CN101656524B - Three-channel surface acoustic wave filter - Google Patents

Abstract

A three-channel surface acoustic wave filter includes three filters with different frequency responses integrated on a piezoelectric crystal sheet, one of which is a single-channel surface acoustic wave filter composed of independent input and output interdigital transducers and a shielding strip therebetween, and the other two are dual-channel surface acoustic wave filters composed of two input-end interdigital transducers and a common output-end interdigital transducer and a shielding strip between the input-end interdigital transducers and the output-end interdigital transducers. An electrical isolation zone composed of a metal strip and an acoustic isolation zone composed of a sound-absorbing material are also integrated on the piezoelectric crystal sheet between the single-channel filter and the dual-channel filter, and each works independently without interfering with each other. The present invention integrates and implements the functions of three surface acoustic wave filters on the same chip in a standard package shell, occupies a smaller chip area, saves a package shell, and has a lower manufacturing cost.

Description

Three-channel SAW filter

technical field

The invention relates to a band-pass filter, in particular to a surface acoustic wave band-pass filter integrated on a piezoelectric crystal material.

Background technique

When a voltage is applied to the electrode of a substrate material with piezoelectric properties (such as lithium niobate single crystal material), mechanical distortion will be formed in the crystal lattice of the piezoelectric crystal material. When the voltage loaded on the electrode of the piezoelectric crystal material is the input electrical signal, a surface acoustic wave will be formed in the lattice on the surface of the piezoelectric crystal material. Elastomechanical waves decrease rapidly with increasing depth into the substrate material.

SAW filters have the characteristics of bandpass filters. The realization of the band-pass filtering function of the surface acoustic wave filter is based on the surface acoustic wave formed in the above-mentioned lattice. The basic structure of the surface acoustic wave filter is to make an aluminum film with a certain thickness on the polished surface of the substrate material (such as lithium niobate single crystal material) with piezoelectric properties, and form a cross on the aluminum film layer by photolithography. Paired comb-shaped aluminum electrode structure, when an electrical signal is applied to the comb-shaped electrode structure, a surface acoustic wave is formed between the fingers of the two comb-shaped electrodes, so the comb-shaped electrode structure acts as an electroacoustic transducer , which is called an interdigital transducer. The excitation area of the transducer is formed between the interdigital fingers of the two comb-shaped electrodes. The comb handle part of the two comb-shaped electrodes connected to each interdigital finger is called a bus bar. The signal voltage is applied to the two bus bars of the interdigitated comb-shaped electrodes. Each bus bar is connected with an external circuit through an electric contact. The interdigital transducer is divided into an input transducer and an output transducer: the input transducer converts the electrical signal into a surface acoustic wave signal, propagates along the crystal surface, and the output transducer converts the received surface acoustic wave signal converted into an electrical signal output. The input transducer and the output transducer constitute a surface acoustic wave transmission channel, and the transmission channel has different surface acoustic wave transmission characteristics or bandpass characteristics according to different weighting structures of the IDTs.

In the prior art, the surface acoustic wave filter has two forms of single channel and double channel. For example, the applicant's patent application, the patent application No. 2008101242125 discloses a single-channel surface acoustic wave filter; the patent application No. 2008101242178 discloses a dual-channel surface acoustic wave filter. In today's TV system, there are both analog signals and digital signals, and different filters need to be used. At the same time, in the filtering of analog signals, different filters must be used for image signals and audio signals. Therefore, it is often necessary to simultaneously Using 2 to 3 surface acoustic wave filters has the disadvantages of consuming a lot of crystal chip materials, outer sealing tube bases, and tube cap materials, and occupying a large area of PCB (printed circuit board).

content of the invention

The applicant provides a three-channel surface acoustic wave filter, which integrates and realizes the functions of three surface acoustic wave filters with completely different frequency responses in a standard package shell and on the same chip, so that the occupied chip area is smaller. Small, consumes less substrate material, lower manufacturing cost, and occupies less PCB area.

Technical scheme of the present invention is as follows:

A three-channel surface acoustic wave filter, comprising two input IDTs integrated on a piezoelectric crystal sheet, the two input IDTs share an output IDT, the A shielding strip is set between the two input IDTs and the common output IDT to form a dual-channel surface acoustic wave filter; the piezoelectric crystal sheet is also integrated with an input IDT A single-channel surface acoustic wave filter composed of an interdigital transducer at the output end and a shielding strip between the two; the dual-channel surface acoustic wave filter and the single-channel surface acoustic wave filter are placed on a piezoelectric crystal sheet The setup also incorporates an electrical isolation strip made of metal strips and an acoustic isolation strip of sound-absorbing material.

