CN2619413Y - Surface acoustic wave sector filter - Google Patents

Abstract

The utility model relates to a surface acoustic wave fan-shaped filter, which comprises: two fan-shaped transducers made of semiconductor planar technology are arranged on a piezoelectric substrate along the sound wave propagation direction, and the utility model is characterized in that: the fan-shaped transducer The resonant single-phase and unidirectional structure is adopted, and the fan-shaped transducer is divided into any sub-filters along the direction of the surface acoustic wave, and the sub-filters are connected in series, parallel or a combination of series and parallel. Compared with the conventional single-phase unidirectional fan-shaped transducer, the fan-shaped filter achieves a rectangularity factor that can only be realized by about twice the length of a common transducer when the device size is certain; when the device’s rectangularity factor is constant, the The sector transducer length can be reduced by half. Compared with the conventional resonant single-phase one-way filter, the relative bandwidth of the conventional resonant single-phase one-way filter is usually less than 10%. The resonant single-phase one-way fan filter inherits the advantages of the fan filter and can achieve more Wide bandwidth, the bandwidth can reach more than 30%.

Description

SAW sector filter

                    

The utility model relates to a surface acoustic wave filter (hereinafter referred to as a SAW filter) in the acoustic technology, in particular to a surface acoustic wave sector filter with a single-phase and one-way structure.

Background technique

A conventional surface acoustic wave filter 1 with a fan-shaped structure, as shown in Figure 1, as described in Document 1, IEEE1998 Ultrasonics Sypisium Proceedings pp27-37: wherein the two fan-shaped transducers 3, 4 use a single electrode width control Phase unidirectional structure (referred to as EWC/SPUDT). In Fig. 1, 2 is a piezoelectric substrate, and the unidirectionality of transducers 3 and 4 is realized by a reflective electrode 5 placed in the middle of the device, especially the effect of all reflective electrodes indicated by the reflective electrode 5 is to radiate sound waves The radiation adds in-phase in the direction towards the other transducer and out-phase and cancels in the direction away from the other transducer.

As another example, a conventional SAW resonant single-phase one-way filter 2, as shown in Figure 2, this type of filter is introduced in Document 2, IEEE1994 Ultrasonics SypisiumProceedings pp1-6, it consists of two The resonant transducers 9, 10 are shown. Among them, 2 in Figure 2 is the substrate; left to right is the forward direction, 11 represents a forward resonant single-phase unidirectional unit, and 12 represents a reverse resonant single-phase unidirectional unit. Transducer 9 is formed by parallel connection of several transducer unit electric terminals same as 11 , and transducer 10 is formed by parallel connection of several transducer unit electric terminals same as 12 . The structure is based on EWC/SPUDT transformation. The width of the transducer array fingers is one-eighth of the wavelength, and the reflection width of the reflection grid can be changed. This structure forms a resonant cavity in the transducer, so that the ratio Higher squareness factor for plain SPUDT. Wherein the resonant single-phase unidirectional transducer unit can be as shown in Fig. 3 (a), in Fig. 3 (a), 13 represents the part with the wavelength in the interval of the forward reflection grating, and 14 represents the part with wavelength in the interval of the reverse reflection grating The wavelength is the part of the period. The part of the forward reflection grid in Figure 3(b) corresponds to 13 in Figure 3(a), the part of the reverse reflection grid corresponds to 14 in Figure 3(a), and the empty reflection grid corresponds to the finger weighting of the reflection grid. As an improved version of the resonant single-phase unidirectional transducer in Figure 3(a) in this example, as introduced in Document 3, IEEE1998 Ultrasonics Sypisium Proceedings pp47-50: The transducer unit of the resonant single-phase unidirectional transducer It can be two structures as shown in Fig. 4 .

