Electricity: electrical systems and devices – Housing or mounting assemblies with diverse electrical... – For electronic systems and devices
Reexamination Certificate
2002-07-24
2004-09-28
Martin, David (Department: 2841)
Electricity: electrical systems and devices
Housing or mounting assemblies with diverse electrical...
For electronic systems and devices
C361S816000, C361S818000, C174S034000, C174S051000, C455S188100, C455S283000
Reexamination Certificate
active
06798668
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to receiving apparatuses for satellite broadcasting. More specifically, the invention relates to receiving apparatuses having a capability of receiving a plurality of video signals and outputting other signals to a plurality of tuners.
BACKGROUND OF THE INVENTION
A radio wave transmitted from a satellite includes at least one polarized wave, and each polarized wave has a video signal. For example, there are several types of polarized waves such as a vertically polarized wave and a horizontally polarized wave (V•H) and a right-hand circularly polarized wave and a left-hand circularly polarized wave (R•L).
Among receiving apparatuses for satellite broadcasting which receive radio waves transmitted from a satellite, there is one type of receiving apparatus for satellite broadcasting with one Low Noise block downconverter (hereinafter referred to as LNB) which receives signals transmitted from a plurality of satellites. Also, there is another type of receiving apparatus for satellite broadcasting with an LNB which extracts a plurality of IF signals (video signal) by utilizing two or more local oscillating circuits having respectively different oscillation frequencies. Currently, the dominating receiving apparatus for satellite broadcasting is the type of apparatus with one LNB which extracts a plurality of video signals (two kinds, four kinds, or more of video signals).
FIG. 1
shows an example of a circuit configuration of the type of LNB which outputs a plurality of IF signals.
The LNB in the example mainly includes the following circuits parts.
(1) Low Noise Amplifiers (hereinafter referred to as LNAs)
1
a
and
1
b
: Amplify weak signals (of 10 GHz band) transmitted from satellites in low noise characteristic.
(2) Band Pass Filters (hereinafter referred to as BPFs)
2
a
and
2
b
: Band-limit the signals amplified in low noise characteristics.
(3) Local oscillating circuits
4
a
and
4
b
: Produce a reference frequency (local signal) for downconverting.
(4) Mixer circuits
3
a
and
3
b
: Mix the signals amplified in the LNA with the local signal, and convert (downconvert) the resultant signals into IF signals (of 1 GHz band).
(5) Switch circuit
5
: Extracts the IF signal selected by a tuner (not shown), which is connected to output terminals
7
a
and
7
b
, from among the signals converted in the mixer circuits
3
a
and
3
b
, and the extracted IF signal is sent to the IF amplifiers
6
a
and
6
b.
(6) IF amplifiers
6
a
and
6
b
: Amplify the IF signal extracted in the switch circuit
5
to output it to the output terminals
7
a
and
7
b.
Incidentally, the receiving apparatus that receives radio waves transmitted from satellites has the problem of isolation characteristic. The isolation characteristic is a capability of preventing the entrance of undesired signals as opposed to desired signals. In the receiving apparatus, it is ideal that undesired signals not being selected never leak out. However, in fact, undesired signals in the range of approximately 20 to 30 dB enter into the terminal to which desired signals should be inputted, because of problems caused by the circuit configuration and the member arrangement in the receiving apparatus.
In order to obtain a better isolation characteristic of the receiving apparatus, it is necessary not only to make the isolation characteristic of the switch circuit
5
better, but also to prevent the video signals after being amplified by the IF amplifiers
6
a
and
6
b
from entering into the respective output terminals
7
b
and
7
a
that are not appropriate terminals to which the IF amplifiers
6
a
and
6
b
should be inputted. However, a conventional receiving apparatus has found a difficulty of achieving this. The reason of the difficulty will be described below.
First, to maintain hermeticity, a receiving apparatus must be generally hermetic in a space where a circuit substrate is included. Conventional methods for hermetically sealing are the following methods: one is the method in which a metallic lid (hereinafter referred to as a back lid
8
) is fixed to a chassis
10
with a packing
9
, as shown in
FIG. 2
(in
FIG. 2
, note that, a reference numeral
10
b
is a groove where the packing is placed); or another is the method in which while a bottom part of the back lid
8
is fit into a groove
10
c
, a seal adhesive such as silicon is filled so that the back lid
8
is fixed to the chassis
10
, as shown in FIG.
3
. These methods for hermetically sealing cause an electrically poor connection between the back lid
8
and the chassis
10
. Accordingly, in these methods for hermetically sealing, the back lid
8
is insufficiently grounded in a radio-frequency band, so that the receiving apparatus is prone to the occurrence of resonance.
Because of this, in the conventional receiving apparatus, there is a high possibility that factors such as resonance cause the video signals selected by the tuner which is connected to one output terminal to enter into the other output terminal, when a back lid that is grounded insufficiently is fit to the receiving apparatus. Therefore, even if the receiving apparatus without the back lid realizes a high isolation characteristic (of, for example, 40 dB or more), the receiving apparatus with the back lid is difficult to realize a high isolation characteristic.
Here, as a technique for shielding a receiving apparatus, Japanese Unexamined Patent Application No. 308219/1993 (Tokukaihei 5-308219, published on Nov. 19, 1993) discloses a microwave detector which realizes a minimum length of connecting path between the mixing diode and an intermediate frequency processing circuit portion, as well as excellent operation with avoiding generation of the noise without a first intermediate frequency filter being affected by an antenna input and/or the output of a first local oscillator. The microwave detector has such a structure that the intermediate frequency processing circuit is installed around an extended portion of the mixing diode on the lower surface of a printed circuit board, that a shield casing is mounted directly on the lower surface side of the printed circuit board in such a manner that it may cover the intermediate frequency processing circuit portion, and that a metal layer is formed on the upper surface of the printed circuit board, thereby completely shielding the intermediate frequency processing circuit.
Also, Japanese Unexamined Patent Application No. 38827/1995 (Tokukaihei 7-38827, published on Feb. 7, 1995) discloses an IF substrate incorporating tuner. To prevent the leakage of spurious radiation to the IF substrate, the IF substrate incorporating tuner has such a structure that a tuner substrate and an IF substrate are shielded from each other by a shield plate, and the tuner substrate and the IF substrate are connected via through capacitor provided on the shield plate. The feature of the invention is that the through capacitor as a connecter section makes it possible to almost completely shield the tuner substrate, thereby preventing the leakage of oscillator to the IF substrate and the deterioration of the radiation.
Furthermore, Japanese Unexamined Patent Application No. 163755/1999 (Tokukaihei 11-163755, published on Jun. 18, 1999) discloses an up/down tuner. To reduce a local oscillator circuits of up converter and a down-converter affecting each other, and inflow noise that comes into the tuner from the outside, the up/down tuner has a structure that an up converter part and a down converter part are connected to each other by an IF connecting part which makes a coaxial shielded structure (a structure that a signal line is shielded by an electrically conductive material grounded).
However, the techniques described in the above patent applications relates to reduction of the noise from other circuits, the leakage of spurious radiation, and inflow noise that comes from the outside, in other words, relates to noise-resistant characteristic. That is, the techniques described in the above patent appli
Bui Hung
Martin David
Sharp Kabushiki Kaisha
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