WO2018145383A1

WO2018145383A1 - Surface acoustic wave filter

Info

Publication number: WO2018145383A1
Application number: PCT/CN2017/088444
Authority: WO
Inventors: 王宁; 董启明; 张忠云; 刘绍侃; 张伟
Original assignee: 深圳华远微电科技有限公司
Priority date: 2017-02-07
Filing date: 2017-06-15
Publication date: 2018-08-16
Also published as: CN106911317B; CN106911317A

Abstract

A surface acoustic wave filter, comprising a piezoelectric substrate (100), two interdigital transducers (10, 11) arranged in parallel on the piezoelectric substrate (100), each of the interdigital transducers (10, 11) comprising a first bus bar (101, 111), a second bus bar (102, 112) opposing the first bus bar (101, 111), a plurality of first electrode strips (103, 113) connected with the first bus bar (101, 111), and a plurality of second electrode strips (104, 114) connected with the second bus bar (102, 112), wherein the plurality of first electrode strips (103, 113) are in cross arrangement with the plurality of second electrode strips (104, 114); the first bus bars (101, 111) of the two interdigital transducers (10, 11) extending upward to form two differential input terminals (1, 2), the second bus bars (102, 112) of the two interdigital transducers (10, 11) extending upward to form two differential output terminals (3, 4), and two reflecting gratings (20) being respectively arranged on two sides of the two interdigital transducers (10, 11) for use in reflecting surface acoustic waves produced by the two interdigital transducers (10, 11).

Description

Surface acoustic wave filter

Technical field

The present invention relates to the field of filtering, and in particular to a surface acoustic wave filter.

Background technique

Since the differential structure has the advantages of suppressing common mode interference and high signal-to-noise ratio, it has been widely used, such as differential filters and differential amplifiers.

In the field of surface acoustic filters, differential structures are typically implemented by multiple resonators. The simplest differential structure acoustic surface filter comprises two series resonators X and one parallel resonator Y, and the surface acoustic wave filter obtained by this method has a large occupied area and high cost.

Summary of the invention

Based on this, it is necessary to provide a surface acoustic wave filter, which can realize a differential structure, suppress common mode interference of the surface acoustic wave filter, enhance signal to noise ratio, occupy small area, and have low cost.

A surface acoustic wave filter comprising:

Piezoelectric substrate;

Two interdigital transducers disposed side by side on the piezoelectric substrate, each interdigital transducer including a first bus bar, a second bus bar opposite the first bus bar, and the first a plurality of first electrode strips connected to the bus bar, and a plurality of second electrode strips connected to the second bus bar, the plurality of first electrode strips intersecting with the plurality of second electrode strips, Forming two differential input terminals on the first bus bar of the two interdigital transducers, and extending the second bus bar of the two interdigital transducers to form two differential output terminals;

Two reflective grids are respectively disposed on both sides of the two interdigital transducers for reflecting surface acoustic waves generated by the two interdigital transducers.

Details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. this invention Other features, objects, and advantages will be apparent from the description, drawings and claims.

DRAWINGS

1 is a schematic structural view of a surface acoustic wave filter in a first embodiment;

2 is a schematic structural view of a surface acoustic wave filter in a second embodiment;

3 is a schematic structural view of a surface acoustic wave filter in a third embodiment;

4 is a schematic structural view of a surface acoustic wave filter in a fourth embodiment;

Figure 5 is a schematic structural view of a surface acoustic wave filter in a fifth embodiment;

Fig. 6 is a schematic structural view of a surface acoustic wave filter in a sixth embodiment.

detailed description

Referring to Fig. 1, Fig. 1 is a schematic structural view of a surface acoustic wave filter in the first embodiment.

In this embodiment, the surface acoustic wave filter includes a piezoelectric substrate 100, two interdigital transducers (IDTs) and two reflective gratings 20 (Reflecting Grating) disposed on the piezoelectric substrate 100. REF).

The two interdigital transducers include a first interdigital transducer 10 and a second interdigital transducer 11, which are disposed side by side on the piezoelectric substrate 100 and are located on the propagation path of the acoustic wave.

The first interdigital transducer 10 includes a first bus bar 101, a second bus bar 102, a plurality of first electrode strips 103 connected to the first bus bar 101, and a plurality of second electrodes connected to the second bus bar 102. Electrode strip 104. The first electrode strip 103 and the second electrode strip 104 are disposed to intersect each other.

The second interdigital transducer 11 includes a first bus bar 111, a second bus bar 112, a plurality of first electrode strips 113 connected to the first bus bar 111, and a plurality of second electrodes connected to the second bus bar 112. Electrode strip 114. The first electrode strip 113 and the second electrode strip 114 are disposed to intersect each other.

