Television – Receiver circuitry – Television receiver adapted to receive radio broadcast or in...
Reexamination Certificate
2000-12-19
2003-10-14
Miller, John (Department: 2614)
Television
Receiver circuitry
Television receiver adapted to receive radio broadcast or in...
C348S735000, C455S188100
Reexamination Certificate
active
06633345
ABSTRACT:
FIELD OF THE INVENTION
The present invention in general relates to a receiver by which a television broadcast signal and an FM radio broadcast signal can be selectively received and can be demodulated and output. More particularly, this invention relates to a receiver which is lightweight and small in size.
BACKGROUND OF THE INVENTION
Recently, accompanied with the prevalence of portable color televisions, for example liquid crystal televisions, a television receiver receiving a general FM broadcast has appeared. This television receiver can receive sound signals of FM radio broadcast signals by employing a high frequency circuit, such as a tuner, and a sound signal demodulation circuit for a television broadcast signal. When a sound signal of an FM radio broadcast signal is demodulated, the demodulation does not employ a video intermediate carrier signal of a television broadcast signal.
FIG. 6
is a block diagram showing the structure of a conventional television receiver which can also receive an FM radio broadcast signal. First, the occasion on which a television broadcast signal is received is explained. A tuner
112
is used for tuning to a television broadcast signal received via an antenna
111
. The tuner
112
down converts the received signal to an intermediate frequency, and outputs this intermediate frequency band signal to SAW filters
113
,
121
. The SAW filter
113
passes the intermediate frequency band having a video intermediate carrier frequency, fo, and outputs it to a VIF amplifier
114
. The VIF amplifier
114
amplifies the intermediate frequency band signal and outputs it to a video detector
116
and also to a switch
120
.
The switch
120
is connected to a terminal to which the output of the VIF amplifier
114
is supplied when receiving the television broadcast signal, and the intermediate frequency band signal is output to an APC (automatic phase control circuit)
118
via the switch
120
. The APC
118
detects the phase difference between (i) the video intermediate carrier frequency fo in the intermediate frequency band signals and (ii) a signal that a voltage control oscillation circuit (VCO)
117
outputs, and outputs the phase difference to the VCO
117
. The VCO
117
outputs the signal of the video intermediate carrier frequency fo which is phase locked to the video intermediate carrier frequency fo to the video detector
116
based on the phase difference. The video detector
116
detects a video signal based on the signal of the video intermediate carrier frequency fo that the VCO
117
outputs and outputs the detected video signal to a terminal
119
. The detection output of the video detector
116
is outputted to a VIFAGC circuit
115
, and the VIFAGC circuit
115
provides gain control to stabilize the amplitude of the detection output of the video detector
116
with respect to the VIF amplifier
114
.
On the other hand, the SAW filter
121
passes an intermediate frequency (fo-fs), and a QIF amplifier
122
amplifies this intermediate frequency based on the gain control by a QIFAGC circuit
123
and outputs it to an intermediate frequency detection circuit (QIFDET)
124
. The intermediate frequency detection circuit
124
mixes the inputted intermediate frequency (fo-fs) with the video intermediate carrier frequency fo output from the VCO
117
and outputs a sound subcarrier frequency, fs. Then, the sound subcarrier frequency fs is extracted via a band pass filter
131
and is amplified by an SIF amplifier
132
, and a sound signal detected and output by an FM detector
133
is output from a terminal
134
.
When receiving the FM radio broadcast signal, the tuner
112
down converts the signal to an intermediate frequency that is the same as the intermediate frequency (fo-fs) and outputs it to the SAW filter
121
. After that, the FM sound intermediate frequency fs is detected by the intermediate frequency detection circuit
124
, similarly to the sound subcarrier frequency fs, and, lastly, a sound signal is output from the terminal
134
. In this case, since the VCO does not output the video intermediate carrier frequency fo, the switch
120
is connected to the input side of the oscillation frequency fo corresponding to the video intermediate carrier frequency fo, and the oscillation frequency fo is output to the APC
118
. In this way, the VCO
117
outputs a phase locked oscillation frequency fo to the intermediate frequency detection circuit
124
and detects and outputs the FM sound intermediate frequency fs.
In the conventional receiver, a video signal related intermediate frequency processing circuit of a television broadcast signal and a sound signal related intermediate frequency processing circuit of a sound signal of a television broadcast signal and a sound signal of an FM radio broadcast signal are independently provided. Accordingly, demodulation characteristic of a sound signal of an FM radio broadcast signal can be set optimally.
However, since the video signal related intermediate frequency processing circuit and the sound signal related intermediate frequency processing circuit are independently provided, many parts and circuit blocks have to be provided, and thus there is a problem that the cost increases and also it is impossible to obtain a lightweight and small size receiver.
SUMMARY OF THE INVENTION
It is an object of the present invention to obtain a receiver by which an FM radio broadcast signal can be received in addition to the reception of a television broadcast receiving signal and which is lightweight and small in size.
In the receiver according to one aspect of this invention, when receiving the television broadcast signal, a first switch selects a video intermediate carrier signal output by an intermediate frequency amplifier and a second switch is switched towards and connected to a first automatic gain controller. A tuner converts the television broadcast signal into an intermediate frequency, and a band limit filter passes this intermediate frequency so that the intermediate frequency is amplified by the intermediate frequency amplifier. On this occasion, the intermediate frequency amplifier is gain controlled so that the amplitude of the video signal that the video detector outputs is made constant by the first automatic gain controller. When receiving the FM radio broadcast, the first switch is switched towards a self-running oscillation signal, and the second switch is switched towards and connected to a second automatic gain controller. The tuner converts the FM radio broadcast signal into an intermediate frequency that is the same as the sound intermediate frequency subcarrier signal when receiving the television broadcast signal and outputs it when receiving the FM radio broadcast signal. The band limit filter passes this intermediate frequency, and the intermediate frequency is amplified by the intermediate frequency amplifier. On this occasion, the intermediate frequency amplifier is gain controlled so that the amplitude of the sound subcarrier signal that the sound band limit filter outputs is made constant by the second automatic gain controller. With this, the band limit filter of the exclusive use of sound, the intermediate frequency amplification circuit of the exclusive use of sound, and the intermediate frequency detection circuit of the exclusive use of sound become unnecessary, and a sound signal having a high quality can be demodulated and outputted even when receiving the FM radio broadcast signal.
In the receiver according to another aspect of this invention, when receiving the television broadcast signal, a first switch selects a video intermediate carrier signal output by an intermediate frequency amplifier, and a second switch is switched towards and connected to a first automatic gain controller. A tuner converts the television broadcast signal into an intermediate frequency, and a band limit filter passes this intermediate frequency so that the intermediate frequency is amplified by the intermediate frequency amplifier. On this occasion, the intermediate frequency amplifi
Izuta Hiroshi
Ohnishi Akio
Leydig , Voit & Mayer, Ltd.
Miller John
Mitsubishi Denki & Kabushiki Kaisha
Yenke Brian
LandOfFree
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