Parallel composite resonator and method for designing same

Abstract

The objective of the present invention is to provide a parallel composite resonator in the form of a parallel combination of two SAW resonators, the parallel composite resonator being capable of improving admittance performance and enhancing skirt characteristics in a frequency response without increasing a die area, and a method for designing same. The parallel composite resonator according to one embodiment of the present invention is configured such that a number of electrode fingers corresponding to an admittance according to design specifications is provided in at least one of a first IDT electrode and a second IDT electrode, on the basis of a reference number of fingers determined from a function representing an amount of change in admittance with respect to the number of electrode fingers.

Description

Parallel composite resonator and design method thereof

[0001] The present invention relates to a parallel composite resonator formed by a parallel combination of two SAW resonators and a method for designing the parallel composite resonator, in order to improve the performance of a SAW resonator that converts an electrical signal into a Surface Acoustic Wave (SAW) of a piezoelectric material or converts a Surface Acoustic Wave back into an electrical signal by utilizing the piezoelectric effect of a piezoelectric material.

[0002] With the advancement of mobile communication devices such as smartphones and tablets, there is a demand for high performance in surface acoustic wave (SAW) devices and components, including SAW resonators and filters utilizing them. In particular, with the advent of the 5G era, the number of RF filters used in mobile phones has increased significantly as the frequency range available for use in mobile environments has expanded. Consequently, as more filters and RF components must be integrated within a limited die area, this requires miniaturization and integration of filter sizes.

[0003] It is necessary to minimize mutual interference between frequencies caused by such a significantly increased number of components, and for this purpose, the steep skirt characteristic on the response curve of the surface acoustic wave (SAW) filter is becoming increasingly important.

[0004] FIG. 1 shows the structure of a conventional SAW resonator. Such a SAW resonator is equipped with an InterDigital Transducer (IDT) electrode (20) configured by arranging metal electrode fingers (21, 22) in parallel and continuously on a piezoelectric substrate (11) made of a piezoelectric material. When an alternating current signal voltage is applied to the IDT electrode (20), an electric field is generated between the electrode fingers (21, 22) inside the IDT electrode, and a deformation occurs on the surface of the substrate due to the piezoelectric effect of the piezoelectric substrate (10), causing surface acoustic waves (SAW) to propagate in both directions of the IDT electrode.

[0005] In this way, the surface acoustic wave generated on the surface of the piezoelectric substrate (10) by the IDT electrode (20) can perform the function of a bandpass filter that passes frequency components tuned to the frequency of the surface acoustic wave and attenuates the remaining signal during the process of converting it back into an electrical signal by the output electrode within the IDT electrode or another IDT placed adjacently.

[0006] At this time, a reflector (14) that forms metal thin film gratings around the IDT electrode (20) on the piezoelectric substrate (10) can be provided to reflect surface acoustic waves generated by the IDT electrode (20) and propagated to the outside back to the IDT electrode (20), thereby reducing loss.

[0007] Bandpass filters can be implemented by configuring various SAW resonators in an appropriate manner, and the performance of the bandpass filter is closely correlated with the performance of the SAW resonator.

[0008] As shown in FIG. 1, parameters that can adjust the performance of the SAW resonator include the width (w) and thickness (t) of the electrode fingers (21, 22) of the IDT electrode, the spacing (s) between fingers, the period (λ) and half period (p=λ / 2) of the IDT electrode, and the aperture length (LA), which is the length of the section where the electrode fingers overlap. By appropriately adjusting these parameters according to the design specifications, the desired performance of the SAW resonator can be achieved.

[0009] The performance of the SAW resonator can be quantified using a quality factor (Q-factor) related to parameters such as the width (w) and thickness (t) of the electrode fingers (21, 22) of the IDT electrode as described above, and the higher the quality factor, the better the performance of the SAW resonator.

[0010] However, while the performance of a SAW resonator can be easily characterized by the quality factor (Q-factor), for filters made from a combination of various resonators, the quality factor alone is insufficient to meet design specifications; therefore, the transition characteristics between the two characteristic frequencies of the SAW resonator can be considered as another characterization index.

[0011] Figure 2 shows the response (Y) of a 1-port resonator. 11 This is a graph showing an example of ), and it can be seen that there is one resonant frequency (fr) and one anti-resonant frequency (fa) as characteristic frequencies on the response curve of the resonator.

[0012] Here, the transition characteristic (U) between two characteristic frequencies (fr, fa) x ) can be defined as in mathematical formula 1 below.

[0013]

[0014] As the aforementioned transition characteristics become steeper, the performance of the resonator improves. This requires a resonator design that shifts the pole (fr) and zero (fa) closer together. To achieve this, it is necessary to connect IDT capacitors or passive capacitors in parallel with the SAW resonator, but this presents the problem of significantly increasing the area of ​​the SAW resonator and filter.

[0015] Furthermore, in the case of filters made by combining various resonators, particularly multiplexers such as duplexers, there are limitations to designing solely to improve the performance of each individual resonator in order to satisfy design specifications that aim to improve the filter skirt characteristics without increasing the die area, as mentioned above.

[0016] A parallel composite resonator, formed by connecting two SAW resonators in parallel, is being used in designs to improve the performance of the resonator while increasing the degree of freedom in filter design, such as multiplexers.

[0017] One method to improve the admittance performance of such a parallel composite resonator is to increase the number of electrode fingers of the IDT electrodes of each resonator. However, as previously explained, this can cause a fatal problem of significantly increasing the die area, and if an external capacitor is used to improve skirt characteristics, the die area can increase even more significantly. Therefore, there is a need for a technology that can easily improve the performance of a parallel composite resonator, which can be primarily utilized for design diversity, without increasing the die area.

[0018] Prior art documents related to the present invention include Japanese Registered Patent No. 6585459, Japanese Registered Patent No. 3487772, Japanese Published Patent No. 2011-130513, and Japanese Published Patent No. 2001-237668.

