Improved surface acoustic wave device

Abstract

The invention relates to a surface acoustic wave device (10) comprising: - at least one transducer (T1, T2); - two acoustic reflectors (M1, M2) disposed on either side of the at least one transducer to form a cavity, each acoustic reflector comprising an array of electrodes (R1, R2) in the form of lines (21) parallel to each other, each array comprising a subset of electrodes connected to a reference potential denoted mass (M) to define a first connection type (CC) and a subset of electrodes not connected to any potential, i.e. with a floating connection defining a second connection type (CO); - at least one switching circuit (CCOM) configured to modify the distribution of the connections of at least one portion of the electrodes of each array between the different connection types.

Description

Technical Field

[0001] This invention relates to the field of telecommunications components based on surface acoustic waves, known as SAW. More specifically, this invention relates to frequency filters or feeds, and according to embodiments of the invention, to frequency agile filters and feeds. Background Technology

[0002] In telecommunications environments, numerous radio frequency (RF) bands are used to transmit or receive information. Each band defines a channel, for which filtering is required to store information. Therefore, the number of filters is as many as the number of RF bands, and switches are also needed to transmit from one to another.

[0003] The feed domain also includes a large number of addressed frequency bands. Again, proper frequency feeding needs to be associated with each frequency band.

[0004] SAW devices are widely used as filtering components in the telecommunications field and as feed sources for generating oscillators. They have a spectral (or frequency) response defined by their design and manufacturing based on their geometry and the materials used. When multiple frequency bands are addressed on the same device, each band is handled by a specific SAW component, which increases the footprint and cost.

[0005] Currently, there is no frequency agility. Frequency agility in filtering equipment or radio frequency (RF) oscillators defines the ability of these devices to vary their operating frequency according to external or internal parameters. This phenomenon can be said to be controlled if other quality factors of the equipment are preserved when the relevant parameters change.

[0006] SAW (Surface Acoustic Wave) is a widely used device in the field of telecommunications components.

[0007] Typically, the operation of these devices is based on the conversion of electrical energy into at least one elastic wave via a transducer, which usually comprises two interdigitated electrode combs deposited on a surface of a material that may or may not be piezoelectric. Reverse effects are also considered. The effectiveness of this conversion is directly related to the inherent electromechanical coupling coefficient of the material, the geometry of the transducer electrodes, and the properties of the metal constituting the electrodes.

[0008] Figure 1 The image shows a surface elastic wave device 20. It primarily includes one or more transducers ( Figure 1 The two transducers T1 and T2 in the middle allow the generation of mechanical vibration phenomena, also known as sound waves.

[0009] A SAW, known as a single-port SAW, consists of a single transducer, an electrode comb connected to the electrical input, and another comb connected to the device's ground. For example... Figure 1As shown, a SAW, referred to as a two-port SAW, includes two transducers, T1 and T2, each of which includes two combs, P1, P1' and P2, P2'. For example, transducer T1 acts as the input (excitation), with its comb P1 connected to the electrical input E, and T2 acts as the output, with its comb P2' connected to the electrical output S (recovery). Combs P1' and P2' are grounded.

[0010] In a delay line configuration, the generated sound waves propagate freely on the material surface. Figure 1 In the resonator configuration of interest shown here, sound waves are captured in the cavity by acoustic reflectors, which will be referred to as mirrors below, and are placed on either side of one or more transducers.

[0011] Transducers can be glued together or separated by gaps (spaces for free wave propagation) or arrays of electrodes (called couplers).

[0012] The acoustic reflectors are Bragg mirrors positioned on both sides of the transducer region. They are formed by depositing a periodic array of electrodes R1 and R2 onto the surface of the same substrate Mat, ensuring a strong reflection coefficient of surface acoustic waves within a certain frequency range, known as the stopband.

[0013] Typically, the electrodes of a reflector are arranged in rows 21 that are parallel to each other and periodically distributed according to a period p. The bars formed by each electrode 21 are characterized by the following geometric parameters: length l, height h, and width a.