The first bus bar 101 of the first interdigital transducer 10 and the first bus bar 111 of the second interdigital transducer 11 extend to form two differential input terminals 1, 2. The second bus bar 102 of the first interdigital transducer 10 and the second bus bar 112 of the second interdigital transducer 11 extend to form two differential output terminals 3, 4. The power is input from the differential input terminals 1, 2, and the signals are output from the differential output terminals 3, 4 to form a difference. The sub-structured surface acoustic wave filter can suppress common mode interference and enhance the signal-to-noise ratio.

Two reflective gratings 20 are respectively disposed on both sides of the two

interdigital transducers

10, 11 for reflecting surface acoustic waves generated by the two

interdigital transducers

10, 11.

The power source is loaded on the two

interdigital transducers

10, 11 such that the piezoelectric substrate 100 excites a bidirectional surface acoustic wave, and the reflective grating 20 receives the surface acoustic wave and reflects it back to realize the transmission of the surface acoustic wave. The power source is an alternating voltage signal, and the

interdigital transducers

10, 11 are very sensitive to frequency, converting the alternating voltage signal into mechanical vibration of the piezoelectric substrate 100, thereby forming a surface acoustic wave, and reflecting back through the reflective grid 20.

In the prior art, a differential structure surface acoustic wave filter requires two series resonators X and one parallel resonator Y to be realized. The structure of a series resonator X is REF+IDT+REF, and only two series resonators need to occupy the space and area of the two structures, which is larger than the REF+IDT+IDT+REF differential structure of the embodiment. The space is large and the cost increases accordingly.

In addition, the surface acoustic wave filter may have other methods of use, such as only one interdigital transducer 10 or interdigital transducer 11 is connected to the circuit, and is used as a resonator, which can be flexibly adapted according to circuit requirements. select.

In one of the embodiments, the center distances of the adjacent two

first electrode strips

103, 113 respectively located on the two

interdigital transducers

10, 11 are (1.5 + n) P, ie, the first interdigital transducing The center distance between the first electrode strip 103 of the device 10 and the adjacent first electrode strip 113 on the second interdigital transducer 11. The center distance of two adjacent second electrode strips 104, 114 respectively located on the two

interdigital transducers

10, 11 is (0.5 + n) P, that is, the second electrode strip of the first interdigital transducer 10 104 is the center distance of the second electrode strip 114 adjacent to the second interdigital transducer 11. Where n=0, 1, 2, 3..., P is the period of the interdigital transducer, and the period is specifically the center distance of two adjacent electrode strips connected on the same bus bar.

When the spacing of the two

interdigital transducers

10, 11 satisfies the above conditions, the structures of the two

interdigital transducers

10, 11 are synchronous, and the coupling degree is high, the resonance intensity is large, and the filtering effect is good.

In a further embodiment, when n=0, the center distances of two adjacent

first electrode strips

103, 113 respectively located on the two

interdigital transducers

10, 11 are 1.5P, respectively. Interdigital transducer The center distance between adjacent two second electrode strips 104, 114 on the

devices

10, 11 is 0.5P. Therefore, the footprint of the surface acoustic wave filter can be minimized.

The center distances of the adjacent two

first electrode strips

103, 113 respectively located on the two

interdigital transducers

10, 11 are greater than the center distances of the adjacent two second electrode strips 104, 114. The

interdigital transducers

10, 11 are sensitive to input power, and the greater the spacing between adjacent electrode strips of the

interdigital transducers

10, 11, the greater the input power can withstand.

In one of the embodiments, referring to FIGS. 2 and 3, the differential input terminals 1, 2 and/or the differential output terminals 3, 4 are connected to a Balance-Unbalance (BALUN) 30. The BALUN30 can realize differential port to single port conversion, and can also realize impedance conversion, making the surface acoustic wave filter of the differential structure more flexible and better filtering effect.

In one of these embodiments, referring to Figures 4 and 5, the differential input terminals 1, 2 and/or the differential output terminals 3, 4 are connected to a Balance Bridge Filter (BBF) 40 to balance the input and output signals.

In one embodiment, referring to FIG. 6, one end of the reflective grid 20 is electrically coupled to the bus bars on the same side of the adjacent

interdigital transducers

10, 11.

Specifically, one end of the reflective gate 20 adjacent to the interdigital transducer 10 is electrically connected to the first bus bar 101, and one end of the reflective gate 20 adjacent to the interdigital transducer 11 is electrically connected to the first bus bar 111. . By increasing the pad or block connection of the bond wire, the insertion loss can be minimized and the useful power of the surface acoustic wave filter can be enhanced.

