Telecommunications – Wireless distribution system – Receiver for satellite broadcast
Reexamination Certificate
2000-10-17
2004-04-27
Tran, Pablo N. (Department: 2685)
Telecommunications
Wireless distribution system
Receiver for satellite broadcast
C455S255000, C455S133000
Reexamination Certificate
active
06728513
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to receiving apparatuses and particularly to a receiving apparatus shared by a plurality of tuners.
2. Description of the Background Art
FIG. 5
is a block diagram showing a structure of a receiving unit of a conventional satellite broadcasting system. Referring to
FIG. 5
, the receiving unit of the satellite broadcasting system includes an antenna
30
having a reflector
31
and an LNB (Low Noise Block down converter)
32
, a receiver
33
having a DBS (Direct Broadcasting by Satellite) tuner
34
, an FM demodulator
35
, a video+audio circuit
36
and an amplifier
37
, and a television receiver
38
.
Radio waves &agr; emitted from a satellite are supplied via reflector
31
to LNB
32
. LNB
32
extracts from the received radio waves a image signals of a plurality of channels, amplifies the signals with noise kept low, and supplies an image signal of a channel selected by DBS tuner
34
to DBS tuner
34
. An output signal of LNB
32
is supplied via DBS tuner
34
to FM demodulator
35
which FM-demodulates the output signal.
The FM-demodulated image signal is converted to a video signal and an audio signal by video+audio circuit
36
, amplified by amplifier
37
and then supplied to television receiver
38
. An image of the channel selected by DBS tuner
34
is displayed on the screen of television receiver
38
.
FIG. 6
is a perspective view showing from the outside a structure of LNB
32
. Referring to
FIG. 6
, LNB
32
has a casing member
41
, and a feed phone
42
and a signal input/output terminal
43
are provided on the surface of casing member
41
. Radio waves &agr; reflected from reflector
31
of antenna
30
are supplied into an opening
42
a
of feed phone
42
. In casing
41
, a signal processing circuit is provided for processing the radio waves &agr; supplied to feed phone
42
. Signal input/output terminal
43
is connected to DBS tuner
34
via a cable.
FIG. 7
is a circuit block diagram showing a structure of the signal processing circuit of LNB
32
. Referring to
FIG. 7
, the signal processing circuit includes LNAs (Low Noise Amplifiers)
44
a
and
44
b
, bandpass filters (BPFs)
45
a
-
45
d
, local oscillators
46
a
and
46
b
, mixers
47
a
-
47
d
, a selector
48
, an IF amplifier
49
, a low-pass filter (LPF)
50
and a regulator
51
.
A horizontally polarized wave signal &phgr;h and a vertically polarized wave signal &phgr;v received by feed phone
42
are respectively amplified by LNAs
44
a
and
44
b
with noise kept low. An output signal of LNA
44
a
is supplied to bandpass filters
45
a
and
45
c
and an output signal of LNA
44
b
is supplied to bandpass filters
45
b
and
45
d.
Signals &phgr;h and &phgr;v have a frequency band of 10.7-12.75 GHz. Bandpass filters
45
a
and
45
b
pass only the frequency components in the range of 10.7 to 11.7 GHz of respective signals &phgr;h and &phgr;v. Bandpass filters
45
c
and
45
d
pass only the frequency components in the range of 11.7 to 12.75 GHz of respective signals &phgr;h and &phgr;v. Respective signals &phgr;h
1
, &phgr;v
1
, &phgr;h
2
and &phgr;v
2
passed through bandpass filters
45
a
-
45
d
are supplied respectively to mixers
47
a
-
47
d.
Local oscillator
46
a
generates a high-frequency signal of 9.75 GHz and supplies it to mixers
47
a
and
47
b
. Local oscillator
46
b
generates a high-frequency signal of 10.6 GHz and supplies it to mixers
47
c
and
47
d
. Signals &phgr;h
1
and &phgr;v
1
are converted respectively by mixers
47
a
and
47
b
into respective IF signals &phgr;
1
and &phgr;
2
of 950-1950 MHz. Signals &phgr;h
2
and &phgr;v
2
are converted respectively by mixers
47
c
and
47
d
into respective IF signals &phgr;
3
and &phgr;
4
of 1000-2150 MHz.