Its further technical scheme is:

The electrical isolation zone can be made of the same or different metal material as that used to form the interdigital transducer; the material of the acoustic isolation zone can be the same as or the same as the sound-absorbing material coated on both ends of the piezoelectric wafer for absorbing reflected waves. different.

The electrical isolation zone can be made of the same or different metal material as the interdigital transducer; the acoustic isolation zone can be made of the same or different sound-absorbing material coated on both ends of the piezoelectric wafer for absorbing reflected waves. The acoustic isolation zone can be overlapped on the electrical isolation zone, or can be arranged on one or both sides of the electrical isolation zone.

The beneficial technical effect of the present invention is:

The present invention integrates three surface acoustic wave filters with completely different frequency responses on the same chip in one packaging shell. An electrical isolation band is set on the piezoelectric wafer between filters with different frequency responses to avoid mutual interference of electrical signals, and an acoustic isolation band is set at the same time to avoid mutual interference of sound waves between different frequency responses, thereby improving the filter performance. selective. Since the functions of three filters are implemented on the same chip, the occupied chip area is smaller, less substrate material is consumed, and the manufacturing cost is effectively reduced.

Description of drawings

Fig. 1 is a schematic diagram of a structural embodiment of the present invention.

FIG. 2 is a schematic diagram of the structure of the weighted envelope of the IDT at the input end of FIG. 1 .

Detailed ways

The specific embodiments of the present invention will be further described below in conjunction with the accompanying drawings.

See Fig. 1, the present invention comprises the IDT 2 of input end, the IDT 5 of input end, the IDT 12 of output end and the IDT of two input ends that are integrated on the piezoelectric crystal plate 7 respectively. The two-channel surface acoustic wave filter 29 formed by the shielding strip 17 between the transducer and the IDT at the output end, two IDTs at the input end and two IDTs at the input end The interdigitated transducers with weighted interdigitated fingers are juxtaposed and staggered, and the two transmission channels formed form two surface acoustic wave transversal filters. Sharing one output IDT 12 can make the output impedances of the two filters exactly the same, which is convenient for circuit matching. In addition, the single-channel surface acoustic wave filter 30 is formed by the IDT 20 at the input end, the IDT 26 at the output end, and the shielding bar 23 between them. Between the two-channel surface acoustic wave filter 29 and the single-channel surface acoustic wave filter 30, on the piezoelectric crystal plate 7, an electrical isolation zone 18 made of metal strips and an acoustic isolation zone made of sound-absorbing material are also integrated. The belt 31 is used to ensure that the dual-channel SAW filter 29 and the single-channel SAW filter 30 work independently without interfering with each other.

The acoustic isolation strip 31 may be the same as or different from the sound-absorbing material strips 32 and 33 coated on both ends of the piezoelectric wafer for absorbing reflected waves, for example, other acoustic isolation structures such as surface grooves may be used. The electrical isolation band 18 can be made simultaneously with the same metal material (aluminum material) and the same manufacturing process as the IDT, or after the IDT is made, it can be separately used such as evaporation (not limited to evaporation) ) and other crafts are made of other metal materials. The acoustic isolation zone 31 can be overlapped on the electrical isolation zone 18 , and can also be arranged on one or both sides of the electrical isolation zone 18 . In the embodiment of FIG. 1 , the electrical isolation strip 18 is connected to the shielding strip 17 and the shielding strip 23 and then grounded.

Description of the working principle of the present invention:

The input IDT 2 and the input IDT 5 of the dual-channel filter are used to convert electrical energy into surface acoustic wave mechanical energy; the output IDT 12 is the opposite, converting surface acoustic wave mechanical energy It is electrical energy, so complete the filtering and transmission of the signal; the input IDT 20 of the single-channel filter is used to convert electrical energy into surface acoustic wave mechanical energy; the output IDT 26 is the opposite, and the acoustic The surface wave mechanical energy is converted into electric energy, so that the filtering and transmission of the signal are completed; the electrical isolation zone 18 and the acoustic isolation zone 31 sound-absorbing material belt 18 ensure that the dual-channel SAW filter and the single-channel SAW filter work independently and mutually Do not interfere.

