Fan-shaped surface acoustic wave band-pass filter

Abstract

The utility model discloses a fan-shaped surface acoustic wave band-pass filter. The fan-shaped surface acoustic wave band-pass filter comprises a filter chip, a ceramic base, a cover plate and an inner lead, the filter chip is located above the ceramic base, and the filter chip is connected with an inner electrode at the leading-out end of the ceramic base through an inner lead; according to the utility model, the shielding strip between the input IDT and the output IDT of the filter chip is provided with the sound absorption material coating position marks, and the sound absorption materials are coated at the different sound absorption material coating position marks according to the needs, thereby achieving the purpose of adjusting the center frequency and bandwidth of the filter.

Description

Technical Field

[0001] This utility model belongs to the field of electronic information signal processing technology, and specifically relates to a fan-shaped surface acoustic wave bandpass filter. Background Technology

[0002] Surface acoustic wave (SAW) bandpass filters are manufactured using semiconductor planar technology, offering advantages such as small size, light weight, good consistency, immunity to electromagnetic interference, no need for tuning, and excellent electrical performance. Therefore, they are widely used in various electronic signal processing fields. In the field of mid-frequency SAW bandpass filters, there are general-purpose transverse SAW filters with a 1 / 8λ finger width, SAW filters using a SPUDT (single-phase unidirectional transducer) structure, and SAW filters with resonant structures. However, to achieve a large relative bandwidth (relative bandwidth = filter bandwidth / filter center frequency), a fan-shaped transducer structure is generally used in the design. It is precisely based on the structural characteristics of the fan-shaped SAW bandpass filter chip that we can adjust the filter's center frequency and bandwidth laterally.

[0003] Conventional surface acoustic wave (SAW) bandpass filter chip transducers typically use metal electrode fingers of uniform width. This type of periodically sampled IDT has the highest acoustic-to-electric conversion efficiency only at its acoustic synchronization frequency. The further away from the center frequency, the lower the acoustic-to-electric conversion efficiency. Therefore, the relative bandwidth of this type of SAW filter is generally in a small range of less than 6%. It is precisely because this type of filter uses metal electrode fingers of uniform width that the center frequency and bandwidth of the filter cannot be adjusted in the later stages. Utility Model Content

[0004] To address the aforementioned shortcomings in the existing technology, this utility model provides a fan-shaped surface acoustic wave bandpass filter that solves the problems of relatively low bandwidth and the inability to adjust the center frequency and bandwidth of conventional surface acoustic wave bandpass filters in the later stages.

[0005] To achieve the above-mentioned utility model objectives, the technical solution adopted by this utility model is as follows: a fan-shaped surface acoustic wave bandpass filter, comprising: a filter chip, a ceramic base, a cover plate, and inner leads; the filter chip is located above the ceramic base, and the filter chip is connected to the inner electrode of the lead-out end of the ceramic base through the inner leads; the cover plate covers the ceramic base.

[0006] Furthermore: the filter chip includes a substrate, and an input IDT, an output IDT, and a shielding strip located on the substrate;

[0007] The shielding strip is located between the input IDT and the output IDT.

[0008] Furthermore, the substrate is a piezoelectric single crystal wafer.

[0009] Further, the input IDT and the output IDT each include n channels.

[0010] Further, the width of each IDT electrode finger of the input IDT and the output IDT gradually decreases along the vertical direction of the chip surface acoustic wave transmission.

[0011] Further, the shielding strip includes uniformly distributed sound-absorbing material coating position marks.

[0012] The utility model discloses the beneficial effects are: through the gradually changed fan shape structure mode of the width of chip electrode finger, coats sound-absorbing material at the proper position of the shielding strip between filter chip input IDT and output IDT, reaches high relative bandwidth and can adjust the filter center frequency and bandwidth later -stage purpose. BRIEF DESCRIPTION OF DRAWINGS

[0013] Figure 1 It is fan-shaped surface acoustic wave bandpass filter structural diagram;

[0014] Figure 2 It is fan-shaped surface acoustic wave bandpass filter chip basic structure diagram;

[0015] Figure 3 It is wide passband frequency response schematic diagram that a plurality of narrow passband frequency responses are combined;

[0016] Figure 4 It is filter center frequency and bandwidth adjustment before frequency response curve diagram;

[0017] Figure 5 It is filter center frequency and sound-absorbing material coating position schematic diagram when adjusting down;