[0019] The present invention aims to provide a parallel composite resonator and a method for designing the same, which can improve admittance performance and skirt characteristics in frequency response in a parallel combination form of two SAW resonators without increasing the die area.

[0020] A parallel composite resonator according to one embodiment of the present invention is a parallel composite resonator configured by connecting a first SAW resonator and a second SAW resonator in parallel, wherein the first SAW resonator includes a first IDT electrode having a plurality of electrode fingers that convert an electrical signal into a surface acoustic wave on a piezoelectric substrate, and the second SAW resonator includes a second IDT electrode having a plurality of electrode fingers that convert an electrical signal into a surface acoustic wave on a piezoelectric substrate, and is configured such that the number of electrode fingers corresponding to the admittance according to the design specifications of the parallel composite resonator is provided in at least one of the first IDT electrode and the second IDT electrode based on a reference finger number determined from a function of the change amount of admittance with respect to the number of electrode fingers.

[0021] Additionally, preferably, the number of electrode fingers at the point where two linearly approximated lines intersect at two locations where the slope of the tangent line of the change in admittance function for the number of electrode fingers changes is determined as the reference finger number, and at least one of the first IDT electrode and the second IDT electrode is determined and provided based on the determined reference finger number.

[0022] Additionally, preferably, the number of electrode fingers provided in at least one of the first IDT electrode and the second IDT electrode is configured to be the number of electrode fingers corresponding to the admittance value according to the design specifications of the parallel composite resonator, within a range less than the reference finger number on the function of the change amount of admittance with respect to the number of electrode fingers.

[0023] Additionally, preferably, the number of electrode fingers provided on the first IDT electrode of the first SAW resonator and the number of electrode fingers provided on the first IDT electrode of the second SAW resonator are provided equally as the number of electrode fingers selected to correspond to the admittance value according to the design specifications of the parallel composite resonator within a range smaller than the reference finger number on the function of the change amount of admittance with respect to the number of electrode fingers.

[0024] Additionally, preferably, the number of electrode fingers provided on the first IDT electrode of the first SAW resonator and the number of electrode fingers provided on the first IDT electrode of the second SAW resonator are each selected and provided as different numbers corresponding to the admittance value according to the design specifications of the parallel composite resonator within a range smaller than the reference finger number on the function of the change amount of admittance with respect to the number of electrode fingers.

[0025] Additionally, preferably, when the number of electrode fingers provided on the first IDT electrode of the first SAW resonator is greater than or equal to the reference number of fingers, the number of electrode fingers corresponding to the admittance value at the reference number of fingers and the admittance value required according to the design specifications are provided on the second IDT electrode of the second SAW resonator, in a function of the change amount of admittance with respect to the number of electrode fingers.

[0026] Additionally, preferably, at least one of the first SAW resonator and the second SAW resonator is configured to include a slit reflector that reflects surface acoustic waves to at least one of the first IDT electrode and the second IDT electrode, respectively, and forms a slit capacitance, which is a slit structure that functions as a capacitance.

[0027] Meanwhile, a design method for a parallel composite resonator according to one embodiment of the present invention is a design method for a parallel composite resonator configured such that a first SAW resonator including a first IDT electrode having a plurality of electrode fingers for propagating surface acoustic waves and a second SAW resonator including a second IDT electrode having a plurality of electrode fingers for propagating surface acoustic waves are connected in parallel, comprising the steps of: determining a reference number of fingers from a function of the change amount of admittance with respect to the number of electrode fingers; and determining a first number of electrode fingers corresponding to the admittance according to the design specifications of the parallel composite resonator based on the determined reference number of fingers as the number of electrode fingers of the first IDT electrode of the first SAW resonator. and includes the step of determining, based on the number of reference fingers determined above, a number of second electrode fingers different from the number of first electrode fingers, corresponding to the admittance according to the design specifications of the parallel composite resonator, as the number of electrode fingers of the second IDT electrode of the second SAW resonator.

[0028] Additionally, preferably, the step of determining the reference finger number comprises: a step of dividing into a first region, a second region, and a third region based on the change in the slope of the tangent line of the function of the change in admittance for the number of electrode fingers; and a step of determining the number of electrode fingers as the reference finger number at the point where the linearly approximated line in the first region and the linearly approximated line in the third region of the function of the change in admittance for the number of electrode fingers intersect.

[0029] Additionally, preferably, in at least one step among the step of determining the number of first electrode fingers and the step of determining the number of second electrode fingers, the method is characterized by including the step of determining the number of electrode fingers corresponding to the admittance value according to the design specifications of the parallel composite resonator within a range smaller than the reference number of fingers as at least one of the number of first electrode fingers and the number of second electrode fingers.

[0030] Additionally, preferably, the step of determining the number of first electrode fingers as the number of electrode fingers of the first IDT electrode of the first SAW resonator includes the step of determining the number of first electrode fingers as the number of reference fingers when the number of electrode fingers corresponding to the admittance value required according to the design specifications in a function of the change amount of admittance for the number of electrode fingers exceeds the number of reference fingers, and the step of determining the number of second electrode fingers as the number of electrode fingers of the second IDT electrode of the second SAW resonator includes the step of determining the number of electrode fingers as the number of second electrode fingers corresponding to the admittance value that is equal to the difference between the admittance value at the number of reference fingers and the admittance value required according to the design specifications in a function of the change amount of admittance for the number of electrode fingers.

[0031] Additionally, preferably, the method further comprises the step of including a slit reflector disposed in the propagation direction of the surface acoustic wave in at least one of the first SAW resonator and the second SAW resonator, which forms a slit capacitance having a slit structure that reflects the surface acoustic wave to at least one of the first IDT electrode and the second IDT electrode and functions as a capacitance.

[0032] The parallel composite resonator and the design method thereof according to the present invention is a parallel composite resonator configured as a parallel combination of two SAW resonators, which can improve admittance performance and improve skirt characteristics in frequency response, and has the effect of not increasing the die area even when such performance is improved.

