Amplifiers – With plural amplifier channels – Amplifying different frequencies in different channels
Reexamination Certificate
2000-08-08
2002-02-19
Pascal, Robert (Department: 2817)
Amplifiers
With plural amplifier channels
Amplifying different frequencies in different channels
C330S059000, C333S109000
Reexamination Certificate
active
06348837
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to amplifiers, and more specifically to amplifiers for amplifying bi-directional signals.
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
.
In a two-way system, an amplifier
125
typically incorporates diplex filters and gain blocks when the amplifier both receives and transmits signals, i.e., when the amplifier processes both forward, downstream signals and reverse, upstream signals. Diplex filters are three-port passive devices, each incorporating a high-pass filter and a low-pass filter for filtering the signals. Amplifiers
125
also include gain blocks for amplifying the signals, as illustrated in FIG.
2
. The diplex filter
202
of the amplifier
125
has an input/output terminal
205
for processing bi-directional signals. More specifically, the input/output terminal
205
receives an input signal in the forward, or downstream, direction, and the input/output terminal
205
transmits an output signal in the reverse, or upstream, direction. The diplex filter
202
also includes an output port
210
for providing the forward signal in the downstream direction and an input port
215
for receiving the reverse signal from the upstream direction. The high-pass filter
220
and low-pass filter
225
of the diplex filter
202
provide isolation between the bi-directional signals.
Continuing to refer to
FIG. 2
, the output port
210
of the downstream diplex filter
202
transmits a filtered forward signal to a forward gain block
230
that amplifies the signal. The forward signal is then filtered through another diplex filter
238
, which includes a high-pass filter
240
for transmitting the amplified forward signal to an input/output terminal
245
of the amplifier
125
and of the diplex filter
238
. The input port
215
of the diplex filter
202
receives an amplified signal from a reverse gain block
235
. The reverse signal has been filtered through a low-pass filter
250
of the diplex filter
238
. This reverse signal is transmitted upstream, within the reverse path of the amplifier
125
, from the input/output terminal
245
of the amplifier
125
. Traditionally, amplifiers utilize a distinct gain block, as shown, for the forward path and a separate gain block for reverse path to preserve isolation between forward and reverse signals.
Conventionally, the reverse path signal is routed through the low-pass filters
225
,
250
in the two diplex filters
202
,
238
due to the frequency of the reverse path being in the low-band frequency spectrum that is typically 5 MHz to 40 MHz. The forward path is routed through the high-pass filters
220
,
240
in the two diplex filters
202
,
238
due to the frequency of the forward path being in the forward frequency spectrum that is typically 52 MHz to 870 MHz.
It will be appreciated, however, that there are variations of the frequency bandwidth values in the low-band and forward-band depending upon the preferences of the cable television system. The conventional amplifier
125
does have the ability to process different forward and reverse splits by utilizing a plug-in diplex filter. The signals are then routed through the respective gain block for amplification of the forward or reverse signal. More specifically, an operator may, for example, choose to use the reverse bandwidth of 5 MHz to 65 MHz and the forward bandwidth of 88 MHz to 750 MHz. Generally, however, the bandwidth splits are rarely changed once decided due to the potential impact on the channel programming in the lower end of the forward bandwidth. For example, if a television program channel is established at a low-end frequency in the forward bandwidth and the reverse bandwidth is increased, thereby changing the bandwidth split, the program channel quality at the low-end will be negatively impacted or eliminated.
There is, however, an increased demand for reverse services, which requires a corresponding increase in reverse bandwidth. As a result of the increased requirements and in light of the difficulties of increasing the conventional reverse bandwidth, cable television systems may, in the future, begin utilizing a higher-band frequency spectrum for the reverse path, in addition to the low-band frequency spectrum. This higher frequency spectrum may, for instance, be in the 900 MHz to 1200 MHz range. If this is done, reverse bandwidth may be increased without impacting the lower frequency channels in the forward bandwidth.
It will be appreciated, however, that installing new amplifiers with an additional gain block to accommodate this higher-band frequency for the reverse path could substantially increase the cost, the complexity, and the size of the amplifiers. Thus, what is needed is an improved amplifier that can better process forward and reverse signals in any bandwidth split in the downstream and upstream paths.
REFERENCES:
patent: 4812779 (1989-03-01), Wagner
patent: 5774458 (1998-06-01), Williamson
patent: 5870395 (1999-02-01), Baran
patent: 5881362 (1999-03-01), Eldering et al.
patent: 6023612 (2000-02-01), Harris et al.
patent: 6091301 (2000-07-01), Vogt
patent: 6215358 (2001-04-01), Hon et al.
Barnhardt III Hubert J.
Couturier Shelley L.
Massaroni Kenneth M.
Nguyen Khanh Van
Pascal Robert
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