[0014] The geometric parameters of the mirror electrodes may be the same as or different from those of the transducer electrodes.

[0015] Conventionally, the electrodes of the reflector are connected to the system's ground, connected by... Figure 1 Line 22 in the middle represents...

[0016] Preferably, the electrodes are grounded at both ends. This option of direct connection to electrical ground allows for easy-to-manufacture components, minimizes parasitic electrical effects at the electrodes, and maximizes the overall efficiency of the mirror.

[0017] Different grounding planes M are of course interconnected, and this connection is represented by the dashed line 23.

[0018] In the case of a filter, a mirror forms a resonant cavity within which one or more electroacoustic transducers generate and receive elastic waves designed to achieve the spectral functionality of the filter. Conventionally, coefficient S11 is used to characterize the filter's reflection (PReflected / Pincident), and coefficient S12 is used to characterize the filter's transmission (PTransmitted / Pincident). These coefficients are calculated directly from the incident radio frequency electrical signals reflected and transmitted at the transducers. Figure 1 The characteristics of coefficients S11 and S12 of the bandpass filter are shown. This device operates at frequency f. R (Also known as the nominal frequency of the filter) depends on many parameters, including the material used for the substrate, the geometry of the electrodes and mirror electrodes that define one or more transducers, and the interactions between these various elements.

[0019] In addition, in order to generate filters with specific characteristics, the conventional approach is to generate SAW arrangements from different basic SAWs set in parallel and / or series. Figure 2 An example of a trapezoidal arrangement of a filter 30 “cascaded” based on basic single-port SAW resonators 20(1), 20(2) and 20(3) is shown, which performs filtering on a signal injected via input 31 and recovered at output 32.

[0020] SAW resonators, according to existing technology, have responses defined by their design and manufacturing. Therefore, producing SAW filters / feeds with different nominal frequencies requires selecting filters with different geometric parameters. Furthermore, it is impossible to produce frequency-agile filters or oscillators.

[0021] The present invention aims to overcome at least one of the above-mentioned disadvantages by proposing a surface acoustic wave device that has frequency behavior dependent on boundary conditions, which can be modified without changing the geometric parameters of the components, i.e., frequency agility. Summary of the Invention

[0022] The subject of this invention is a surface acoustic wave device, comprising:

[0023] -At least one transducer

[0024] - Two acoustic reflectors are disposed on either side of the at least one transducer to form a cavity. Each acoustic reflector includes an electrode array arranged in parallel rows. Each array includes: a subset of electrodes connected to a reference potential denoted as ground to define a first type of connection, and a subset of electrodes not connected to any potential, i.e., having a floating connection defining a second type of connection.

[0025] - At least one switching circuit (CCOM) is configured to modify the distribution of connections of at least a portion of the electrodes of each array between different types of connections.

[0026] Preferably, the surface acoustic wave device according to the invention comprises one or two transducers.

[0027] According to the first variant, each electrode may have only a first type of connection or a second type of connection.

[0028] According to a second variant, the surface acoustic wave device according to the invention further includes, for at least a subset of the electrodes of each mirror, defining a third type of connection between the impedance of each electrode in the subset and ground.

[0029] Preferably, the distribution of electrode connections between different types is symmetrical about the at least one transducer.

[0030] According to one embodiment, the connection of the electrodes is performed individually for each array.

[0031] According to another embodiment, for each array, the electrodes are linked together to define a bundle, and the connection is made per bundle.

[0032] According to one embodiment, for each array, a subset of adjacent electrodes located at one end of the array is connected to ground.

[0033] According to one embodiment that can be combined with the foregoing embodiments, for each array, a subset of adjacent electrodes disposed at one end of the array has a floating connection.

[0034] According to one embodiment that can be combined with the foregoing embodiments, for each array, the electrodes form a periodic pattern, the pattern including a floating electrode and at least one electrode connected to ground.

[0035] According to one embodiment, for each array, the electrodes are individually linked to the switching circuit, so that modifications to the connection of the electrodes can be applied individually.