[0033] Figure 1 is a diagram illustrating the configuration and main parameters of a conventional type of SAW resonator.

[0034] Figure 2 is a graph showing an example of the frequency-admittance response of a typical 1-port resonator.

[0035] FIG. 3 is a diagram showing one form of a parallel composite resonator according to one embodiment of the present invention.

[0036] FIG. 4 is a graph showing the functional relationship of admittance relative to the number of electrode fingers for determining the number of electrode fingers of each SAW resonator constituting a parallel composite resonator according to one embodiment of the present invention.

[0037] Figure 5 is a graph showing the results of comparing the response curves of a single SAW resonator, a symmetric parallel composite resonator, and an asymmetric parallel composite resonator.

[0038] FIG. 6 is a diagram showing a configuration in which a slit reflector is applied to a SAW resonator equipped in a parallel composite resonator according to one embodiment of the present invention.

[0039] Figure 7 is a diagram showing the results of comparing the frequency-admittance response curves of a SAW resonator with a basic configuration and a SAW resonator with an external capacitor, a SAW resonator equipped with a forward reflector and a slit reflector as shown in Figure 6 (b).

[0040] FIG. 8 is a flowchart illustrating a design method for a parallel composite resonator according to one embodiment of the present invention.

[0041] FIG. 9 is a flowchart illustrating a design method for a parallel composite resonator according to another embodiment of the present invention.

[0042] Specific details regarding the parallel composite resonator and the design method thereof according to the present invention will be described in detail below with reference to the drawings.

[0043] First, the configuration of a parallel composite resonator according to one embodiment of the present invention will be described with reference to FIG. 3.

[0044] As shown in FIG. 3, the parallel composite resonator according to the present invention can be configured by connecting a first SAW resonator (100a) and a second SAW resonator (100b) in parallel with each other.

[0045] The first SAW resonator (100a) and the second SAW resonator (100b) may have the same basic configuration as each other, or they may have different configurations such as IDT electrodes.

[0046] The first SAW resonator (100a) is provided with a first IDT electrode (110) that is provided on a piezoelectric substrate made of a material having a piezoelectric effect and converts an electrical signal into a surface acoustic wave on the piezoelectric substrate or, conversely, converts a surface acoustic wave on the piezoelectric substrate into an electrical signal or performs both. The first IDT electrode (110) is configured to have a plurality of electrode fingers (122, 132) that convert an electrical signal into a surface acoustic wave on the piezoelectric substrate.

[0047] The first IDT electrode (110) described above has a configuration in which a plurality of metal electrodes, i.e., a plurality of electrode fingers having a comb structure as shown in FIG. 3, are divided into an input IDT electrode section (120) and an output IDT electrode section (130), and a plurality of input electrode fingers (122) and a plurality of output electrode fingers (132) are alternately arranged. When an electric signal is applied through the input IDT electrode section (120), a surface acoustic wave is generated on a piezoelectric substrate by the electric field between the plurality of input electrode fingers (122) and the output electrode fingers (132), and the surface acoustic wave is converted back into an electric signal and output to the output IDT electrode section (130).

[0048] At this time, the surface acoustic waves generated from the first IDT electrode (110) propagate in both directions, that is, in the left and right directions in the drawing, respectively. By providing a reflector (140) that forms gratings of a metal thin film at both ends of the first IDT electrode (110), the surface acoustic waves generated by the first IDT electrode (110) and propagated outward can be reflected back to the first IDT electrode (110), thereby reducing the loss due to the propagation of the surface acoustic waves. That is, the above-mentioned reflector (140) serves to confine the surface acoustic waves generated from the first IDT electrode (110) by reflecting them at both ends of the first IDT electrode (110) in accordance with the Bragg condition.

[0049] The second SAW resonator (100b) also has the same basic configuration as the first SAW resonator (100a) described above, and is equipped with a second IDT electrode (160). The second IDT electrode (160) has a configuration in which a plurality of electrode fingers having a comb structure are divided into an input IDT electrode section (170) and an output IDT electrode section (180), and a plurality of input electrode fingers (172) and a plurality of output electrode fingers (182) are alternately arranged. It may also be equipped with a reflector (190) that forms gratings of a metal thin film on both ends of the second IDT electrode (160).

[0050] A parallel composite resonator according to one embodiment of the present invention can be implemented by connecting a first SAW resonator (100a) and a second SAW resonator (100b) having the configuration described above in parallel as shown in FIG. 3.

[0051] In order to improve the performance of such parallel composite resonators, that is, to improve the performance of each SAW resonator, the number of electrode fingers of the IDT electrode of each SAW resonator can be increased.

[0052] However, increasing the number of electrode fingers of the IDT electrode causes an increase in the die area, and if the number of electrode fingers of the IDT electrode is minimized to minimize the die area, there is a problem of degrading the performance of the resonator. Therefore, it is necessary to maximize the performance of the resonator within a range that satisfies the desired design specifications while simultaneously avoiding an increase in the die area.

[0053] To this end, information on the appropriate number of electrode fingers for maximizing performance and minimizing the die area can be derived from a function of the change in admittance with respect to the number of electrode fingers.

[0054] FIG. 4 shows the number of electrode fingers (N) constituting the IDT electrode of the SAW resonator. IDT Admittance (Y) relative to ) 11 This is a graph representing the relationship of the function (y = f(n)). N IDT Y about 11 The function (y = f(n)) is a transcendental function and is a non-linear function.

[0055] A parallel composite resonator according to one embodiment of the present invention may be configured such that a reference number of fingers is determined from a function of the change in admittance with respect to the number of electrode fingers as shown in FIG. 4, and the number of electrode fingers corresponding to the admittance according to the design specifications based on the determined reference number of fingers is provided in at least one of the first IDT electrode and the second IDT electrode.

