摘要:
A longitudinally coupled resonator type surface acoustic wave filter having a balance-unbalance conversion function achieves improved amplitude balance and phase balance. The surface acoustic wave filter includes first, second and third IDTs. The second IDT is positioned in the center of the three IDTs and has an even number of electrode fingers. The polarity of the electrode finger of the first IDT adjacent to the second IDT is opposite to the polarity of the electrode finger of the third IDT adjacent to the second IDT.
摘要:
A longitudinally coupled resonator type surface acoustic wave filter having a balance-unbalance conversion function achieves improved amplitude balance and phase balance. The surface acoustic wave filter includes first, second and third IDTs. The second IDT is positioned in the center of the three IDTs and has an even number of electrode fingers. The polarity of the electrode finger of the first IDT adjacent to the second IDT is opposite to the polarity of the electrode finger of the third IDT adjacent to the second IDT.
摘要:
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.
摘要:
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;.
摘要:
A surface acoustic wave apparatus includes three longitudinally-coupled-resonator-type interdigital transducers (IDTs) having a balanced-to-unbalanced conversion function, which are provided on a piezoelectric substrate in a direction in which a surface acoustic wave (SAW) propagates. Weighting is applied to at least one of the IDTs. For example, among the electrode fingers of the IDT located on the left side, an apodization-weighted electrode finger is provided for one of the electrode fingers positioned adjacent to the central IDT.
摘要:
A surface acoustic wave filter device, having a balanced-to-unbalanced conversion function, in which input/output impedances are different and in which the in-band degree of balance is satisfactory, is obtained. The surface acoustic wave filter device has a balanced-to-unbalanced conversion function, in which the spacing of input/output IDTs of a second surface acoustic wave filter element is larger by approximately half the wavelength of the surface-acoustic wave than that of a first surface acoustic wave filter element so that the phase is inverted, wherein the total of the electrostatic capacitance values of a plurality of IDTs of the second surface acoustic wave filter element is larger than the total of the electrostatic capacitance values of a plurality of IDTs of the first surface acoustic wave filter element.
摘要:
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.
摘要:
An elastic wave filter device having improved sharpness of filter characteristics includes a longitudinally-coupled resonator-type elastic wave filter section including first to third IDT electrodes each including a plurality of electrode fingers, and first and second reflectors. The first to third IDT electrodes include narrower-pitch portions provided in end portions thereof, which are each adjacent to another IDT electrode in a direction of propagation of elastic waves, each of the narrower-pitch portions having a smaller period of electrode fingers than a period of electrode fingers in the remaining portion of the relevant IDT electrode. The number of electrode fingers in the narrower-pitch portion of the second IDT electrode, which is disposed on the side closer to the first IDT electrode, and the number of electrode fingers in the narrower-pitch portion of the second IDT electrode, which is disposed on the side closer to the third IDT electrode, differ from each other.
摘要:
An elastic wave device includes an unbalanced terminal and first and second balanced terminals. A longitudinally-coupled-resonator-type first elastic wave filter is provided between the unbalanced terminal and the first balanced terminal. An elastic wave filter, which is connected in parallel with the first elastic wave filter, is connected between the unbalanced terminal and the second balanced terminal. The current paths through which IDT electrodes of the elastic wave filters of the elastic wave device are connected to ground terminals, are not symmetrical.
摘要:
An acoustic wave filter device includes first to fourth longitudinally coupled resonator type surface acoustic wave filters that are configured such that the first and second filters are connected to a first balanced signal terminal, the third and fourth filters are connected to a second balanced signal terminal, and a transmission phase of a signal output from the first balanced signal terminal relative to an input signal differs by about 180 degrees with respect to a transmission phase of a signal output from the second balanced signal terminal relative to an input signal. In addition, the number of pairs of electrode fingers of at least one of IDTs of at least one of the first to fourth longitudinally coupled resonator type surface acoustic wave filters is different from the number of pairs of electrode fingers of corresponding IDTs of the remaining first to fourth filters.