Wave transmission lines and networks – Coupling networks – Frequency domain filters utilizing only lumped parameters
Reexamination Certificate
2002-04-25
2004-04-13
Ham, Seungsook (Department: 2817)
Wave transmission lines and networks
Coupling networks
Frequency domain filters utilizing only lumped parameters
C333S174000, C333S101000
Reexamination Certificate
active
06720843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a filter switching circuit for selecting one of a plurality of bandpass filters having different frequency bands that allow signals to pass through them.
2. Description of the Related Art
When using television signals on many channels arranged in a broad frequency band, a television signal transmitter divides the television signals into a plurality of smaller bands for transmission in order to prevent disturbance from occurring due to a beat signal between television signals on each channel, harmonics, etc. Accordingly, a plurality of bandpass filters for transmitting the signals in the smaller bands are provided, and one of the bandpass filters is selected.
FIG. 2
shows a conventional filter switching circuit that selects one of a plurality of bandpass filters and connects the selected one between two amplifiers. A printed circuit board
51
has a first amplifier
52
and a second amplifier
53
thereon, with a distance provided therebetween. The first amplifier
52
is formed in an almost rectangular area having a longitudinal dimension Y
1
and a lateral dimension X
1
, and the second amplifier
53
is formed in an almost rectangular area having a longitudinal dimension Y
2
and a lateral dimension X
2
. The output end
52
a
of the first amplifier
52
and the input end
53
a
of the second amplifier
53
are opposed to each other.
In an area between the first amplifier
52
and the second amplifier
53
, on a side (the lower side in
FIG. 2
) to a straight line (not shown) connecting the output end
52
a
and the input end
53
a
, a plurality of bandpass filters (called a “bandpass filter
54
-
1
” to a “bandpass filter
54
-
8
” from the top) (hereinafter referred to also as “bandpass filters
54
” for denoting the entirety of the bandpass filters
54
-
1
to
54
-
8
) are provided in parallel so as to be almost perpendicular to the straight line and to have equal distances to the output end
52
a
and the input end
53
a.
The bandpass filters
54
are designed so that eight bands obtained by dividing a frequency range (e.g., 50 MHz to 600 MHz) can pass through them. The bandpass filter
54
-
1
has the highest frequency passband (510 MHz to 600 MHz).
The bandpass filters
54
-
2
to the
54
-
7
have sequentially lower frequency passbands, and the bandpass filter
54
-
8
has the lowest frequency passband (50 MHz to 60 MHz).
Between the first amplifier
52
and the bandpass filters
54
, a plurality of relays
55
-
1
to
55
-
7
(hereinafter referred to also as “relays
55
” for denoting the entirety of the relays
55
-
1
to
55
-
7
) respectively corresponding to the bandpass filters
54
-
1
to
54
-
7
are provided. Between the bandpass filters
54
and the second amplifier
53
, a plurality of relays
56
-
1
to
56
-
7
(hereinafter referred to also “relays
56
” for denoting the entirety of the relays
56
-
1
to
56
-
7
) respectively corresponding to the bandpass filters
54
-
1
to
54
-
7
are provided.
The relays
55
and
56
consist of, for example, relays having identical structures. Each of the relays
55
and
56
includes a switching terminal a, two fixed terminals to which the switching terminal a selectively connects, that is, a first fixed terminal b and a second fixed terminal c.
Among the relays
55
, only the switching terminal a of the relay
55
-
1
is connected in the smallest distance to the output end
52
a
. The other relays
55
-
2
to
55
-
7
are connected to the output end
52
a
in seven stages in cascade such that their switching terminals a are sequentially connected to their second fixed terminals c when these are connected to the output end
52
a.
Similarly, among the relays
56
, only the switching terminal a of the relay
56
-
1
is connected in the smallest distance to the input end
53
a
. The other relays
56
-
2
to
56
-
7
are connected to the input end
53
a
in seven stages in cascade such that their switching terminals a are sequentially connected to their second fixed terminals c when these are connected to the input end
53
a.
The bandpass filter
54
-
1
having the highest frequency passband is connected between the first fixed terminals b of the relays
55
-
1
and
56
-
1
, and the bandpass filter
54
-
2
having the second highest frequency passband is connected between the first fixed terminals b of the relays
55
-
2
and
56
-
2
. Similarly, the bandpass filters
54
-
3
to
54
-
6
, which have sequentially lower frequency passbands, are connected between the relays
55
and the relays
56
. The bandpass filter
54
-
8
is connected between the second fixed terminals c of the relays
55
-
7
and
56
-
7
.
The switching terminals a of pairs of corresponding relays, that is, a pair of the relays
55
-
1
and
56
-
1
to a pair of the relays
55
-
7
and
56
-
7
are switched in cooperation so as to be connected to their first fixed terminals b or their second fixed terminals c.
For example, the relay
55
-
1
and the corresponding relay
56
-
1
in the first stage are switched in cooperation, and the relay
55
-
2
and the corresponding relay
56
-
2
are switched in cooperation. Similarly, the other pairs of relays are switched.
In the above structure, a bandpass filter having a higher frequency passband is connected by a smaller number of relays to the output end
52
a
and the input end
53
a
in the smallest distance. Therefore, also in a case in which the frequency of a signal to be transmitted is high, signal loss and level deterioration are reduced. In addition, influence on characteristics of the relays
55
and
56
, such as a cutoff frequency and transmission loss, are reduced.
“Nevertheless, in the above structure, the bandpass filter having a higher frequency passband is selected by a smaller number of relays. However, since the bandpass filters
54
and the relays
55
and
56
are provided on one side to the straight line connecting the output end
52
a
of the first amplifier
52
and the input end
53
a
of the second amplifier
53
, a space B is formed on the other side between the first amplifier
52
and the second amplifier
53
is formed. Accordingly, the space-using efficiency of the printed circuit board
51
deteriorates, thus causing a problem in that the entire size of the printed circuit board
51
enlarges.”
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a switching circuit that selects a bandpass filter having a higher frequency passband by using a smaller number of relays and connects between two amplifiers in a distance as shortest as possible.
To this end, according to an aspect of the present invention, the above object is achieved through provision of a filter switching circuit including a first amplifier formed on a printed circuit board, a second amplifier formed on the printed circuit board separately from the first amplifier, the second amplifier having an input end opposed to the output end of the first amplifier, a plurality of filters having different frequency passbands, and a plurality of relays each having two fixed terminals and a switching terminal for connecting to one of the fixed terminals, the relays connecting one of the filters between the output end and the input end. The filters and the relays are arranged in parallel in columns in an area between the first amplifier and the second amplifier on the printed circuit board so as to cross a straight line connecting the output end and the input end so that one relay among the relays is positioned almost on the straight line while the switching terminal of the one relay is connected to the output end or the input end, and the other relays are connected in cascade to one fixed terminal of the one relay by connecting each switching terminal thereof to either fixed terminal while connecting each of the filters to the other fixed terminal, whereby the frequency passbands of filters having closer connections to the one relay are sequentially higher increased.
According to another aspect of the present
Alps Electric Co. ,Ltd.
Brinks Hofer Gilson & Lione
Ham Seungsook
Takaoka Dean
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