[0036] According to another embodiment, for each array, electrodes are linked to each other to form bundles, each bundle being linked to a switching circuit, such that modifications to the electrode connections are applied per bundle.

[0037] According to another aspect, the present invention relates to a frequency filter comprising a surface acoustic wave device according to the present invention.

[0038] Preferably, the frequency filter comprises a plurality of surface acoustic wave devices according to the invention arranged in series and / or in parallel.

[0039] According to another aspect, the present invention relates to an oscillator comprising an inverting circuit and a surface acoustic wave device according to the invention arranged in parallel with said inverting circuit, the surface acoustic wave device comprising two transducers.

[0040] The following description presents several exemplary embodiments of the device of the present invention: these examples do not limit the scope of the invention. These exemplary embodiments illustrate the essential features of the invention and additional features related to the embodiments considered. For clarity, the same elements will have the same reference numerals in different figures. Attached Figure Description

[0041] The invention will be better understood from the following detailed description and with reference to the accompanying drawings, which are given by way of non-limiting example, and other features, objects and advantages thereof will become apparent, wherein:

[0042] already cited Figure 1 A surface acoustic wave (SAW) device according to the prior art is shown.

[0043] already cited Figure 2 The arrangement of a basic SAW using a trapezoidal filter configuration according to the prior art is shown.

[0044] Figure 3A The principle of a first variant of the surface acoustic wave device according to the present invention is shown.

[0045] Figure 3B A first embodiment of the device according to the invention is shown, wherein the electrodes are individually linked to the switching circuit, thereby allowing modifications to the electrode connections to be applied individually.

[0046] Figure 3C A second embodiment of the device according to the invention is shown, wherein electrodes are linked to each other to form bundles, each bundle being linked to a switching circuit, thereby applying modifications to the connection of the electrodes on a per-bundle basis.

[0047] Figure 4 The scattering characteristics of two different configurations of mirrors are shown for the electric boundary conditions applied to each electrode in these mirrors.

[0048] Figure 5 The stopband variation is shown for two cases: 100% grounded and 100% floating, depending on the a / p parameters of the mirror electrodes.

[0049] Figure 6 The frequency variation of the modulus of the simulated acoustic reflection coefficient of the mirror is shown for the two electrical boundary conditions applied to the electrodes of these mirrors.

[0050] Figure 7 The changes in frequency of the resonator's electrical parameter S11 are shown when the conditions on the reflector are modified according to four different configurations.

[0051] Figure 7b Four connection configurations for the electrodes of the reflector are shown, based on the electrical coefficient S12 of the frequency f of the complex filter employing a trapezoidal configuration of three devices according to the invention.

[0052] Figure 8 The grayscale level illustrates one aspect based on the number of electrodes n under floating conditions. CO(From 0 to 90), on the other hand, the parameter S11 of the single-port resonator varies according to the frequency.

[0053] Figure 9a , 9b Figures 9c illustrate an embodiment of the invention, wherein, for each array, electrodes are linked to each other to define a bundle, and the connection is made per bundle. Figure 9a , 9b 9c also shows different arrangements of two types of connections, CC and CO, that can be combined together. Figure 9a and 9b In this configuration, for each array, a subset of adjacent electrodes located at the ends of the array opposite the transducers are connected to ground. Figure 9c In the diagram, for each array, multiple consecutive electrodes show alternations of ground connection CC and floating connection CO.

[0054] Figure 10 A second variant of the device according to the invention is shown, wherein for at least a subset of the electrodes of each reflector, an impedance Z is introduced between each electrode of the subset and ground to define a third type of connection CZ.

[0055] Figure 11 An oscillator whose frequency is stabilized by means of a device according to the invention is shown. Detailed Implementation

[0056] The principle of the surface acoustic wave device 10 according to the present invention is shown in FIG3. The device has a structure close to that of a surface acoustic wave (SAW) according to the prior art, but the electrical boundary conditions of the mirrors have been modified.

