on the top of the cap head 216 by the
cap plate 224 causing the carrier 212 to move inward toward the
center of the housing member 114. The carrier 212 can retract into
the recess 222 formed in the wall of the housing member 114 until
the retention block 186 abuts the outer side wall of the recess
230. The carrier 212 can be extended across the recess 230 until
the retention block 186 abuts the inner side wall of the of the
recess 230 with a portion of the carrier 212 moving into a slot 232
formed in the dividing wall 234 between the channels 118 and
120.
[0039] Placing the probing tips 106, 108 on a transmission line
structure on a printed circuit board and applying downward pressure
on the housing 104 applies downward forces on the probing tips 106,
108 by the first compression springs 150 being compressed by the
rearward end walls 156, 158 of the channels 118, 120 in the housing
104. At the same time, the probing tips 106, 108 begin to retract
into the housing 104. Continued downward pressure on the housing
104 causes the probing tips 106, 108 to continue to retract in the
housing and the pogo pins 164, 166, 168 of the second electrically
conductive contacts 184, 194 of the first and second pressure
sensors 180 and 190 to engage the first electrically conductive
contacts 182, 184 of the first and second pressure sensors 180,
190. The making of the contacts of the first and second pressure
sensors 180, 190 passes an activation signal to the control modules
which activates a relay to couple the probing tips 106, 108 to the
TDR sampling module. At the same time, the compression springs in
the pogo pins 164, 166, 168 apply additional downward forces to the
probing tips 106, 108. The use of the first and second compressive
elements 146, 148, 160, 162 with the first and second coaxial probe
assemblies 122, 124 allows the assemblies to move independently of
each other.
[0040] Referring to FIG. 5, there is a close-up perspective view of
the front end of the differential TDR measurement probe 100 showing
the ground clip system 92. The probing tips 106,108 lay in a common
plane 248 that is normal to the front end of the differential TDR
measurement probe 100. The ground clip system 92 has a spring wire
member 250, a bore 252 formed in the end of the differential TDR
measurement probe 100, and a protrusion 254 extending from the end
of the differential TDR measurement probe 100. In the preferred
embodiment, the bore 252 and the protrusion are formed in the
retention block 196 of the second coaxial probing assembly 124. The
bore 252 is preferably angled toward the probing tip 108 at twenty
degrees but other angles may be employed so long as the spring wire
member maintains contact with the outer shielding conductors 130 of
the probing tips 106,108 at all times. A threaded bore is formed in
the retention block 196 for receiving a cap screw 258 for securing
the spring wire member 250 to the differential TDR measurement
probe 100. The spring wire member 250 has various angled bends and
a flat portion formed therein for allowing the spring wire member
250 to contact the outer shielding conductors 130 of the probing
tips 106, 108 at any spacing between the probing tips 106,108.
[0041] Referring to FIG. 6, there is shown a side and top plan
views of the spring wire member 250. The spring wire member 250 is
preferably formed of a 0.014 diameter beryllium-copper wire. The
spring wire member 250 has a lateral section 260 that transitions
at one end to a substantially vertical section 262 having a nominal
angle to the lateral section of eighty-eight degrees. At the
opposite end of the lateral section 260 is an angled section 264
that extends in the opposite direction from the substantially
vertical section 262. The angled section 264 has an angle relative
to the lateral section 260 that ranges from ninety-two degrees to
ninety-six degrees with the preferable angle being ninety-six
degrees. In this embodiment, the lateral section 260, the
substantially vertical section 262 and the angled section 264 lay
in a common plane 266 defined in the drawing by the drawing sheet.
The nominal length of the lateral section 260 is 0.181 inches. The
nominal length of the substantially vertical section 262 is 0.104
inches and the nominal height of the angled section 264 is 0.147
inches.
[0042] Extending from the end of the angled section 264 is a
protruding section 268 and a flattened section 270. The protruding
section 268 extends outward from the plane 266 at an nominal angle
of approximately forty-five degrees. The protruding section 268 has
a nominal inside dimension of 0.010 inches for probing tips 106,
108 having a diameter of 0.085 inches. The inside dimension of the
protruding section 268 varies with the diameter of the probing tips
106, 108 with lager diameter probing tips 106, 108 requiring a
larger inside dimension for the protruding section 268. The
flattened section 270 extends from the protruding section 268 and
is angled toward the common plane 266 of the lateral section 260,
the substantially vertical section 262 and the angled section 264.
