Telecommunications – Receiver or analog modulated signal frequency converter – Local control of receiver operation
Reexamination Certificate
2000-05-09
2003-04-15
Chin, Vivian (Department: 2682)
Telecommunications
Receiver or analog modulated signal frequency converter
Local control of receiver operation
C455S232100, C455S234100, C455S234200, C455S324000, C375S322000, C375S324000, C375S328000, C375S345000, C375S346000
Reexamination Certificate
active
06549763
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a receiving apparatus and method, and more particularly to a receiving apparatus and method which can be suitably used to receive and directly orthogonally detect a digital modulated wave.
A broadcasting signal of a digital satellite broadcast such as, for example, the SKY PerfecTV (trademark) is a signal digitally modulated using the QPSK (Quadrature Phase Shift Keying). Accordingly, a receiving apparatus for receiving a digital modulated wave of the broadcasting signal includes an orthogonal detector which detects an I-component signal and a Q-component signal of the digital modulated wave.
FIG. 1
shows an example of a construction of a conventional orthogonal detector. Referring to
FIG. 1
, in the orthogonal detector shown, a digital modulated wave received by an antenna (not shown) and frequency converted into a signal of 950 MHz to 2,150 MHz in the L band is inputted as an input signal to an input terminal
1
of a preamplifier (AMP)
2
. The preamplifier
2
amplifies the input signal and outputs a resulting signal to a variably controlled band-pass filter (BPF)
3
. The variably controlled band-pass filter
3
removes an image interfering frequency included in the input signal thereto from the preamplifier
2
in response to a channel selection voltage from a low-pass filter built in a PLL (Phase Lock Loop) circuit
23
, and outputs a resulting signal to an attenuator (ATT)
4
. The image interfering frequency signifies a signal generated by heterodyne detection of a mixer
6
and having a frequency equal to an (oscillation frequency F
1
of a local oscillator
22
)+(intermediate frequency (480 MHz) outputted from the mixer
6
).
The attenuator
4
limits the level of the signal from the variably controlled band-pass filter
3
to a fixed level based on an AGC (Automatic Gain Control) signal inputted thereto from the outside of the orthogonal detector, and outputs a resulting signal to an amplifier
5
. The amplifier
5
amplifies the signal from the attenuator
4
and outputs the amplified signal to the mixer
6
.
The mixer
6
multiplies the signal inputted thereto from the amplifier
5
by the signal inputted thereto from the local oscillator
22
to obtain an intermediate frequency signal (480 MHz) and outputs the intermediate frequency signal to an IF amplifier
7
. The frequency (oscillation frequency) LF of the signal oscillated by the local oscillator
22
is determined with a control signal for controlling the dividing ratio of the PLL circuit
23
in response to a channel selection operation of a user so that the following expression (1) may be satisfied:
oscillation frequency
LF
=reception frequency
F
in+intermediate frequency
IF
(480 MHz) (1)
In particular, output pulses of the voltage controlled oscillator built in the PLL circuit
23
corresponding to the control signal are integrated by a low-pass filter built in the PLL circuit
23
so that they are converted into a dc voltage. The dc voltage is supplied as a channel selection voltage to a resonance circuit (TANK)
24
and varies the voltage controlled variable capacitance of the resonance circuit
24
thereby to control the frequency of the signal to be oscillated by the local oscillator
22
. Further, the channel selection voltage from the low-pass filter of the PLL circuit
23
is supplied also to the band-pass filter
3
.
The IF amplifier
7
amplifies the intermediate frequency inputted thereto from the mixer
6
and outputs the amplified intermediate frequency to a SAW filter
8
. The SAW filter
8
limits the frequency band of the intermediate frequency inputted thereto from the IF amplifier
7
and outputs a resulting signal to an IF amplifier
9
. The IF amplifier
9
corrects amplitude loss of the SAW filter
8
and outputs a resulting signal to an attenuator
10
. The attenuator
10
limits the level of the signal from the IF amplifier
9
to a fixed level based on the AGC signal and outputs a resulting signal to a pair of mixers
11
and
12
.
The mixer
11
multiplies the signal from the attenuator
10
by a signal outputted from an oscillator
18
which is controlled by a SAW oscillator
17
, and outputs a resulting signal to a baseband amplifier
13
. The baseband amplifier
13
amplifies the signal from the mixer
11
and outputs the amplified signal to a low-pass filter
15
. The low-pass filter
15
attenuates, among signals inputted thereto from the base band amplifier
13
, those signals of frequencies higher than the intermediate frequency band. The low-pass filter
15
outputs a resulting signal as an I-(In-Phase) component signal from an output terminal
20
.
The mixer
12
multiplies the signal from the attenuator
10
by the signal from the oscillator
18
having a phase shifted by 90 degrees by a 90° phase shifter
19
and outputs a resulting signal to a baseband amplifier
14
. The baseband amplifier
14
amplifies the signal from the mixer
12
and outputs the amplified signal to a low-pass filter
16
. The low-pass filter
16
attenuates, among signals inputted thereto from the baseband amplifier
14
, those signals of frequencies higher than the intermediate frequency band. The low-pass filter
16
outputs a resulting signal as a Q-(Quadrature-Phase) component signal from another output terminal
21
.
It is to be noted that, for the I-component and Q-component signals outputted from the orthogonal detector, Viterbi decoding, error correction processing, decoding processing and so forth are thereafter performed successively.
While the orthogonal detector shown in
FIG. 1
produces an intermediate frequency from an input signal of the L band and detects I-component and Q-component signals from the intermediate frequency signal, an orthogonal detector of the direct detection type has been developed in recent years. The orthogonal detector of the direct detection type is simplified in circuit construction such that it detects I-component and Q-component signals directly from an input signal of the L band.
FIG. 2
shows an example of a construction of an orthogonal detector of the direct detection type. It is to be noted that the orthogonal detector of the direct detection type is hereinafter referred to simply as direct orthogonal detector.
Referring to
FIG. 2
, in the direct orthogonal detector shown, an input signal of the L band amplified by a preamplifier
2
is inputted to an attenuator
4
. The attenuator
4
limits the level of the input signal of the L band from the preamplifier
2
to a fixed level based on an AGC signal inputted thereto from the outside of the direct orthogonal detector and outputs a resulting signal to an amplifier
5
. The amplifier
5
amplifies the input signal of the L band from the attenuator
4
and outputs a resulting signal to a pair of mixers
31
and
32
.
The mixer
31
multiplies the input signal of the L band from the amplifier
5
by a signal outputted from an oscillator
37
and outputs a resulting signal to a variable gain amplifier
33
. The variable gain amplifier
33
limits the level of the signal from the mixer
31
in response to the AGC signal and outputs a resulting signal to a low-pass filter
35
. The low-pass filter
35
attenuates, among signals inputted thereto from the variable gain amplifier
33
, those signals of frequencies higher than an intermediate frequency. The low-pass filter
35
outputs a resulting signal as an I-component signal from an output terminal
20
.
The mixer
32
multiplies the input signal of the L band from the amplifier
5
by the signal from the oscillator
37
having a phase shifted by 90 degrees by a 90° phase shifter
40
and outputs a resulting signal to a variable gain amplifier
34
. The variable gain amplifier
34
limits the level of the signal from the mixer
32
in response to the AGC signal and outputs a resulting signal to a low-pass filter
36
. The low-pass filter
36
attenuates, among signals inputted thereto from the variable gain amplifier
34
, those signals of frequencies higher than the
Imai Tadashi
Kobayashi Kozo
Afshar Kamran
Chin Vivian
Frommer William S.
Frommer & Lawrence & Haug LLP
Polito Bruno
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