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Surface acoustic wave filter and surface acoustic wave duplexer with the same

A surface acoustic wave and filter technology, applied in electrical components, impedance networks, etc., can solve problems such as poor band-pass characteristics of surface acoustic wave filters and form factors

Inactive Publication Date: 2004-05-05
TAIYO YUDEN KK
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

AI Technical Summary

Problems solved by technology

[0007] However, in general, the bandpass characteristics of surface acoustic wave filters have a poorer form factor compared to filter devices including dielectric elements or FBARs

Method used

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  • Surface acoustic wave filter and surface acoustic wave duplexer with the same
  • Surface acoustic wave filter and surface acoustic wave duplexer with the same
  • Surface acoustic wave filter and surface acoustic wave duplexer with the same

Examples

Experimental program
Comparison scheme
Effect test

no. 1 example

[0040] figure 2 is a plan view of a ladder-type surface acoustic wave (SAW) filter device 1 according to a first embodiment of the present invention. like figure 2As shown in , in a ladder structure, a ladder-type surface acoustic wave (SAW) filter device 1 includes four series branch resonators S1 to S4 arranged in series branches, and two parallel branches arranged in parallel branches way resonators P1 and P2.

[0041] Here, the series branch resonators of the ladder-type SAW filter will be explained. figure 2 The ladder-type SAW filter device 1 shown in has a 4-level structure starting from the series branch resonator S1, and its circuit structure can be expressed as S-P-P-S-S-P-P-S, where each series branch resonator is represented by S, and each parallel resonator is represented by P express. image 3 A circuit diagram of the structure is shown. figure 2 The ladder-type SAW filter device 1 shown in 1 combines every two adjacent parallel branch resonators (P01 an...

no. 2 example

[0076] Refer below Figure 14 , a second embodiment of the present invention in the form of a ladder-type SAW filter device 2 is described in detail.

[0077] The structure and structure of the ladder type SAW filter device 2 of the present embodiment figure 2 The structure shown in is basically the same. Additionally, the piezoelectric substrate 10 is a 42° Y-cut X-propagation LiTaO 3 The substrate, which is the same as in the first embodiment.

[0078] In this structure, the electrode finger pitches of the series branch resonators S1, S2 and S4 are all 2.12 μm, and only the electrode finger pitch of the series branch resonator S3 is changed. If the static capacitance of the series branch resonator S1 is 1, then the relative static capacitances of the series branch resonators S2 to S4 are 1, 1 and 0.75, respectively. At the same time, the electrode finger pitches of the parallel branch resonators P1 and P2 are both 2.16 μm, and the relative static capacitance is 0.8.

...

no. 3 example

[0081] Refer below Figure 15 and 16 , to describe the third embodiment of the present invention in detail. In this embodiment, the ladder type SAW filter device 1 of the first embodiment is used as the relatively lower frequency side filter 1a, and the longitudinally coupled SAW resonator filter is used as the relatively higher frequency side filter 1b. These filters are installed in one package to form the 1.9GHz band antenna duplexer 1A. Figure 15 Such an antenna duplexer 1A according to the present embodiment is shown.

[0082] Figure 16 The filtering characteristics of this antenna duplexer 1A are shown in . from Figure 16 As can be clearly seen in , the high-frequency side form factor of the filter 1a on the low-frequency side is excellent. Therefore, although the frequency gap between the transmission band and the reception band is only 20 MHz, the attenuation rate of the antenna duplexer 1A of this embodiment is maintained at -40 dB or higher in the reception ...

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Abstract

A surface acoustic wave filter includes a series-arm resonators and parallel-arm resonators that are connected in a ladder-like structure, each having an interdigital transducer formed on a piezoelectric substrate, and at least one of the series-arm resonators having a different static capacitance from the other series-arm resonators. In this surface acoustic wave filter, at least one of the series-arm resonators except the series-arm resonator located at the first stage in the ladder-like structure has a lower average resonant frequency than the other series-arm resonators.

Description

technical field [0001] The present invention relates generally to surface acoustic wave filters, and more particularly to a surface acoustic wave filter for a high frequency unit of a mobile communication device, the filtering characteristics of which requires a high form factor. The present invention also relates to a surface acoustic wave duplexer (antenna duplexer) having the surface acoustic wave filter. Background technique [0002] Today, the transmission and reception bands of mobile communication systems are very close to each other, so that the limited frequency band area can be efficiently used. For example, in PCS (Personal Communications Services) in North America, although the passband is at 1.9 GHz, the frequency gap between the transmission band and the reception band is only 20 MHz. [0003] In order to avoid crosstalk in such a mobile communication system, in an antenna duplexer that separates a transmission signal and a reception signal, the frequency regi...

Claims

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Application Information

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Patent Type & Authority Applications(China)
IPC IPC(8): H03H9/145H03H9/64H03H9/72
CPCH03H9/725H03H9/6483H03H9/64
Inventor 堤润井上将吾松田隆志上田政则
Owner TAIYO YUDEN KK
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