Tuner structure and cable modem tuner using the same

Details Tuner structure and cable modem tuner using the same Tuner structure and cable modem tuner using the same

2000-04-12

2001-10-09

Gandhi, Jayprakash N. (Department: 2841)

Electricity: electrical systems and devices

Housing or mounting assemblies with diverse electrical...

For electronic systems and devices

C361S752000, C334S085000, C455S090300

Reexamination Certificate

active

06301117

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a so-called “tuner” or a front end of a radio frequency (RF) receiver section integrated into a television transmitter/receiver or the like, and more particularly relates to a tuner structure with a reduced thickness and a cable modem tuner using the same.
2. Description of the Related Art
An exemplary conventional tuner structure is shown in
FIG. 18
, from which a shield cover has been omitted. As shown in
FIG. 18
, a circuit board
50
formed by mounting various circuit components (the respective circuit components are not shown) including resistors, capacitors, coils and transistors on a printed circuit board is incorporated into a chassis angle
51
(or the sides of a chassis disposed vertically with respect to the circuit board
50
) having a folded metal plate structure. In general, a shield plate for isolating the internal circuits is also formed as an integral part of the chassis angle
51
. A signal received through an antenna or the like is input through a connector
52
mounted onto a side of the chassis angle
51
. In addition, terminals are also provided for supplying power, connecting control signals and retrieving output signals for the internal circuits. As the terminals, capacitor integrated terminals of a special type called “feedthrough capacitors (or feedthrough terminals)”
53
are used.
A tuner generally has an oscillator circuit therein. As a result, radio waves leak out of the tuner through the power supply terminals thereof and the like, thereby causing unnecessary radiation. In addition, when a noise is received through the terminals of the tuner, the noise is adversely mixed into the output of the tuner so that the output signal thereof is deteriorated. The feedthrough terminals (or feedthrough capacitors)
53
are provided for dealing with these problems.
The chassis angle
51
, together with the shield cover, covers the body of the tuner and provides a satisfactory ground potential having a low impedance in an RF region. The feedthrough capacitor
53
has such a cross-sectional structure as that shown in FIG.
19
. In the feedthrough capacitor
53
, a terminal bar
53
A extends through a dielectric
54
and an inner electrode
55
inside the dielectric
54
is satisfactorily electrically conductive with the terminal bar
53
A via a solder layer
56
formed around the terminal bar
53
A. On the other hand, an outer electrode
57
of the dielectric
54
is satisfactorily electrically conductive with the chassis angle
51
via a solder connection
58
.
FIGS. 20A and 20B
respectively show a method for evaluating the grounding effects for a case of using a feedthrough capacitor
53
and a case of using a chip capacitor
49
formed as a separate component. As shown in
FIGS. 20A and 20B
, the measurement is performed by connecting an RF signal source
202
(having a signal source impedance of 50&OHgr;) to a level meter
204
(having a load impedance of 50&OHgr;), inserting a capacitor to be tested between a signal line and a ground therebetween, and sweeping a frequency from 0 GHz to 3 GHz. The capacitor is connected to a pair of coaxial cables
48
having an impedance of 50&OHgr; connected to the RF signal source
202
and the level meter
204
, respectively.
FIGS. 21A and 21B
respectively show the measurement results for the case of using the feedthrough capacitor
53
and the case of using the chip capacitor
49
. As seen from these figures, in the case of using the feedthrough capacitor
53
, more satisfactory attenuation characteristics are realized in the frequency region of about 0.5 GHz or higher. The reason is presumably as follows. Since the outer electrode
57
of the feedthrough capacitor
53
is directly connected to the chassis angle
51
of the tuner, no parasitic inductance is generated therebetween so that satisfactory grounding effects are realized.
On the other hand, in the case where a capacitor formed as a separate component (e.g., the chip capacitor
49
) is provided between a terminal and a ground instead of using the feedthrough capacitor
53
, the same effects as those of the feedthrough capacitor
53
can be surely attained in a low frequency region. However, since a copper case pattern inevitably exits when the electrode of the chip capacitor
49
is connected to a terminal or a ground and the capacitor
49
itself has a metal electrode pattern therein, these patterns function as parasitic inductances. As a result, in a high frequency region (e.g., 0.5 GHz or higher) where the influence of these parasitic inductances is not negligible, expected attenuation characteristics cannot be attained.
The tuner may be mounted onto a main substrate
64
either in a vertical mount fashion shown in
FIGS. 22A and 22B
or in a horizontal mount fashion shown in
FIGS. 23A and 23B
.
FIG. 22A
is a plan view showing a side on which an input terminal or the connector
52
has been mounted, while
FIG. 22B
is a plan view showing the side orthogonal to the side shown in FIG.
22
A. On the other hand,
FIG. 23A
is a plan view showing the side on which an input terminal or the connector
52
has been mounted, while
FIG. 23B
is a plan view showing the side orthogonal to the side shown in FIG.
23
A. The horizontal mount fashion shown in
FIGS. 23A and 23B
is used for a case where the space in the direction vertical to the substrate
64
on which the tuner is mounted is limited. For example, this type of mount is used for mounting a tuner onto an extended board of a personal computer.
FIG. 26
shows an exemplary internal structure of a conventional tuner structure to be mounted onto a substrate
64
in the horizontal mount fashion shown in
FIGS. 23A and 23B
. Chip components
60
and insert components
61
such as coils have been mounted onto a circuit board
50
. A feedthrough capacitor
53
has been attached to a chassis angle
51
disposed vertically to the circuit board
50
. The leg
53
a
of the feedthrough capacitor
53
is folded at a right angle, thereby electrically and mechanically connecting the feedthrough capacitor
53
to the main substrate
64
. The outer sides of the tuner are covered with shield covers
65
and the tuner is electrically and mechanically connected to the main substrate
64
via the leg
51
a
of the chassis angle
51
.
Next, a representative wiring process for assembling a tuner will be briefly described.
1) First, the chip components
60
and the insert components
61
, such as coils which have been provisionally adhered to the circuit board
50
inside the tuner, are connected by a flow soldering method in which copper foil pattern surface of the circuit board
50
is immersed in a solder tank filled with molten solder.
2) Second, the extra line portion of a reed line of each of the insert components
61
such as coils is cut off.
3) Finally, the circuit board
50
is inserted into the chassis angle
51
to which the feedthrough capacitors
53
and the input connector
52
have been attached. Then, the circuit board
50
is connected to chassis angle
51
, the terminals of the feedthrough capacitors
53
are connected to the terminal of the input connector
52
by a similar flow soldering method to that described in 1).
However, a conventional tuner structure has the following problems.
For example, in the tuner structure of the horizontal mount type shown in
FIGS. 23A and 23B
, since the feedthrough capacitors
53
extend from a side of the chassis angle
51
, the legs
53
a
thereof to be used as terminals are required to be folded. In the case of employing such a tuner structure, the following disadvantages cannot be prevented.
1) Since the terminals
53
a
protrude from the chassis angle
51
, the area of the main substrate
64
required for mounting the tuner thereon is increased.
2) The terminals
53
a
protruding from the chassis angle
51
are so long that the positions of the terminals
53
a
possibly deviate because of the contact of the terminals
53
a
with something during the fabrication proces

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