Electric circuit providing selectable short circuit for...

Details Electric circuit providing selectable short circuit for... Electric circuit providing selectable short circuit for...

2001-06-29

2002-11-19

Le, N. (Department: 2858)

Electricity: measuring and testing

Fault detecting in electric circuits and of electric components

Of individual circuit component or element

Reexamination Certificate

active

06483318

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to an electric circuit used in instrumentation applications, and more particularly, an electronic circuit providing a selectable short circuit for use in instrumentation applications such as measuring the total resistance of pairs of associated electrical conductors in transmission lines having a plurality of conductor pairs.
Use of electronic circuits in instrumentation applications is well known. Included among such applications is the measurement of the total resistance for a pair of associated electrical conductors included within a transmission line having a plurality of associated electrical conductor pairs. One such transmission line is a cable having a plurality of associated electrical conductor pairs. Those skilled in the art will appreciate that a multi-pair cable tester such as a local area network (LAN) cable tester is generally utilized to measure the wire pair resistance as part of the testing conducted in order to ensure that the cable functions properly in accordance with its required specifications. The wire pair resistance test is performed for each pair of associated electrical conductors included within the tested cable. This test is carried out one pair at a time. Alternatively, one select pair of associated electrical conductors will constitute a cable tester or certifier pair, and will be the pair of conductors subject to testing.
In order to perform the wire pair resistance test, for each electrical conductor pair, the adjacent ends positioned at one end of the transmission line (i.e., shorting end) are selectively electrically coupled together by a short circuit provided between those ends. For the pair under test, a current source is selectively electrically coupled to its opposite end positioned at the other end of the transmission line (i.e., measurement end). As such, the current source selectively drives an electrical current through that electrical conductor of the pair, through the selectable short electrically coupling the conductors, and through the other electrical conductor of the pair. The measurement end of the other conductor of the pair is selectively electrically coupled to a specified reference voltage or return path, thereby completing a circuit path for the electrical current driven through the associated conductors of the pair by the current source.
At the measurement end, voltage sensing circuitry is selectively electrically coupled across the associated electrical conductors of the pair. The differential voltage of the conductors is measured by the voltage sensing circuitry, indicating the voltage drop across the electrical conductors and the selectable short circuit. From the measured voltage and the test current, the total resistance for the electrical conductors can be determined. In effect, this value can be determined by dividing the magnitude of the sensed voltage by the known magnitude of the electrical current produced by the current source. This calculation is well known by those skilled in the art as an application of Ohm's law.
When pairs of associated electrical conductors in transmission lines are tested, several different tests are conducted on each conductor pair. As a result, and as those skilled in the art will appreciate, it is impractical to electrically couple the shorting ends of each conductor in the pair with a simple short. In addition to total resistance, other parameters are also measured, such as capacitance, electrical length, and radio frequency (RF) response parameters. Multiplexer circuitry is generally electrically coupled at each end of the electrical conductors in the transmission line to permit the selected pair of associated conductors to be electrically coupled to the measurement and/or shorting circuits for the variety of measurements to be taken during testing.
FIG. 1
illustrates a prior art cable conductor pair resistance test circuit generally designated
10
. Test circuit
10
is designed to permit determination of the total resistance for selected pairs of the electrical conductors included within a transmission line such as cable
12
shown in
FIG. 1
by providing a selectable short between the conductor pairs being measured. In its illustrated form, cable
12
includes a first pair of associated electrical conductors
14
,
16
, a second pair of associated electrical conductors
18
,
20
, a third pair of associated electrical conductors
22
,
24
, and a fourth pair of associated electrical conductors
26
,
28
.
Test circuit
10
includes measurement circuit components grouped together and identified by reference numeral
30
positioned at the measurement end of the test circuit, and shorting circuit components grouped together and identified by reference numeral
32
positioned at the shorting end of the test circuit. In the illustrated form, measurement circuit components
30
include a multiplexer circuit
34
shown in the form of a four-wire differential four-to-one multiplexer. Multiplexer circuit
34
includes a plurality of terminals such as pins incorporated in an integrated circuit packaging. Among the terminals of multiplexer circuit
34
, for present purposes, select ones of those terminals are designated DRV+, DRV−, SEN+, SEN−, A+, A−, B+, B−, C+, C−, D+, and D−.
Measurement circuit components
30
also include a current source
36
, a differential voltage sensing amplifier
38
, and the combination of a series-coupled resistor
40
and voltage source
42
, all of which are electrically coupled to multiplexer circuit
34
. In particular, current source
36
is electrically coupled at one of its ends to the DRV+ terminal of multiplexer circuit
34
, and at its other end to a voltage reference, as shown. The input terminals of differential amplifier
38
are electrically coupled to the SEN+ and SEN− terminals of multiplexer circuit
34
, while its output terminal is preferably electrically coupled to additional voltage sensing circuitry (not shown). The combination of resistor
40
and voltage source
42
is electrically coupled to the DRV− terminal of multiplexer circuit
34
at one of its ends, and electrically coupled to a voltage reference at its other end.
As further shown, with respect to the electrical conductors included within cable
12
, conductor
14
is electrically coupled to terminal A+ of multiplexer circuit
34
, conductor
16
is electrically coupled to terminal A− of multiplexer circuit
34
, and so forth, as shown. With this arrangement, determination of the total resistance for pairs of associated electrical conductors of cable
12
can be measured by measurement circuit
30
.
Shorting circuit components
32
include a multiplexer circuit
44
illustrated as a differential four-to-one multiplexer. Similar to multiplexer circuit
34
, multiplexer circuit
44
includes a plurality of terminals such as pins of the type used in integrated circuit packaging technology. Among the terminals of multiplexer circuit
44
, for present purposes, select ones have been designated A+, A−, B+, B−, C+, C−, D+, D−, SEN+, and SEN−.
Shorting circuit
32
also includes a relay or semiconductor switch
46
having two terminals. One terminal of relay/switch
46
is electrically coupled to the SEN+ terminal of multiplexer
44
, while the other terminal of relay/switch
46
is electrically coupled to the SEN− terminal of multiplexer circuit
44
.
With respect to the electrical conductors included within cable
12
, their respective shorting ends to be electrically coupled by a short circuit due to relay/switch
46
during the test are electrically coupled to select ones of the terminals for multiplexer circuit
44
. In particular, electrical conductor
14
is electrically coupled to terminal A+ of multiplexer circuit
44
, electrical conductor
16
is electrically coupled to terminal A− multiplexer circuit
44
, and so forth, as sh

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