Television – Image signal processing circuitry specific to television – Switching
Reexamination Certificate
2000-02-03
2002-11-26
Miller, John (Department: 2614)
Television
Image signal processing circuitry specific to television
Switching
C348S706000, C348S555000, C348S565000, C340S002800, C370S357000
Reexamination Certificate
active
06486924
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to improving the reception of a broadcast, cable or game port television signal, and more particularly relates to isolating alternate paths of the television signal.
2. Description of the Prior Art
As towns and cities become more populated, the number of obstructions to broadcast signals, such as those used for television and radio, also increases. These obstructions introduce substantial signal reflections, which result in intolerable reductions in the signal-to-noise ratio (SNR) of the broadcast signal after it is received. Additional factors that decrease the SNR include the increased use of cellular and mobile communications, broadcast signals that are received over greater distances, and the increased utilization of available bandwidth.
Amplification of the broadcast signal can largely overcome problems associated with reductions in the SNR. However, amplification is neither always necessary nor desirable, such as when a receiver is in close proximity to a transmission station. In this case, providing an alternate path for the broadcast signal, which exhibits essentially unity gain, optimizes reception.
FIG. 1
is a block diagram of a typical indoor television antenna having a switchable amplifier circuit, more generally referred to as a television signal switching circuit
10
. The switching circuit
10
includes an amplification/unity gain signal path
12
and a game port signal path
14
. The amplification/unity gain signal path
12
is coupled in series between an antenna
16
and a television receiver
18
.
The amplification/unity gain signal path
12
includes the series connection of an amplifier circuit
20
, a direct current (DC) blocking capacitor
21
, and a diode isolation circuit
23
. The antenna
16
is coupled to an input of the amplifier circuit
20
, and an output of the amplifier circuit
20
is coupled to a first end of the capacitor
21
. A second end of the capacitor
21
is coupled to an input of the diode isolation circuit
23
, and the output of the diode isolation circuit
23
is coupled to the television receiver
18
. The amplifier circuit
20
is also coupled to an amplification control circuit
22
, which can selectively, under the control of a user, supply power to the amplifier circuit
20
and adjust the amount of gain provided by the amplifier circuit
20
.
The diode isolation circuit
23
includes two diodes coupled in series. The anode of a first diode is coupled to the input of the diode isolation circuit
23
, and selectively coupled to a DC bias. The cathode of the first diode is coupled to the anode of a second diode, and the cathode of the second diode is coupled to the output of the diode isolation circuit
23
.
The game port signal path
14
is coupled in series between a game port input
17
and the television receiver
18
. The game port signal path
14
includes the series connection of a DC blocking capacitor
25
and a diode isolation circuit
27
. The game port input
17
is coupled to a first end of the capacitor
25
, and a second end of the capacitor
25
is coupled to an input of the diode isolation circuit
27
.
The diode isolation circuit
27
is substantially the same as the diode isolation circuit
23
already described. The output of both diode isolation circuits
23
,
27
are coupled to each other, a first end of a direct current (DC) leakage resistor
29
, and the television receiver
18
. A second end of the resistor
29
is coupled to ground and provides a path for residual charge introduced by the DC bias to escape.
If the DC bias is applied to the diode isolation circuit
27
in the game port signal path
14
, the diodes in the isolation circuit
27
become forward biased and a game port signal in the game port signal path
14
is allowed to pass to the television receiver
18
. By applying the DC bias to the isolation circuit
27
in the game port signal path
14
, the DC bias is not applied to the isolation circuit
23
in the amplification/unity gain signal path
12
. This causes the diodes in the path
12
to remain off or in a non-conductive state, which isolates the output of the amplifier circuit
20
from the television receiver
18
.
Likewise, if the DC bias is applied to the diode isolation circuit
23
in the amplification/unity gain signal path
12
, the diodes in the isolation circuit
23
become forward biased and a television signal in the amplification/unity gain signal path is allowed to pass to the television receiver
18
. By applying the DC bias to the isolation circuit
23
in the amplification/unity gain signal path
14
, the DC bias is not applied to the isolation circuit
27
in the game port signal path
14
. This causes the diodes in the path
14
to remain off or in a non-conductive state, which isolates the game port input
17
from the television receiver
18
.
If the user chooses to provide power to the amplifier circuit
20
via the amplification control circuit
22
, the television signal seen by the television receiver
18
exhibits that amount of gain chosen by the user. In contrast, if the user chooses not to provide power to the amplifier circuit
20
, the amplifier circuit
20
essentially becomes a short circuit and the television receiver
18
sees the television signal with essentially unity gain.
However, one disadvantage with the conventional approach shown in
FIG. 1
is that the diode isolation circuits
23
,
27
do not completely isolate the amplification/unity gain signal path
12
and game port signal path
14
. For instance, portions of the amplification/unity gain signal path
12
remain in the circuit even if the game port signal path
14
is chosen. These portions act as stubs terminated by an impedance that creates reflections, and thus noise, in the television signal. In addition, the diodes in the isolation circuit
23
introduce leakage of either the television signal or the game port signal into the chosen path due to their poor isolation.
Thus, the approach shown in
FIG. 1
does not result in two independent and isolated paths. Rather, this approach results in two essentially composite paths, each of which includes signal reflections and leakage introduced by the path not selected.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide an apparatus for improving the reception of a television signal by a television receiver.
It is a further object of the present invention to provide an apparatus for reducing signal reflection, crosstalk, and noise in and between alternate paths of a broadcast, cable or game port television signal having different gains associated therewith.
It is yet a further object of the present invention to provide an apparatus for amplifying off air broadcast television signals over a broad range of gains, which increases the associated signal-to-noise ratio (SNR) without disrupting cable or game port signals.
It is still another object of the present invention to provide an apparatus for selectively applying unit gain or a variable gain to off air broadcast television signals, which increases the SNR of the television signal without disrupting cable or game port signals.
It is a further object of the present invention to provide an apparatus for maximizing isolation between alternate paths of a broadcast, cable or game port television signal having different gains associated therewith.
In accordance with one form of the present invention, a television signal switching circuit is provided, which includes an amplification signal path and a unity gain signal path. A first switching circuit and a second switching circuit, which preferably include relays, substantially isolate the amplification signal path from the unity gain signal path. One or more antennas receive the television signal and output it to an input of the first switching circuit. The amplification and unity gain signal paths are coupled in parallel between the first and second switching circuits. An output of the second switching circuit is coupled
Krikorian Nina
Paraskevopoulos Nicholas G.
Bodner Gerald T.
Miller John
Natnael Paulos
Terk Technologies Corp.
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