As mentioned above, the EWC/SPUDT fan-shaped filter adopted by the filter 1 can obtain the square coefficient and low insertion loss of the filter. In filter 2, the filter composed of a resonant single-phase unidirectional transducer structure has the following characteristics. It can form a resonant cavity in the middle of the transducer and increase the length of the impulse response, so that the device size can be kept constant. Under the premise of achieving a smaller square factor, or under the condition of a certain square factor, the size of the device is reduced. But there are some cases where the resonant single-phase unidirectional transducer structure is not practical, such as broadband filters. The fingers of the sector filter are oblique. According to the research, the frequency response of the sector filter can be calculated as follows: Differentiate the aperture of the sector filter into several small channels connected in series at the end, as shown in Figure 1 , each channel j is called a sub-filter. For the sub-filter (such as the jth channel in Figure 1), when its aperture is small enough relative to the wavelength corresponding to the center frequency of the sector filter, the sub-filter can be regarded as an ordinary filter with non-sloping aperture device. The center frequency of the sub-filter is determined by the width of the fingers of the sub-filter, that is, the wavelength. In the fan-shaped transducer, the narrow end of the sector corresponds to the sub-filter with high frequency, and the wide end of the sector corresponds to the sub-filter with low frequency. 11 in the shaded part of Figure 2. Like ordinary uniform aperture filters, each sub-filter contains left and right transducers as shown in the shaded parts 7 and 8 in Figure 1, so that the sub-filter can be calculated as an ordinary filter with uniform aperture, and the sub-filter The frequency response of the filter can also be solved according to the method of the ordinary filter, and the total frequency response of the sector filter is equal to the sum of the frequency responses of all sub-filters. Although the fan-shaped transducer structure adopted by filter 1 can achieve a smaller square factor, in some special applications, such as the same device size, a smaller square factor is required, or the same square factor When a smaller device size is required in some cases, fan-shaped filters using conventional methods cannot meet the requirements.

Contents of the invention

The purpose of this utility model is to provide a surface acoustic wave sector filter with a single-phase one-way structure composed of a piezoelectric substrate and two single-phase one-way sector transducers, which can maintain the existing sector filter Advantages, while the size remains unchanged, the square coefficient of the filter can be further reduced, or the purpose of further reducing the size of the device can be achieved when the square coefficient remains unchanged, thereby solving the problem that is still difficult to solve in the prior art.

The purpose of this utility model is achieved in that:

The surface acoustic wave fan-shaped filter provided by the utility model includes: on the piezoelectric substrate, there are two fan-shaped transducers made of semiconductor planar technology along the sound wave propagation direction, and it is characterized in that: the fan-shaped transducer adopts Resonant single-phase unidirectional structure, the fan-shaped transducer is divided into any number of sub-filters along the direction of the surface acoustic wave, and the sub-filters are connected in series, parallel or a combination of series and parallel, as shown in Figure 5.

The series connection between the sub-filters means that the sub-filters are sequentially connected to the next sub-filters next to each other end-to-end.

The parallel connection between the secondary filters is that the electric terminals of each secondary filter connected end to end adopt a parallel structure, and the fan-shaped filter shown in Figure 6 (a) is divided into two secondary filters. The electrical terminals of the two sub-filters are connected in parallel, that is, the narrow end of the upper sub-filter is connected to the wide end of the lower sub-filter which is closely connected to it through electrodes, and the connection position of the upper and lower finger strips next to the connecting electrodes of the two sub-filters is the same, and they are connected in The electrodes of the two filters appear alternately from the input end and the ground end, and then all the input ends and the ground end are connected together through the electrodes.

The sub-filters are connected in series in sections, wherein the sub-filter is composed of two resonant single-phase unidirectional transducers on the left and right, wherein each resonant single-phase unidirectional transducer includes 2 or 2 The above resonant single-phase unidirectional units, (as shown in Fig. 3(a) and 4), each electric terminal of each resonant single-phase unidirectional unit can be serially connected in segments, as shown in Fig. 6(c), each The transducers of a pair of filters are connected in series with a resonant single-phase unidirectional unit structure, that is, the left and right sides of the transducer are adjacent to two resonant single-phase unidirectional units, and the first unit is connected to the fingers of the upper and lower electrodes. Then select the wide end or the narrow end of the electrodes in the two units to connect, and disconnect the other end to form a segmented series structure of the transducers in the sub-filter. Finally, each sub-filter is connected at the end to form this fan-shaped transducer. The series structure of the energy device is shown in Fig. 6(b).

The resonant single-phase unidirectional units in the secondary filter can adopt a series and parallel hybrid structure, that is, several secondary filters can be connected in parallel according to the parallel structure, and then a segmented series structure can be used for each secondary filter ; Or it can first adopt segmental series connection for each pair of filters, and then use parallel structure connection for each segment after series connection, as shown in Figure 6 (d), it is first divided into two pairs of filters and connected in parallel, and then adopts two pairs of filters for each pair of filters segments in series.

It also includes the fingers of the resonant single-phase unidirectional sector filter that can be aperture-weighted to make the fingers of the filter curved; as shown in FIG. 7 .

It also includes the reflective electrode in the single transducer in the resonant single-phase single-directional sector filter, which can adopt EWC/SPUDT weighting, thumb weighting or a combination of both.

