Patent ID: 7902940

Claim:
A duplexer comprising: a transmission filter having a ladder circuit configuration; and a reception filter; wherein one end of the transmission filter and one end of the reception filter are connected to each other and are connected to an antenna terminal; the reception filter includes an input terminal, first and second reception output terminals, and first, second, third, and fourth longitudinally coupled resonator filter elements, a phase of an output signal with respect to an input signal of the first longitudinally coupled resonator filter element being different by about 180 degrees from that of the second longitudinally coupled resonator filter element, a phase of an output signal with respect to an input signal of the third longitudinally coupled resonator filter element being different by about 180 degrees from that of the fourth longitudinally coupled resonator filter element; each of the first to fourth longitudinally coupled resonator filter elements includes a plurality of IDTs and is connected to the input terminal via at least one of the plurality of IDTs, and the IDTs of the first to fourth longitudinally coupled resonator filter elements which are connected to the input terminal are connected in parallel to each other; the third longitudinally coupled resonator filter element is connected to the first reception output terminal via another one of the plurality of IDTs, and the fourth longitudinally coupled resonator filter element is connected to the second reception output terminal via another one of the plurality of IDTs; the IDT of the third longitudinally coupled resonator filter element which is connected to the first reception output terminal is connected in series to a corresponding one of the plurality of IDTs of the first longitudinally coupled resonator filter element; and the IDT of the fourth longitudinally coupled resonator filter element which is connected to the second reception output terminal is connected in series to a corresponding one of the plurality of IDTs of the second longitudinally coupled resonator filter element.