Tuners – Combined diverse-type tuners
Reexamination Certificate
2000-11-14
2003-07-15
Lee, Benny (Department: 2817)
Tuners
Combined diverse-type tuners
C334S015000
Reexamination Certificate
active
06593835
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In general, the present invention relates to a multiple-tuning circuit employed in a tuner capable of switching a tuning frequency among a plurality of frequency bands by turning a switch diode on and off. More particularly, the present invention relates to a multiple-tuning circuit employed in a tuner capable of preventing a frequency selection characteristic thereof from deteriorating due to an undesired new tuning circuit formed by a static capacitance generated in a non-conductive state of a switch diode.
2. Description of the Related Art
A multiple-tuning circuit employed in the conventional tuner is explained by referring to
FIGS. 4
,
5
,
6
and
7
. As shown in
FIG. 5
, the tuning circuit comprises a primary tuning circuit
51
and a secondary tuning circuit
52
. The first tuning circuit
51
includes a series circuit of a direct-current-blocking capacitor
53
and a varactor diode
54
. The first tuning circuit
51
also includes another series circuit of a tuning coil
55
for high-band reception, a tuning coil
56
for low-band reception, a resistor
57
, a coupling coil
58
and a direct-current-blocking capacitor
59
, which are connected to each other in an order shown in that figure. The series circuit and the other series circuit form a parallel circuit. The anode and the cathode of the varactor diode
54
are connected to the ground and the direct-current-blocking capacitor
53
respectively. The other terminal of the direct-current-blocking capacitor
59
is also connected to the ground. The connection point between the direct-current-blocking capacitor
53
and the tuning coil
55
for high-band reception serves as an input terminal of the multiple-tuning circuit. This input terminal is connected to a high-frequency amplifier
60
at the preceding stage.
A series circuit comprising a direct-current blocking capacitor
61
, a switch diode
62
and a direct-current blocking capacitor
63
is connected between the connection point between the tuning coil
55
for high-band reception and the tuning coil
56
for low-band reception and the ground. In this series circuit, the anode and the cathode of the switch diode
62
are connected to the direct-current-blocking capacitor
61
and the direct-current-blocking capacitor
63
respectively.
The connection point between the direct-current-blocking capacitor
61
and the switch diode
62
is connected to a switch terminal HB
65
for high-band reception through a power-feeding resistor
64
.
The connection point between the switch diode
62
and the direct-current-blocking capacitor
63
is connected to a switch terminal LB
67
for low-band reception through a power-feeding resistor
66
.
In addition, the connection point between the switch diode
62
and the direct-current-blocking capacitor
63
is connected to ground through a bias resistor
68
.
The connection point between the varactor diode
54
and the direct-current-blocking capacitor
53
is connected to a tuning-voltage terminal TU
70
through a power-feeding resistor
69
.
The second tuning circuit
52
includes a parallel circuit comprising a varactor diode
71
and a series circuit. The series circuit comprises a tuning coil
72
for high-band reception, a tuning coil
73
for low-band reception, a resistor
74
, a direct-current-blocking capacitor
75
, the coupling coil
58
and the direct-current-blocking capacitor
59
, which are connected to each other in an order shown in the figure. The anode and the cathode of the varactor diode
71
are connected to the ground and the tuning coil
72
for high-band reception respectively. The connection point between the varactor diode
71
and the tuning coil
72
for high-band reception is connected to a series circuit of a varactor diode
76
and a direct-current-blocking capacitor
77
. The anode and the cathode of the varactor diode
76
are connected to the direct-current-blocking capacitor
77
and the tuning coil
72
for high-band reception respectively. The other end of the direct-current-blocking capacitor
77
is connected to an output terminal of the multiple-tuning circuit. The output terminal is connected to a mixer
78
at the succeeding stage. In the mixer
78
, an oscillation signal generated by an oscillator not shown in the figure is mixed with a signal output by the multiple-tuning circuit to produce an intermediate-frequency signal.
A series circuit of a direct-current blocking capacitor
79
and a switch diode
80
is provided between the connection point of the tuning coils
72
and
73
and the connection between the switch diode
62
and the direct-current-blocking capacitor
63
. The anode and the cathode of the switch diode
80
are connected to the direct-current-blocking capacitor
79
and the direct-current-blocking capacitor
63
.
The connection point between the direct-current-blocking capacitor
79
and the switch diode
80
is connected to the switch terminal
65
for high-band reception through a power-feeding resistor
81
.
On the other hand, the connection point between the direct-current-blocking capacitor
63
and the switch diode
80
is connected to a switch terminal
67
for low-band reception through a power-feeding resistor
66
.
The connection point between the tuning coil
72
for high-band reception and the varactor diode
71
is connected to the tuning-voltage terminal TU
70
through a power-feeding resistor
82
.
In the configuration described above, when a voltage is applied to the terminal HB
65
for high-band reception, the switch diodes
62
and
80
are each put in a conductive state. In addition, a power supply voltage is supplied from power supply terminal MB. When a voltage is applied to the terminal LB
67
for low-band reception, on the other hand, the switch diodes
62
and
80
are each put in a non-conductive state. In this way, the multiple-tuning circuit can be switched from a high-band reception state to a low-band reception state or vice versa.
By the way, in order to switch the multiple-tuning circuit of a tuner shown in
FIG. 5
to a state of reception of high-band television signals each having a frequency in the range 170 MHz to 222 MHz for example, a voltage of typically 5 V is applied to the terminal
65
for high-band reception and no voltage is applied to the terminal
67
for low-band reception. With a voltage of 5 V applied to the terminal
65
for high-band reception, a voltage is applied to the switch diodes
62
and
80
in the forward direction, putting both the switch diodes
62
and
80
in a conductive state. In this conductive state, the connection point between the tuning coil
55
for high-band reception and the tuning coil
56
for low-band reception as well as the connection point between the tuning coil
72
for high-band reception and the tuning coil
73
for low-band reception are connected to the ground. As a result, the varactor diode
54
and the tuning coil
55
for high-band reception in the first tuning circuit
51
form a parallel circuit. Similarly, the varactor diode
71
and the tuning coil
72
for high-band reception in the second tuning circuit
52
also form a parallel circuit as well. A high-frequency equivalent circuit resulting in this state is a multiple-tuning circuit shown in
FIG. 6
wherein the direct-current-blocking capacitors and the resistors are ignored. A multiple-tuning circuit is formed by the varactor diode
54
, the high-band tuning coil
55
, the varactor diode
71
, and the high-band tuning coil
72
. By adjusting the voltages applied to the varactor diodes
54
and
71
, a desired tuning frequency can be obtained.
In order to switch the multiple-tuning circuit of a tuner shown in
FIG. 5
to a state of reception of low-band television signals each having a frequency in the range 90 MHz to 108 MHz for example, a voltage of typically 5 V is applied to the terminal
67
for low-band reception and no voltage is applied to the terminal
65
for high-band reception. With a voltage of 5 V applied to the terminal
67
for low-band r
Yamamoto Akira
Yamamoto Masaki
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Lee Benny
LandOfFree
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