The finger width of the fan-shaped filter is determined by the passband frequency of its frequency response: the wavelength λ _max corresponding to the widest end of the fan-shaped filter corresponds to the lowest end frequency f ₀ -BW/2 of the passband, and its narrowest end corresponds to The wavelength λ _min corresponds to the highest end frequency f ₀ +BW/2 of the passband frequency, and the wavelength λ(f) corresponding to the finger width in the middle of the filter corresponds to the frequency f in the middle of the passband of its frequency response. f ₀ : the center frequency of the filter, BW: the bandwidth of the filter. The secondary filter for each frequency point of the frequency response passband corresponds to an ordinary resonant single-phase one-way filter. Therefore, the finger width and arrangement of the secondary filter are the same as those of the ordinary resonant single-phase one-way filter.

The advantage of the utility model is that the surface acoustic wave resonant sector filter with a single-phase and one-way structure provided by the utility model has a resonant type The single-phase unidirectional fan-shaped filter can achieve a square factor that is about twice the length of an ordinary transducer; when the device square factor is constant, the length of the fan-shaped transducer in the device can be reduced by half. Compared with the conventional resonant single-phase one-way filter, the relative bandwidth of the conventional resonant single-phase one-way filter is usually less than 10%. The resonant single-phase one-way fan filter inherits the advantages of the fan filter and can achieve more Wide bandwidth, the bandwidth can reach more than 30%.

Description of drawings

Fig. 1 is a schematic plan view of a conventional EWC/SPUDT fan filter.

Fig. 2 is a schematic plan view of a conventional resonant single-phase single-directional structural filter.

Fig. 3 (a) is to be in the plane perpendicular to wafer and finger bar, the sectional sketch of the resonant type single-phase unidirectional unit structure that can adopt in a conventional resonant type single-phase unidirectional structure filter; Wherein refers to wide and narrow It is 1/8 wavelength, and the wide one is 1/8-3/8 wavelength; the interval between dotted lines is 1 wavelength;

The part of the forward reflective grid in Figure 3(b) corresponds to 13 in Figure 3(a), the part of the reverse reflective grid corresponds to 14 in Figure 3(a), and the empty reflective grid corresponds to the finger weighting of the reflective grid.

Fig. 4 is in the plane that is perpendicular to wafer and finger bar, the sectional outline of the improved resonant type single-phase unidirectional unit structure that can adopt in a conventional resonant type single-phase unidirectional structure filter; Finger width among the figure: narrow 1/8 wavelength, wide 1/8-3/8 wavelength;

Fig. 5 is a schematic plan view of the structure of the SAW sector filter of the present invention.

Fig. 6 (a) is a schematic plan view of a fan filter with a parallel structure in the surface acoustic wave fan filter of the present invention

Fig. 6(b) is a schematic plan view of a sector filter with a series structure in the surface acoustic wave sector filter of the present invention.

Fig. 6(c) is a schematic plan view of the secondary filter of the present invention adopting a series structure.

Fig. 6(d) is a schematic plan view of a sub-filter with a series-parallel hybrid structure in the SAW sector filter of the present invention.

Fig. 7 is a schematic plan view of an aperture-weighted fan filter that can be used for a fan filter of the present invention.

Fig. 8 is a schematic plan view of an embodiment of a structure of the sector filter of the present invention.

Fig. 9 is a schematic plan view of an embodiment of a structure of the sector filter of the present invention.

Fig. 10 is a schematic plan view of an embodiment of another structure of the sector filter of the present invention.

Graphic description:

1-Filter 2-Substrate

3-Left transducer of sector filter 4-Right transducer of sector filter

5-reflection grating 6-secondary filter

7- left transducer of sub-filter 8- right transducer of sub-filter

9-Left transducer of resonant filter 10-Right transducer of resonant filter

11-Forward resonant single-phase unidirectional unit 12-Reverse resonant single-phase unidirectional unit

13-The part of the period of the wavelength in the forward reflection grating interval,

14-The wavelength-period part of the retroreflective grating interval

Detailed ways

Example 1:

