A SAW filter comprising a piezoelectric substrate and at least two filter tracks formed on the substrate, each having at least two IDT electrodes for input and output. The two filter tracks have substantially the same phase within a pass band, while it is substantially inverse-phased outside the pass band. For realizing the above-described conditions, input IDT electrode of one filter track is connected in parallel with input IDT electrode of the other filter track, while output IDT electrode of one filter track is connected in parallel with output IDT electrode of the other filter track. Furthermore, frequency values of said two filter tracks substantially coincide at a point 3dB lower from the peak transfer function value. Thus the above-configured SAW filter of the present invention is smaller in the overall size and offers a broad pass band and a steep attenuation characteristic.

Surface-acoustic-wave filter

Acoustic resonators such as surface acoustic wave (SAW) devices and thin film bulk acoustic resonators (FBAR) can be configured to produce a band reject filter. Such a filter overcomes the insertion loss and power handling limitations of conventional band pass configurations and as such can be used in power amplifier and duplexer applications.

Band reject filters

A filter, particularly suitable for radio frequency applications comprises a first filter which, in turn, comprises at least a pair of intercoupled resonators (RES1, RES2), and a SAW filter (SAW) which is coupled between the two intercoupled resonators so that a signal input to the filter at its input (IN) is coupled through the SAW filter to provide an output signal at its output (OUT). This provides a filter with all the advantages of a SAW filter, but with the ability to withstand the high power requirements of radio frequency applications. If three or more resonators are present in the first filter, then an amplifier can also be integrated in the filter. The SAW filter (and the amplifier if present) are inductively or capacitively coupled to the resonators depending upon the type of filter that is required.

Filter having resonators coupled by a saw filter and a duplex filter formed therefrom

There is provided a resonant circuit includes a resonator, an inductor connected in parallel with the resonator, and a capacitor connected in parallel with the resonator. There are also provided a filter and an antenna duplexer having the above-described resonant circuit.

Resonant circuit, filter, and antenna duplexer

A low-loss acoustic wave filter includes a piezoelectric substrate, a first strongly unidirectional acoustic wave transducer and a second strongly unidirectional acoustic wave transducer. Each of the first and second strongly unidirectional acoustic wave transducers are acoustically coupled to one another. Each of the first and second strongly unidirectional acoustic wave transducers further comprises an acoustic wave reflector and a weakly unidirectional acoustic wave transducer. The acoustic wave reflector and the weakly unidirectional acoustic wave transducer are coupled to the piezoelectric substrate.

Method and apparatus for an acoustic wave filter

A surface acoustic wave (SAW) waveguide-coupled resonator filter is overcoupled to produce an essentially constant conductance and susceptance over at least the bandwidth of a desired notch filter. The SAW resonator filter is embedded in a bridged-T allpass circuit to provide the pair of equal capacitances of the circuit, and the resonator ground is connected to one terminal of the parallel inductor of the circuit having the other terminal connected to a system ground.

Sunder G. Gopani

Papers

Surface acoustic wave waveguide-coupled resonator notch filter