[0057] Device 10 includes at least one transducer. Preferably, it includes one (single-port SAW) or two (dual-port SAW). (Non-limiting) Figure 1 The SAW according to the invention is shown, which is a dual-port SAW with two transducers T1 and T2. The device 10 also includes two acoustic reflectors disposed on both sides of at least one transducer to form a cavity, each acoustic reflector comprising an array of electrodes R1, R2 arranged in rows 21 parallel to each other.

[0058] Each electrode array includes: a subset of electrodes connected to a reference potential called ground M to define a first type of connection CC (short circuit), and a subset of electrodes not connected to any potential, that is, having a floating connection to define a second type of connection CO (open circuit), as shown in FIG3. The open circuit (floating) connection is represented by arcs at both ends of the electrode. Therefore, unlike SAW in the prior art, some electrodes of the device according to the invention have a floating type of connection.

[0059] Figure 3 illustrates a first variant of the invention, according to which each electrode may have only a first (CC) or second (CO) type connection.

[0060] The device 10 according to the invention further includes at least one switching circuit CCOM configured to modify the distribution of connections of at least a portion of the electrodes in each array between different types of connections. This potential reconfiguration of connections dynamically imparts frequency agility to the device according to the invention.

[0061] Therefore, electrical control of frequency agility is achieved by modifying the electrical boundary conditions in the mirror. The concept of this invention considers modifying the electrical boundary conditions for each basic electrode of the mirror. In summary, these modifications correspond to a distribution function within the mirror, which is a priori fixed or can be dynamically modified via switching circuitry. This distribution function allows control of the mirror's stop band and thus modifies the resonance conditions of the standing waves within the cavity.

[0062] Controlled frequency agility ensures the integrity of the filter's quality factor, which is transposed to each new nominal frequency determined by the frequency agility phenomenon.

[0063] according to Figure 3B In the first embodiment shown, the electrodes are individually linked to the switching circuit, thereby allowing for individual modification of the electrode connections.

[0064] according to Figure 3C In the second embodiment shown, the electrodes are linked to each other to form bundles, each bundle being linked to a switching circuit, such that the connection of the electrodes is modified on a per-bundle basis.

[0065] In the following text, for clarity, the frequency behavior of the device will be explained without any switching circuitry. For each array, this circuit, or these circuits, may connect all electrodes or only a portion of them, with others directly connected to ground or simply left unconnected, and therefore cannot be reconfigured.

[0066] To better understand the effect of this modification of the connection conditions of the mirror electrodes on SAW behavior, the inventors introduced the concept of a resistance band, which will now be described.

[0067] In an infinite periodic structure, for a given direction of propagation, the scattering curves show the variation of the frequency of the sound wave propagating in the structure with respect to the wave number k. These curves allow for the identification of the passband, the band in which the wave propagates and is characterized by the true wave number k, and the stopband, under certain conditions, the band in which the wave fades and is characterized by the complex wave number k. In these bands, there are no propagation modes in the mirror, and therefore the reflection coefficient of the incident surface acoustic wave on the mirror can take a value close to one (total internal reflection). Therefore, in these bands, mirrors typically constitute good acoustic reflectors.

[0068] The inventors have demonstrated that modifications to the connection of the reflector's electrodes affect the stopband. Figure 4 The characteristic scattering curves of the surface wave in the mirror up to π / p (where p is the spatial period of the electrode array) on the Brillouin zone are shown for two different configurations of electrical boundary conditions applied to each electrode.

[0069] Figure 4 Calculations have been performed on an example of a LiNbO3(YXl) / 128 substrate, which includes an array of aluminum electrodes on its surface with a thickness of h = 400 nm, a width of a = 6.8 μm, and a period of p = 19.4 μm (a / p = 0.35). The propagation direction is perpendicular to the length of the electrodes.

[0070] The solid lines correspond to all electrodes of the reflector connected by a short circuit (100% CC), that is, connected to ground. Stopband 33 [Fe; Fint] is denoted as π / p. This stopband 33 is very narrow because the phononic crystal can be considered a quasi-homogeneous material with zero potential on its surface.

