Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
1999-05-25
2002-05-14
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S195000, C333S133000, C310S31300R
Reexamination Certificate
active
06388545
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention generally relates to SAW (surface-acoustic-wave) filter devices and more particularly to a SAW-filter device for use in ultra-high frequency applications including the RF unit of portable telephone apparatuses.
SAW-filter devices are used extensively in the RF unit of portable telephone apparatuses as a filter element. A SAW filter device achieves the desired filtering of ultra-high frequency signals by using a SAW excited on a piezoelectric substrate by piezoelectric effect. In the application of a SAW-filter in portable telephone apparatuses, it is required that the SAW-filter device provides a pass-band of about 900 MHz and a sharp attenuation outside the pass-band. Further, it is required that the SAW-filter device is capable of effectively suppressing the spurious frequency components having a much higher frequency, in the order of several GHz. In the RF unit of portable telephone apparatuses, in which a number of SAW-filter devices having respective, different pass-bands are used in various parts such as antenna duplexer, inter-stage filter circuit, IF filter circuit, and the like, there is a case that a spurious component having such a GHz-band frequency is formed as a result of the interference of the SAW-filter devices. Thus, in order to ensure a proper operation of the portable telephone apparatus, it is necessary to suppress such a GHz-band spurious components by way of a SAW-filter device.
Generally, a SAW-filter device includes a SAW-filter body carrying various reflectors and interdigital electrodes on a piezoelectric substrate in such a state that the SAW-filter body is accommodated in a package body. Thereby, the SAW-filter device thus accommodating therein the SAW-filter body is mounted on a printed circuit board by soldering the soldering pads formed on the package body.
Hereinafter, the reflectors and interdigital electrodes formed on the piezoelectric substrate will be explained briefly.
FIG. 1A
shows the construction of a double-mode, single-type SAW-filter
10
.
Referring to
FIG.1A
, the SAW-filter
10
includes an input interdigital electrode pair
11
disposed at a center and output interdigital electrode pairs
12
and
13
are disposed at both lateral sides of the central interdigital electrode pair
11
. Further, reflectors
14
and
15
are disposed at further outer sides of the output interdigital electrode pairs
12
and
13
, respectively.
The input interdigital electrode pair
11
is formed of a primary side electrode
11
−1
connected to an input terminal
20
and a secondary side electrode
11
−2
connected to a ground
21
, while the output interdigital electrode pair
12
includes a primary side electrode
12
−1
connected to an output terminal
22
and a secondary side electrode
12
−2
connected to a ground
23
. Further, the output interdigital electrode pair
13
includes a primary side electrode
13
−1
connected to the foregoing output terminal
22
commonly to the electrode
12
−1
and a secondary side electrode
13
−2
connected to a ground
24
.
The SAW-filter
10
thus formed in a double-mode filter as noted before and uses a first-order mode having a frequency f
1
and a second-order mode having a frequency f
3
both formed between the reflectors
14
A and
15
B as represented in FIG.
1
B. Thereby, a frequency characteristic having a pass-band between the frequency f
1
and the frequency f
3
is obtained as represented in FIG.
2
. It should be noted that
FIG. 1B
represents the distribution of the SAW energy in the structure of FIG.
1
A.
FIG. 3
shows the construction of a double-mode SAW-filter
40
in which two SAW-filters
10
each having the construction of
FIG. 1A
are cascaded with each other. In the explanation below, those parts corresponding to the parts described already with reference to
FIG. 1A
are designated by the same reference numerals and the description thereof will be omitted.
Referring to
FIG. 3
, it can be seen that two SAW-filter elements
10
−1
and
10
−2
, each having a construction similar to that of the SAW-filter
10
of
FIG. 1A
, are cascaded in series in the SAW-filter
40
, wherein the SAW-filter element
10
−1
is a single type SAW-filter element and includes a central input electrode pair corresponding to the input electrode pair
11
of FIG.
1
A and thus designated by the same reference numeral
11
. In the construction of
FIG. 3
, the input electrode pair
11
is surrounded laterally by a pair of output electrode pairs corresponding to the output electrode pairs
12
and
13
of FIG.
1
A and thus designated by the reference numerals
12
and
13
. Further, reflectors corresponding to the reflectors
14
and
15
of FIG.
1
A and designated by the same reference numerals of
14
and
15
are disposed at further outer sides of the output electrode pairs
12
and
13
. In the SAW-filter element
10
−1
, the primary side interdigital electrode
11
−1
of the central input electrode pair
11
is connected to the input terminal
20
.
On the other hand, the SAW-filter element
10
−2
is a single type SAW-filter element similar to the SAW-filter element
10
−1
and includes a central output electrode pair
41
surrounded laterally by a pair of input electrode pairs
42
and
43
, and a pair of reflectors
44
and
45
are disposed at further outer sides of the input electrode pairs
42
and
43
. The central output electrode pair
41
includes a primary side interdigital electrode
41
−1
and a secondary side interdigital electrode
41
−2
, wherein the primary side interdigital electrode
41
−1
is connected to an output terminal
46
and the secondary side interdigital electrode
41
−2
is connected to a ground
47
. Further, the input electrode pair
42
includes a primary side interdigital electrode
42
−1
connected to the primary side interdigital electrode
12
−1
of the output electrode pair
12
constituting the SAW-filter unit
10
and a secondary side interdigital electrode
42
−2
connected to a ground
48
. Similarly, the input electrode pair
43
includes a primary side interdigital electrode
43
−1
connected to the primary side interdigital electrode
13
−1
of the output electrode pair
13
constituting the SAW-filter unit
10
and a secondary side interdigital electrode
43
−2
connected to a ground
49
.
The SAW-filter
40
of
FIG. 3
has a frequency characteristic improved over the frequency characteristic of the SAW-filter
10
of FIG.
1
.
FIG. 4
,
FIGS. 5A-5C
, FIG.
6
and
FIG. 7
show the construction of another conventional SAW-filter package device
60
, wherein
FIG. 4
shows the SAW-filter package device
60
in an exploded state while
FIGS. 5A-5C
show the SAW-filter respectively in a top plan view, a side view and a bottom plan view. Further,
FIG. 6
shows the SAW-filter package device
60
in a cross-sectional view taken along a line VI—VI of
FIG. 5A
, while
FIG. 7
shows the electrical interconnection formed in the SAW-filter package device
60
.
Referring to the drawings, the SAW-filter package device
60
includes a rectangular package body
62
accommodating therein a SAW-filter body
101
to be described with reference to
FIG. 12 and a
cap
63
sealing the package body
62
. The SAW-filter body
101
carries thereon ground terminals
21
A,
23
A,
47
A and
48
A as represented in FIG.
12
.
The package body
62
, in turn, includes a bottom plate
64
and a rectangular frame member
65
holding therein the bottom plate
64
, wherein the bottom plate
64
carries, on a top surface thereof, a ground pad
70
, an input pad
71
and an output pad
72
as represented also in FIG.
7
. Further, the bottom plate
64
carries, on a bottom surface thereof, a pair of ground foot patterns
73
and
74
so as to face each other diagonally on a first diagonal line, wherein the bottom plate
64
further carries, on the bottom surface thereof, an input foot pattern
75
Kawachi Osamu
Suga Akira
Ueda Masanori
Arent Fox Kintner & Plotkin & Kahn, PLLC
Fujitsu Limited
Lee Benny
Summons Barbara
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