The angle of the flattened section 270 relative to the common plane
266 has a range of eight to fifteen degrees with the nominal angle
being eight degrees. The flattened section 270 further has an
obtuse angle relative to the lateral section 260 that ranges from
two to four degrees with the nominal angle being two degrees. The
flattened section 270 has a thickness ranging from 0.0045 to 0.0060
inches and an overall nominal length of 0.260 inches. The
flattening of the beryllium-copper wire lowers the spring constant
of that flattened section 270 of the wire normal to the flat
surface. This lowers the torsion force the flattened section 270
exerts on the junction 272 of the angled section 264 and the
protruding section 268. After the spring wire member 250 is formed
into the proper shape, it is heat treated at 600.degree. F. for two
hours to increase the hardness of the beryllium copper wire.
[0043] The substantially vertical section 262 of the spring wire
member 250 is inserted into the angled bore 252 with the lateral
section 260 laying flush with the surface of the retention block
196 and the end of the lateral section 260 adjacent to the angled
section 264 positioned against the inside surface of the protrusion
254 adjacent to the probing tips 108. The junction 272 of the
angled section 264 and the protruding section 268 abuts the outer
shielding conductor 130 of the probing tip 108. Because of the
twenty degree angle applied to the angled section 264 by the spring
wire member 250 being inserted into the angled bore 252, the
lateral section 260 has the tendency to spring outward from the
probing tip 108. The protrusion 254 retrains the lateral section
260 from springing outward so as to maintain a strong spring force
of the junction 272 on the outer shielding conductor 130 of the
probing tip 108 as represented by the vector F.sub.1 in FIG. 7.
[0044] FIG. 7 is a simplified end view of the probing tip
assemblies 106, 108 looking toward the end of the differential TDR
measurement probe 100. The probing tip 106 is movable relative to
the probing tip 108 as represented by the doubled arrow dashed
line. The flattened section 270 of the spring wire member 250
engages the outer shielding conductor 130 of the probing tip 106.
When the probing tips 106, 108 are separated at their greatest
distance from each other, the junction 272 of the angled section
264 and the protruding section 268 is positioned toward the probing
tip 106 on the outer shielding conductor 130 of the probing tip
108. At the same time the obtuse angle between the lateral section
260 and the angled section 264 increases. The spring constant of
the beryllium copper wire seeks to maintain the original obtuse
angle which generates a force F.sub.2 on the junction 272 as
represented by the vector F.sub.2. The resulting vector force on
junction 272 is directed toward the central signal conductor 128 of
the probing tip 108.
[0045] As the probing tip 106 is moved toward the probing tip 108,
the junction 272 of the spring wire member 250 moves along the
surface of the outer shielding conductor 130 of the probing tip 108
as represented by the dashed probing tips 106, the flattened
section 270 and the protruding section 268. The flattened section
270 of the spring wire member 250 has a reduce spring constant
compared to the circular portions of the spring wire member 250 due
to the flattening process. Because of this, the torsional force
applied by the flattened section 270 on the junction 272 is
reduced. This results in the junction 272 maintaining a strong
mechanical contact with the outer shielding conductor 130 of the
probing tip 108. Without the reduced spring constant of the
flattened section 270, the junction 272 would pull away from the
outer shielding conductor 130 of the probing tip 108.
[0046] FIGS. 8A and 8B illustrates further embodiments of the
ground clip system 92. Like elements from the previous drawings are
labeled the same in FIGS. 8A and 8B. The views in FIGS. 8A and 8B
are looking parallel to the lateral section 260. In FIG. 8A, the
spring wire member 250 is modified so that the substantially
vertical section 262 is angled relative to a common plane 280
containing the lateral section 260 and the angled section 264. The
angle of the substantially vertical section 262 to the common plane
280 is nominally twenty degrees. The bore 252 in the retention
block 196 is changed from an angled bore of twenty degrees to a
vertical bore that is normal to the surface of the retention block
196. Alternately, the substantially vertical section 262 may have
an angle of less than twenty degrees to the common plane 280 and
the bore 252 may be angled at less than twenty degrees where the
total angle of the substantially vertical section 262 and the
angled bore 252 is twenty degrees.
[0047] In FIG. 8B, the spring wire member 250 is modified so that
the angled section 264 is angled relative to a common plane 282
containing the lateral section 260 and the substantially vertical
section 262. The angle of the angled section 264 to the common
plane 282 is nominally twenty degrees. The bore 252 in the
retention block 196 is changed from an angled bore of twenty
degrees to a vertical bore that is normal to the surface of the
retention block 196.
[0048] The differential measurement probe 10 and the differential
TDR measurement probe 100 with the ground clip systems 12, 102
provide a virtual ground to the signals being measured by the
probe. The use of the ground clip systems 12, 102 achieves greater
bandwidth into the 20 Ghz range than previous differential
measurement probes.
[0049] It will be obvious to those having skill in the art that
many changes may be made to the details of the above-described
embodiments of this invention without departing from the underlying
principles thereof. The scope of the present invention should,
therefore, be determined only by the following claims.
* * * * *