[0071] The dashed line corresponds to all electrodes of the floating mirror (100% CO). The upper limit of the stopband 34 [Fint; Fs] is denoted as π / p.

[0072] These two stopbands, 33 and 34 (connected to ground or floating conditions), are linked to the same geometry and the same material. They are distinguished only by the applied electrical boundary conditions. This is why they are called resistance bands (BIE).

[0073] The relative width of the resistance band is linked to the electromechanical coupling coefficient associated with the surface waves propagating in the piezoelectric substrate of the SAW structure.

[0074] Figure 5 The variations of stopbands 33 (100% CC) and 34 (100% CO) based on the a / p parameter are shown (refer to the previous example). It was found that, depending on the ratio a / p between the size of electrode a and the periodicity p, several cases can exist: superimposed, offset, widened, or narrowed stopbands.

[0075] Modifying the stopband under applied electrical conditions causes a change in the reflection coefficient of the incident surface wave on the mirror. Figure 6The diagram illustrates the variation of the modulus CRM frequency of the simulated reflectance coefficient of the mirror as a function of the frequency when the electrical boundary conditions applied to the electrode are connected to ground (100% CC), curve 61, or under floating conditions (100% CO), curve 62, for an electrode thickness h of 200 nm, a period p of 19.4 μm, a width a = 6.8 μm, and the substrate material is made of LiNbO3, and cut (YXl) / 128.

[0076] Note that the frequency bands 33' and 34' where the reflection is equal to 1 (0dB) are close to Figure 4 The stopband exhibited in the image is slightly shifted due to variations in electrode thickness. The two reflection bands are offset yet continuous. Therefore, the acoustic reflection bands of the mirror can be electrically controlled.

[0077] This modification of the reflectivity of the mirror has a direct impact on the frequency characteristics of the SAW generated by the mirror.

[0078] Consider now a single-port resonator comprising a transducer T1 and two Bragg mirrors previously studied on either side (see Figure 3). Each mirror comprises an array of 90 electrodes with an a / p ratio of 0.35, and the central transducer comprises 48 electrodes with an a / p ratio of 0.45. The electrical energy reflected by the resonator is related to the square of the parameter S11. Figure 7 The diagram illustrates how the resonator parameter S11 changes with frequency when the conditions on the reflector are modified according to four different configurations:

[0079] -90 electrodes CC (grounded)

[0080] -90 electrodes CO (floating)

[0081] -58 electrodes CC –32 electrodes CO

[0082] -80 electrodes CC – 10 electrodes CO

[0083] In the last two configurations, the 32 or 10 electrodes set to floating condition are those that are close to transducer T1.

[0084] The minimum value of parameter S11 corresponds to the elastic resonance of the transducer + mirror assembly, where a large amount of incident electrical energy is converted into mechanical energy.

[0085] When all electrodes of the reflector are connected to ground, the main resonance is observed at 100 MHz.

[0086] When all electrodes of the reflector are in a floating condition, this resonance is hardly modified by changes in the electrical boundary conditions, but more resonances with strong mass coefficients can be observed. The curves for all electrodes of the reflector in a floating condition highlight the multimode characteristics of the single-port resonator.

[0087] The other two curves correspond to two intermediate cases, where the reflector electrodes closer to the transducer are gradually set to floating conditions.

[0088] It can be seen that the potential of the device according to the present invention, for the same geometric parameters, can have different frequency behaviors due to the connection configuration of the mirror electrodes.

[0089] Preferably, the distribution of electrode connections between different types of connections is symmetrical about one or more transducers. This facilitates simulation and makes the selection of audio frequencies more accurate.

[0090] Preferably, a grounding connection is made at both ends of each electrode 21. This allows the top ground plane to connect to the bottom ground plane, thereby ensuring grounding continuity.

[0091] With the device according to the invention, the electrical boundary conditions of the mirror are modified to modify the operating frequency of the resonator without changing the characteristics of the device (substrate material, geometric parameters, etc.) and at the same time maintaining the integrity of the filtering function.

