Television – Receiver circuitry – Tuning
Reexamination Certificate
2000-04-17
2003-06-03
Miller, John (Department: 2614)
Television
Receiver circuitry
Tuning
C348S729000, C348S733000
Reexamination Certificate
active
06573949
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to television signal receiving tuners, and more particularly relates to a television signal receiving tuner that is capable of receiving terrestrial television broadcasts and that has a trap circuit for attenuating frequency-modulation broadcast-band signals.
2. Description of the Related Art
A conventional television signal receiving tuner (hereinafter referred to as simply a tuner) is shown in FIG.
3
. In the tuner shown in
FIG. 3
, one terminal
31
a of a filter
31
is connected to an antenna for receiving a terrestrial television broadcast or a cable for receiving cable television (CATV) signals (neither are shown). Another end
31
b
of the filter
31
is connected to an input terminal of a VHF (very high frequency) unit
32
and that of a UHF (ultrahigh frequency) unit
33
which are connected in parallel with each other. An output terminal of the VHF unit
32
and an output terminal of the UHF unit
33
are each connected to an integrated circuit
34
.The integrated circuit
34
has a mixer, an oscillator, and a PLL (phase locked loop) incorporated therein. The mixer frequency-converts a high frequency signal in the VHF band or in the UHF band into an intermediate frequency signal IF and outputs the intermediate frequency signal IF.
The VHF unit
32
is constructed by sequentially connecting in series a trap circuit
35
, a VHF antenna tuning circuit
36
, a VHF high frequency amplifier
37
and a VHF interstage tuning circuit
38
. Likewise, the UHF unit
33
is constructed by sequentially connecting in series a UHF antenna tuning circuit
39
, a UHF high frequency amplifier
40
, and a UHF interstage tuning circuit
41
.
The trap circuit
35
attenuates FM broadcast signals which interfere with terrestrial television broadcast signals when terrestrial television broadcast signals are received. A parallel resonant circuit constructed with an inductor
42
and a capacitor
43
is connected, via a direct current blocking capacitor
44
, in parallel with a switch diode
45
, the cathode of which is connected to an input terminal
35
a
of the trap circuit
35
and the anode is connected to an output terminal
35
b
thereof. The resonant frequency of the parallel resonant circuit formed by the inductor
42
and the capacitor
43
is set within the FM broadcast-band. The cathode of the switch diode
45
is grounded via a resistor
46
which is provided between the input terminal
35
a
ground. A trap circuit control voltage V
f
is applied via a feeding resistor
47
from the integrated circuit
34
to a node between the switch diode
45
and the resistor
46
.
In the VHF unit
32
, the VHF antenna tuning circuit
36
outputs a desired VHF band television signal to the VHF high frequency amplifier
37
. The VHF high frequency amplifier
37
amplifies the input television signal, and the VHF interstage tuning circuit
38
outputs the amplified television signal to the integrated circuit
34
. Operations of the circuits that comprise the UHF unit
33
are the same as those circuits described in the VHF unit
32
. Therefore, descriptions of the UHF circuits are omitted.
The integrated circuit
34
outputs a band selection voltage or a tuning voltage in accordance with channel selection data DA input from a television receiver (not shown). The band selection voltage consists of a voltage V
lo
for selecting a low band in the VHF band, a voltage V
hi
for selecting a high band in the VHF band, and a voltage V
u
for selecting the UHF band. When each band is selected, the integrated circuit
34
outputs a voltage of 5 V. The band selection voltages V
lo
and V
hi
for the VHF band are applied to the VHF antenna tuning circuit
36
, the VHF high frequency amplifier
37
, and the VHF interstage tuning circuit
38
.The band selection voltage V
u
for the UHF band is applied to the UHF high frequency amplifier
40
. A tuning voltage V
t
is applied to the VHF antenna tuning circuit
36
, the VHF interstage tuning circuit
38
, the UHF antenna tuning circuit
39
, and the UHF interstage tuning circuit
41
.
For example, in the United States frequency assignments for VHF and UHF band television channels and the FM broadcast-band are shown in Table 1. It should be noticed that the frequency band assigned to channel six is adjacent to that of the FM broadcasting range.
Furthermore, some CATV channels are assigned to the FM broadcast-band (for example, in the United States, between 88 MHz and 108 MHz). Accordingly, the trap circuit
35
is activated when signals for channel six or for particular CATV channels are received; otherwise the trap circuit
35
is not activated.
TABLE 1
Freq.
Att.
Band
Freq.
Band
Ch. No.
(MHz)
V
f
(MHz)
Terrestrial
VHF Low Band
2 to 5
54 to 82
OFF
—
Television
6
82 to 88
ON
91.25
Broadcasting
VHF High Band
7 to 13
174 to 216
OFF
—
UHF
14 to 83
470 to 890
OFF
—
Cable
VHF Low Band
2 to 6
54 to 88
OFF
TV
Midband
A-5 to 1
90 to 174
OFF
—
VHF High Band
7 to 13
174 to 216
OFF
Superband
J to W
216 to 300
OFF
—
Hyperband
W + 1 to
300 to 648
OFF
—
W + 58
FM
—
88 to 108
—
—
When signals having frequencies within the terrestrial television broadcasting channel six are received, the trap circuit control voltage V
f
, (e.g., a 5 V voltage), is applied via the feeding resistor
47
from the integrated circuit
34
to the trap circuit
35
. Since the switch diode
45
is reverse-biased, the switch diode
45
is switched off. With the switched diode
45
switched off, the trap circuit
35
attenuates a signal having a particular frequency, such as 91.25 MHz within the FM broadcast-band, which is in the proximity of the frequency band of channel six.
When the terrestrial television broadcast VHF low band, apart from the band of channel six, or VHF high band is received, the trap circuit control voltage V
f
is not applied to the trap circuit
35
and the band selection voltage V
hi
or V
lo
is applied to the VHF antenna tuning circuit
36
. Since the switch diode
45
is forward-biased, the switch diode
45
is switched on. With the switch diode
45
switched on, the input terminal
35
a
and the output terminal
35
b
of the trap circuit
35
are short-circuited, allowing high frequency signals to be received by the VHF antenna tuning circuit
36
without being attenuated by the trap circuit
35
.
When CATV signals are received, the trap circuit control voltage V
f
is not applied to the trap circuit
35
and the band selection voltage V
hi
or V
lo
is applied to the VHF antenna tuning circuit
36
. Since the switch diode
45
is forward-biased, the switch diode
45
is switched on. With the switch diode
45
switched on, the input terminal
35
a
and the output terminal
35
b
of the trap circuit
35
are short-circuited, and the CATV signals within the entire VHF band are received by the VHF antenna tuning circuit
36
without being attenuated by the trap circuit
35
.
When the above-described conventional tuner receives VHF television signals within the terrestrial television broadcast-band, the integrity of the VHF television signals can be impaired. The frequencies of some of these received signals correspond to twice the frequencies of the FM broadcast-band (between 88 MHz and 108 MHz). It is the second harmonic of these FM broadcast signals that can also interfere with the television signals received by the high frequency amplifier
37
and other components. The quality of the received image is thus degraded if the second harmonic of these FM broadcast signals is not removed.
SUMMARY OF THE INVENTION
According to a first aspect of the invention, a television signal tuner capable of receiving at least terrestrial television broadcast signals is provided. The television signal receiving tuner includes a trap circuit for attenuating frequency-modulation (FM) broadcast-band signals that interfere with the terrestrial television broadcast signals. The trap circuit passes select terrestrial television signals while attenuating (or d
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Miller John
Tran Trang U.
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