Telecommunications – Receiver or analog modulated signal frequency converter – Frequency modifying or conversion
Reexamination Certificate
1999-03-04
2002-01-15
Trost, William (Department: 2683)
Telecommunications
Receiver or analog modulated signal frequency converter
Frequency modifying or conversion
C455S403000, C310S31300R, C333S193000, C333S195000
Reexamination Certificate
active
06339704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave device and a communication apparatus.
2. Description of the Related Art
As a conventional surface acoustic wave device, an inter-digital transducer structure (hereinafter referred to as IDT structure) as shown in
FIG. 14
has been known. In the IDT structure device, electrodes
71
to
77
including signal input terminals
71
and
72
and signal output terminals
73
and
74
formed in a comb line shape are disposed between reflectors
78
and
79
. In addition, a structure, where a serial resonator is connected to such an IDT structure surface acoustic wave device, is well known (see Japanese Patent Laid-Open Application No. 7-30367).
Such a surface acoustic wave device has been used as a filter of a mobile communication apparatus. Input terminals and output terminals of such a device are connected in an unbalanced state. However, in recent years, there are needs to use either or both input terminals and output terminals in a balanced state so as to directly connect such a filter to a peripheral circuit (for example, a mixer) disposed downstream thereof.
FIG. 15
is a schematic diagram showing the electrode structure of a surface acoustic wave filter having a serial resonator.
As shown in
FIG. 15
, the surface acoustic wave filter has balanced output terminals
53
and
54
. The balanced output terminals
53
and
54
are directly connected to leads of output IDTs
55
,
57
, and
59
. The balanced output terminals
53
and
54
are also connected to for example a balanced type mixer (not shown) disposed downstream of the balanced output terminals
53
and
54
. Input IDTs
56
and
58
are disposed among the output IDTs
55
,
57
, and
59
. The input IDTs
56
and
58
are connected to a low noise amplifier (LNA) disposed upstream thereof through a serial resonator
60
. Reflectors
70
are disposed outside the IDTs
55
to
59
. In addition, reflectors
70
are disposed outside the serial resonator
60
. In
FIG. 15
, L represents an aperture length. The aperture length L is the width of each transducer. Since the serial resonator
60
, located at the input side of the surface acoustic wave filter, widens the band width of a signal, the serial resonator
60
may be omitted depending on the band width of the signal.
When the input side of the filter is unbalanced and the output side of the filter is balanced, although an overvoltage at the unbalanced input terminals
51
and
52
is blocked by the serial resonator
60
, an overvoltage at the balanced output terminals
53
and
54
is directly applied to the IDTs
55
,
57
, and
59
.
If a part of the IDTs
55
,
57
, and
59
short-circuits due to discharging, a surge voltage, or the like, the performance of the filter deteriorates.
When the output side of the filter is balanced, the amplitude of an output signal of the balanced output terminal
53
in the case that the balanced output terminal
54
is terminated should be almost the same as the amplitude of an output signal of the balanced output terminal
54
in the case that the balanced output terminal
53
is terminated. In addition, the phase of the output signal of the balanced output terminal
53
in the case that the balanced output terminal
54
is terminated should be different by around 180° from the phase of the output signal of the balanced output terminal
54
in the case that the balanced output terminal
53
is terminated. These conditions are required to obtain a good balanced output signal.
However, depending on the number of electrodes (or the number of pairs) of the IDT
55
to
59
, the aperture length L thereof, and the polarities (directionality) thereof, an output signal of the balanced output terminal
54
may slightly differ from an output signal of the balanced output terminal
53
. Thus, it is difficult to adjust such factors for a good balanced output signal.
FIG. 16
shows another electrode structure of a surface acoustic wave device used as a filter. In the structure shown in
FIG. 16
, output IDTs
62
and
64
are disposed among input IDTs
61
,
63
, and
65
. However, the structure shown in
FIG. 16
is the same as that shown in
FIG. 15
except that the connecting method of leads of individual electrodes shown in
FIG. 16
is different from that shown in FIG.
15
. Thus, the same problem takes place against an overvoltage in the inverse direction.
Thus, in the conventional electrode structures, when an overvoltage in the inverse direction of a normal signal or noise is applied, the withstand voltage of the filter deteriorates.
In addition, it is difficult to satisfy conditions for a good balanced output signal and a good balanced input signal.
SUMMARY OF THE INVENTION
The present invention is made from the above-described point of view.
A first object of the present invention is to provide a surface acoustic wave device and a communication apparatus with an electrode structure that suppresses the withstand voltage from deteriorating against an overvoltage applied to a balanced terminal such as a balanced output terminal or a balanced input terminal.
A second object of the present invention is to provide a surface acoustic wave device and a communication apparatus that satisfy better balanced output conditions and better balanced input conditions.
To accomplish such objects, a first aspect of the present invention is a surface acoustic wave device, comprising an unbalanced input terminal to which a signal is added in an unbalanced state, an input transducer unit for exciting a surface acoustic wave with the electrical input added signal from the unbalanced input terminal, an output transducer unit for receiving the surface acoustic wave excited by the input transducer unit and obtaining a desired signal, a first balanced output terminal and a second balanced output terminal for outputting the desired signal obtained by the output transducer unit in a balanced state, a first resonator disposed between the first balanced output terminal and the output transducer unit, and a second resonator disposed between the second balanced output terminal and the output transducer unit.
A second aspect of the present invention is a surface acoustic wave device, comprising a first balanced input terminal and a second balanced input terminal to which a signal is added in a balanced state, an input transducer unit for exciting a surface acoustic wave with the signal added from said first balanced input terminal and said second balanced input terminal, an output transducer unit for receiving the surface acoustic wave excited by said input transducer unit and obtaining a desired signal, an unbalanced output terminal for outputting the desired signal obtained by said output transducer unit in an unbalanced state, a first resonator disposed between said first balanced input terminal and said input transducer unit, and a second resonator disposed between said second balanced input terminal and said input transducer unit.
A third aspect of the present invention is a surface acoustic wave device, comprising a balanced input terminal to which a signal is added in a balanced state, an input transducer unit for exciting a surface acoustic wave with the signal added from said balanced input terminal, An output transducer unit for receiving the surface acoustic wave excited by said input transducer unit and obtaining a desired signal, a first balanced output terminal and a second balanced output terminal for outputting the desired signal obtained by said output transducer unit in a balanced state, a first resonator disposed between said first balanced output terminal and said output transducer unit; and a second resonator disposed between said second balanced output terminal and said output transducer unit.
A fourth aspect of the present invention is a surface acoustic wave device, comprising an unbalanced input terminal to which a signal is added in an unbalanced state, a balanced output terminal from which a signal is put out in a balanced state, a latt
Kabushiki Kaisha Toshiba
Tran Conguan
Trost William
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