Television – Receiver circuitry – Television receiver adapted to receive radio broadcast or in...
Reexamination Certificate
1999-08-27
2002-02-05
Kostak, Victor R. (Department: 2711)
Television
Receiver circuitry
Television receiver adapted to receive radio broadcast or in...
C348S731000, C348S706000
Reexamination Certificate
active
06344881
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a television tuner capable of receiving a CATV broadcasting signal in which a television broadcasting signal and an FM broadcasting signal are mixed and a ground wave FM broadcasting signal received via an FM broadcast receiving antenna (hereinbelow, simply called an FM antenna).
2. Description of the Related Art
A conventional television tuner will be described with reference to FIG.
3
. In
FIG. 3
, a television tuner comprises a tuner unit
31
for receiving a CATV broadcasting signal and a ground wave FM broadcasting signal, an intermediate frequency circuit
32
, a frequency converting circuit
33
, a first demodulator
34
and a second demodulator
35
.
An input change-over switch
36
is connected to the input terminal
31
a
of the tuner unit
31
. A CATV cable
37
and an FM antenna
38
are connected to the input change-over switch
36
. A CATV broadcasting signal led from the CATV cable
37
or a ground wave FM broadcasting signal received by the FM antenna
38
is received by the tuner unit
31
. An output change-over switch
39
which operates interlockingly with the switching operation of the input change-over switch
36
is connected to the output terminal
31
b
of the tuner unit
31
. To the output change-over switch
39
, the intermediate frequency circuit (hereinbelow, called an IF circuit)
32
and the frequency converting circuit
33
are connected.
When the tuner unit
31
is connected to the CATV cable
37
by the input change-over switch
36
, it is connected to the IF circuit
32
. When the tuner unit
31
is connected to the FM antenna
38
by the input change-over switch
36
, it is connected to the frequency converting circuit
33
by the output change-over switch
39
.
The tuner unit
31
has a VHF circuit unit
31
c
and a UHF circuit unit
31
d
each comprising a tuning circuit, a mixing circuit, a local oscillating circuit, and the like (which are not shown). The tuner unit
31
frequency converts each of the CATV broadcasting signal and the ground wave FM broadcasting signal supplied to the input terminal
31
a
into an intermediate frequency signal (hereinbelow, referred to as an IF signal) and outputs the IF signal. Since the frequency of the ground wave FM broadcasting signal is close to the frequency of the low band of the VHF band in the CATV broadcasting signal, the ground wave FM broadcasting signal is received by the VHF circuit unit
31
c.
At the occasion of receiving the broadcasting signal in the VHF band in the CATV broadcasting signal or the ground wave FM broadcasting signal, the received broadcasting signal in the VHF band or ground wave FM broadcasting signal is supplied to the VHF circuit unit
31
c
and is frequency converted into an IF signal. Similarly, at the occasion of receiving the UHF band broadcasting signal, the received UHF band broadcasting signal is supplied to the UHF circuit unit
31
d
and is frequency converted into an IF signal.
The IF signal of the CATV broadcasting signal outputted from the tuner unit
31
is supplied to the IF circuit
32
. For example, the IF signal in a US channel includes an audio intermediate frequency signal (having a frequency of 41.25 MHz) S and a video intermediate frequency signal (having a frequency of 45.75 MHz) P and is supplied to the first demodulator
34
. The IF signal is demodulated by the first demodulator
34
into an audio signal A and a video signal V. The audio and video signals A and V are thus obtained.
In case of receiving the ground wave FM broadcasting signal, the IF signal outputted from the VHF circuit unit
31
c
in the tuner unit
31
is supplied to the frequency converting circuit
33
. The IF signal of the ground wave FM broadcasting signal has the same frequency as that of the audio IF signal S of the CATV broadcasting signal.
The IF signal outputted from the VHF circuit unit
31
c
is, generally, frequency converted by the frequency converting circuit
33
to generally used 10.7 MHz and the audio signal A is obtained by the second demodulator
35
as a general demodulator for FM radio which is connected to the next stage.
Such a CATV broadcasting signal includes not only a regular television broadcasting signal having what is called a video signal but also an FM broadcasting signal having only an audio signal and no video signal. Since a conventional television tuner, however, performs demodulation into the audio signal after obtaining a beat signal between the video IF signal P and the audio IF signal S, the FM broadcasting signal in the CATV broadcasting signal having no video IF signal P cannot be received.
SUMMARY OF THE INVENTION
The invention has been achieved to solve the problem and its object is to receive a television broadcasting signal and an FM broadcasting signal in a CATV broadcasting signal and a ground wave FM broadcasting signal which are led through a cable.
In order to solve the problem, a television tuner of the invention comprises: a tuner unit for receiving a CATV broadcasting signal in which a VHF band television broadcasting signal, a UHF band television broadcasting signal, and an FM broadcasting signal are mixed and a ground wave FM broadcasting signal, frequency converting each of the VHF band television broadcasting signal, the UHF band television broadcasting signal, the FM broadcasting signal, and the ground wave FM broadcasting signal into an intermediate frequency signal, and outputting the intermediate frequency signal; an intermediate frequency circuit for generating an audio intermediate frequency signal and a video intermediate frequency signal from the intermediate frequency signal; a demodulator for demodulating the audio intermediate frequency signal and the video intermediate frequency signal; and a pseudo carrier wave oscillator for outputting a pseudo carrier wave having the same frequency as that of the video intermediate frequency signal, wherein when the tuner unit receives the FM broadcasting signal in the CATV broadcasting signal or the ground wave FM broadcasting signal, the pseudo carrier wave is supplied to the demodulator. Accordingly, both of the FM broadcasting signal and the television broadcasting signal can be demodulated by the common demodulator.
According to a television tuner of the invention, the tuner unit comprises: an antenna switch circuit having a first input terminal to which the CATV broadcasting signal is supplied, a second input terminal to which the ground wave FM broadcasting signal is supplied, and an output terminal from which the supplied CATV broadcasting signal and the ground wave FM broadcasting signal are outputted, in which a first switching diode is provided between the first input terminal and the output terminal, and a second switching diode is provided between the second input terminal and the output terminal; a VHF circuit unit which is connected to the output terminal of the antenna switch circuit, to which the VHF band television broadcasting signal, the FM broadcasting signal, and the ground wave FM broadcasting signal are supplied, and from which an intermediate frequency signal is outputted; and a UHF circuit unit which is connected to the first input terminal, to which the UHF band television broadcasting signal is supplied, and from which an intermediate frequency signal is outputted through the output terminal, wherein when the VHF band television broadcasting signal or the FM broadcasting signal is received, the second switching diode is brought out of conduction and the first switching diode is brought into conduction, and when the ground wave FM broadcasting signal is received, the first switching diode is brought out of conduction, and the second switching diode is brought into conduction. Consequently, when the VHF circuit unit receives the VHF band television broadcasting signal or the FM broadcasting signal from the cable, the FM antenna is disconnected from the VHF circuit unit by the antenna switch circuit. When the VHF circuit unit receives the ground wave broadcast
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Kostak Victor R.
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