Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2000-04-28
2002-04-30
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S193000
Reexamination Certificate
active
06380823
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an antenna duplexer and, more particularly, to an antenna duplexer constructed of a combination of antenna duplexers which include surface acoustic wave (SAW) filters used for mobile communication devices.
2. Description of the Related Art
With recent development of mobile communication systems, mobile phones, portable communication terminals and other mobile communication devices have been rapidly coming into widespread use. Because these devices are desired to be smaller in size and more powerful in performance, components used in these devices are also required to be reduced in size and improved in performance.
As regards mobile phones, two kinds of radio communication systems, i.e., digital and analog, are employed, and a diversity of frequencies in a 800 MHz to 1 GHz band and a 1.5 GHz to 2.0 GHz band are used for radio communications.
In mobile communication devices, antenna duplexers are used as components in RF sections which branch and generate signals transmitted and received through antennae.
FIG. 30
is a block diagram illustrating the construction of a high frequency part of a conventionally used mobile phone.
Audio signals
100
input from a microphone are modulated into modulated signals by a modulator
101
according to a modulation system of the mobile phone, and further converted to a designated carrier frequency by a local oscillator
108
. Thereafter the converted audio signals pass through an interstage filter
102
for selecting signals of the designated transmitting frequency alone, are amplified to a desired signal amplitude by a power amplifier
103
and sent to an antenna duplexer
105
. The antenna duplexer sends signals of the designated transmitting frequency alone to an antenna
104
, from which the signals are transmitted into the air as radio signals.
On the other hand, signals received by the antenna
104
are sent to the antenna duplexer
105
, where only signals of a designated frequency are selected. The selected signals are amplified by a low-noise amplifier
106
and passed through an interstage filter
107
. Only speech signals are selected by an IF filter and taken out as audio signals
100
by a demodulator
111
. The antenna duplexer
105
is located between the antenna
104
and what is called an audio signal processing circuit, and has the functions of distributing transmitted and received signals and avoiding their interference.
Further, for responding to diversification of radio communication systems, dual-mode and dual-band techniques are employed for imparting higher-levels of functions to mobile phones.
The dual-mode technique means, for example, a technique for providing a single mobile phone with analog/digital compatibility or TDMA (time-division multiplexing access)/CDMA (code-division multiplexing access) compatibility in digital communications.
The dual-band technique means a technique for providing a single mobile phone with access to two bands, for example, 800 MHz band and 1.9 GHz band, or 900 MHz band and 1.8 GHz band (or 1.5 GHz band).
For supporting such high-levels of functions of mobile phones, it is demanded that filters used for mobile phones also have a dual-port or dual-band function (hereinafter the phase “have a dual function” is used for indicating having either function). As filters having a dual function, filters having two inputs and two outputs and filters having one input and two outputs have been developed. As regards the one-input two-output filters, a phase matching circuits is usually added outside the filters because terminals on a commonized side must be gathered together.
In the case of filters used between stages in the RF section for branching and generating signals from/to the antenna, an IF section and other sections (so-called interstage filters), combinations of transmitting filters alone and combinations of receiving filters alone are put to practical use as dual-function filters.
For providing the dual-band access to antenna duplexers, antenna duplexers have been developed which uses dielectric duplexers for branching and generating signals of least one pass band.
FIG. 27
shows the construction of a dual-function antenna duplexer D
3
which is composed of a duplexer D
1
for branching and generating signals of a higher pass band frequency and a duplexer D
2
for branching and generating signals of a lower pass band frequency.
Here, PA denotes a power amplifier, LNA denotes a low-noise amplifier, and SW
1
, SW
2
and SW
3
denote circuit changing switches. The duplexers D
1
and D
2
are each composed of a transmitting filter (T
1
or T
2
), a receiving filter (R
1
or R
2
) and a phase matching circuit (L
1
or L
2
).
In the North American PCS system and the European DCS1800 system which require a narrow frequency band gap (or transition band) between transmitting and receiving pass band frequencies, if dielectric duplexers are used, the size of the duplexers themselves becomes as large as about 2.8 cm×0.9 cm×0.5 cm, which prevents reduction in size and in thickness of portable terminal devices.
Also antenna duplexers have been developed in which SAW filters are used for the transmitting filters (T
1
, T
2
) and the receiving filters (R
1
, R
2
) shown in FIG.
27
.
As such duplexers constructed with use of SAW filters, proposed are module-type duplexers in which two SAW filters and matching circuits are packaged on printed circuit boards and one-piece duplexers in which two SAW filters of a bare type are mounted in multi-layered ceramic packages and matching circuits are mounted within the packages. Such SAW filters can be reduced in size and thickness to a volume of about one-third to about one-fifth of that of dielectric filters and to a thickness of about half to about one-third of that of the dielectric filters.
In
FIG. 27
, one duplexer D
1
has three terminals ANT
1
, Tx
1
, Rx
1
and grounding terminals, not shown. These terminals and external terminals (SW
1
, SW
2
, SW
3
, PA, etc.) are connected to a filter chip via terminals provided to the package by wire bonding or the like.
One duplexer as shown in
FIG. 27
is a so-called three-port device having three terminals ANT
1
, Tx
1
and Rx
1
. In the antenna duplexer D
3
having two of such duplexers in combination, it is difficult to construct circuits so as to separate a transmitting circuit (Tx
1
, Tx
2
, SW
2
and PA), a receiving circuit (Rx
1
, Rx
2
, SW
3
, LNA) and an antenna circuit (SW
1
, ANT
2
, ANT
2
) from the viewpoint of connection to external circuits.
In other words, an inappropriate arrangement of the connecting terminals such as Tx
1
, Rx
1
and the like may lead to crossing of connecting wires, which results in interference of signals and/or generation of noises. Consequently, desired filter characteristics may not be obtained.
A well-designed wiring on printed circuit boards for mounting filter chips may enable the separation of the above-mentioned three circuits to some extent. However, at the stage of designing circuit boards, it is extremely difficult to decide patterns and layouts for the circuits with considering interference between signals and required specifications of a small-sized dual-function antenna duplexer.
Therefore, for responding to demand for dual function and size reduction, it is necessary to contrive a clever arrangement of connecting terminals on the package of the antenna duplexer D
3
containing the two duplexers D
1
and D
2
.
As regards SAW filters used for the transmitting filter T
1
and the receiving filter R
1
of the duplexer, in general, size reduction is considered to be possible if an increased number of filter chips are mounted in one filter package or if an increased number of SAW filters are formed on one filter chip.
However, even if a large number of SAW filters are formed on each of filter chips which are then made into two pairs of transmitting filters and receiving filters, further idea is still necessary for avoiding interference between the filter characteristics
Ikata Osamu
Matsuda Takashi
Nishihara Tokihiro
Satoh Yoshio
Armstrong Westerman & Hattori, LLP
Fujitsu Limited
Lee Benny
Summons Barbara
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