Abstract: A longitudinally-coupled-resonator-type surface acoustic wave filter includes three interdigital transducers provided on a piezoelectric substrate in the direction in which surface acoustic waves propagate. An interdigital transducer disposed at the approximate center among the three interdigital transducers of the longitudinally-coupled-resonator-type surface acoustic wave filter is divided into two parts substantially symmetrically in the propagation direction of the surface acoustic waves and the two parts are connected to balanced signal terminals, respectively. Left and right interdigital transducers of which the polarities are inverted relative to each other are connected to an unbalanced signal terminal to provide a balanced-to-unbalanced conversion function. A reactance component provided on the piezoelectric substrate, inside a package, or outside the package is connected to either of the balanced signal terminals.

Abstract: A SAW device includes two surface-acoustic-wave filter elements arranged so as to have a balanced-to-unbalanced conversion function. The surface-acoustic-wave filter elements include two first reflectors and two second reflectors. In each surface-acoustic-wave filter element, three IDTs are arranged on a piezoelectric substrate in a direction in which surface acoustic waves are transmitted so as to be positioned between one first reflector and one second reflector. The first reflectors differ in structure from the second reflectors.

Abstract: A longitudinally coupled resonator type surface acoustic wave filter includes a small pitch electrode finger portion having electrode fingers of which the pitch is smaller than that of the other electrode fingers. The small pitch electrode finger portion is provided in the end of at least one of interdigital transducers which is adjacent to the other interdigital transducer. Moreover, the small pitch electrode finger portion includes two adjacent electrode fingers in at least one position thereof which are electrode-inverted so that the polarities of the two adjacent electrode fingers are made the same.

Abstract: A longitudinally-coupled resonator surface acoustic wave (SAW) filter includes a piezoelectric substrate and at least two IDTs arranged in the direction along which a SAW propagates on the piezoelectric substrate. At least one of the IDTs has an electrode finger wherein the metallization ratio of the electrode finger is different from that of the other electrode fingers of the IDT.

Abstract: A surface acoustic wave apparatus includes at least one longitudinally-coupled-resonator surface acoustic wave filter having at least three IDTs arranged on a piezoelectric substrate along the propagation direction of surface acoustic waves and at least one surface acoustic wave resonator that is connected in series to at least two of the IDTs of the longitudinally-coupled-resonator surface acoustic wave filter. The parasitic capacitance between the longitudinally-coupled-resonator surface acoustic wave filter and the surface acoustic wave resonator is about 6.5×102/f0 [pF] or less, where f0 represents the center frequency (MHz) within the pass band of the longitudinally-coupled-resonator surface acoustic wave filter.

Abstract: A longitudinally connected resonator type surface acoustic wave filter has a balanced-unbalanced conversion function, achieves a fourfold increase in the input/output impedance, and provides an improved balance degree between balanced terminals. In this longitudinally connected resonator type surface acoustic wave filter, a balanced-unbalanced conversion is achieved using first and second longitudinally connected resonator type surface acoustic wave filters, each having a plurality of IDTs which are successively arranged on a piezoelectric substrate along the propagation direction of a surface acoustic wave, and the duties of electrode fingers in the narrow-pitch electrode finger portion are different between the first and second longitudinally connected resonator type surface acoustic wave filters, whereby the balance degree between a pair of balanced signal terminals is effectively improved.

Abstract: A surface acoustic wave device includes a plurality of surface acoustic wave filters having different center frequencies contained in a package. In the surface acoustic wave device, one of the input terminal or the output terminal of at least one of the plurality of surface acoustic wave filters is a balanced terminal and the other is an unbalanced terminal.

Abstract: A surface acoustic wave filter device has a balance-unbalance conversion function and substantially equal input impedance and output impedance so as to increase out-of-passband attenuation. The surface acoustic wave filter device includes an unbalanced signal terminal, first and second balanced signal terminals, and first and second surface acoustic wave filters having input and output impedances. In each filter, one of the input and output impedances is approximately four times the other impedance. Additionally, 2n−1 first surface acoustic wave filters are connected between the unbalanced signal terminal and the first balanced signal terminal, and 2n−1 second surface acoustic wave filters are connected between the unbalanced signal terminal and the second balanced signal terminal, where n is an integer of 1 or more. The second surface acoustic wave filters are 180 degrees out-of-phase with respect to the first surface acoustic wave filters.

Abstract: A longitudinally-coupled resonator mode SAW filter portion having at least two interdigital transducers (IDTs) is disposed on a piezoelectric substrate. At least one SAW resonator is electrically connected in parallel with the SAW filter portion such that the at least one SAW resonator is disposed between an input terminal or an output terminal and the SAW filter portion. The resonance point of the SAW resonator is disposed in the pass band of the SAW filter portion.

Abstract: A longitudinally coupled resonator type surface acoustic wave filter includes a piezoelectric substrate and first, second and third IDTs provided on the piezoelectric substrate and arranged in a surface wave propagating direction such that the second IDT is interposed between the first and the third IDTs. Each of the first, second and third IDTs has a plurality of electrode fingers. The first and second IDTs have narrow electrode-finger pitch sections that have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the first and second IDTs adjacent to each other. The second and third IDTs have narrow electrode-finger pitch sections that have an electrode-finger pitch narrower than the remaining electrode-finger pitches, at respective end portions of the second and third IDTs adjacent to each other.

Abstract: A plurality of surface acoustic wave filters having different center frequencies is provided on a piezoelectric substrate. Either input terminals or output terminals, or both input terminals and output terminals of the surface acoustic wave filters are integrated. Of the surface acoustic wave filters, a surface acoustic wave filter having a higher center frequency is configured so as to suppress a spurious response in the proximity of the high-frequency side in or outside a passband in the filter characteristics of a surface acoustic wave filter having a lower center frequency, for example, such that the width or pitch of electrode fingers in at least one region of reflectors differs from that in other regions.

