Electrical transmission or interconnection systems – Plural supply circuits or sources
Reexamination Certificate
1999-07-08
2001-08-07
Ballato, Josie (Department: 2836)
Electrical transmission or interconnection systems
Plural supply circuits or sources
C307S091000
Reexamination Certificate
active
06271603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a frequency conversion apparatus preferably used in a receiver or a transmitter which executes frequency conversion at least two times.
2. Description of the Related Art
FIG. 3
is a block schematic diagram of a conventional frequency conversion apparatus for, for example, a television signal transmitter. A metal case
51
is formed in a rectangular frame shape with side plates
51
a
and
51
b
opposing each other in one direction and side plates
51
c
and
51
d
opposing each other in the other direction. Three partitioned chambers
51
h
,
51
i
and
51
j
are formed in parallel with each other by being separated from each other by shield plates
51
e
to
51
g
, which are interposed between the side plates
51
a
and
51
b
in parallel with the side plate
51
c
. Further, partitioned chambers
51
m
,
51
n
,
51
o
and
51
p
are formed by being separated from each other by shield plates
51
k
and
51
l
which are disposed in a cross state in the region surrounded by the shield plate
51
g
and the side plates
51
a
,
51
b
and
51
d
. As a result, the partitioned chamber
51
h
is located adjacent to the side plate
51
c
and the partitioned chambers
51
o
and
51
p
are located adjacent to the side plate
51
d
. A printed circuit board (not shown) is disposed in each of the partitioned chambers and a circuit is formed on the printed circuit board.
A first mixer
52
and a first local oscillator
53
are disposed in the partitioned chamber
51
h
, and external signals, for example, intermediate frequency signals Si for television broadcasting images (for example, 45.75 MHz), are supplied to the first mixer
52
. The first local oscillator
53
supplies oscillation signals of about 1254 MHz to the first mixer
52
. As a result, the first mixer
52
outputs first intermediate frequency signals of about 1300 MHz.
A first-stage first intermediate frequency amplifier
54
and a first stage band-pass filter
55
are disposed in the partitioned chamber
51
i
adjacent to the partitioned chamber
51
h
. The first intermediate frequency signals are supplied to the first-stage first intermediate frequency amplifier
54
and then sent to the next partitioned chamber
51
j
through the first stage band-pass filter
55
.
A second-stage first intermediate frequency amplifier
56
and a second stage band-pass filter
57
are disposed in the partitioned chamber
51
j
. The first intermediate frequency signals are amplified with the second-stage first intermediate frequency amplifier
56
and further sent to the next partitioned chamber
51
m
through the second stage band-pass filter
57
.
The partitioned chamber
51
m
is located adjacent to the partitioned chamber
51
n
and these partitioned chambers
51
m
and
51
n
are located adjacent to the partitioned chamber
51
j
. The partitioned chamber
51
p
is located adjacent to the partitioned chamber
51
m
and the partitioned chamber
51
o
is located adjacent to the partitioned chamber
51
n
. The partitioned chamber
51
p
and the partitioned chamber
51
o
are located adjacent to the side plate
51
d.
A second mixer
58
is disposed in the partitioned chamber
51
m
, a second local oscillator
59
is disposed in the partitioned chamber
51
o
, an oscillation signal amplifier
60
is disposed in the partitioned chamber
51
n
, and a second intermediate frequency amplifier
61
is disposed in the partitioned chamber
51
p.
The first intermediate frequency signals having passed through the second stage band-pass filter
57
are supplied to the second mixer
58
.
In contrast, the oscillation signals from the second local oscillator
59
are amplified with the oscillation signal amplifier
60
and supplied to the second mixer
58
. The oscillation frequency of the second local oscillator
59
changes from about 1348 MHz to about 2305 MHz. Therefore, second intermediate frequency signals so having any frequency from about 50 MHz to about 1000 MHz are output from the second mixer
58
, amplified with the second intermediate frequency amplifier
61
and supplied to the outside from the partitioned chamber
51
p
. The second intermediate frequency signals So are transmitted to subscribers as cable television signals through a CATV cable (not shown).
A shield cover (not shown) is attached to the metal case
51
to integrally cover each of the partitioned chambers. The end surfaces of the shield plate
51
e
and the like are in contact with the shield cover when the shield cover is attached to the metal case
51
, whereby the respective partitioned chambers are shielded from each other.
Power is supplied to the first mixer
52
, the first local oscillator
53
, and the like disposed in the respective partitioned chambers through conductive patterns
62
(shown by thick lines in
FIG. 3
) formed on the printed circuit boards in the partitioned chambers.
Incidentally, while the two local oscillators
53
and
59
oscillate with a different frequency, they output a multiplicity of higher harmonics at the same time.
On the other hand, while the shield cover is attached to the metal case
51
, if small gaps exist between the end surfaces of the shield plate
51
e
, and the like of the metal case
51
and the shield cover, the higher harmonics from, for example, the first local oscillator
53
disposed in the partitioned chamber
51
h
, enter the partitioned chamber
51
m
, in which the second mixer
58
is disposed, through the gaps of the three shield plates
51
e
,
51
f
and
51
g.
Further, the oscillation signals from the second local oscillator
59
are also supplied to the second mixer
58
and the higher harmonics are also supplied thereto.
For example, when the second local oscillator
59
oscillates with a frequency of 1904 MHz to set the frequency of the second intermediate frequency signals to about 604 MHz, if the second higher harmonics (frequency: 2508 MHz) of the first local oscillator
53
are supplied to the second mixer
58
, beat signals having a frequency which is the difference therebetween (2508−1904=604 MHz) are generated by the second mixer
58
. The signals act as interference signals to the second intermediate frequency signals of 604 MHz.
SUMMARY OF THE INVENTION
An object of the present invention is to reduce interference caused by the existence of two local oscillators without increasing the size of a metal case.
To solve the above problem a frequency conversion apparatus of the present invention comprises a first metal case having a first accommodating site and a second accommodating site; a first frequency conversion section disposed in the first accommodating site and having a first oscillator; a second frequency conversion section disposed in the second accommodating site and having a second oscillator; double shield plates standing between the first accommodating site and the second accommodating site; and a first power supply line disposed in a partitioned chamber surrounded by the double shield plates. Power is supplied from the first power supply line to the first frequency conversion section and the second frequency conversion section.
In a preferred embodiment, the frequency conversion apparatus of the present invention comprises a second metal case which is larger than the first metal case, wherein the first metal case is accommodated in the second metal case, a second power supply line is interposed between the first metal case and the second metal case, the first power supply line is connected to the second power supply line, and power is supplied from the first power supply line and the second power supply line to the first frequency conversion section and the second frequency conversion section.
In a preferred embodiment, the frequency conversion apparatus of the present invention comprises a first shield cover attached to the first metal case for covering the first accommodating site, the second accommodating site and the partitioned chamber, and a second shield cover attached to the second metal
Alps Electric Co. ,Ltd.
Ballato Josie
Brinks Hofer Gilson & Lione
Polk Sharon
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