Saw filter using low-pass configuration and method of providing the same

A method for improving insertion loss in a passband while maintaining rejection in a stopband of a duplexer transmitter filter, comprising the steps of:

• providing a piezoelectric substrate;
• disposing at least one series resonator being electrically connected in series with the at least on series resonator including a plurality of aluminum interdigitated electrodes on the substrate having a periodicity defining an acoustic frequency within the passband of the filter, wherein the electrodes have a predetermined thickness such that a resonant frequency of the series resonators have reduced average energy loss;
• and
• disposing at least one shunt resonator being electrically connected in shunt with the at least one shunt resonator including a plurality of aluminum interdigitated electrodes on the substrate having a periodicity defining an acoustic frequency within the stopband of the filter, wherein the electrodes have a predetermined thickness such that a resonant frequency of the shunt resonators compensate for any degradation of Q at the antiresonant frequency of the series resonators in the stopband.

A transmitter acoustic wave filter for a duplexer, comprising:

• a piezoelectric substrate having an upper surface;
• two series resonators each including a plurality of interdigitated electrodes disposed on the upper surface, when electrically energized the electrodes causing acoustic waves to resonate at a passband frequency of the transmitter, the series resonators having an antiresonant frequency at a stopband frequency corresponding to a receiver frequency;
• three shunt resonators each including a plurality of interdigitated electrodes disposed on the upper surface, when electrically energized the electrodes causing acoustic waves to resonate substantially at the stopband frequency;
• and
• the series resonators being electrically connected in series and each shunt resonator being electrically connected in shunt to provide a ladder network.

A radio communication device, the device including a duplexer transmitter filter, comprising:

• a piezoelectric substrate having an upper surface;
• at least one series resonator including a plurality of interdigitated electrodes disposed on the upper surface, when electrically energized the electrodes causing acoustic waves to resonate at a first resonant frequency;
• at least one shunt resonator including a plurality of interdigitated electrodes disposed on the upper surface, when electrically energized the electrodes causing acoustic waves to resonate at a second resonant frequency higher than the first resonant frequency;
• and
• the series resonators being electrically connected in series and each shunt resonator being electrically connected in shunt to provide a ladder network, the series resonators are configured to provide a low-pass frequency response, and the shunt resonators are used as capacitive impedance inverters within a passband of the filter.