Television – Receiver circuitry – Tuning
Reexamination Certificate
1998-10-01
2002-06-04
Miller, John W. (Department: 2614)
Television
Receiver circuitry
Tuning
C348S725000, C348S726000, C348S727000, C455S130000, C455S191100, C455S296000, C455S300000
Reexamination Certificate
active
06400419
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to television tuner systems and, more particularly, to a circuit layout (arrangement) of a television tuner system.
2. Description of the Related Art
FIG. 3
is a plan view illustrating a circuit layout of a known television tuner system. Referring to
FIG. 3
, a metallic frame
51
has four side plates
51
a
,
51
b
,
51
c
, and
51
d
, and a connector
52
for receiving television signals is attached to the side plate
51
d
of the frame
51
. A printed board
53
is disposed within the frame
51
. Formed on the printed board
53
are a tuner disposed in a region
53
a
near the connector
52
and an intermediate frequency circuit in a region
53
b
away from the connector
52
. Ground conductors
54
and
55
, which are connected to the frame
51
, are formed in parallel to each other at the boundary between the regions
53
a
and
53
b
. The ground conductor
54
is formed at the periphery of the region
53
a
of the printed board
53
and is connected to the frame
51
with a ground conductor
56
connected to the side plate
51
a
therebetween. The ground conductor
55
is formed at the periphery of the region
53
b
of the printed board
53
and is connected to the frame
51
with a ground conductor
57
connected to the side plate
51
a
therebetween.
In the region
53
a
where the tuner is formed, there are disposed not only a high frequency amplifier and a tuning circuit, both of which are not shown, but also a mixer, a local oscillator, and an intermediate frequency amplifier. The mixer, the local oscillator, and the intermediate frequency amplifier are integrated into an integrated circuit (IC) component
58
within a single package. A tuning circuit connected to the local oscillator within the IC component
58
is disposed in a region
53
c
adjacent to the ground conductor
54
. The IC component
58
is placed in proximity with the region
53
c.
With the above arrangement, television signals input into the connector
52
are amplified in the high frequency amplifier (not shown), and a television signal RF of a desired channel is selected in the tuning circuit (not shown). The television signal RF is then input into the mixer within the IC component
58
. In the mixer, the television signal RF is mixed with an oscillation signal output from the local oscillator and is converted into an intermediate frequency signal. The intermediate frequency signal is temporarily extracted from the IC component
58
and input into an intermediate frequency tuning circuit
59
formed on the printed board
53
, and again returns to the intermediate frequency amplifier formed within the IC component
58
. The intermediate frequency signal is amplified in the intermediate frequency amplifier, and the amplified signal IF is then output via a conductor pattern
60
formed on the printed board
53
to the intermediate frequency circuit disposed in the region
53
b.
A surface acoustic wave (SAW) filter
61
and a detector
62
are provided for the intermediate frequency circuit in the region
53
b
. The SAW filter
61
is formed generally in a rectangular prism shape and has a plurality of terminals, such as an input terminal
61
a
, a ground terminal
61
b
, and output terminals
61
c
and
61
c
, which are sequentially aligned and project in the same direction from one side of the SAW filter
61
. The SAW filter
61
is placed in proximity with the ground conductor
55
in such a manner that the terminals
61
a
,
61
b
,
61
c
and
61
c
are aligned parallel to the ground conductor
55
and that the output terminals
61
c
and
61
c
are placed near the ground conductor
57
. In this state, the input terminal
61
a
is connected to the conductor pattern
60
, and the ground terminal
61
b
is connected to a ground conductor portion
55
a
projecting from the ground conductor
55
.
The detector
62
is also formed generally in a rectangular prism shape as an IC component. Intermediate frequency signal input terminals
62
a
and
62
a
, and detector output terminals
62
b
and
62
c
project from the respective two sides of the detector
62
. The detector
62
and the SAW filter
61
are placed side by side in such a manner that the intermediate frequency signal input terminals
62
a
and
62
a
face the SAW filter
61
. The output terminals
61
c
and
61
c
of the SAW filter
61
are respectively connected to the intermediate frequency signal input terminals
62
a
and
62
a
of the detector
62
with conductor patterns (not shown). The detector output terminals
62
b
and
62
c
are respectively connected via conductor patterns
63
and
64
to terminals
65
and
66
attached to the side plate
51
c
of the frame
51
.
An intermediate frequency signal input into the input terminal
61
a
of the SAW filter
61
is provided with predetermined selectivity characteristics in the SAW filter
61
, and the balanced signals are output from the output terminals
61
c
and
61
c
. The balanced signals are then input into the intermediate frequency signal input terminals
62
a
and
62
a
of the detector
62
and are detected by the detector
62
, thereby extracting a video signal V and a sound signal S.
However, the above conventional television tuner system presents the following problems.
The SAW filter
61
is located on the printed board
53
in such a manner that the terminals
61
a
,
61
b
,
61
c
and
61
c
are aligned substantially parallel to the two ground conductors
54
and
55
formed at the boundary of the two regions
53
a
and
53
b
of the printed board
53
. Accordingly, the output terminals
61
c
and
61
c
, as well as the input terminal
61
a
, of the SAW filter
61
are placed in proximity with the local oscillator (which is integrated within the IC component
58
) disposed in the region
53
a
. Thus, an oscillation signal output from the local oscillator may be accidentally input into the output terminals
61
c
and
61
c
of the SAW filter
61
, and the level of the signal is accordingly increased. The oscillation signal is then input into the detector
62
. Since the detector
62
is provided with a voltage controlled oscillator for synchronous detection, an unwanted interruption signal (beat signal) is generated due to the local oscillation signal from the detector
62
and the oscillation signal from the voltage controlled oscillator.
The ground terminal
61
b
of the SAW filter
61
is connected to the frame
51
with the ground conductor portion
55
a
therebetween, thereby increasing the distance from the ground terminal
61
b
to the frame
51
. According, the grounding effect of the ground terminal
61
b
is impaired. Thus, the selectivity characteristics of the SAW filter
61
are lowered, thereby failing to sufficiently attenuate the band in an adjacent channel.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to inhibit a local oscillation signal from being accidentally input into output terminals of a SAW filter, which would otherwise cause the generation of interruption signals, and also to maintain the performance of the SAW filter by preserving its selectivity characteristics.
In order to achieve the above object, according to the present invention, there is provided a television tuner system including a printed board disposed in a metallic frame having a side plate. A tuner has a mixer and a local oscillator and converts a received television signal into an intermediate frequency signal. An intermediate frequency circuit has at least a SAW filter and detects the intermediate frequency signal output from the tuner. The tuner and the intermediate frequency circuit are arranged adjacent to each other on the printed board. A first ground conductor is connected to the frame and is disposed on the printed board between the tuner and the intermediate frequency circuit in such a manner that it is disposed substantially perpendicular to the side plate. A second ground conductor is connected to the frame and is disposed along the side p
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Lo Linus H.
Miller John W.
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