Multiplexer/branching filter

Details Multiplexer/branching filter Multiplexer/branching filter

2000-02-28

2002-01-01

Bettendorf, Justin P. (Department: 2817)

Wave transmission lines and networks

Plural channel systems

Having branched circuits

C333S132000, C333S185000

Reexamination Certificate

active

06335663

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a multiplexer/demultiplexer for use in mobile communication devices such as portable telephones.
BACKGROUND OF THE INVENTION
FIG. 14
represents a circuit construction of a conventional multiplexer/demultiplexer. In
FIG. 14
, the circuit is comprised of a low-pass filter
101
, a high-pass filter
102
, phase shifters
103
,
104
, input terminals
105
,
106
, and an output terminal
107
. Here, low-pass filter
101
and high-pass filter
102
are configured as &pgr;-shaped 3-stage circuits.
In a filter of this configuration, as the filter functions closer to short-circuiting as the signal frequency goes away from the pass band, it will not function as a multiplexer/demultiplexer by simply connecting each filter as it is. Accordingly, by connecting phase shifters
103
,
104
as shown in
FIG. 14
on the side the filters are mutually connected, the phase of a signal outside of the pass band is shifted by about 180 degrees thereby to open the circuit. Phase shifters
103
and
104
are comprised of a transmission line such as a strip line.
However, this configuration suffered serious problems of difficulty in miniaturization because of the larger size of transmission lines composing phase shifters
103
,
104
compared with other components and of a large loss due to longer line lengths.
SUMMARY OF THE INVENTION
The present invention is directed to providing an easy-to-miniaturize, low loss, high-performance multiplexer/demultiplexer.
In order to achieve the above purpose, the multiplexer/demultiplexer of the present invention includes first to third ports each externally terminated with a pure resistance, in which the third port is made to be a common port by connecting a first resonant circuit between the first port and the ground. The first resonant circuit makes serial resonance at a frequency within a first frequency band or in its proximity. An inductive element is connected in series between the first port and the third port, and a second resonant circuit is connected between the second port and the ground. The second resonant circuit makes serial resonance at a frequency within a second frequency band which is different from the first frequency band or in its proximity. A capacitive element is connected in series between the third port and the second port. This way, it is made possible to easily obtain a small and high-performance multiplexer/demultiplexer with a simple circuit with an exceptionally small number of elements without using a transmission line which tends to cause a loss.


REFERENCES:
patent: 5880649 (1999-03-01), Tai
patent: 6140891 (2000-10-01), Nakakubo
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patent: 3-123201 (1991-05-01), None
patent: 4-207806 (1992-07-01), None
patent: 7-122905 (1995-05-01), None
patent: 9-153842 (1997-06-01), None
Dipl.-Ing. Max Borchert, entitled “HF-Weichen, ein Überblick über Probleme und Schaltugen Teil II”, Radio Mentor, vol. 26, No. 5, May 1960, pp. 378-382.

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