Abstract: A surface acoustic wave device having an unbalanced-to-balanced conversion function, which is capable of improving balanced characteristics, includes a first resonator filter and a second resonator filter, having a plurality of interdigital transducers disposed along the propagation direction of a surface acoustic wave. The surface acoustic wave device has an unbalanced-to-balanced conversion function as a result of the phase of the second resonator filter being reversed by 180° with respect to that of the first resonator filter. The surface acoustic wave device further includes a first resonator connected in series to an unbalanced signal terminal side of the first resonator filter, and a second resonator connected in series to an unbalanced signal terminal side of the second resonator filter. The first resonator and the second resonator have different design parameters.

Abstract: A surface acoustic wave filter includes, on a piezoelectric substrate, longitudinally coupled resonator type surface acoustic wave filter sections, including interdigital transducers, each having a narrow-pitched electrode finger portion in an area where interdigital transducers are adjacent to each other, first surface acoustic wave resonators, between the surface acoustic wave filter sections and an input terminal, and second surface acoustic wave resonators between the surface acoustic wave filter sections and output terminals. The resonance point of the surface acoustic wave resonators falls within the passband of the surface acoustic wave filter sections, and the antiresonance point of the surface acoustic wave resonators is in the vicinity of the high frequency side of the passband.

Abstract: A surface acoustic wave (SAW) device includes at least one longitudinally coupled resonator SAW filter and at least one SAW resonator connected in series to the SAW filter on a piezoelectric substrate. The SAW resonator is arranged such that the resonant frequency is located within the pass band of the SAW filter and the antiresonant frequency is located outside the pass band of the SAW filter. A dummy electrode is provided between an electrode finger and a bus bar of an interdigital transducer (IDT) of the SAW resonator. The gap between the dummy electrode and the electrode finger of the IDT is about 0.5&lgr; or less when the wavelength determined by the pitch between the electrode fingers of the interdigital transducers of the SAW resonator is indicated by &lgr;.

Abstract: A surface acoustic wave device includes a first surface acoustic wave filter connected between an input terminal and an output terminal, a second surface acoustic wave filter having a different center frequency from that of the first surface acoustic wave filter, and which is connected between the input terminal and the output terminal and in parallel with the first surface acoustic wave filter, and at least one one-port surface acoustic wave resonator connected in series with the first or second surface acoustic wave filter, on at least one side between the input terminal and at least one of the first and second surface acoustic wave filters, or between the output terminal and at least one of the first and second surface acoustic wave filters.

Abstract: A surface acoustic wave device includes two surface acoustic wave filters. Each of the filters includes an odd number of at least three IDTs arranged in the propagation direction of a surface acoustic wave on a piezoelectric substrate. The phase of an output signal relative to an input signal in one of the two filters is inverted by 180° with respect to the phase in the other filter such that an unbalanced-to-balanced transformer function is obtained. When the number of the IDTs is indicated by N, IDTs having a number equal to (N−1)/2+1 are connected to an unbalanced signal terminal and IDTs having a number equal to (N−1)/2 are connected to a balanced signal terminal in each filter. The total number of electrode fingers of the IDTs in each filter is at least 71.

Abstract: A surface acoustic wave filter that minimizes parallel capacitances generated at the interstage junction of longitudinally connected surface acoustic wave elements so that the impedance of each element is hardly capacitive, includes a piezoelectric substrate, two longitudinally-coupled resonator-type surface acoustic wave elements having a plurality of interdigital transducers disposed on the piezoelectric substrate in a direction in which a surface acoustic wave propagates, electrode pads defining input/output terminals of the longitudinally-coupled resonator-type surface acoustic wave elements, and wiring patterns for electrically connecting the longitudinally-coupled resonator-type surface acoustic wave elements. The two longitudinally-coupled resonator-type surface acoustic wave elements are longitudinally connected to each other via the wiring patterns. At least one of the electrode pads is arranged between the two longitudinally connected surface acoustic wave elements.

Abstract: In a longitudinally coupled resonator type surface acoustic wave filter including narrow pitch electrode finger portions provided in the end portions of the neighboring IDT's, respectively each which contains a portion of the electrode fingers of the IDT having a narrower pitch than the remaining portions of the electrode fingers of the IDT, the inter-center distance between the centers of at least one pair of adjacent electrode fingers is deviated from 0.25&lgr;A+0.25&lgr;B, in which &lgr;A represents the wavelength determined by the pitch of one of the electrode fingers, and &lgr;B represents the wavelength determined by the pitch of the other electrode.

Abstract: A surface acoustic wave filter includes a longitudinally-coupled resonator-type surface acoustic wave filter having at least two interdigital transducers disposed on a piezoelectric substrate along the propagation direction of a surface acoustic wave, and at least one surface acoustic wave resonator connected between an input terminal and/or an output terminal and the longitudinally-coupled resonator-type surface acoustic wave filter. In this surface acoustic wave filter, a pass band is formed by utilizing at least one of the resonant modes of the longitudinally-coupled resonator-type surface acoustic wave filter and the inductance of the surface acoustic wave resonator.

Abstract: A surface acoustic wave filter unit having three interdigital transducers arranged along the surface acoustic wave propagation direction is disposed on a piezoelectric substrate. An unbalanced signal terminal and balanced signal terminals are provided for the surface acoustic wave filter unit. At least one of the three interdigital transducers is out of phase relative to the other interdigital transducers. Reflectors are arranged so as to sandwich the three interdigital transducers therebetween. The reflectors are grounded. Thus, a surface acoustic wave filter having a balance-to-unbalance conversion function and having high balance between the balanced signal terminals is achieved.