Selector
48
selects any of four IF signals &phgr;
1
-&phgr;
4
according to a DC voltage V
1
and a clock signal CLK supplied from DBS tuner
34
via input/output terminal
43
and low-pass filter
50
and supplies the selected IF signal to DBS tuner
34
via IF amplifier
49
and input/output terminal
43
. The DC voltage V
1
is 18 V or 13 V. The clock signal CLK has a frequency of 22 KHz and an amplitude of 0.6 V. Low-pass filter
50
allows DC voltage V
1
and clock signal CLK to pass while it does not pass IF signals &phgr;
1
-&phgr;
4
.
If DC voltage V is 18 V, signals &phgr;
1
and &phgr;
3
are selected. If DC voltage V
1
is 13 V, signals &phgr;
2
and &phgr;
4
are selected. If no clock signal CLK is input, signals &phgr;
1
and &phgr;
2
are selected and signals &phgr;
3
and &phgr;
4
are selected if clock signal CLK is input. Accordingly, signal &phgr;
1
is selected if DC voltage V
1
is 18 V and no clock signal CLK is input, signal &phgr;
2
is selected if DC voltage V
1
is 13 V and no clock signal CLK is input, signal &phgr;
3
is selected if DC voltage V
1
is 18 V and clock signal CLK is input, and signal &phgr;
4
is selected if DC voltage V
1
is 13 V and clock signal CLK is input.
DC voltage V
1
is also used as the supply voltage of regulator
51
. Regulator
51
uses DC voltage V
1
as the supply voltage to generate a DC constant voltage V
2
of 9 V and a DC constant voltage V
3
of 5 V. DC constant voltage V
2
of 9 V generated by regulator
51
is applied to IF amplifier
49
as its supply voltage, and DC constant voltage V
3
of 5 V generated by regulator
51
is applied to LNAs
44
a
and
44
b
and local oscillators
46
a
and
46
b
as their supply voltage.
In recent years, there arises a need to share one LNB by a plurality of DBS tuners
34
. For example, referring to
FIG. 8
, an LNB
55
shared by two DBS tuners
34
is provided with one feed phone
57
and two signal input/output terminals
58
a
and
58
b
on a casing member
56
.
Regarding such an LNB
55
, there is a problem that how supply voltages V
2
and V
3
for the LNA, local oscillator and IF amplifier should be generated. For example, according to the following description in conjunction with
FIG. 9
, two signal input/output terminals
58
a
and
58
b
are connected to a power supply node
61
a
of a regulator
61
via respective low-pass filters
59
a
and
59
b
and respective diodes
60
a
and
60
b
. Diodes
60
a
and
60
b
are provided for preventing, when one of the two signal input/output terminals
58
a
and
58
b
is supplied with 18 V and the other thereof is supplied with 13 V, current flow from one signal input/output terminal to the other signal input/output terminal to cause malfunction or breakdown of DBS tuners
34
.
In this case, supposing that consumption current of LNB
55
is 200 mA, if DC voltages applied respectively to two signal input/output terminals
58
a
and
58
b
are the same (18 V or 13 V), currents of the same value (100 mA) flow through respective two signal input/output terminals
58
a
and
58
b
. However, if 18 V and 13 V are supplied respectively to signal input/output terminals
58
a
and
58
b
, current of 200 mA flows through signal input/output terminal
58
a
and no current flows through signal input/output terminal
58
b
. On the contrary, if signal input/output terminals
58
a
and
58
b
are supplied with 13 V and 18 V respectively, current of 200 mA flows through signal input/output terminal
58
b
and no current flows through signal input/output terminal
58
a
. For this reason, each time a channel is switched, current flowing from two DBS tuners
34
to LNB
55
greatly varies, generating noise. This noise causes a selector to malfunction, resulting in selection of a channel different from a desired channel or disorder of an image on a television receiver
38
.
SUMMARY OF THE INVENTION
One object of the present invention is accordingly to provide a receiving apparatus which can be shared by a plurality of tuners while noise is reduced.
According to the present invention, a receiving apparatus includes a plurality of signal input/output terminals connected respectively to a plurality of tuners, an extraction/amplification circuit extracting/amplifying a plurality of i
Nixon & Vanderhye P.C.
Sharp Kabushiki Kaisha
Tran Pablo N.
LandOfFree
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