Interactive video distribution systems – Video distribution system components – Transmission network
Reexamination Certificate
2000-02-18
2003-06-17
Miller, John (Department: 2614)
Interactive video distribution systems
Video distribution system components
Transmission network
C725S078000, C725S128000
Reexamination Certificate
active
06581208
ABSTRACT:
BACKGROUND OF THE INVENTION
(i) Field of the Invention
The present invention relates to an up-converter used for frequency-converting an upward signal outputted from a terminal unit to an in-building upward signal in an in-building CATV system in which an external bi-directional CATV system transmission path and an in-building terminal are interconnected to transmit upward and downward signals in both directions. The present invention further relates to a down-converter for converting the frequency of the in-building upward signal transmitted from the side of the terminal unit via the up-converter to a transmission frequency in the bi-directional CATV system to transmit the signal onto the transmission path of the bi-directional CATV system.
(ii) Description of the Related Art
In a conventionally known in-building CATV system connected to a lead-in wire from an external bi-directional CATV system, a downward signal transmitted from a central apparatus of the bi-directional CATV system via the lead-in wire is transmitted to a terminal in the building via a transmission line in the building. Additionally, an upward signal inputted from the terminal unit is transmitted to the lead-in wire, and outputted toward the central apparatus of the bi-directional CATV system via the lead-in wire.
Moreover, in the in-building CATV system, noises generated in the building are superposed to the in-building transmission line via the terminal on the subscriber side, flow together, and are outputted to the external bi-directional CATV system together with the upward signal.
To reduce the confluent noises flowing out to the external bi-directional CATV system, in a heretofore proposed method, an up-converter is used to once frequency-convert the upward signal generated in the terminal unit such as a cable modem on the subscriber side, that is, the signal with a frequency band, for example, of 5 to 42 MHz which can be transmitted by the bi-directional CATV system to an upward signal (hereinafter referred to as the in-building upward signal) with a UHF band (e.g., 913 to 950 MHz) which is higher than the original frequency and which does not overlap and is much higher than the transmission frequency (e.g., 54 to 860 MHz) of the downward signal. The in-building upward signal is transmitted to the lead-in wire, and the down-converter is used to convert the frequency of the in-building upward signal to the original frequency, that is, the transmission frequency of the upward signal in the bi-directional CATV system, immediately before the upward signal is outputted to the lead-in wire via the in-building transmission line.
The up-converter for use in the conventional in-building CATV system is usually constituted as shown in FIG.
5
A.
Specifically, first, the up-converter needs not only to frequency-convert the upward signal outputted from the terminal unit to the in-building upward signal, but also to output the downward signal transmitted via the transmission line of the in-building CATV system toward the terminal unit. For this purpose, in the conventional up-converter, in order to form two upward and downward paths in the up-converter, the up-converter is provided with distribution circuits SP
1
and SP
2
, and a first terminal Tin connected to the terminal unit on the subscriber side and a second terminal Tout connected to the in-building CATV system are connected to the distribution circuits SP
1
and SP
2
, respectively.
Moreover, the upward signal inputted to the first terminal Tin from the terminal unit is inputted to a frequency converter
94
via a low-pass filter (hereinafter referred to as LPF)
92
which is connected to one distribution terminal of the distribution circuit SP
1
. Furthermore, the in-building upward signal outputted from the frequency converter
94
is inputted to one distribution terminal of the distribution circuit SP
2
connected to the second terminal Tout via a high-pass filter (hereinafter referred to as HPF)
96
, and then outputted to the transmission line of the in-building CATV system from the second terminal Tout via the distribution circuit SP
2
.
Furthermore, the downward signal transmitted to the second terminal Tout is transmitted from the other distribution terminal of the distribution circuit SP
2
, via a downward signal transmitting path provided with an LPF
98
, to the other distribution terminal of the distribution circuit SP
1
. Then, the downward signal is outputted to the terminal unit on the subscriber side from the first terminal Tin via the distribution circuit SP
1
.
Additionally, the LPF
92
disposed in the previous stage of the frequency converter
94
selectively passes the upward signal from the side of the terminal unit, the HPF
96
disposed in the subsequent stage of the frequency converter
94
selectively passes the in-building upward signal outputted from the frequency converter
94
, and the LPF
98
disposed on the downward signal path selectively passes the downward signal.
However, in the conventional up-converter constituted as described above, since the upward signal path provided with the frequency converter
94
and the downward signal path are separated using the distribution circuits SP
1
, SP
2
, there is a problem that signal losses are increased when the signals pass through the distribution circuits SP
1
, SP
2
.
Moreover, the upward signal inputted to the first terminal Tin from the terminal unit is not only transmitted to the frequency converter
94
through the LPF
92
, but also outputted onto the transmission line of the in-building CATV system from the second terminal Tout through the LPF
98
which allows to pass low frequency signals. This adversely affects the operation of a bi-directional amplifier disposed on the transmission line of the in-building CATV system as shown in FIG.
5
B.
Specifically, the downward signal and the in-building upward signal are to be transmitted by the in-building CATV system provided with the down-converter. Even when the upward signal different in frequency from these signals is transmitted to the transmission line of the in-building CATV system from the up-converter, no problem basically arises. However, when the bi-directional amplifier is disposed on the transmission line of the in-building CATV system, as shown in
FIG. 5B
, the in-building upward signal and the downward signal are amplified by amplification circuits AMP
1
, AMP
2
provided with HPF, LPF for signal selection both in previous and subsequent stages, respectively. In this constitution, the upward signal outputted from the up-converter is inputted to the output side of the amplification circuit AMP
2
for amplifying the downward signal. When the upward signal is inputted in this manner, the upward signal turns to the input side of the amplification circuit AMP
2
via the feedback circuit of the amplification circuit AMP
2
, and the amplification circuit AMP
2
oscillates.
Furthermore, the down-converter for use in the conventional in-building CATV system is usually constituted as shown in FIG.
6
A.
Specifically, first, the down-converter needs not only to frequency-convert the in-building upward signal transmitted from the terminal side via the in-building transmission line to the upward signal with a lower frequency, but also to transmit the downward signal inputted from the bi-directional CATV system via the lead-in wire onto the in-building transmission line. For this purpose, in the conventional down-converter, in order to form two upward and downward paths in the down-converter, the down-converter is provided with distribution circuits SP
3
and SP
4
, and an external connection terminal T
4
connected to the lead-in wire from the bi-directional CATV system and an internal connection terminal T
3
connected to the in-building transmission line are connected to the distribution circuits SP
4
and SP
3
, respectively.
Moreover, the in-building upward signal inputted to the internal connection terminal T
3
is outputted to a frequency converter
194
via an HPF
192
which is connected to one distributi
Beliveau Scott
Davis & Bujold P.L.L.C.
Masprodenkoh Kabushikikaisha
Miller John
LandOfFree
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