Electrical transmission or interconnection systems – Anti-induction or coupling to other systems
Reexamination Certificate
2001-01-11
2003-05-20
Sircus, Brian (Department: 2836)
Electrical transmission or interconnection systems
Anti-induction or coupling to other systems
C381S124000, C381S077000, C200S051030, C200S051050, C200S051110
Reexamination Certificate
active
06566767
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to cable interconnection between electronic equipment and, more particularly, to a connector and/or cable capable of selectively opening or closing a ground connection between two pieces of electronic equipment.
Noise problems often occur when undesirable ground loops are produced. Such ground loops are often formed when multiple pieces of electronic equipment are connected to one another through cables. To illustrate this problem, reference is made to
FIG. 1
, which shows a first piece of electronic equipment
10
connected to a second piece of electronic equipment
20
by way of a cable
30
. The cable
30
includes a first connector
32
and a second connector
34
that are operable to mate with the first piece of electronic equipment
10
and the second piece of electronic equipment
20
, respectively. The cable
30
also includes signal wires
36
a
,
36
b
and a ground wire
36
c
for electrically connecting respective signal and ground leads
12
,
14
,
16
of the first piece of electronic equipment
10
to signal and ground leads
22
,
24
,
26
of the second piece of electronic equipment
20
. The first piece of electronic equipment
10
includes a connection from earth ground
1
to ground lead
16
(and/or chassis). Similarly, the second piece of electronic equipment
20
includes a connection from earth ground
2
to ground lead
26
(and/or chassis).
An undesirable ground loop may be produced when the cable
30
electrically connects the ground lead
16
of the first piece of electronic equipment
10
to the ground lead
26
of the second piece of electronic equipment
20
. This is so because the respective earth grounds
1
,
2
of the first and second pieces of electronic equipment
10
,
20
, respectively, are not at precisely the same potential as a function of time. Thus, noise currents flow between the earth grounds
1
,
2
by way of the ground wire
36
c
of the cable
30
. The connections to the respective earth grounds
1
,
2
are often made by way of respective AC power cords and chassis connections for the first and second pieces of electronic equipment
10
,
20
. Consequently, the noise currents are often in the audible range, for example, 60 Hz, 120 Hz, 180 Hz, etc. (often referred to as “hum”).
With reference to
FIG. 2
, the ground loop problem illustrated in
FIG. 1
may be solved by replacing the first piece of electronic equipment
10
with a piece of electronic equipment
40
that includes a switch
42
that is operable to interrupt the electrical path between the earth ground
1
and the ground lead
16
. Unfortunately, very few pieces of electronic equipment include such a switch
42
. When a piece of electronic equipment includes such a switch
42
, it often is a very high-end unit with a correspondingly high purchase price. Consequently, users often opt for the electronic equipment
10
,
20
of FIG.
1
and either live with the undesirable hum or take other, less advantageous, approaches to eliminating the noise currents. For example, users may attempt to disconnect the earth ground
1
from, for example, the first piece of electronic equipment
10
by removing the earth ground terminal from the AC power cord or utilizing a three-prong to two-prong adapter (often called a “cheater”), which performs the same function. In either case, the chassis of the first piece of electronic equipment
10
will float with respect to earth ground
1
and, therefore, present an electrical shock hazard to those handling the first piece of electronic equipment
10
.
With reference to
FIG. 3
, it is noted that a cable
50
may include a connector
52
having a switch
58
coupled between signal leads
54
,
56
. In order to achieve a mute condition, a user may connect leads
54
,
56
together by way of the switch
58
(thereby shorting any differential signal from reaching the second piece of electronic equipment
20
). The muting switch
58
, however, does not solve the ground loop problem between earth grounds
1
,
2
.
Accordingly, there is a need in the art for a connector and/or cable that can effectively eliminate ground loop noise problems while still maintaining one or more signal connections between equipment.
SUMMARY OF THE INVENTION
In accordance with at least one aspect of the present invention, a signal cable includes: a first connector having at least one signal lead and a ground lead, and being operable to couple to a first mating connector of a first piece of electronic equipment; a second connector having at least one signal lead and a ground lead, and being operable to couple to a second mating connector of a second piece of electronic equipment; at least one signal wire and a ground wire electrically connecting the respective at least one signal leads and the respective ground leads of the first and second connectors; and at least one switch disposed with at least one of the first and second connectors, the at least one switch having selectable make/break contacts coupled between the ground lead and the ground wire of the at least one of the first and second connectors such that an electrical path between the ground leads of the first and second connectors may be selectively opened and closed.
Preferably, the first and second mating connectors of the first and second pieces of electronic equipment each include at least one mating signal lead and a mating ground lead for connection to the respective at least one signal lead and ground lead of one of the first and second connectors; the mating ground leads are electrically connected to respective chassis grounds of the first and second pieces of electronic equipment; and the at least one switch is operable to selectively open and close an electrical path between the chassis grounds of the first and second pieces of electronic equipment.
In accordance with at least one further aspect of the present invention, a connector operable to couple to a mating connector of a piece of electronic equipment includes: at least one signal lead and a ground lead operable to electrically connect to at least one signal wire and a ground wire, respectively, of a cable; and at least one switch having selectable make/break contacts, one of the make/break contacts being electrically connected to the ground lead and the other make/break contact being operable to electrically connect to the ground wire of the cable such that an electrical path between the ground lead and the ground wire may be selectively opened and closed.
In accordance with at least one further aspect of the present invention, a system includes: a first piece of electronic equipment having a first mating connector that includes at least one mating signal lead and a mating ground lead, the ground lead being electrically connected to a chassis ground of the first piece of electronic equipment; a second piece of electronic equipment having a second mating connector that includes at least one mating signal lead and a mating ground lead, the ground lead being electrically connected to a chassis ground of the second piece of electronic equipment; and a signal cable including: a first connector having at least one signal lead and a ground lead, and being operable to couple to the first mating connector of the first piece of electronic equipment; a second connector having at least one signal lead and a ground lead, and being operable to couple to the second mating connector of the second piece of electronic equipment; at least one signal wire and a ground wire electrically connecting the respective at least one signal leads and the respective ground leads of the first and second connectors; and at least one switch disposed with at least one of the first and second connectors, the at least one switch having selectable make/break contacts coupled between the ground lead and the ground wire of the at least one of the first and second connectors such that an electrical path between the chassis grounds of the first and second pieces of electronic equipment may be selectively opened and closed.
I
DeBeradinis Robert L
Lerner David Littenberg Krumholz & Mentlik LLP
Peavey Electronics Corporation
Sircus Brian
LandOfFree
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