Protection of double end exposed systems

Details Protection of double end exposed systems Protection of double end exposed systems

2002-03-22

2004-03-02

Toatley, Jr., Gregory J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

High voltage dissipation

C361S091100

Reexamination Certificate

active

06700770

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the field of telecommunication networks. The present invention is also directed to systems and methods for protecting devices such as micro electro-mechanical system (MEMS) and electronic relay devices in telecommunication systems. More particularly, the present invention is directed to systems and methods for protecting cross connect units that are implemented with MEMS or solid state relay devices in double end exposed systems.
BACKGROUND OF THE INVENTION
Micro electro-mechanical system (MEMS) and solid-state relay (SSR) devices are used as alternatives for conventional electromechanical switching devices. As is well known, the conventional devices possess some highly desirable characteristics such as low contact resistance, high voltage breakdown, and relatively high current handling capability, which characteristics make them ideal for use in telecommunication systems. However, such conventional devices are not well suited for miniaturization or integration.
MEMS and SSR devices can perform the standard functions of conventional relays and are well suited for miniaturization and integration. MEMS devices are basically miniaturized electro-mechanical devices that are fabricated using techniques similar to those used for semiconductor integrated circuits and are well suited for low cost and high volume production. MEMS device applications have been used as pressure sensors, chemical sensors, light reflectors, switches, and relays. MEMS devices are low cost devices due to the use of microelectronic fabrication techniques, and new functionality may also be provided because they are much smaller than conventional devices.
However, MEMS and SSR devices have several major shortcomings and disadvantages. The most notable disadvantage is that these devices are relatively fragile in current carrying and voltage breakdown capabilities. For example, because MEMS and SSR devices are relatively fragile, lightning or AC power surges can completely destroy them. Lightning is characterized by very high voltage and current of very short duration pulses, i.e., less than 1.0 ms, whereas AC power surges or faults are characterized by very high voltage and current of relatively long duration pulses, i.e., seconds. As a result, systems having MEMS or SSR devices therein can become disabled and/or destroyed quite easily.
There are currently different systems and methods for protecting MEMS and SSR devices from lightning and/or AC power surges. But, none of these conventional systems and methods is directed towards protecting MEMS and SSR devices that are implemented within units such as cross connect systems, e.g., the “CX 100 CrossConnect System” from Turnstone Systems, Inc. The CX100 Copper CrossConnect System is a platform that automates the physical layer infrastructure in the central office, enabling ILECs (incumbent local exchange carrier) and CLECs (competitive local exchange carrier) to remotely control, test, and manage a copper loop. Additional information regarding Turnstone System's CX100 Copper CrossConnect System can be found at its web site turnstone.com. It is also noted that other systems and units providing similar functionalities as the CX100 Copper CrossConnect System can be implemented in the present invention.
In cross connect applications, the system can be configured in either a “single end exposed system” or a “double end exposed system.” For a more comprehensive understanding of the above-identified systems and the present invention, the following terms have been defined as follows:
(1) a “pass-through system” is a system that provides connection between an input port and an output port through a pair of metallic conductors characterized by relatively low ohmic resistance;
(2) an “ingress port” is a signal entering an equipment; and
(3) an “egress port” is a signal exiting an equipment.
FIG. 1
illustrates a simplified block diagram of a conventional single end exposed system. The single end exposed system is a system where one port, such as the ingress port
2
, is connected to an “outside plant” equipment, and the other port, such as the egress port
4
, is connected to an “in-building” equipment or termination unit, such as a Central Office (CO) equipment. In this diagram, the ingress port
2
is identified by terminals T
1
and R
1
, while the egress port
4
is identified by terminals T
2
and R
2
.
In greater detail, the ingress port
2
provides connection to the “outside plant”, an over voltage protector (“OVP”)
6
, and an Equipment Under Protection (“EUP”)
8
. The egress port
4
provides connection to the EUP
8
and the termination within the “in-building” equipment. The EUP
8
represents a metallic cross connect unit or the like and is implemented with MEMS or SSR devices. As discussed above, over voltage and/or over current can easily damage the MEMS or SSR devices within the EUP
8
. Typically, the OVP
6
protects the MEMS or SSR devices from over voltage conditions. An over current protector (“OCP”) (not shown) can also be used to protect the MEMS or SSR devices from over current conditions. The OCP function is usually performed by the termination unit with a current limiter, such as a resistor of appropriate value.
The OVP
6
is implemented only in between the ingress port
2
and the EUP
8
. Since the connection between the egress port
4
and the EUP
8
is generally not exposed to voltage surges, another OVP is not required in between the egress port
4
and the EUP
8
. A co-pending U.S. patent application Ser. No. 09/677,483, commonly owned by the assignee of record, discloses improved methods and systems for protecting MEMS and SSR devices in the single end exposed system.
FIG. 2
illustrates a simplified block diagram of a conventional double end exposed system. The double end exposed system is a system where both ports, ingress
2
and egress
4
, are connected to the “outside plant” equipment. The double end exposed system includes over voltage protectors, OVP-I
12
and OVP-E
14
, near the ingress and egress ports, respectively, which ports can be exposed to lightning and AC power surges. In other words, lightning and AC power surges can enter from either side of the EUP
8
and thus, both sides of the EUP
8
need to be protected.
FIG. 3
illustrates a more detailed diagram of the conventional double end exposed system of FIG.
2
. In
FIG. 3
, the term “OP” replaces the term “OVP” of
FIG. 2
for ease of explanation. As illustrated, the ingress port represented by terminals T
1
and R
1
can be connected to the V
s
and Rs, where V
s
represents a surge source generator and Rs represents the corresponding source resistance. Likewise, the egress port represented by terminals T
2
and R
2
can be connected to a termination equipment
20
. The over voltage protectors are represented by OP
1
and OP
2
in proximity to the ingress port, and by OP
3
and OP
4
in proximity to the egress port. In addition, the resistors RC
1
and RC
2
represent the finite contact resistance associated with the MEMS device
22
. The EUP
8
is represented by the MEMS device
22
for ease of explanation.
The over voltage protectors or OPs are characterized by many parameters, but the key parameters for the purposes of understanding the present invention is the break-over or switching voltage represented by V
bo
and the device on-state voltage represented by V
on
. Other key parameters include the current handling capability, switching speed, and the standoff voltage V
drm
. The standoff voltage V
drm
is defined as the maximum voltage across the device without having to turn the device “on,” and the break-over voltage V
bo
is defined as the minimum voltage across the device to turn it on (i.e., device changing from “off” to “on” state). The selection of this voltage is dictated by the maximum voltage that the MEMS device
22
can withstand without failure. The on-state voltage V
on
is the voltage drop across the device when it is turned on and is generally in the range of 1.0 to 3.0 volts, dependi

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