[0056] Here, the number of reference fingers can be determined using a linear approximation function of the change in admittance with respect to the number of electrode fingers as shown in FIG. 4, and the number of reference fingers is denoted as n0.

[0057] The standard number of fingers is N as shown in Fig. 4. IDT Y about 11 At two locations (P1, P2) where the slope of the tangent line of the function (y = f(n)) changes, two linearly approximated lines (i.e., the linearly approximated function y=f at location P1) low The linear approximation function y=f at positions (n) and P2 high (n)) can be determined as the number of electrode fingers (n0) at the point (P0) where they intersect.

[0058] That is, as shown in Fig. 4, N IDT Y about 11 It is divided into a first, second, and third region based on the change in the slope of the tangent line of the function (y = f(n)), and, for example, in the first region, y=f by linear approximation through Taylor expansion low Derive (n) and obtain y=f by linear approximation through Taylor expansion in the third region high By deriving (n), the aforementioned linearly approximated y=f low (n) and y=f high The number (n0) at the intersection (P0) of (n) can be determined as the number of reference fingers mentioned above.

[0059] Expressed as a formula, the number of reference fingers (n0) can be represented by the following mathematical formula 2.

[0060]

[0061] And the linear approximation function y=f derived using Taylor expansion low (n) and y=f high(n) can be expressed by the following mathematical formulas 3 and 4, respectively.

[0062]

[0063]

[0064] In Fig. 4, the first and third regions are N IDT Y about 11 The second region is a region where the slope of the tangent line on the curve according to the function of is almost unchanged, and the second region is an intermediate region between the first and third regions.

[0065] And in mathematical equations 2, 3, and 4, n1 is N IDT Y about 11 It is the number of electrode fingers corresponding to point P1 within the first region of the function, and n2 is N IDT Y about 11 It is the number of electrode fingers corresponding to point P2 in the third region of the function.

[0066] The above P1 is N in the first region IDT Y about 11 It may be the position where the slope of the tangent line of the function begins to change, and the number of electrode fingers at this time is n1. The above P2 is N in the third region. IDT Y about 11 It may be the position where the slope of the tangent line of the function begins to change, and the number of electrode fingers at this time is n2.

[0067] And as explained earlier, the reference finger count (n0) is the tangent (y=f) when the electrode finger count is n1. low (n1)) and the tangent line when the number of electrode fingers is n2 (y=f high (n2)) is the number of electrode fingers at the intersection (P0).

[0068] N in Fig. 4 IDT Y about 11 Looking at the curve of the function (y=f(n)), in the case where the number of electrode fingers equipped on the IDT electrodes of the SAW resonator is less than the reference number of fingers (NIDT For the case where < n0), the number of electrode fingers (N IDT As ) increases, admittance (Y 11 While ) increases rapidly, in the case where the number of electrode fingers is greater than the reference number of fingers (N IDT For the case where > n0), the number of electrode fingers (N IDT It can be seen that even if ) increases, the increase in resonance performance may not be significant (it can be seen that the curve rises sharply before point n0 of the admittance curve, but rises gradually after point n0).

[0069] Therefore, it can be seen that an optimal composite resonator can be designed by making the number of electrode fingers provided on each IDT electrode of a plurality of SAW resonators constituting a parallel composite resonator according to one embodiment of the present invention smaller than the reference number of fingers (n0).

[0070] This means that by selecting an appropriate number of electrode fingers provided on the IDT electrode within a range smaller than the reference number of fingers (n0) to form a composite resonator, the resonance performance can be improved to meet the desired design specifications without increasing the die area.

[0071] When the number of electrode fingers provided on the first IDT electrode of the first SAW resonator of a parallel composite resonator according to one embodiment of the present invention is denoted as the first number of electrode fingers, and the number of electrode fingers provided on the second IDT electrode of the second SAW resonator is denoted as the second number of electrode fingers, if the required admittance value according to the design specifications in the function of the change amount of admittance with respect to the number of electrode fingers as shown in FIG. 4, the first number of electrode fingers of the first SAW resonator can be determined as the reference number of fingers (n0), and the admittance value at this time is Yc, and the number of electrode fingers n corresponding to the admittance value Yd, which is the admittance value Δα, the difference between the required admittance value Yr and the current admittance value Ycd It can be determined as the number of second electrode fingers of the second IDT electrode of the second SAW resonator.

[0072] In this way, a parallel composite resonator according to one embodiment of the present invention can improve resonance performance to meet desired design specifications without increasing the die area.

[0073] A parallel composite resonator according to one embodiment of the present invention may be configured such that the number of electrode fingers of the IDT electrode of the first SAW resonator constituting the same (number of first electrode fingers) and the number of electrode fingers of the IDT electrode of the second SAW resonator (number of second electrode fingers) are smaller than the reference number of fingers and thus have the same number, or, as previously explained, the number of first electrode fingers is set to n0 and the number of second electrode fingers is set to n d It can also be composed of different numbers, such as doing it this way.

[0074] In the former case, M Sym comp denoted as , and the latter case as M Asym comp In the case of a single SAW resonator denoted as (M single Figure 5 shows a comparison of the frequency response with ).

[0075] In the admittance-frequency response comparison graph shown in Fig. 5, when the Co curve is a single SAW resonator (M single It is the response curve of ), and in the case where the Cs curve indicated by the dotted line is a parallel composite resonator of two SAW resonators having the same number of electrode fingers (M Sym comp It is the response curve of ), and the Ca curve indicated by the solid line is in the case where it is a parallel composite resonator of two SAW resonators having different numbers of electrode fingers (M Asym comp It is the response curve of ).

[0076] Here, the period length (λ), which is an important design parameter of the SAW resonator,P ), aperture length (L A ) and the number of electrode fingers of the IDT electrode (N IDT Based on ), M ≡ {λ P , L A , N IDT It can be represented as}, and the parameters used in Fig. 5 are M1, M2, and M3, where M1 = {4.39, 120, 151}, M2 = {4.39, 120, 108}, and M3 = {4.39, 120, 85}.