[0018] Figure 6 It is filter center frequency and frequency response curve diagram after adjusting down;

[0019] Figure 7 It is filter center frequency and sound-absorbing material coating position schematic diagram when adjusting up;

[0020] Figure 8 It is filter center frequency and frequency response curve diagram after adjusting up;

[0021] Figure 9 It is sound-absorbing material coating position schematic diagram when only adjusting filter bandwidth;

[0022] Figure 10 It is filter frequency response curve diagram after only adjusting bandwidth;

[0023] Wherein: 1, filter chip;2, ceramic base;3, cover plate;4, inner lead;11, substrate;12, input IDT;13, output IDT;14, shielding strip;15, sound-absorbing material coating position mark. DETAILED DESCRIPTION

[0024] The specific embodiments of the present application are described below to enable those skilled in the art to understand the present application, but it should be clear that the present application is not limited to the scope of the specific embodiments, and for those skilled in the art, as long as various changes are within the spirit and scope of the present application defined and determined by the appended claims, these changes are obvious, and all the inventions utilizing the concept of the present application are within the scope of protection.

[0025] As shown in the drawings, Figure 1 In an embodiment of the present application, a fan-shaped surface acoustic wave bandpass filter is provided, comprising: a filter chip 1, a ceramic base 2, a cover plate 3 and an inner lead 4;

[0026] The filter chip 1 is located above the ceramic base 2, and the filter chip 1 is connected through the inner lead 4; the cover plate 3 covers above the ceramic base 2.

[0027] The filter chip 1 comprises a substrate 11, and an input IDT 12, an output IDT 13 and a shielding strip 14 located on the substrate 11.

[0028] The shielding strip 14 is located between the input IDT 12 and the output IDT 13.

[0029] The substrate 11 adopts a piezoelectric single crystal wafer.

[0030] As shown in the drawings, Figure 2 In this embodiment, in order to realize a larger relative bandwidth of the intermediate frequency surface wave filter, the chip of the filter generally adopts a fan-shaped structure (the shape of the filter IDT is similar to a fan that is opened); specifically: along the vertical direction of the surface acoustic wave transmission of the chip, the width of each IDT electrode finger is variable, the lower part of the electrode finger has a larger width, which excites the signal of the low frequency part of the passband, corresponding to a low starting frequency; the upper part of the electrode finger has a smaller width, which excites the signal of the high frequency part, corresponding to a high terminal frequency.

[0031] According to the requirements of the filter for bandwidth and other indicators, along the vertical direction of the surface acoustic wave propagation, the filter chip IDT can be divided into multiple groups of sub-channels with different center frequencies, each sub-channel corresponds to a narrower bandpass filter, and then all the sub-channel bandpass filters are combined into a wideband bandpass filter; as Figure 3 By weighting the electrode length of each group of sub-channels, a flat frequency response curve can be realized within a wider band, and by weighting the structure of the IDT such as phase, a better filter out-of-band suppression can be realized.

[0032] Therefore, in the embodiment, the input IDT 12 and the output IDT 13 are both provided with n channels, and the width of each IDT electrode finger of the input IDT 12 and the output IDT 13 is regularly reduced along the vertical direction of the chip surface acoustic wave transmission.

[0033] The shielding strip 14 is provided with uniformly distributed sound-absorbing material coating position marks 15, and the sound-absorbing material is coated at the corresponding position of the sound-absorbing material coating position marks 15 according to the amount of adjustment of the filter center frequency or the amount of adjustment of the bandwidth, when the center frequency needs to be adjusted downward, the sound-absorbing material is coated at the appropriate position of the upper end (the end with thinner electrode fingers) of the shielding strip between the input and output IDTs of the filter, the more the center frequency is adjusted downward, the closer the coating position is to the middle of the chip; conversely, when the center frequency needs to be adjusted upward, the sound-absorbing material is coated at the appropriate position of the lower end (the end with wider electrode fingers) of the shielding strip between the input and output IDTs of the filter, the more the center frequency is adjusted upward, the closer the coating position is to the middle of the chip; when the center frequency is not adjusted and only the filter bandwidth needs to be adjusted, the sound-absorbing material needs to be simultaneously coated at the appropriate position of both ends of the shielding strip between the input and output IDTs of the filter.