[0092] In a two-port configuration, the standard operation of the device 10 of the present invention is directly of the filtering type. The concept of the invention can also be extended to SAW filters, referred to as cascaded SAW filters. In this case, filters are generated using multiple surface acoustic wave devices 10 according to the invention, each having a single port electrically associated according to a series and / or parallel arrangement. As is known, combinations of different SAWs, controlled by the form of the filter strips (which are preferably desired to have steep flanks), their width, their nominal frequency, etc., make it possible to produce filters conforming to defined specifications.

[0093] Figure 7b It shows that in such Figure 2 The performance of the complex filter in the trapezoidal configuration shown is illustrated, but the SAW according to the prior art has been replaced by the SAW according to the present invention.

[0094] The two devices connected in parallel (equivalent to 20(1) and 20(2)) are identical, single-port, and generated by the same transducer T1, and have the following characteristics:

[0095] T1: 18 electrode pairs, p = 19.1 μm, a / p = 0.3, h = 0.17 μm

[0096] Each mirror array has 60 electrodes, where p = 19 μm, a / p = 0.4, and h = 0.17 μm.

[0097] The serial device (equivalent to 20(3)) is also single-port and generated by sensor T1', with the following characteristics:

[0098] T1': 11 electrode pairs, p = 18.5 μm, a / p = 0.5, h = 0.17 μm

[0099] Each mirror array has 60 electrodes, where p = 19.2 μm, a / p = 0.4, and h = 0.17 μm.

[0100] The four curves 70 to 73 show the trapezoidal filter through its parameter S 12 The theoretical transmittance depends on the frequency f of the different connection configurations of the reflector electrodes.

[0101] For the three devices, curve 70 corresponds to the 60 electrodes connected to ground.

[0102] For the three devices, curve 71 corresponds to the 55 electrodes connected to ground (CC) and the 5 electrodes closest to the transducer open circuit (CO).

[0103] For the three devices, curve 72 corresponds to 50 electrodes CC and the 10 electrodes closest to the transducer CO.

[0104] For the three devices, curve 73 corresponds to 40 electrodes CC and the 20 electrodes closest to the transducer CO.

[0105] It was found that a bandpass filter had indeed been produced, with different connection configurations causing a shift of approximately 1 MHz in the filter's nominal frequency without degrading other quality factors of the filter.

[0106] Furthermore, the manufacture of complex filters is facilitated by generating them from one and the same basic filter 10 (with the same geometric parameters) according to the present invention.

[0107] Specification adjustments can also be performed post-manufacturing by locally modifying the connection type of the selected electrodes.

[0108] Figure 8 The parameters S11 of the single-port resonator are presented in grayscale, based on the frequency and the number of electrodes n under floating conditions. CO (Change from 0 to 90)

[0109] The dark area corresponds to resonance. This diagram is very informative:

[0110] -When all electrodes of the reflector are connected to ground (n CO =0), resonance was found at 100MHz, see 81.

[0111] -When all electrodes of the reflector are in a floating condition (n COAt 90 MHz, a resonance was found near 99.8 MHz (see 82), as well as other lower resonances (around 99 MHz - see 83) and higher resonances (around 103 MHz - see 84), highlighting the multimode nature of the device.

[0112] -When a small number of electrodes are in floating condition (n CO When <10), a slight change in resonance (around a few kHz around the center frequency of 100 MHz) was observed. This is a sustained but weak agility of the main resonance (see 81).

[0113] - Resonances varying continuously from 97.3 MHz to 99.8 MHz were observed with 5-10 electrodes and up to 90 electrodes in floating condition (see 85). The relative variation is 2.5%, which is a continuous agility of the secondary resonance over a wide bandwidth. This secondary resonance represents the stopband input frequency of the device: along the variation of the number of electrodes in the floating potential.

[0114] - When approximately 30 to 40 electrodes are in floating condition, a noticeable resonance is observed near 103.5 MHz (see 86). Setting these electrodes to floating condition can be viewed as a jump in the resonator's dominant frequency. This results in a frequency switching function.

