Television – Receiver circuitry – Tuning
Reexamination Certificate
2001-07-17
2004-06-29
Lee, Michael H. (Department: 2614)
Television
Receiver circuitry
Tuning
C348S725000
Reexamination Certificate
active
06757029
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a television receiving apparatus having a receiving circuit that can receive both a digital television signal and an analog television signal.
2. Description of the Related Art
In recent years, digital television broadcasts such as digital CS (Communication Satellite) broadcast, BS (Broadcast Satellite) broadcast, and digital ground wave broadcast have been performed. It is predicted that analog television broadcasts will be gradually shifted to digital television broadcasts.
However, even most television broadcasts have been shifted to digital broadcasts, existing analog television broadcasts cannot be stopped. Thus, in the transient period of which the analog television broadcasts are shifted to the digital television broadcasts, both analog television digital broadcasts and digital television digital broadcasts will coexist.
When both analog television broadcasts and digital television broadcasts are performed, television receivers that can receive both analog television broadcasts and digital television broadcasts are desired.
FIG. 1
is a block diagram showing an example of the structure of a receiving circuit of a conventional television receiver. The receiving circuit can receive both digital television broadcasts and analog television broadcasts.
Referring to
FIG. 1
, an RF (Radio Frequency) signal is received from an antenna (not shown). The RF signal is supplied to an antenna input terminal
101
. The signal that is input from the antenna input terminal
101
is supplied to a power splitter
102
. The power splitter
102
splits the received signal into an analog broadcast signal and a digital broadcast signal.
The analog broadcast signal is supplied from the power splitter
102
to an analog broadcast tuner
103
.
The analog broadcast tuner
103
selects a signal having a desired carrier frequency from the RF signal received through the power splitter
102
. The selected signal is converted into an IF (Intermediate Frequency) signal. A frequency set signal is supplied from a controller
115
to the analog broadcast tuner
103
. Corresponding to the frequency set signal, the oscillation frequency of a PLL (Phase Locked Loop) synthesizer of the analog broadcast tuner
103
is set. Corresponding to the oscillation frequency, the reception frequency is set. An AGC control signal is supplied from an analog demodulating circuit
108
to an AGC (Automatic Gain Control) circuit of the analog broadcast tuner
103
.
An output of the analog broadcast tuner
103
is supplied to an SAW (Surface Acoustic Wave) filter
107
. The SAW filter
107
has a pass band for the IF signal received from the analog broadcast tuner
103
. The SAW filter
107
should have an excellent characteristic for the analog broadcast.
An output of the SAW filter
107
is supplied to an analog demodulating circuit
108
. The analog demodulating circuit
108
amplitude-demodulates the analog television signal to an NTSC format video signal. The demodulated NTSC format analog video signal is output from an output terminal
109
.
The digital broadcast signal is supplied from the power splitter
102
to a digital broadcast tuner
104
.
The digital broadcast tuner
104
selects a signal having a desired carrier frequency from the RF signal received through the power splitter
102
and converts the selected signal into a predetermined IF (Intermediate Frequency) signal. A frequency set signal is supplied from the controller
115
to the digital broadcast tuner
104
. Corresponding to the frequency set signal, the oscillation frequency of a PLL synthesizer of the digital broadcast tuner
104
is set. Corresponding to the oscillation frequency, the reception frequency is set. An AGC control signal is supplied from a digital demodulating circuit
112
to an AGC circuit of a digital broadcast tuner
106
.
An output of the digital broadcast tuner
104
is supplied to an SAW filter
110
. An output of the SAW filter
110
is supplied to an SAW filter
111
. The SAW filters
110
and
111
have a pass band for the IF signal received from the digital broadcast tuner
104
. A filter composed of the SAW filters
110
and
111
accomplishes an optimum characteristic for the digital broadcast.
An output of the SAW filter
111
is supplied to the digital demodulating circuit
112
. The digital demodulating circuit
112
performs a demodulating is process such as QAM (Quadrature Amplitude Modulation), VSB (Vestigial Sideband Amplitude Modulation), or OFDM (Orthogonal Frequency Division Multiplex). An output of the digital demodulating circuit
112
is output from an output terminal
113
.
Thus, according to the related art reference, the analog broadcast tuner
103
and the digital broadcast tuner
104
are independently disposed. The analog broadcast signal and the digital broadcast signal are split by the power splitter
102
.
This is because the required characteristic for the analog broadcast signal is different from that for the digital broadcast signal.
In other words, in the analog broadcast, since a video signal is amplitude-modulated, a high video amplitude characteristic is desired. In addition, a high S/N ratio is required. On the other hand, in the digital broadcast, since QAM, VSB, OFDM, or the like is used, an excellent phase characteristic is required. Moreover, in the digital broadcast, a filter having a sharp characteristic is required. In the analog broadcast, when a filter having a sharp characteristic is used, the resolution deteriorates.
To solve such a problem, the power splitter
102
splits the received signal into an analog broadcast signal and a digital broadcast signal. The split analog broadcast signal is processed by the analog broadcast tuner
103
, the SAW filter
107
, and the analog demodulating circuit
108
. The split digital broadcast signal is processed by the digital broadcast tuner
104
, the SAW filters
110
and
111
, and the digital demodulating circuit
112
.
The SAW filter
107
has an optimum characteristic for the analog broadcast.
The SAW filters
110
and
111
have optimum characteristics for the digital broadcast. In the digital system, the SAW filter
110
and the SAW filter
111
are tandem-connected so that a sharp characteristic for the digital broadcast can be obtained.
In the receiving circuit of the conventional television receiver that receives both a conventional analog broadcast and a digital broadcast, since the power splitter
102
splits the RF signal into an analog broadcast signal and a digital broadcast signal, a power loss takes place in the power splitter and thereby the S/N ratio deteriorates.
In addition, the receiving circuit of the television receiver that receives both a conventional analog broadcast and a digital broadcast is provided with the analog broadcast tuner
103
and the digital broadcast tuner
104
. In addition, the receiving circuit is provided with the SAW filter
107
for the analog broadcast and the SAW filters
110
and
111
for the digital broadcast. Thus, the circuit scale becomes large.
OBJECTS AND SUMMARY OF THE INVENTION
Therefore, an object of the present invention is to provide a television receiving apparatus that can receive both an analog television broadcast and a digital television broadcast and that allows the circuit scale to be reduced.
Another object of the present invention is to provide a television receiving apparatus that can receive both an analog television broadcast and a digital television broadcast and that allows the S/N ratio to be improved.
The present invention is a television receiving apparatus for receiving an analog television broadcast and a digital television broadcast, comprising a tuner means for receiving both an analog television broadcast signal and a digital television broadcast signal, selecting a signal having a desired carrier frequency from the received signals, and converting the selected signal having the desired carrier frequency into an intermediate frequency signal, an analog demodulating means for
Fromer Lawrence & Haug LLP
Frommer William S.
Lee Michael H.
Natnael Paulos
Sony Corporation
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