Electricity: measuring and testing – Testing potential in specific environment – Voltage probe
Reexamination Certificate
2001-05-24
2003-04-22
Le, N. (Department: 2858)
Electricity: measuring and testing
Testing potential in specific environment
Voltage probe
C324S149000, C324S754090
Reexamination Certificate
active
06552523
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to measurement probes and more particularly to a combination low capacitance probe tip and socket for a measurement probe.
Voltage measurement probes couple an electrical signal from a device under test to a measurement test instrument, such as an oscilloscope and the like. Measurement probes include a probe head, a transmission line, such as a coaxial cable, and a connector housing having a signal connector, such as a BNC, SMA, BMA connector or the like, that connects to a mating signal connector on the measurement instrument. The probe head generally includes a metal tube or housing in which is disposed a substrate. A probing tip or socket is disposed in a holder that is inserted into one end of the probe head. The probe tip or socket extends from the holder and is electrically coupled to the substrate. The substrate has passive or active circuitry formed thereon that provides high impedance to the circuit generating the signal under test. The substrate circuitry is electrically coupled to the transmission line. The other end of the transmission line is electrically coupled to the signal connector.
High frequency measurement probes, such as those for probing signals in the 3 GHz to 4 GHz range, require high input impedance values and low input capacitances. Generally, these types of probes have an active transistor input stage for low circuit loading and have a frequency bandwidth up to 4 GHZ or more. An example of such a probe is the P6217 Active FET Probe, manufactured and sold by Tektronix, Inc., Beaverton, Oreg. and assignee of the instant application.
FIG. 1
is a side-sectional view of the P6217 probe
10
showing the internal configuration of the probe elements. The probe
10
has an electrically conductive circular tubular housing
12
in which is disposed a substrate
14
. The substrate is slightly off center in the tubular housing so that the upper surface of the substrate is centered in the housing. The end of the substrate
14
extends slightly outward from the end of the tubular housing and is tapered to provide clearance for a probe tip holder
16
. Passive and active electrical components
18
, such as bipolar transistors, resistors, capacitors and the like are mounted on the substrate. A gold foil contact
20
extends over the front end of the substrate
14
for providing an electrical connection between the substrate
14
and a probing tip
22
. The probe tip holder
16
is made of insulating material, such as plastic or the like, and is secured within the end of the housing
12
. The holder
16
has a cavity
24
with a tapered end
26
that receives a portion of the substrate
14
extending out past the end of the housing
12
. The tapered end
26
is centrally formed in the holder
16
and has a bore
28
extending therefrom to the front end of the holder
16
. The probing tip
22
has a head
30
and a shank
32
that is disposed in the holder
16
with the head
30
positioned in the tapered end
26
and the shank
32
extending through the bore
28
with the tip of the shank
32
exposed at the front end of the holder
16
. A resilient elastomeric member
34
is disposed in the tapered end
26
between the probing tip head
30
and the holder to provide a compressive force between the head
30
and the gold foil contact
20
on the end of the substrate
14
. An insulating boot
36
is positioned over a substantial portion of the tubular housing
12
to electrically insulate the housing
12
from the user.
Referring to
FIG. 2
, there is shown a side-section view of another type of probe
40
having active circuitry. In this particular probe design, a socket
42
is provided in the probe tip holder
44
. An example of such a probe is the P6245 Active probe, manufactured and sold by Tektronix, Inc., Beaverton, Oreg. The socket type active probe has a frequency bandwidth up to 1.5 GHz. The probe has a rectangular cross-section electrically conductive housing
46
. A substrate
48
having active and passive circuitry
49
mounted thereon is mounted on a carrier
50
that is inserted into the housing
46
. A gold foil contact
52
extends over the front end of the substrate
48
for providing an electrical connection between the substrate
48
and the socket
42
. The probe tip holder
44
has a bore
54
there through in which is positioned the electrically conductive socket
42
. An electrically conductive elastomeric material
56
is positioned between the socket
42
and the edge of the substrate
48
to electrically connect the socket to the circuit board and to provide a compressive force. A second socket
58
is positioned and electrically coupled to the housing
46
to provide a ground connection. An insulating boot
60
is positioned over a substantial portion of the housing
46
to electrically insulate the housing from the user. The socket
42
is designed to allow placement on square pin connectors mounted on a circuit board under test. Also, various types of probe tip adapters are provided with the probe for different types of probing operations. For example, a pointed tip may be inserted into the socket for placing the probe on circuit board traces, IC leads and the like.
A drawback to the socket style tip is that the metal socket diameter is much larger than the needle tip, so the socket is closer to the probe's metal tubular housing, increasing capacitance. The increased capacitance at the probe tip results in lower frequency bandwidth. Adding the various probe tip adapters further increases the tip capacitance. Likewise, adding a socket tip adapter to the probing tip of the higher frequency probe reduces the overall frequency bandwidth. What is needed is a measurement probe that allows both probing using a probing tip and a socket type connection, without the higher capacitance of a socket type connection.
SUMMARY OF THE INVENTION
Accordingly, the present invention is to a low capacitance probe tip and socket for a measurement probe having an insulating plug disposed in one end of a probe head. The insulating plug has a bore there through for receiving a low capacitance probe tip and a recess defining a socket. The socket has an aperture formed therein that provides access to the low capacitance probe tip. An electrically conductive contact is disposed in the aperture that extends into the socket and is in electrical contact with the low capacitance probe tip. In one embodiment, the socket is formed parallel to the low capacitance probe tip. The electrically conductive contact is then a spring contact formed on the probe tip and extends through the aperture into the socket. The spring contact is an electrically conductive beryllium-copper wire affixed to the probe tip and has a fold therein that extends through the aperture into the socket. In a further embodiment, the socket is formed at an angle to the low capacitance probe tip. The electrically conductive contact is then an electrically conductive elastomeric material disposed at the distal end of the socket in electrical contact with the low capacitance probe tip.
A measurement probe has a probe head that includes the low capacitance probe tip and socket. The probe head has a substrate disposed therein with probe circuitry formed on the substrate and an insulating plug disposed in one end of the probe head having a bore there through for receiving a low capacitance probe tip that is electrically coupled to the substrate. The insulating plug has a recess defining a socket with the socket having an aperture formed therein to access the low capacitance probe tip. An electrically conductive contact is disposed in the aperture that extends into the socket and is in electrical contact with the low capacitance probe tip. In one embodiment, the socket is formed parallel to the probe tip and in a further embodiment the socket is formed at an angle to the low capacitance probe tip. In the first embodiment, the electrically conductive element is a spring contact formed on the probe tip and extends through the aperture into t
Bucher William K.
Kerveros James C.
Le N.
Tektronix Inc.
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