[0115] According to one embodiment, the electrode connections are performed individually for each array, as shown in Figure 3. According to a first example, all electrodes are individually connected via a switching circuit, such as... Figure 3B As shown, and according to the second example, individual connections are made only to a portion of the devices via a switching circuit.

[0116] according to Figure 3C and Figure 9a , 9b In another embodiment shown in 9c, for each array, the electrodes are linked together to define a bundle, and the connection is made by the bundle. Figure 9a The diagram shows a connection consisting of a series of electrodes connected to ground, and Figure 9b Floating electrodes that are also interconnected are shown. The inventors have shown that these bundles of floating electrodes also have the effects described above, but slightly different. According to the first example, all electrodes are connected by electrode bundles via a switching circuit, as shown... Figure 3C As shown, and according to the second example, only a portion of the connections are made in bundles via a switching circuit. These two embodiments can, of course, be combined, with or without a switching circuit, where some connections are made in bundles and others individually.

[0117] Figure 9a , 9b Figures 9c also show different examples of arrangements of two types of connections that can be combined together.

[0118] exist Figure 9a and Figure 9b In this configuration, for each array, a subset of adjacent electrodes located at one end of the array (opposite to the transducer) is connected to ground.

[0119] Also in Figure 9a and 9b In this configuration, for each array, a subset of adjacent electrodes located at one end of the array (here, on one side of the transducer) has floating connections.

[0120] exist Figure 9c In each array, there is a "homogeneous" block consisting of two CCs (with the ends on the side opposite the transducer), and several consecutive electrodes with alternating connections to the ground CC and floating COs. Figure 9c An array of periodic patterns including connections of 1CC / 1CO type electrodes is shown, but other types of periodic patterns are of course possible, such as 1CC / 2CO or 1CC / 3CO. Therefore, according to this embodiment, for each array, the electrodes form a periodic pattern, the pattern including at least one electrode connected to ground and one floating electrode.

[0121] Using a periodic pattern with multiple connections also allows the resistance band to be opened up to a fractional frequency nF / N, where F is the initial operating frequency of the resonator, N is the number of electrodes in the pattern, and n is an integer. Thus, for example, in the case of a double-period pattern, if one electrode in every pair is connected to ground and another electrode in every pair is in a floating condition, the resistance band at the resonator's operating frequency remains, and additional resistance bands appear at half the frequency and 1.5 times the frequency with the same relative width. These observations are general for triple, quadruple, and other periods. Therefore, fractional operating frequencies can be obtained by simply modifying the electrical boundary conditions of the mirrors.

[0122] Typically, grouped or periodic pattern-based electrical connections increase the possibilities for the devices provided according to the invention.

[0123] according to Figure 10In a second variant of the device 10 according to the invention, for at least a subset of the electrodes of each reflector, an impedance Z is introduced between each of the electrodes in the subset and ground to define a third type of connection CZ. This third type of connection allows for a wider range of filter design possibilities by introducing a whole set of intermediate cases between the CO condition (equivalent to infinite impedance between the electrode and ground) and the CC condition (equivalent to zero impedance between these two points). The key points described above still apply to all three types of connections. Furthermore, the impedance Z can be of the conventional R, L, or C type, or more complex, such as a negative capacitor. This can be a passive or active circuit (external capacitor: positive or negative, variable inductor). This third type of connection can be implemented either directly to ground or via a switching circuit.

[0124] One or more switching circuits of the device 10 according to the invention generate a dynamic reconfiguration of the connection type distribution of the reflector's electrodes, which allows for possible real-time modification of the filter's frequency characteristics, such as its nominal frequency. By employing... Figure 8 The teachings have revealed that, depending on the different connection configurations of the selected electrodes, the device according to the invention provides a variety of types of agility:

[0125] (1) Continuous but weakly agile operating frequency (a fraction of the operating frequency),

[0126] (2) Continuous and significant agility of operating frequency (a percentage of the operating frequency),

[0127] (3) Jumps in operating frequency (a percentage of the operating frequency),

[0128] (4) If the device’s transducer is broadband, the device is used at a partial operating frequency.