According to Fig. 5, a SAW sector filter with a single-phase and one-way structure is fabricated, with a center frequency of f ₀ =49 MHz and a bandwidth of BW = 14 MHz. The sub-filter adopts the conventional resonant single-phase unidirectional transducer structure shown in Figure 2, and the resonant single-phase unidirectional unit of the sub-filter adopts the unit shown in Figure 3(a). In FIG. 3( a ), 13 represents the part whose period is the wavelength in the interval of the forward reflection grating, and 14 represents the part whose period is the wavelength in the interval of the reverse reflection grating. The part of the forward reflection grid in Figure 3(b) corresponds to 13 in Figure 3(a), the part of the reverse reflection grid corresponds to 14 in Figure 3(a), and the empty reflection grid corresponds to the finger weighting of the reflection grid. The filter 1 includes: on the YX-128 ° lithium niobate substrate 2 along the sound wave propagation direction, two fan-shaped transducers 3 and 4 are made by semiconductor planar technology, the thickness of the aluminum plating film is 1500 angstroms, and the aperture is 100λ ₀ , the sector filter fingers are arranged in such a way that the left transducer 3 is composed of 128 forward resonant single-phase and one-way units 11 as in Fig. 2, which are not segmented. The right transducer 4 is composed of 84 anti-resonant single-phase unidirectional units 12 as shown in Figure 2, which are not segmented. λ ₀ : the wavelength corresponding to the center frequency of the fan-shaped transducer.

The finger width of the sector transducer is determined by the passband frequency of its frequency response: that is, the wavelength λ _max corresponding to the widest end of the sector filter is corresponding to the lowest end frequency f ₀ -BW/2 of the passband, which is 42MHz, The wavelength λ _min corresponding to its narrowest end corresponds to the highest end frequency f ₀ +BW/2 of the passband frequency, ie 56MHz. Therefore, the width of the widest end reflective grid (electrode) 5 of the fan-shaped transducer, the transducing electrode (finger bar other than the reflective grid bar), and the finger bar spacing are: 1/4λ _max and 1/8λ _max , 1/ 8λ _max , the widths of the narrowest reflective grating (electrode) 5 and transducing electrodes (fingers other than the reflective grating) are 1/4λ _min and 1/8λ _min , 1/8λ _min respectively. In this way, each finger bar is connected by the widest end and the narrowest end to form a trapezoidal finger bar, and the height of the trapezoid is the aperture of the fan-shaped transducer.

Since all sub-filters use resonant single-phase one-way filter 2, it can achieve a higher squareness coefficient than ordinary single-phase one-way filter. The sum of the frequency responses of all sub-filters is the frequency response of the total sector transducer, so this structure again has the advantage of the large relative bandwidth of a conventional sector transducer.

Embodiment 2: Make a SAW sector filter with a single-phase and unidirectional structure according to FIG. 9 , the center frequency of the sector filter is f ₀ =65 MHz, and the bandwidth BW=9 MHz. Its basic structure is identical with embodiment 1. The difference is: substrate material: model YZ lithium niobate, aluminum film thickness 1600 angstroms, the left transducer 3 is divided into two sections connected in series according to Fig. 6(b). That is, the sub-filter is as shown in Fig. 6(c). The left transducer of each filter adopts a resonant single-phase one-way unit structure in series, that is, the left and right transducers are adjacent to two resonant single-phase one-way units, and one of the ground units is connected to the fingers of the upper and lower electrodes Reverse direction, then select the wide end or the narrow end of the electrodes in the two units to connect, and disconnect the other end to form a segmented series structure of the transducers in the sub-filter, and finally each sub-filter is connected at the end to form The series structure of this fan-shaped transducer.

Embodiment 3: Make a SAW sector filter with a single-phase and unidirectional structure according to FIG. 9 , the center frequency of the sector filter is f ₀ =70MHz, and the bandwidth BW=9MHz. Its basic structure is identical with embodiment 1. The difference is: substrate material: quartz, aluminum film thickness 1200 angstroms, parallel structure is adopted between the two filters of the left transducer, the fan-shaped filter shown in Figure 6(a) is divided into two sub-filters , the electrical terminals of the two sub-filters are connected in parallel, that is, the narrow end of the upper sub-filter is connected to the wide end of the lower sub-filter which is closely connected to it through electrodes, and the connection positions of the upper and lower fingers next to the connecting electrodes of the two sub-filters are the same, The electrodes connected to the two filters appear alternately from the input terminals and the ground terminals, and then all the input terminals and the ground terminals are connected together through the electrodes. The arrangement of transducer fingers is realized by weighting after Hamming weighting, and the number of finger logarithms is 186 pairs. The resonance unit adopts the forward resonant single-phase one-way unit 11 as shown in Figure 2. When the reflection grid adopts the transducer Finger weighting implementation after domain convolution. The right transducer adopts a transducer composed of 260 reverse-resonant single-phase unidirectional units 12 as shown in Figure 2 without segmented resonant single-phase unidirectional units. Post-finger weighting is implemented. The aperture is 90λ ₀ .