[0077] Here, M single = M1, M Sym comp = (M1∥M1), M Asym comp The comparison result of Fig. 5 was derived by setting it to = (M2∥M3). (M1∥M1) means connecting two SAW resonators of the above-mentioned M1 (period length 4.39, aperture length 120, number of electrode fingers 151) in parallel, and (M2∥M3) means connecting the SAW resonator of the above-mentioned M2 (period length 4.39, aperture length 120, number of electrode fingers 108) and the SAW resonator of M3 (period length 4.39, aperture length 120, number of electrode fingers 85) in parallel.

[0078] As shown in Fig. 5, M single In the case of , the admittance performance at the resonant frequency is significantly low, whereas M Sym comp and M Asym comp In the case of , M shows much higher performance. single In the case of M rather than Sym comp Me, M Asym comp It can be seen that a parallel composite resonator like this is more desirable.

[0079] In addition, looking at the skirt characteristics TLs and TLa at the resonant frequency, M having identical SAW resonators Symcomp having a SAW resonator different from the skirt features (TLs) It can be seen that the skirt feature (TLa) has a steeper slope, and since the Q-factor increases as the slope becomes steeper, M Sym comp See M Asym comp It can be seen that it is a more desirable form in that the Q-factor is larger (M Sym comp Compared to the Q-factor of which is approximately 325, M Asym comp The Q-factor of is much larger at approximately 510).

[0080] In addition, M is a parallel composite resonator formed by connecting a SAW resonator with M2 characteristics and a SAW resonator with M3 characteristics in parallel. Asym comp In the case of M, it is a parallel composite resonator formed by connecting two identical SAW resonators with M1 characteristics in parallel. Sym comp It can be seen that this is a much more desirable shape because the die area can be reduced by about 23%.

[0081] Therefore, rather than maximizing the number of electrode fingers of multiple SAW resonators constituting a parallel composite resonator, it is desirable to derive a reference number of fingers from the relationship between admittance and the number of electrode fingers described above and design appropriately based on this. For example, as described above, in the function of the change in admittance with respect to the number of electrode fingers, if the number of electrode fingers corresponding to the admittance value required according to the design specifications exceeds the reference number of fingers, the number of first electrode fingers of the first SAW resonator is determined as the reference number of fingers, and the number of electrode fingers corresponding to the admittance value that is equal to the difference between the admittance value at the reference number of fingers and the admittance value required according to the design specifications is determined as the number of second electrode fingers of the second SAW resonator. By configuring the parallel composite resonator in this way, not only can improved skirt characteristics be realized, but the die area can also be reduced.

[0082] Meanwhile, in a SAW resonator, the characteristic frequencies, namely the resonant frequency and the anti-resonant frequency, are closely related to the number of electrode fingers. Although the resonant frequency changes in value to a negligible degree even when the number of electrode fingers changes, the anti-resonant frequency can undergo a significant change that cannot be ignored as the number of electrode fingers changes. Therefore, when multiple SAW resonators constituting a parallel composite resonator have different numbers of electrode fingers, the resonant frequency changes almost nothing, but a frequency mismatch may occur in the anti-resonant frequency.

[0083] To adjust for such a mismatch in the anti-resonant frequency, it may be necessary to shift the position of the anti-resonant frequency using capacitance.

[0084] As previously described in FIG. 3, the first SAW resonator and the second SAW resonator of a parallel composite resonator according to one embodiment of the present invention are each equipped with an IDT electrode and a reflector of a basic structure, respectively. However, as the number of electrode fingers of each IDT electrode of the first SAW resonator and the second SAW resonator differs, a mismatch may occur in the respective anti-resonant frequencies.

[0085] To improve this, one could consider providing an external capacitance connected to the IDT electrode, but this presents the problem of significantly increasing the die area.

[0086] Accordingly, a parallel composite resonator according to one embodiment of the present invention proposes configuring the reflector structure of each resonator as a slit reflector to adjust the mismatch in anti-resonant frequency while not increasing the die area when the number of electrode fingers of each IDT electrode of the first SAW resonator and the second SAW resonator is configured differently.

[0087] FIG. 6 (a) and (b) respectively show examples in which a slit reflector structure is applied to the reflector of a SAW resonator constituting a parallel composite resonator according to one embodiment of the present invention.

[0088] As illustrated in FIG. 6(a), a SAW resonator constituting a parallel composite resonator according to one embodiment of the present invention may include an IDT electrode (200) provided on a piezoelectric substrate (101) that converts an electrical signal into a surface acoustic wave on the piezoelectric substrate (101) or, conversely, converts a surface acoustic wave on the piezoelectric substrate (101) into an electrical signal, and may include a slit reflector (300, 400) that includes a capacitive reflector with a capacitor function and forms a slit-shaped slit capacitance within the reflector.

[0089] The slit reflector basically performs the function of a conventional reflector and is positioned on a piezoelectric substrate in the direction of propagation of surface acoustic waves generated from the IDT electrode (200) to reflect the surface acoustic waves to the IDT electrode (200).

[0090] As illustrated in FIG. 6(a), the IDT electrode (200) has a configuration in which a plurality of metal electrodes, i.e., a plurality of fingers, having a comb structure are divided into an input IDT electrode section (210) and an output IDT electrode section (220), and a plurality of input IDT fingers (212) and a plurality of output IDT fingers (222) are alternately arranged. When an electric signal is applied through the input IDT electrode section (210), a surface acoustic wave is generated on the piezoelectric substrate (100) by the electric field between the plurality of input fingers (212) and the output fingers (222), and the surface acoustic wave is converted back into an electric signal and output to the output IDT electrode section (220).

[0091] At this time, the surface acoustic waves generated from the IDT electrode (200) propagate in both directions, that is, in the left and right directions in the drawing.