[0129] One or more circuits in a CCOM can operate either slowly, such as adjusting a filter after a temperature measurement, or quickly (one to several switches per microsecond), such as in telecommunications or military applications.

[0130] For example, the circuit CCOM is a micro switch based on microelectromechanical components (RF-MEM) in the RF domain.

[0131] The coupling between RF-MEMS and SAW allows for control over the connection type of each electrode. Other switching systems (e.g., FET-based, diode-based, low-capacity MOS-based) are also possible. Electronic circuit-based switching eliminates the duality of ground / float condition connections by enabling CZ-type connections.

[0132] Frequency agility also allows for a reduction in the size of filtering equipment and lower energy consumption.

[0133] According to another operating mode, the device according to the invention enables the generation of an oscillator. Therefore, according to another aspect, the invention relates to... Figure 11 The oscillator 50 shown includes an inverting circuit Inv and a surface acoustic wave device 10 according to the invention arranged in parallel with the inverting circuit. For this application, device 10 must have two transducers defining the input and output. The resulting oscillator will oscillate at the frequency defined by the surface acoustic wave device.

Claims

1. A frequency-agile surface acoustic wave device (10), comprising: -At least one transducer (T1, T2), - Two acoustic reflectors (M1, M2) are disposed on both sides of the at least one transducer to form a cavity. Each acoustic reflector includes an array of electrodes (R1, R2) arranged in rows (21) parallel to each other. Each array includes: a subset of electrodes connected to a reference potential denoted as ground (M) to define a first type connection (CC), and a subset of electrodes not connected to any potential, that is, having a floating connection defining a second type connection (CO). - At least one switching circuit (CCOM) configured to modify the distribution of connections of at least a portion of the electrodes in each array between different types of connections.

2. The surface acoustic wave device (10) as claimed in claim 1, comprising one or two transducers.

3. The surface acoustic wave device (10) as described in any one of claims 1 and 2, wherein, Each electrode can have only the first type of connection (CC) or the second type of connection (CO).

4. The surface acoustic wave device (10) as described in any one of claims 1 and 2, further comprising: For at least one subset of the electrodes of each reflector, the impedance (Z) between each of the electrodes in the subset and the ground is used to define a third type of connection (CZ).

5. The surface acoustic wave device (10) as described in claim 1, wherein, The distribution of the connections between the electrodes of different types is symmetrical about the at least one transducer.

6. The surface acoustic wave device as described in claim 1, wherein, For each array, the connection of the electrodes is performed individually.

7. The surface acoustic wave device as described in claim 1, wherein, For each array, the electrodes are linked together to define a bundle, and the connection is made per bundle.

8. The surface acoustic wave device (10) as claimed in claim 1, wherein, For each array, a subset of adjacent electrodes located at one end of the array are connected to the ground.

9. The surface acoustic wave device (10) as claimed in claim 1, wherein, For each array, a subset of adjacent electrodes located at one end of the array has a floating connection.

10. The surface acoustic wave device (10) as claimed in claim 1, wherein, For each array, the electrodes form a periodic pattern, the pattern including at least one electrode connected to the ground and a floating electrode.

11. The surface acoustic wave device as claimed in claim 1, wherein, For each array, the electrodes are individually linked to the switching circuit, allowing for individual modifications to the electrode connections.

12. The surface acoustic wave device as claimed in claim 1, wherein, For each array, electrodes are linked together to form bundles, and each bundle is linked to the switching circuit, such that the connections of the electrodes are modified on a bundle-by-bundle basis.

13. A frequency filter comprising the surface acoustic wave device as described in any one of claims 1 to 12.

14. A frequency filter comprising a plurality of surface acoustic wave devices as described in any one of claims 1 to 12, arranged in series and / or in parallel.

15. An oscillator (50) comprising an inverting circuit (Inv) and a surface acoustic wave device (10) as described in any one of claims 1 to 12, arranged in parallel with the inverting circuit, the surface acoustic wave device comprising two transducers.

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