Wave transmission lines and networks – Plural channel systems – Having branched circuits
Reexamination Certificate
2001-03-05
2003-08-12
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Plural channel systems
Having branched circuits
C333S193000, C333S195000
Reexamination Certificate
active
06606016
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave device for use as a band-pass filter, and more particularly, to a surface acoustic wave device including a plurality of band-pass filters.
2. Description of the Related Art
In recent years, multiband-capable portable telephones which include a plurality of communication systems have been developed. Furthermore, with the increase in the number of subscribers, portable telephones using a plurality of frequency bands such as the 800 MHz band of the Japanese PDC have also been developed.
These portable telephones are required for wide-band interstage band-pass filters in order to cover a plurality of frequency bands.
Moreover, in recent portable telephones, systems in which the transmission-side frequency band and the reception-side frequency band are close to each other increase in the number, and hence it is necessary to increase the steepness of the filter characteristics in the immediate vicinity of a desired pass band.
Japanese Unexamined Patent Application Publication No. 9-121138 discloses an example of a filter device capable of covering a plurality of pass bands.
FIG. 17
is a circuit diagram for explaining the filter device according to this conventional art. Herein, the input terminal and the output terminal of filter elements
101
and
102
each including a surface acoustic wave filter are each shared between these filter elements
101
and
102
. Specifically, the input ends of the filter elements
101
and
102
are connected to the input terminal
103
, and the output ends of the filter elements
101
and
102
are connected to the output terminal
104
. By causing the input terminal and output terminal to be shared between the filter elements
101
and
102
, a reduction in the size and weight of a radio-signal portion is achieved.
Transmission lines
105
and
106
are connected between the input terminal
103
and one filter element
101
, and between the output terminal
104
and the one filter element
101
, respectively. Also, a capacitor
107
is connected between the filter element
102
and the input terminal
103
, and an inductance element
108
is connected between the connection point between the input terminal
103
and the capacitor
107
and the ground potential. Similarly, a capacitor
109
is connected between the output end of the filter element
102
and the output terminal
104
, and an inductance element
110
is connected between the connection point between the capacitor
109
and the output terminal
104
and the ground potential.
That is, phase adjusting circuits including the transmission lines
105
and
106
are connected between the filter element
101
and the input terminal
103
and the output terminal
104
, respectively. Also, phase adjusting circuits including the capacitor
107
and the inductance element
108
, and phase adjusting circuits constituted of the capacitor
109
and the inductance element
110
are connected between the filter element
102
and the input terminal
103
and the output terminal
104
, respectively.
By providing the above-described phase adjusting circuits, each of the filter elements
101
and
102
is brought into a high impedance state in the band where it is not required, whereby superior pass band characteristics are obtained.
In addition, in the filter device according to this conventional art, a structure in which the above-described capacitors
107
and
109
and inductance elements
108
and
110
are disposed inside or outside the package of the filter device, or a structure in which the above-described transmission lines
105
and
106
are disposed on the laminated portion of the package, is disclosed.
However, as described in the above-described conventional art, when capacitors and inductance elements are provided inside or outside the package of the filter device in order to form phase adjusting circuits, the package itself inevitably becomes large, or the mounting area when the filter device is mounted on a circuit board of a portable telephone or other device must become large.
Also, when the transmission lines are disposed on the laminated portion of the package, fine-adjustments of the impedance cannot be performed if another surface acoustic wave filter is mounted on the same package. This requires that an exclusive package for each filter to be mounted must be used.
SUMMARY OF THE INVENTION
In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave device including a plurality of surface acoustic wave filters having different center frequencies and sharing an input terminal and an output terminal therebetween, the plurality of surface acoustic wave filters being connected in parallel, which allows the number of inductance elements and capacitor elements provided inside or outside the package to be reduced, and which enables the mounting area when the device is mounted on a circuit board or other substrate to be decreased.
In accordance with a preferred embodiment of the present invention, a surface acoustic wave device includes a first surface acoustic wave filter connected between an input terminal and an output terminal, a second surface acoustic wave filter having a center frequency that is different from that of the first surface acoustic wave filter, and which is connected between the input terminal and the output terminal and in parallel with the first surface acoustic wave filter, and at least one one-port surface acoustic wave resonator connected in series with the first or second surface acoustic wave filter, on at least one side between the input terminal and at least one of the first and second surface acoustic wave filters, or between the output terminal and at least one of the first and second surface acoustic wave filters. In this surface acoustic wave device, the anti-resonance frequency of the one one-port surface acoustic wave resonator is positioned on the side of higher frequencies than those of the pass band of the surface acoustic wave filter disposed on the side where the one-port surface acoustic wave resonator is connected in series.
In accordance with a particular aspect of at least one preferred embodiment of the present invention, the center frequency of the second surface acoustic wave filter is higher than that of the first surface acoustic wave filter, and a first one-port surface acoustic wave resonator and a second one-port surface acoustic wave resonator are connected in series between the second surface acoustic wave filter and the input terminal, and between the second surface acoustic wave filter and the output terminal, respectively.
In accordance with another aspect of at least one preferred embodiment of the present invention, a plurality of the one-port surface acoustic wave resonators are connected in a multi-stage series connection.
In accordance with another particular aspect of at least one preferred embodiment of the present invention, at least two of the one-port surface acoustic wave resonators are connected in series, on at least one side between the first or second surface acoustic wave filter and the input terminal, or between the first or second surface acoustic wave filter and the output terminal, and the plurality of one-port surface acoustic wave resonators which are connected in series with each other, are arranged so as to differ, from each other, in the frequency determined by the pitch of the interdigital transducers (hereinafter referred to as a “IDTs”) thereof.
In accordance with another aspect of various preferred embodiments of the present invention, each of the first and second surface acoustic wave filters includes a longitudinally-coupled surface acoustic wave filter having three IDTs disposed along the surface wave propagation direction.
In accordance with another particular aspect of at least one preferred embodiment of the present invention, in the first and second longitudinally-coupled surface acoustic wave filters each having three
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Summons Barbara
LandOfFree
Surface acoustic wave device using two parallel connected... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Surface acoustic wave device using two parallel connected..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Surface acoustic wave device using two parallel connected... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3094944