See Figure 1, where bus bar 1, bus bar 4, bus bar 6, bus bar 11, bus bar 13, bus bar 19, bus bar 22, bus bar 24, and bus bar 25 are all power-connecting ports. Pin connection to the package case. The bus bar 1, bus bar 4, bus bar 6, bus bar 19, and bus bar 22 connected to the electrical port at the input end can choose different power connection methods, so that the surface acoustic wave filters of the three channels correspond to different frequency responses, for example It can have different performances such as center frequency, bandwidth, square factor, out-of-band rejection, etc. When the two bus bars of the IDT at the input of the dual-channel filter have different potentials, the IDT can excite surface acoustic waves; and when the two bus bars of the IDT at the input end When the root bus bars have the same potential, the surface acoustic wave cannot be excited. For example, in Figure 1, when bus bar 1 and bus bar 4 are connected to different potentials, and bus bar 4 and bus bar 6 have the same potential, IDT 2 at the input end works, and IDT 5 at the input end does not. Work. When the potentials of bus bar 1 and bus bar 4 are the same, but the potentials of bus bar 4 and bus bar 6 are different, the IDT 2 at the input end does not work, and the IDT 5 at the input end works. When the bus bar 1, the bus bar 4, the bus bar 4, and the bus bar 6 have different potentials, the input IDT 2 and the input IDT 5 work simultaneously. The operation of the single-channel filter 30 and the above-mentioned dual-channel filter 29 do not interfere with each other. When the potentials of the bus bar 19 and the bus bar 22 are different, the IDT 20 at the input end works normally.

As shown in Fig. 2, the cut-finger envelope 15 and the cut-finger envelope 16 are the envelopes formed by the input end interdigital transducer 2 after the cut-finger weighting, the cut-finger envelope 8 and the cut-finger envelope 9 is the envelope formed by the IDT 5 at the input end after being weighted by the cut finger, the cut finger envelope 21 and the cut finger envelope 27 are the envelope formed by the cut finger transducer 20 at the input end after the cut finger weight Coil. The abscission envelope 8, the abscission envelope 9 on the input end IDT 5 of the two interleaved abscission weighted input end and the abscission envelope 9 on the input end IDT 2 15. The main lobe area 10 and the main lobe area 14 respectively formed by the cut finger envelope 16 are arranged in a staggered manner, and are in the position of intersecting and overlapping each other. The incisor envelope 21 and the incisor envelope 27 of the IDT 20 at the input end form a main lobe area 28 . The IDT at the input end obtains the required frequency characteristics by changing the weighting method of the interdigital length. The intersecting parts of the IDTs of the input IDT 2, the input IDT 5, and the input IDT 20 form the excitation main lobe area 14 and the main lobe area of the IDT. 10 and the main lobe area 28, the electrical energy is converted into surface acoustic wave energy in the excitation area. The output end IDT 12 and the output end IDT 26 are isodigital IDTs, the abscisal envelope of which is a straight line, and the surface acoustic wave energy received in its excitation area is converted into electrical energy.

What is described above is only a preferred embodiment of the present invention, and the present invention is not limited to the above examples. It can be understood that other improvements and changes directly derived or conceived by those skilled in the art without departing from the spirit and concept of the present invention should be considered to be included in the protection scope of the present invention.

Claims (4)

1. A three-channel surface acoustic wave filter, comprising a first input IDT (2) and a second input IDT (5) integrated on a piezoelectric crystal sheet (7), The two input-end IDTs share the first output-end IDT (12), and the two input-end IDTs and the shared output IDT are arranged The first shielding bar (17) constitutes a dual-channel surface acoustic wave filter (29); the piezoelectric crystal sheet (7) is also integrated with the third input terminal interdigital transducer (20), the second output terminal fork Refer to the single-channel surface acoustic wave filter (30) formed by the transducer (26) and the second shielding bar (23) between the two; it is characterized in that the two-channel surface acoustic wave filter (29) and the single-channel surface acoustic wave filter An electrical isolation zone (18) made of metal strips and an acoustic isolation zone (31) made of sound-absorbing material are also integrated on the piezoelectric crystal sheet (7) between the channel surface acoustic wave filters (30). 2. The three-channel surface acoustic wave filter as claimed in claim 1, characterized in that: said electrical isolation zone (18) can be made of the same or different metal material as forming the interdigital transducer; said acoustic isolation The material of the band (31) can be the same as the sound-absorbing material coated on both ends of the piezoelectric chip for absorbing the reflected wave, or different sound-absorbing materials can be used. 3. The three-channel surface acoustic wave filter as claimed in claim 1 or 2, characterized in that: the acoustic isolation zone (31) overlaps with the electrical isolation zone (18), and the acoustic isolation zone (31) is positioned at the electrical isolation zone. Top with (18). 4. The three-channel surface acoustic wave filter according to claim 1 or 2, characterized in that: the acoustic isolation zone (31) is located on one side or both sides of the electrical isolation zone (18).

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