Telecommunications – Wireless distribution system – Receiver for satellite broadcast
Reexamination Certificate
1999-01-08
2001-08-07
Urban, Edward F. (Department: 2683)
Telecommunications
Wireless distribution system
Receiver for satellite broadcast
C455S319000, C455S310000, C725S070000
Reexamination Certificate
active
06272312
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a satellite broadcasting receiving tuner for receiving a digital system satellite broadcasting.
2. Description of the Related Art
A conventional satellite broadcasting receiving tuner will be described with reference to FIG.
2
. Initially, a digital system satellite broadcasting signal (hereinafter simply referred to as a satellite broadcasting signal) is transmitted from a satellite in the frequency band ranging 11 to 12 GHz, frequency-converted by an outdoor down-converter, not shown, into a band ranging from about 950 MHz to 2150 MHz, and then inputted to an input terminal
21
of a satellite broadcasting receiving tuner.
The satellite broadcasting signal inputted to the input terminal
21
is sequentially passed through a bandpass filter
22
, a low-noise amplifier
23
, a variable attenuator
24
and an amplifier
25
and inputted to a first demodulator
26
and a second demodulator
27
. The bandpass filter
22
comprises a so-called variable bandpass filter and has a frequency band (about 27 and several MHz to 36 MHz) of a satellite broadcasting signal of one channel wherein a center frequency thereof is changed in response to a frequency of a satellite broadcasting signal of a desired reception channel. The variable attenuator
24
is comprised of a pin-diode, not shown, and a current flowing through this pin-diode is changed in response to the level of the received satellite broadcasting signal, thereby resulting in an attenuation amount being controlled.
The first demodulator
26
and the second demodulator
27
constitute a QPSK demodulator. A local oscillation signal (first local oscillation signal Lol) from a local oscillator
28
is directly inputted to the first demodulator
26
. A local oscillation signal (second local oscillation signal Lo
2
) which results from delaying the local oscillation signal from the local oscillator
28
by &pgr;/2 (90 degrees) with a phase-shifter
29
is inputted to the second demodulator
27
. Here, the frequency (local oscillation frequency) of the local oscillation signal is oscillated at the same frequency (specifically, almost center frequency of the band of the satellite broadcasting signal of that channel) as the frequency of the satellite broadcasting signal of the desired reception channel.
Then, the first demodulator
26
generates an I signal serving as a first baseband signal by mixing the inputted satellite broadcasting signal and the first local oscillation signal Lo
1
. The second demodulator
27
generates a Q signal serving as a second baseband signal by mixing the inputted satellite broadcasting signal and the second local oscillation signal Lo
2
. Accordingly, this satellite broadcasting receiving tuner directly obtains the baseband signal from the received satellite broadcasting signal, and hence comprises so-called direct conversion tuner.
The I signal outputted from the first demodulator
26
is amplified by a first baseband signal amplifier
30
, eliminated in higher harmonic component by a first low-pass filter
31
, and then introduced from an output terminal
32
to a circuit of the succeeding stage within a satellite broadcasting receiver, not shown.
Similarly, the Q signal outputted from the second demodulator
27
is amplified by a second baseband signal amplifier
33
, eliminated in higher harmonic component by a second low-pass filter
34
, and then introduced from an output terminal
35
to a circuit of the succeeding stage within a satellite broadcasting receiver, not shown.
However, in the conventional satellite broadcasting receiving tuner, a plurality of inputted satellite broadcasting signals are arranged in the band of 950 MHz to 2150 MHz. In addition, a difference between the frequency of the satellite broadcasting signal of the channel in which the frequency is lowest and the frequency of the satellite broadcasting signal of the channel in which the frequency is highest is more than 1 octave. Further, since the frequency of the inputted satellite broadcasting signal is as high as in the GHz band, it is difficult to make a transmission characteristic (so-called skirt characteristic) of the bandpass filter
22
steep. Therefore, when the satellite broadcasting signal (e.g. frequency is 1000 MHz) of the channel in which the frequency is lowest is received, the satellite broadcasting signal (e.g. frequency is 2000 Hz) of the channel in which the frequency is doubled is inputted to the first demodulator
26
and the second demodulator
27
under the condition that it holds a certain level.
On the other hand, although the local oscillator
28
is oscillated at the same frequency (e.g. 1000 MHz) as the frequency of the received satellite broadcasting signal, this local oscillation signal contains a twice higher harmonic wave (2000 MHz) in addition to a fundamental wave (1000 MHz). Therefore, although the first demodulator
26
and the second demodulator
27
output baseband signals based on the received satellite broadcasting signal (1000 MHz), in addition, the satellite broadcasting signal (2000 MHz) whose frequency is higher by 1 octave and the twice higher harmonic wave (2000 MHz) from the local oscillator
28
are mixed so that the baseband signal based on the satellite broadcasting signal in which the frequency is higher by 1 octave is also outputted. As a result, the satellite broadcasting receiver has the problem that a disturbance is caused by the baseband signal based on the satellite broadcasting signal in which the frequency is higher by 1 octave.
SUMMARY OF THE INVENTION
In view of the aforesaid aspect, it is an object of the present invention to provide a satellite broadcasting receiving tuner in which a disturbance by a satellite broadcasting signal of a channel in which a frequency is higher by 1 octave may be prevented from being caused in a satellite broadcasting signal of a desired reception channel.
According to an aspect of the present invention, there is provided a satellite broadcasting receiving tuner which is comprised of first and second demodulators to which satellite broadcasting signals of a plurality of channels arranged within a frequency band higher than 1 octave are inputted, a local oscillator which oscillates at the same frequency of the frequency of a desired reception satellite broadcasting signal of the satellite broadcasting signals and a higher harmonic wave attenuating device for passing a fundamental wave of a local oscillation signal from the local oscillator and attenuating a higher harmonic wave, wherein the local oscillation signal is inputted through the higher harmonic wave attenuating device to the first and second demodulators, a phase of a local oscillation signal inputted to the first demodulator and a phase of a local oscillation signal inputted to the second demodulator are shifted from each other by 90 degrees, and the first and second demodulators output baseband signals, respectively.
Further, in the satellite broadcasting receiving tuner according to the present invention, the higher harmonic wave attenuating device is a bandpass filter whose passband frequency is changed in response to the change in the frequency of the local oscillation signal.
Furthermore, in the satellite broadcasting receiving tuner according to the present invention, the higher harmonic wave attenuating device is a low-pass filter whose cutoff frequency is changed in response to the change in the frequency of the local oscillation signal.
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patent: 5787126 (1998-07-01), Itoh et al.
patent: 5918167 (1999-06-01), Tiller et al.
patent: 6091931 (2000-07-01), Ben-Efraim et al.
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Okada Minobu
Takayama Akira
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Urban Edward F.
LandOfFree
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