[0092] Since the slit reflectors (300, 400) described above are positioned in the propagation direction of surface acoustic waves generated from the IDT electrode (200), it is preferable that they be provided on one end side and the other end side of the IDT electrode (200), respectively.

[0093] The above-described slit reflectors (300, 400) are positioned in the direction of propagation of surface acoustic waves generated from the IDT electrode (200) and reflect the propagating surface acoustic waves back to the IDT electrode (200), respectively, and form a slit capacitance which is a slit structure that functions as a capacitance.

[0094] That is, the slit reflector (300, 400) may include a plurality of reflector units (310 and 320, 410 and 420) arranged in parallel in a direction perpendicular to the propagation direction of the surface acoustic wave, and a slit capacitance formed by separating each reflector unit to form at least one slit (301, 401) and connecting a power source (600) to each of the reflector units (310 or 410) and the reflector unit (320 or 420) of the slit (301 or 401).

[0095] An input side connection part (230) that connects the input part (630) of the power supply to the input IDT electrode part (210) and the first reflection unit (310), respectively, and an output side connection part (240) that connects the output part (640) of the power supply to the output IDT electrode part (220) and the second reflection unit (320), respectively, may be provided, and the input side connection part (230) may be configured to connect the input power supply to both the input IDT electrode part (210) and the reflection units (310, 410) on both sides thereof, and the output side connection part (240) may be configured to connect the output power supply to both the output IDT electrode part (220) and the reflection units (320, 420) on both sides thereof.

[0096] As illustrated in FIG. 6(a), in a slit reflector (300) on one side, a first reflector unit (310) and a second reflector unit (320) are arranged in parallel in a direction perpendicular to the propagation direction of surface acoustic waves (vertical direction in the drawing) and a slit (301) is formed by leaving a gap between them. When the input part (630) of a power source (600) is connected to the first reflector unit (310) and the output part (640) is connected to the second reflector unit (320) and current is applied, a potential difference is created between the first reflector unit (310) of the input power source and the second reflector unit (320) of the output power source, and accordingly, the slit (301) is filled with charge and can become a slit capacitance that functions as a capacitor.

[0097] The configuration of the one-sided slit reflector (300) is applied in the same way to the other-sided slit reflector (400). That is, the configurations referred to by reference numerals 310, 320, and 301 regarding the one-sided slit reflector (300) correspond to the configurations referred to by reference numerals 410, 420, and 401 regarding the other-sided slit reflector (400).

[0098] As shown in FIG. 6(a), the slit reflector (300, 400) described above can prevent surface acoustic waves generated from the IDT electrode from leaking through the slit if the width (Ws) of the slit (301, 401) formed between the first reflector unit and the second reflector unit is large. Therefore, the width (Ws) of the slit is formed to be shorter than the wavelength (SAW wavelength) of the surface acoustic waves generated from the IDT electrode (200), thereby preventing the surface acoustic waves from leaking through the slit. That is, it is preferable that (width (Ws) of the slit) < (wavelength of the surface acoustic waves).

[0099] In addition, the length (Ls) of the slit (301, 401) formed between the two reflection units is related to the capacitance value. That is, the longer the length (Ls) of the slit, the larger the capacitance capacity.

[0100] In addition, the embodiment illustrated in FIG. 6(a) relates to a structure in which a slit reflector is divided into two parts, a first reflector unit and a second reflector unit, and a slit is formed between them. By changing the structure of the reflector to form two or more slits and implementing multiple slit capacitances, the effect of connecting multiple capacitors in series or in parallel can be obtained.

[0101] Meanwhile, Figure 6(b) shows an example of implementing a reflector using a slit reflector and a forward reflector.

[0102] A SAW resonator as shown in FIG. 6(b) can be configured by providing slit reflectors (710, 810) on each side of an IDT electrode (200) and forward reflectors (510, 520) between the IDT electrode (200) and the slit reflectors (710, 810).

[0103] A slit reflector (710) can form a slit (702) by arranging a first reflector unit (711) and a second reflector unit (712) in parallel in a direction perpendicular to the propagation direction of the surface acoustic wave (vertical direction in the drawing) and leaving a gap between them, and can implement slit capacitance through the slit (702) by connecting the input part (630) of the power supply (600) to the first reflector unit (711) and connecting the output part (640) to the second reflector unit (712) to apply current.

[0104] At this time, a forward reflector (510) including one or more metal electrodes (512) between the slit reflector (710) and the IDT electrode (200) (in front of the slit reflector (710)) may be provided without a power connection.

[0105] Accordingly, the surface acoustic wave generated from the IDT electrode (200) is first reflected by the forward reflector (510), and the remainder is reflected by the slit reflector (710).

[0106] In this way, by providing a forward reflector (510) without a power connection, it can perform the function of a normal reflector, and at the same time, the effect of the slit capacitance of the slit reflector (710) can also be obtained.

[0107] The configuration of the one-sided slit reflector (710) and the front reflector (510) is applied in the same way to the other-sided slit reflector (810) and the other-sided front reflector (520). That is, the configurations referred to by reference numerals 711, 712, and 702 regarding the one-sided slit reflector (710) correspond to the configurations referred to by reference numerals 811, 812, and 802 regarding the other-sided slit reflector (810), and the configuration of the one-sided front reflector (510) also corresponds to the configuration of the other-sided front reflector (520).

[0108] Figure 7 shows a comparison of the frequency-admittance response curves of a SAW resonator equipped with a forward reflector and a slit reflector as shown in Figure 6(b), a SAW resonator with a basic configuration, and a SAW resonator with an external capacitor.

[0109] In the comparison graph of frequency-admittance response curves shown in Fig. 7, Ro refers to the response curve of a basic type of SAW resonator, Rc refers to the response curve of a SAW resonator equipped with an external capacitor, and Rs refers to the response curve of a SAW resonator equipped with a forward reflector and a slit reflector as shown in Fig. 6 (b) above.