[0034] When the filter center frequency or bandwidth needs to be adjusted, the position of the sound-absorbing material coating position mark 15 on which the sound-absorbing material is coated is determined according to the direction and amount of adjustment of the filter center frequency or bandwidth, and the coated filter can be tested for the center frequency or bandwidth by using a network analyzer, and the sound-absorbing material can be re-coated when the center frequency or bandwidth does not reach the expectation.

[0035] In an embodiment of the utility model, we make a center frequency 46.5MHz, 3dB bandwidth 21.9MHz sectorial surface acoustic wave band-pass filter, and the relative bandwidth of the filter is 47.1%, and taking the filter as an example, the adjustment method of the filter center frequency and bandwidth is illustrated, the center frequency and bandwidth adjustment before the frequency response curve of the filter is as shown in the figure, Figure 4 .

[0036] As shown in the figure, Figure 5 , when the filter center frequency needs to be adjusted downward, the sound-absorbing material is coated at the appropriate position of the sound-absorbing material coating position mark 15 on the upper end (the end with thinner electrode fingers) of the shielding strip 14; as shown in the figure, Figure 6 , after the sound-absorbing material is coated, the high-end curve of the filter frequency response curve shrinks to the low end, the filter center frequency is adjusted from 46.49MHz to 45.99MHz, and the filter bandwidth is adjusted from 21.9MHz to 20.9MHz.

[0037] As shown in the figure, Figure 7As shown, when it is necessary to adjust the center frequency of the filter upwards, sound-absorbing material is applied to the appropriate position on the sound-absorbing material coating position mark 15 at the lower end of the shielding strip 14 (referring to the thicker end of the strip); as shown... Figure 8 As shown, after coating with sound-absorbing material, the low end of the filter's frequency response curve shrinks towards the high end, the filter's center frequency is adjusted from 46.49MHz to 47.01MHz, and the filter bandwidth is adjusted from 21.9MHz to 20.86MHz.

[0038] like Figure 9 As shown, when only the filter bandwidth needs adjustment and the center frequency of the filter does not need adjustment, sound-absorbing material is applied to the appropriate positions marked 15 on both the upper and lower ends of the filter chip shielding strip 14 (referring to the thinner and thicker ends of the strip); for example... Figure 10 As shown, after coating with sound-absorbing material, the low-end frequency response curve of the filter shrinks towards the high end, and the high-end frequency response curve of the filter shrinks towards the low end. The center frequency of the filter remains basically unchanged, and the filter bandwidth is adjusted from 21.9MHz to 19.92MHz.

[0039] In summary, this application applies sound-absorbing material coating at appropriate positions on the sound-absorbing material coating position mark 15 on the shielding strip 14 of the fan-shaped surface acoustic wave bandpass filter chip to block the transmission of surface acoustic waves in the low-frequency or high-frequency sub-channels of the chip surface, thereby achieving the purpose of adjusting the center frequency and bandwidth of the filter.

[0040] In the description of this utility model, it should be understood that the terms "center," "thickness," "upper," "lower," "horizontal," "top," "bottom," "inner," "outer," and "radial," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this utility model. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or the number of implicitly specified technical features. Therefore, a feature defined by "first," "second," and "third" may explicitly or implicitly include one or more of that feature.

Claims

1. A sectoral acoustic surface wave bandpass filter, characterized by, The application relates to a filter chip, a ceramic base, a cover plate and inner leads. The filter chip is located above the ceramic base, and the filter chip is connected with the inner electrode of the ceramic base through the inner leads. The filter chip comprises a substrate, an input IDT, an output IDT and a shielding strip.

2. The sector-shaped acoustic surface wave bandpass filter according to claim 1, characterized in that, The shielding strip is located between the input IDT and the output IDT. The substrate is a piezoelectric single crystal substrate.

3. The sector-shaped acoustic surface wave bandpass filter according to claim 2, characterized in that Each of the input IDT and the output IDT comprises n channels.

4. The sector-shaped acoustic surface wave bandpass filter according to claim 2, characterized in that, The width of each IDT electrode finger of the input IDT and the output IDT decreases regularly along the vertical direction of the chip surface acoustic wave transmission.

5. The sector-shaped acoustic surface wave bandpass filter according to claim 2, wherein, The shielding strip comprises uniformly distributed sound-absorbing material coating position marks.

6. The sector-shaped acoustic surface wave bandpass filter according to claim 2, wherein ​

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