Embodiment 4: According to Fig. 10, a SAW sector filter with a single-phase and unidirectional structure is manufactured, the center frequency of the sector filter is f ₀ =60MHz, and the bandwidth BW=8.2MHz. Its basic structure is identical with embodiment 3. The difference is: Substrate material: 36°Y-cut lithium tantalate type, aluminum film thickness 1300 angstroms, the left transducer is divided into two sub-filters with equal apertures, and the parallel structure is adopted between the two sub-filters. In Embodiment 3, the sub-filter adopts a series structure, which is the same as in Embodiment 2. The number of forward resonance units as shown in Figure 2 is 70 for the left transducer making two pairs of filters, and the number of reverse resonance units for the right transducer is 100 as shown in Figure 2. The aperture is 80λ ₀ .

The specific manufacturing steps of the resonant single-phase unidirectional fan-shaped filter are as follows: the square coefficient of a single sub-filter is preliminarily determined according to the square coefficient requirements of the device. According to the usual optimization method, the combined structure of the resonant single-phase unidirectional unit of the two sub-filters in the same channel is obtained, and the frequency response of the sub-filter is obtained; each sub-filter corresponds to a center frequency, and the fan-shaped The center frequency of the sub-filter of the filter corresponds to its wavelength (the narrowest finger width is 1/8 wavelength), the center frequency of the sub-filter at the widest end corresponds to the lowest point of the passband frequency of the sector filter, and the sub-filter at the narrowest end The center frequency corresponds to the highest point of the passband frequency of the fan-shaped filter; for different sub-filters have different center frequencies, the frequency response of all sub-filters is obtained according to the same principle, and then summed for all sub-filters, Get the total filter response.

Claims (8)

1. A surface acoustic wave sector filter, comprising: on the piezoelectric substrate along the sound wave propagation direction there are two sector transducers that adopt semiconductor planar technology to make, it is characterized in that: described sector transducer adopts resonant Single-phase unidirectional structure, the fan-shaped transducer is divided into any number of sub-filters along the surface acoustic wave direction, and the sub-filters are connected in series, parallel or a combination of series and parallel. 2. The surface acoustic wave fan filter according to claim 1, characterized in that: the sub-filters are connected in series so that all sub-filters are connected end-to-end with the next sub-filter next to them. 3. The surface acoustic wave fan filter according to claim 1, characterized in that: the electric terminals are connected in parallel between the described sub-filters; the narrow end of the sub-filters above it is closely connected with the following sub-filters by electrodes. The wide end of the filter is connected, and the connection position of the upper and lower finger strips adjacent to the connecting electrodes of the two filters is the same. The electrodes connected to the two filters appear alternately from the input end and the ground end, and then all the input ends and the ground end are respectively connected through the electrodes. connected together. 4. The surface acoustic wave fan filter according to claim 1, characterized in that: the connection between the secondary filters adopts the secondary filter and its next secondary filter to be connected end to end, including each resonant type The electric terminals of the single-phase one-way unit adopt segmental series connection; the left and right of the left transducer are adjacent to one of the two resonant single-phase one-way units, and one unit is connected to the fingers of the upper and lower electrodes, and then the electrode width of the two units is selected. One end or one narrow end is connected, and the other end is disconnected to form a segmented series structure of the transducers in the sub-filter, and finally each sub-filter is connected end-to-end to form a segmented series structure. 5. The surface acoustic wave fan filter according to claim 1, characterized in that: the connection between the secondary filters adopts a resonant single-phase one-way unit in the filter, which can adopt a series and parallel hybrid structure. 6. by the described surface acoustic wave sector filter of claim 1, it is characterized in that: also comprise the reflective electrode in the single transducer in the resonant type single-phase unidirectional sector filter can adopt control electrode width weighting, draw finger Weighted or a combination of both. 7. by the described surface acoustic wave sector filter of claim 1, it is characterized in that: the finger width of secondary filter is determined by the passband frequency of its frequency response, the corresponding finger width of the widest end of the finger width of its sector filter The width corresponds to the lowest end frequency of the passband, the finger width corresponding to the narrowest end corresponds to the highest end frequency of the passband frequency, and the finger width in the middle of the filter corresponds to the frequency corresponding to the middle of the passband of its frequency response. 8. The surface acoustic wave sector filter according to claim 1, characterized in that: the secondary filter is composed of two left and right resonant single-phase unidirectional transducers, wherein each resonant single-phase single-phase transducer The directional transducer is composed of 2 or more resonant single-phase unidirectional units.

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