In one embodiment, the thickness of the

first bus bars

101, 102 and the

second bus bars

111, 112 is greater than the thickness of the first electrode strips 103, 104, the second electrode strips 113, 114, and the first bus bar 101, The thickness of the 102 and

second bus bars

111, 112 is greater than the thickness of the electrode strip of the reflective grid 20, and the resistance loss of the surface acoustic wave filter can be reduced. The electrode strip 201 of the reflective grid 20 is as shown in FIG. 1 .

In one of the embodiments, the half wavelength of the reflective grid 20 is the same as the half wavelength of the

interdigital transducers

10, 11. The half wavelength of the reflective grid 20 and the half wavelength of the

interdigital transducers

10, 11 refer to the center distance of two adjacent electrode strips.

In one embodiment, the surface acoustic wave filter can implement various sound wave filtering processes, including surface acoustic waves, leaky sound waves or other forms of sound waves, remove noise, obtain sound waves in a specific frequency band, and have a good filtering effect.

The surface wave filter described above can realize a surface acoustic wave filter of a differential structure by arranging two

interdigital transducers

10 and 11 side by side on the piezoelectric substrate 100, suppressing common mode interference, enhancing signal to noise ratio, and occupying area. Small and low cost. By reasonably setting the spacing between the two

interdigital transducers

10, 11, the coupling degree can be enhanced, so that the resonance intensity is large and the filtering effect is good. Differential port-to-single port conversion can be achieved by connecting BALUN 30 to the differential inputs and differential outputs, as well as impedance conversion or access to the BBF40. By electrically connecting one end of the reflective grid 20 to the bus bar on the same side of the adjacent interdigital transducer, the connection of the bonding pad or the metal block is increased, and the insertion loss can be reduced while the thickness of the bus bar is reduced. The thickness of the electrode strips that are set larger than the

interdigital transducers

10, 11 and the reflective grid 20 can reduce their resistance loss. The surface acoustic wave filter can realize filtering processing of various sound waves, remove noise, obtain sound waves in a specific frequency band, and have good filtering effect.

The technical features of the above embodiments may be arbitrarily combined. For the sake of brevity of description, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, It is considered to be the range described in this specification.

The above embodiments are merely illustrative of several embodiments of the present invention, and the description thereof is more specific and detailed, but is not to be construed as limiting the scope of the invention. It should be noted that a number of variations and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention. Therefore, the scope of the invention should be determined by the appended claims.

Claims

A surface acoustic wave filter comprising:

Piezoelectric substrate;

Two interdigital transducers disposed side by side on the piezoelectric substrate, each interdigital transducer including a first bus bar, a second bus bar opposite the first bus bar, and the first a plurality of first electrode strips connected to the bus bar, and a plurality of second electrode strips connected to the second bus bar, the plurality of first electrode strips intersecting with the plurality of second electrode strips, Forming two differential input terminals on the first bus bar of the two interdigital transducers, and extending the second bus bar of the two interdigital transducers to form two differential output terminals;

Two reflective grids are respectively disposed on both sides of the two interdigital transducers for reflecting surface acoustic waves generated by the two interdigital transducers.
The surface acoustic wave filter according to claim 1, wherein a center distance between adjacent two first electrode strips respectively located on the two interdigital transducers is (1.5+n)P, respectively The center distance of two adjacent second electrode strips on the two interdigital transducers is (0.5+n)P;

Where n = 0, 1, 2, 3...; P is the period of the interdigital transducer.
The surface acoustic wave filter according to claim 2, wherein the center distances of the adjacent two first electrode strips respectively located on the two interdigital transducers are 1.5P, respectively located at the two The center distance of two adjacent second electrode strips on the interdigital transducers is 0.5P.
A surface acoustic wave filter according to claim 1, further comprising a balun, said differential input terminal and/or differential output terminal being connected to said balun.
The surface acoustic wave filter according to claim 1, further comprising a balanced bridge filter, said differential input terminal and/or differential output terminal being connected to said balanced bridge filter.
The surface acoustic wave filter according to claim 1, wherein one end of said reflective gate is electrically connected to a bus bar on the same side of an adjacent said interdigital transducer.
The surface acoustic wave filter according to claim 1, wherein a thickness of the bus bar of the interdigital transducer is larger than a thickness of the electrode strip, and a thickness of the bus bar is larger than the inverse The thickness of the electrode strip of the gate.
The surface acoustic wave filter according to claim 1, wherein a half wavelength of said reflective grating is the same as a half wavelength of said interdigital transducer.