Amplifiers – With semiconductor amplifying device – Including protection means
Reexamination Certificate
2000-11-10
2003-07-01
Pascal, Robert (Department: 2817)
Amplifiers
With semiconductor amplifying device
Including protection means
C330S20700P
Reexamination Certificate
active
06587002
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to cable television systems, and more specifically to amplifiers that are used in such systems.
BACKGROUND OF THE INVENTION
A communication system
100
, such as a two-way cable television system, is depicted in FIG.
1
. The communication system
100
includes headend equipment
105
for generating forward signals that are transmitted in the forward, or downstream, direction along a communication medium, such as a fiber optic cable
110
, to an optical node
115
that converts optical signals to radio frequency (RF) signals. The RF signals are further transmitted along another communication medium, such as coaxial cable
120
, and are amplified, as necessary, by one or more distribution amplifiers
125
positioned along the communication medium. Taps
130
included in the cable television system split off portions of the forward signals for provision to subscriber equipment
135
, such as set top terminals, computers, and televisions. In a two-way system, the subscriber equipment
135
can also generate reverse signals that are transmitted upstream, amplified by any distribution amplifiers
125
, converted to optical signals, and provided to the headend equipment
105
.
Within the communication system
100
, the electrical devices, and specifically the RF portion of the communication system
100
, can be designed and installed using an overhead cable system, an underground cable system, or a combination of both. The overhead cable system mounts the electrical devices used in the communication system
100
on coaxial cable
120
hung on poles. The underground cable system mounts the electrical devices in pedestals located on top of or under the ground, and the coaxial cable between the devices is located underground. Typically, the underground cable system is able to maintain a constant temperature within the pedestals; however, at times the electrical devices may overheat due to one or all of the following conditions: poor air circulation in the pedestal; the summer heat; or being in direct sunlight.
Generally, the electrical devices in a communication system
100
, such as a cable television system, do not have internal circuitry to protect the devices from excess heat. Electrically, each amplifier
125
utilizes a thermal circuit to ensure the amplifier
125
maintains a unity gain throughout the cascade of the communication system
100
regardless of the surrounding temperature; however, this does not protect the components in an amplifier
125
from overheating. For example, as a result of the excess heat, the sensitive integrated circuits (IC) that are within the amplifier
125
may fail. With a failure of this type, the amplifier
125
will no longer function, resulting in service outages to subscribers in the area. Consequently, the cable television operator wastes time and money locating and fixing the problem, as well as suffers from any lost revenue from the affected subscribers. Thus, what is needed is a protective circuit that protects the components of the electrical devices from overheating, which may cause a catastrophic amplifier failure that results in service outages.
REFERENCES:
patent: 4727337 (1988-02-01), Jason
patent: 4878034 (1989-10-01), Gross et al.
patent: 5723998 (1998-03-01), Saito et al.
patent: 5994945 (1999-11-01), Wu et al.
Pentium® III Processor for the PGA370 Socket at 500 MHz to 1.0B GHz Data Sheet, Intel®.
Barnhardt III Hubert J.
Choe Henry
Couturier Shelley L.
Massaroni Kenneth M.
Pascal Robert
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