Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
1999-07-21
2001-12-11
Pascal, Robert (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S150000, C310S31300R
Reexamination Certificate
active
06329887
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an SAW(Surface Acoustic Wave) filter package, and more particularly, to an SAW filter package which can reduce an electromagnetic feed-through for improving an SAW filter performance.
2. Background of the Related Art
Being a filter of a piezoelectric material, the SAW filter is widely used as an intermediate frequency filter because the SAW filter permits multipoint drive and reception, has excellent earthquake and impact resistances as being supported from a substrate, and permits independent control of amplitude and phase, and has an excellent filter performance.
Referring to
FIG. 1
, a related art SAW filter is provided with an input terminal IDT (Inter-Digital Transducer)
12
for providing an input signal Vs with an impedance Rs, an output terminal IDT
13
connected to an output impedance R
0
, and absorber
14
for absorbing a reflected wave.
Shown in
FIG. 2
are details of the input terminal IDT
12
and the output terminal IDT
13
, both are of a withdrawal weighting type, respectively having one side with an input port
15
and the other side with a ground terminal
17
, and one side with a ground terminal
17
and the other side with an output port
16
. And, there is a slightly tilted blocking bar
18
disposed between the input terminal IDT
12
and the output terminal IDT
13
having both ends connected to the ground terminal
17
for reducing the electromagnetic feed-through.
FIGS.
3
A~
3
D illustrate details of a general SMD(Surface Mounted Device) package for mounting the SAW filter, wherein
FIG. 3A
illustrates a back of the package,
FIG. 3B
illustrates a side of the package,
FIG. 3C
illustrates a plan view of the package with a cover closed, and
FIG. 3D
illustrates a plan view of the package with a cover opened.
Referring to FIGS.
3
A~
3
D, an SMD package is provided with a base
20
of ceramic, a metal plated frame
21
projected vertical from the base
20
along a periphery of the base
20
, a plurality of gold plated pads
22
formed in sides of the base
20
, a ground terminal
23
of a gold plating formed on an inside surface of the base
20
, and a cover
24
for sealing the mounted filter. And, the SAW filter is mounted on the ground terminal
23
of the SMD package. The reference numeral
25
is a pad connection terminal.
Upon application of a high frequency electric field to the input terminal IDT
12
, a surface acoustic wave is excited by a piezoelectric action in the related art SAW filter, transmitted to the output terminal IDT
13
through a surface of the piezoelectric material
11
, and converted into the high frequency electric field again by a reverse piezoelectric action, to generate an electric signal. When the surface acoustic wave, generated upon application of a high frequency electric field to the input terminal IDT
12
, is transmitted through surface of the piezoelectric material
11
, there is an electromagnetic feed-through directly transmitted from the input terminal IDT
12
to the output terminal IDT
13
in a form of electric or emissive energy. This is caused by the close proximity of the input terminal IDT
12
and the output terminal IDT
13
, which is increased as the applied frequency is increased and makes interference with the surface acoustic wave to deteriorate an SAW filter performance because the electromagnetic feed-through is transmitted at a speed of light different from an energy carried by the surface acoustic wave that is the basic operation principle of the SAW filter.
The electromagnetic feed-through is caused by the following major two reasons.
The first one is that, as in general upper and lower surfaces of the package are formed of conductive material and the piezoelectric material of the SAW filter is a ferroelectric material, the package with the SAW filter mounted thereon forms a dielectric waveguide because a ferroelectric material present between the input/output terminal IDTs, which are formed on surfaces of the piezoelectric material, and the package. In this instance, even though a wave fed through a dielectric waveguide is leaky, an energy transmitted by the electromagnetic feedthrough is relatively great in comparison to other secondary effect because the input terminal IDT and the output terminal IDT are at a close proximity.
Another one is that emission occurs between the input/output terminal IDTs and bonding wires. Since the input/output terminal IDTs and the bonding wires actually act as antennas, they emits electromagnetic waves within the SAW filter package, causing the electromagnetic feed-through. As shown in
FIG. 2
, in the related art, in order to reduce the electromagnetic feed-through, the metallic conductive blocking bar
18
is placed on the surface of the piezoelectric material
11
between the input terminal IDT
12
and the output terminal IDT
13
, with the bar
18
tilted at a given angle and both ends of the bar
18
grounded. This configuration can reduce the electromagnetic feed-through because the electromagnetic feed-through from the input terminal IDT
12
to the output terminal IDT
13
through the surface of the piezoelectric material
11
is absorbed by the blocking bar
18
and discharged through the ground terminals at both ends thereof.
However, as there is only the blocking bar provided in the related art SAW filter package, the related art SAW filter package can not but remove a portion of the electromagnetic feed-through flowing through the surface of the piezoelectric material, allowing the other portion to cause interference with the surface acoustic wave, that deteriorates the filter performance.
SUMMARY OF THE INVENTION
Accordingly, the present invention is directed to an SAW filter package that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an SAW filter package which can improve an SAW filter package performance.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the SAW filter package includes a base having a frame around a periphery, a ground part formed of a metal plating on an inside surface of the base for attaching an acoustic surface wave filter thereto, cut-away portions formed by cutting the metal plating of the ground part in two places, and a metal piece electrically separated from the metal plating by the cut-away portions.
In a case of the SAW filter package of the present invention which is provided with the two cut-away portions and the center grounded metal piece in the ground portion, the negative current at the output terminal is very weak because the negative current generated at the input terminal is, not only blocked by the cut-away portions to be reduced significantly, but also becomes very weak at the output terminal even if a weak negative current passes through the cutaway portion by the waveguide effect as the weak negative current is drained to the ground, thereby significantly reducing an unwanted electromagnetic feed-through.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
REFERENCES:
patent: 4126839 (1978-11-01), Yamanoi et al.
patent: 4365219 (1982-12-01), Nathan
patent: 4409567 (1983-10-01), Setsune et al.
patent: 4500807 (1985-02-01), Yuhara et al.
patent: 5237235 (1993-08-01), Cho et al.
patent: 5281883 (1994-01-01), Ikata et al.
patent: 6-97757 (1994-04-01), None
patent:
Fleshner & Kim LLP
LG Electronics Inc.
Pascal Robert
Summons Barbara
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