Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2000-09-06
2002-10-15
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S187000, C310S366000
Reexamination Certificate
active
06466106
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an energy trap type piezoelectric filter device using a second harmonic wave of a thickness-extension vibration mode. In particular, the present invention relates to a piezoelectric filter device having a structure including two piezoelectric filters, which are electrically connected to each other via a relay capacitor.
2. Description of the Related Art
FIG. 10
is a sectional view illustrating a conventional energy trap type piezoelectric filter device using a second harmonic wave of a thickness-extension vibration mode.
As shown in
FIG. 10
, a piezoelectric filter
51
including a piezoelectric substrate plate
52
, which is polarized in its thickness direction, is provided. A ground electrode
53
is disposed in the center of the piezoelectric substrate plate
52
. On the upper surface of the piezoelectric substrate plate
52
, an input electrode
54
is arranged opposite to a portion of the ground electrode
53
with the piezoelectric substrate plate being partially interposed therebetween. On the bottom surface of the piezoelectric substrate plate
52
, an output electrode
55
is provided. Similarly, the output electrode
55
is arranged opposite to a portion of the ground electrode
53
with the piezoelectric substrate plate being partially interposed therebetween. Further, the output electrode
55
is provided in a position so as not to overlap the input electrode
54
through the piezoelectric substrate plate
52
.
Using the above structure, as soon as an input signal is applied between the input electrode
54
and the ground electrode
53
, the piezoelectric filter
51
functions as a double mode filter that operates by virtue of a second harmonic wave of a thickness-extension vibration, thus producing an output signal through the output electrode
55
.
Another conventional piezoelectric filter device includes two piezoelectric filters
51
, and the two piezoelectric filters
51
are electrically connected to the ground potential via a relay capacitor.
However, in the above described conventional piezoelectric filter device, when the two piezoelectric filters
51
are electrically connected with each other through a relay capacitor, the height of the ground electrode
53
of one piezoelectric filter
51
is different from that of another ground electrode. As a result, it is difficult for the piezoelectric filter device to obtain consistent characteristics.
In the above piezoelectric filter
51
, the ground electrode
53
is located at a central position in the thickness direction of the piezoelectric substrate plate
52
. The piezoelectric filter
51
is usually obtained by cutting a mother piezoelectric substrate plate. However, in a mother piezoelectric substrate plate, it is impossible to avoid warpage and waviness.
Nevertheless, when a piezoelectric filter
51
produced via this method is tested, the height of the ground electrode
53
differs from one piezoelectric filter to another. As a result, in the above described conventional piezoelectric filter device in which the two piezoelectric filters
51
are electrically connected with each other via a relay capacity, the height of the ground electrode
53
of one piezoelectric filter
51
differs from that of another ground electrode. Accordingly, it is difficult to obtain consistent characteristics with this piezoelectric filter device.
SUMMARY OF THE INVENTION
In order to overcome the above-described problems, preferred embodiments of the present invention provide a piezoelectric filter device, which is free from the above-described defects existing in the above-described prior art. More particularly, preferred embodiments of the present invention provide an improved piezoelectric filter device which includes two energy trap type piezoelectric filters each having an ground electrode disposed within a piezoelectric substrate plate and operating using a second harmonic wave of a thickness-extension vibration, thereby producing an improved piezoelectric filter device having stabilized filter characteristics.
According to preferred embodiments of the present invention, a piezoelectric filter device operates using a second harmonic wave of a thickness-extension vibration mode and includes a first piezoelectric filter and a second piezoelectric filter which are electrically connected to each other with a relay capacitor interposed therebetween, the first and second piezoelectric filters are polarized in the thickness directions thereof and include a pair of mutually opposing piezoelectric substrate plates each having a first main surface and a second main surface, a ground electrode provided within each of the piezoelectric substrate plates, an input electrode provided on the first main surface of each piezoelectric substrate plate such that the input electrode is opposite to one portion of the ground electrode with the piezoelectric substrate plate being partially interposed therebetween, an output electrode provided on the second main surface of each piezoelectric substrate plate such that the output electrode is opposite to the ground electrode except in the one portion thereof, with the piezoelectric substrate plate being partially interposed therebetween.
When a distance between the first main surface of the first piezoelectric filter and the adjacent ground electrode is ta
1
, a distance between the second main surface of the first filter and the adjacent ground electrode is tb
1
, a distance between the second main surface of the second piezoelectric filter and the adjacent ground electrode is ta
2
, a distance between the first main surface of the second piezoelectric filter and the adjacent ground electrode is tb
2
, the thicknesses of the piezoelectric substrate plates of the first and second piezoelectric filters are T
1
and T
2
respectively, tb
1
−ta
1
is 0 to 0.1 T
1
, Tb
2
−ta
2
is 0 to 0.1 T
2
, alternatively, tb
1
−ta
1
is −0.1 T
1
to 0, Tb
2
−ta
2
is 0.1 T
2
to 0.
Preferably, the thicknesses T
1
and T
2
of the piezoelectric substrate plates of the first and second piezoelectric filters are substantially equal to each other.
More preferably, when the thicknesses T
1
and T
2
of the piezoelectric substrate plates of the first and second piezoelectric filters are substantially equal to each other, and when the thicknesses are T, in a perpendicular coordinate system including tb
1
−ta
1
and tb
2
−ta
2
, the value of tb
1
−ta
1
and the value of tb
2
−ta
2
will fall within either a range A or a range B as shown in FIG.
1
.
Further, in the piezoelectric filter device according to preferred embodiments of the present invention, the first and second piezoelectric filters may either be formed separately, or they can be laminated together to define an integral body in a manner such that the vibrations of the piezoelectric vibration sections thereof are not suppressed.
Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments hereof with reference to the attached drawings.
REFERENCES:
patent: 5065066 (1991-11-01), Nakatani et al.
patent: 5084647 (1992-01-01), Inoue et al.
patent: 5274293 (1993-12-01), Inoue et al.
patent: 5294860 (1994-03-01), Gamo
patent: 5444326 (1995-08-01), Yoshida
patent: 3-97314 (1991-04-01), None
patent: 5-259805 (1993-10-01), None
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Pascal Robert
Summons Barbara
LandOfFree
Piezoelectric filter device with a ground electrode that is... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Piezoelectric filter device with a ground electrode that is..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Piezoelectric filter device with a ground electrode that is... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2989930