[0110] In Figure 7, fr and fa refer to the resonant frequency and anti-resonant frequency on the response curve (Ro) of the basic SAW resonator, respectively. It can be seen that while there is no distinct difference between Ro, Rc, and Rs near the resonant frequency (fr), there is a significantly distinct difference near the anti-resonant frequency (fa).

[0111] As shown in Fig. 7, compared to the anti-resonant frequency (fa) of the response curve (Ro) of the basic type of SAW resonator, each anti-resonant frequency on the response curve (Rs) of the SAW resonator equipped with a slit reflector has shifted further toward the resonant frequency by Δfs, and it can be seen that the anti-resonant frequency on the response curve (Rc) of the SAW resonator equipped with an external capacitor has also shifted by approximately Δfs.

[0112] Through this, it can be seen that the anti-resonant frequency can be shifted by changing the reflector structure from a basic form of SAW resonator to a slit reflector structure or by installing an external capacitor, thereby resolving the discrepancy in the anti-resonant frequency caused by the difference in the number of electrode fingers of a parallel composite resonator.

[0113] However, as shown in FIG. 7, a SAW resonator equipped with an external capacitor has the problem of increasing the die area because an external capacitor is additionally mounted to the basic form of the resonator, whereas a resonator employing a slit reflector structure as shown in FIG. 6 (a) or (b) is much more desirable because it can achieve the same effect as adding a capacitor by modifying the existing reflector structure without increasing the die area.

[0114] Accordingly, in a parallel composite resonator according to one embodiment of the present invention, if a mismatch in the anti-resonant frequency occurs due to a difference in the number of electrode fingers of each IDT electrode of the first SAW resonator and the second SAW resonator, the problem of mismatch in the anti-resonant frequency can be solved by forming at least one of the first SAW resonator and the second SAW resonator's reflector structure in the form of a slit reflector (300, 400) including a slit capacitance (301, 401) as shown in FIG. 6 (a), or by forming it in a form including a slit reflector (710, 810) including a slit capacitance (702, 802) and a forward reflector (510, 520) as shown in FIG. 6 (b).

[0115] Meanwhile, a design method for a parallel composite resonator according to an embodiment of the present invention will be described with reference to FIGS. 8 and 9.

[0116] As previously explained, a parallel composite resonator according to one embodiment of the present invention is configured by connecting a first SAW resonator and a second SAW resonator in parallel. In this case, the number of electrode fingers of the IDT electrode of the first SAW resonator and the number of electrode fingers of the IDT electrode of the second SAW resonator can be determined based on a reference number of fingers (n0) derived from a function of the change in admittance with respect to the number of electrode fingers. In this case, the number of electrode fingers of the first SAW resonator and the second SAW resonator may be the same (hereinafter referred to as 'symmetric type') or the number of electrode fingers of the first SAW resonator and the second SAW resonator may be different (hereinafter referred to as 'asymmetric type'). Although the asymmetric type offers better performance than the symmetric type, there is a potential problem of mismatch in the anti-resonant frequency; however, this can be resolved by providing a slit reflector including slit capacitance. Consequently, it can be seen that an asymmetric parallel composite resonator equipped with a slit reflector is a more desirable form. there is.

[0117] The above content has been explained through FIGS. 3 to 7, but it will be summarized with reference to the flowcharts shown in FIGS. 8 and 9.

[0118] As illustrated in FIG. 8, a design method for a parallel composite resonator according to one embodiment of the present invention first determines the number of reference fingers from a function of the change in admittance with respect to the number of electrode fingers (S100). The specific method for determining the number of reference fingers has been described above and is therefore omitted.

[0119] The number of electrode fingers of each IDT electrode of the first SAW resonator and the second SAW resonator is determined based on the above-mentioned reference number of fingers, but the number of electrode fingers corresponding to the admittance value according to the design specifications within a range smaller than the reference number of fingers can be determined as at least one of the number of first electrode fingers of the first SAW resonator and the number of second electrode fingers of the second SAW resonator (S110).

[0120] At this time, if the number of electrode fingers of the IDT electrodes of the first SAW resonator and the second SAW resonator are different from each other, a mismatch in the anti-resonant frequency may occur, but this can be resolved by forming at least one of the first SAW resonator and the second SAW resonator's reflector structure as a slit reflector as described above (S130).

[0121] Meanwhile, as illustrated in FIG. 9, a design method for a parallel composite resonator according to another embodiment of the present invention first determines the number of reference fingers from a function of the change in admittance with respect to the number of electrode fingers (S100). The specific method for determining the number of reference fingers has been described above and is therefore omitted.

[0122] In a function of the change amount of admittance with respect to the number of electrode fingers, if the number of electrode fingers corresponding to the admittance value required according to the design specifications exceeds the reference number of fingers, the number of first electrode fingers of the first SAW resonator can be determined as the reference number of fingers (S140).

[0123] And, in a function of the change amount of admittance with respect to the number of electrode fingers, the number of electrode fingers corresponding to the admittance value that is the difference between the admittance value when there is a reference number of fingers and the admittance value required according to the design specifications can be determined as the number of second electrode fingers of the second SAW resonator (S150).

[0124] In this case, since the number of electrode fingers of the first SAW resonator is the number of reference fingers and the number of electrode fingers of the second SAW resonator is less than the number of reference fingers, a mismatch in the anti-resonant frequency may occur, which can be resolved by forming at least one of the first SAW resonator and the second SAW resonator's reflector structure as a slit reflector as described above (S160).

[0125] As explained above, the parallel composite resonator according to the present invention, configured as a parallel combination of two SAW resonators, can improve admittance performance and improve skirt characteristics in frequency response, and has the advantage of not increasing the die area even when such performance is improved.

[0126] The parallel composite resonator and the method for designing the same according to the present invention have industrial applicability in the technical field concerning components of communication-based equipment such as GPS, Bluetooth, and digital TV, as well as digital wireless communication terminals such as smartphones, tablets, and personal handheld terminals.

