Television – Receiver circuitry – Demodulator
Reexamination Certificate
1998-07-30
2002-03-05
Lee, Michael (Department: 2614)
Television
Receiver circuitry
Demodulator
C348S725000, C348S729000, C348S705000, C455S045000, C455S229000
Reexamination Certificate
active
06353462
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a television signal and FM broadcast signal demodulator and a television signal and FM broadcast signal receiver.
2. Description of the Prior Art
A prior-art television signal and FM broadcast signal receiver will be described with reference to FIG.
6
. Referring to
FIG. 6
, a VHF band television signal or an FM broadcast signal is inputted from an input terminal
31
of a receiver to a VHF tuner unit
32
. The VHF tuner unit
32
includes a tuner, a mixer, a local oscillator or the like, though not shown, to select a received television signal or FM broadcast signal from the inputted television signal or FM broadcast signal and in which the mixer and the local oscillator frequency-convert a selected television signal or FM broadcast signal to provide a television intermediate frequency signal IF. Here, the intermediate frequency signal IF is frequency-converted in such a manner that a television video intermediate frequency signal VIF may have a frequency of 58.75 MHz. A frequency of a television audio intermediate frequency signal SIFtv becomes 54.25 MHz accordingly. Also, an FM audio intermediate frequency signal SIFfm is frequency-converted in such a manner that its frequency becomes 54.25 MHz which is the same frequency as that of this television audio intermediate frequency SIFtv.
Then, when a television signal is received, the video intermediate frequency signal VIF and the audio intermediate frequency signal SIFtv are inputted through an intermediate frequency circuit
33
to a demodulator
34
. The demodulator
34
demodulates the video intermediate frequency signal VIF and the audio intermediate frequency signal SIFtv to provide a video signal V and an audio signal Atv. Also, when an FM broadcast signal is received, a second mixer
35
and a second local oscillator
36
frequency-convert an FM audio intermediate frequency signal SIFfm (54.25 MHz) outputted from a VHF tuner unit
32
to provide an audio intermediate frequency signal of 10.7 MHz, and an FM detector
37
outputs an audio signal Afm. The VHF tuner unit
32
is able to also receive an FM broadcast signal having a frequency lower than that of the television signal accordingly.
FIG. 7
is a block diagram of the demodulator
34
for demodulating the television signal. As shown in
FIG. 7
, the intermediate frequency signal IF from the intermediate frequency circuit
33
contains the video intermediate frequency signal VIF and the audio intermediate frequency signal SIFtv. These video and audio intermediate frequency signals VIF and SIFtv are inputted to a video intermediate frequency amplifier (simply referred to as “VIFAMP”)
41
and an audio intermediate frequency amplifier (simply referred to as “SIFAMP”)
42
, respectively. Then, the video intermediate frequency signal VIF that was amplified by the VIFAMP
41
is inputted to a video detector
43
and an automatic phase controller (simply referred to as “APC”)
44
. The APC
44
phase-compares an oscillation signal from a voltage-controlled oscillator (simply referred to as “VCO”)
45
and the video intermediate frequency signal VIF. A compared voltage corresponding to a phase difference is inputted from the APC
44
to the VCO
45
. As a consequence, the VCO
45
oscillates at 58.75 MHz which is a frequency of a video carrier of the video intermediate frequency signal VIF. Thus, the APC
44
and the VCO
45
comprise a PLL (phase-locked loop) circuit and serves as a video carrier generator to generate a video carrier. This video carrier is inputted to the video detector
43
.
Then, the video detector
43
synchronously detects the video intermediate frequency signal VIF by the video carrier of 58.75 MHz to provide a video signal V.
The audio intermediate frequency signal SIFtv that was amplified by the SIFAMP
42
is inputted to an audio intermediate frequency detector
46
, and the video carrier from the VCo
45
also is inputted to this audio intermediate frequency detector
46
. Then, since an audio carrier of the audio intermediate frequency signal SIFtv is 54.25 MHz, the audio intermediate frequency detector
46
outputs a second audio intermediate frequency signal SIF
2
of 4.5 MHz which is a difference of frequencies between the video carrier and the audio carrier. That is, the audio intermediate frequency detector
46
intercarrier-detects the audio intermediate frequency signal SIFtv to provide the second audio intermediate frequency signal SIF
2
.
Then, this second audio intermediate frequency signal SIF
2
is inputted through a bandpass filter
47
having a center frequency of 4.5 MHz to an FM detector
48
. This FM detector
48
outputs an audio signal Atv.
On the other hand, when an FM broadcast signal is received, since the intermediate frequency signal SIFfm based on the FM broadcast signal outputted from the intermediate frequency circuit
33
does not contain the video intermediate frequency signal VIF, the VCO
45
is unable to output the carrier of 58.75 MHz. Accordingly, the audio intermediate frequency detector
46
also is unable to output the second audio intermediate frequency signal SIF
2
of 4.5 MHz. As a result, the demodulator
34
cannot FM-detect the FM broadcast signal.
In order to solve the above-mentioned problem, as mentioned before, after the second mixer
35
and the second local oscillator
36
have frequency-converted the audio intermediate frequency signal SIFfm based on the FM broadcast signal from the VHF tuner
32
to provide the audio intermediate frequency signal of 10.7 MHz, the FM detector
37
FM-detects this audio intermediate frequency signal.
As described above, according to the prior-art circuit arrangement, since the demodulator
34
for obtaining the television video signal V and audio signal Atv cannot FM-detect the FM broadcast signal, the second mixer
35
and the second local oscillator
36
are used to frequency-convert the FM broadcast signal to provide the audio intermediate frequency signal of 10.7 MHz, and then the audio intermediate frequency signal is FM-detected. For this reason, since the prior-art receiver required the second mixer
35
, the second local oscillator
36
and the FM detector
37
extra, the circuit arrangement of the prior-art receiver becomes complicated, and the prior-art receiver becomes expensive unavoidably.
SUMMARY OF THE INVENTION
In view of the aforesaid aspect, it is an object of the present invention to provide a television signal and FM broadcast signal demodulator in which both of a television signal and an FM broadcast signal may be demodulated only by switching the reception of the television signal and the reception of the FM broadcast signal.
It is another object of the present invention to provide a television signal and FM broadcast signal receiver in which, when an FM broadcast signal is received, a common demodulator may obtain television video signal and audio signal and an audio signal of FM broadcast signal without using a second mixer for frequency-converting an audio intermediate frequency signal of 54.25 MHz to provide an audio intermediate frequency signal of 10.7 MHz.
According to a first aspect of the present invention, there is provided a television signal and FM broadcast signal demodulator which is comprised of a first input terminal to which a video intermediate frequency signal in a television intermediate frequency signal is inputted, a second input terminal to which an audio intermediate frequency signal in the intermediate frequency signal or an FM broadcast signal, which is frequency-converted so as to have the same frequency as that of the audio intermediate frequency signal, is inputted, a third input terminal to which a pseudo carrier having the same frequency as that of a video carrier in the intermediate frequency signal is inputted, a change-over switch for selecting either the video intermediate frequency signal inputted to the first input terminal or the pseudo carrier inputted to the third input terminal, a video detector to which one of t
Furuta Toshiro
Kudo Yasuharu
Osada Shigeru
Suzuki Masashi
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Lee Michael
Lo Linus M.
LandOfFree
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