Claims

1. A parallel composite resonator configured by connecting a first SAW resonator and a second SAW resonator in parallel, The first SAW resonator comprises a first IDT electrode having a plurality of electrode fingers that convert an electrical signal into a surface acoustic wave on a piezoelectric substrate, and the second SAW resonator comprises a second IDT electrode having a plurality of electrode fingers that convert an electrical signal into a surface acoustic wave on a piezoelectric substrate. A parallel composite resonator characterized by being configured such that the number of electrode fingers corresponding to the admittance according to the design specifications of the parallel composite resonator, based on a reference finger number determined from a function of the change amount of admittance with respect to the number of electrode fingers, is provided in at least one of the first IDT electrode and the second IDT electrode.

2. In Paragraph 1, A parallel composite resonator characterized by determining the number of electrode fingers at the point where two linearly approximated lines intersect at two locations where the slope of the tangent line of the change in admittance function for the number of electrode fingers changes, respectively, as the reference finger number, and determining and providing at least one electrode finger number among the first IDT electrode and the second IDT electrode based on the determined reference finger number.

3. In Paragraph 1, A parallel composite resonator characterized by being configured such that the number of electrode fingers provided in at least one of the first IDT electrode and the second IDT electrode is provided as the number of electrode fingers corresponding to the admittance value according to the design specifications of the parallel composite resonator, within a range less than the reference finger number on the function of the change amount of admittance with respect to the number of electrode fingers.

4. In Paragraph 1, A parallel composite resonator characterized in that the number of electrode fingers provided on the first IDT electrode of the first SAW resonator and the number of electrode fingers provided on the first IDT electrode of the second SAW resonator are identically provided as the number of electrode fingers selected to correspond to an admittance value according to the design specifications of the parallel composite resonator within a range smaller than the reference finger number on the function of the change amount of admittance with respect to the number of electrode fingers.

5. In Paragraph 1, A parallel composite resonator characterized in that the number of electrode fingers provided on the first IDT electrode of the first SAW resonator and the number of electrode fingers provided on the first IDT electrode of the second SAW resonator are each selected and provided as different numbers corresponding to an admittance value according to the design specifications of the parallel composite resonator within a range smaller than the reference finger number on the function of the change amount of admittance with respect to the number of electrode fingers.

6. In Paragraph 1, A parallel composite resonator characterized by being configured such that, when the number of electrode fingers provided on the first IDT electrode of the first SAW resonator is greater than or equal to the reference number of fingers, the number of electrode fingers corresponding to the admittance value at the reference number of fingers and the admittance value required according to the design specifications are provided on the second IDT electrode of the second SAW resonator.

7. In Paragraph 1, A parallel composite resonator characterized in that at least one of the first SAW resonator and the second SAW resonator is configured to include a slit reflector that reflects surface acoustic waves to at least one of the first IDT electrode and the second IDT electrode, respectively, and forms a slit capacitance, which is a slit structure that functions as a capacitance.

8. A method for designing a parallel composite resonator configured such that a first SAW resonator including a first IDT electrode having a plurality of electrode fingers for propagating surface acoustic waves and a second SAW resonator including a second IDT electrode having a plurality of electrode fingers for propagating surface acoustic waves are connected in parallel. A step of determining the number of reference fingers from a function of the change in admittance with respect to the number of electrode fingers; A step of determining, based on the above-determined reference finger count, the number of first electrode fingers corresponding to the admittance according to the design specifications of the parallel composite resonator as the number of electrode fingers of the first IDT electrode of the first SAW resonator; and A step of determining, based on the determined reference number of fingers, a second number of electrode fingers different from the first number of electrode fingers, corresponding to the admittance according to the design specifications of the parallel composite resonator, as the number of electrode fingers of the second IDT electrode of the second SAW resonator; A design method for a parallel composite resonator including 9. In paragraph 8, the step of determining the number of reference fingers is, A step of dividing into a first region, a second region, and a third region based on the change in the slope of the tangent line of the function of the change in admittance with respect to the number of electrode fingers, and A method for designing a parallel composite resonator, characterized by including the step of determining the number of electrode fingers as the reference finger number at the point where the linearly approximated straight line in the first region and the linearly approximated straight line in the third region of the function of the change amount of admittance with respect to the number of electrode fingers intersect.

10. In Paragraph 8, A method for designing a parallel composite resonator, characterized by including, in at least one step among the step of determining the number of first electrode fingers and the step of determining the number of second electrode fingers, the step of determining the number of electrode fingers corresponding to an admittance value according to the design specifications of the parallel composite resonator within a range smaller than the reference number of fingers as at least one of the number of first electrode fingers and the number of second electrode fingers.

11. In Paragraph 8, The step of determining the number of the first electrode fingers as the number of electrode fingers of the first IDT electrode of the first SAW resonator is: In a function of the change amount of admittance with respect to the number of electrode fingers, if the number of electrode fingers corresponding to the admittance value required according to the design specification exceeds the number of reference fingers, the method includes the step of determining the number of first electrode fingers as the number of reference fingers. The step of determining the number of the second electrode fingers as the number of electrode fingers of the second IDT electrode of the second SAW resonator is: A method for designing a parallel composite resonator, characterized by including the step of determining the number of electrode fingers as the second number of electrode fingers, wherein the number of electrode fingers corresponds to the admittance value equal to the difference between the admittance value at the reference number of fingers and the admittance value required according to the design specifications in a function of the change amount of admittance with respect to the number of electrode fingers.

12. In Paragraph 8, A method for designing a parallel composite resonator, further comprising the step of including a slit reflector that is positioned in the propagation direction of a surface acoustic wave in at least one of the first SAW resonator and the second SAW resonator, reflects the surface acoustic wave to at least one of the first IDT electrode and the second IDT electrode, and forms a slit capacitance which is a slit structure that functions as a capacitance.

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