Multiplexer, radio frequency front-end circuit, and communication device

A multiplexer comprising:

• a common terminal;
• a first filter that is an acoustic wave filter electrically connected to the common terminal and that has a pass band;
• and
• a second filter that is electrically connected to the common terminal and that has a pass band on a higher frequency side of the pass band of the first filter;
• wherein the first filter includes:
• a first input/output terminal;
• a second input/output terminal;
• a series arm circuit provided on a path connecting the first input/output terminal and the second input/output terminal;
• and
• a parallel arm circuit electrically connected to a node on the path and ground;
• in the parallel arm circuit or the series arm circuit, a frequency at which an impedance is locally minimum is defined as a resonant frequency, and a frequency at which an impedance is locally maximum is defined as an anti-resonant frequency, a frequency at which an impedance of a resonator is locally minimum is defined as a resonant frequency, and a frequency at which an impedance of the resonator is locally maximum is defined as an anti-resonant frequency,
• and the parallel arm circuit has a resonant frequency located on a lower frequency side of a frequency at a low frequency end of the pass band of the first filter;
• the parallel arm circuit includes a first parallel arm resonator electrically connected between the node and the ground, and a second parallel arm resonator electrically connected in parallel to the first parallel arm resonator;
• a resonant frequency of the first parallel arm resonator is lower than the frequency at the low frequency end of the pass band of the first filter, and a resonant frequency of the second parallel arm resonator is higher than the resonant frequency of the first parallel arm resonator;
• and
• the series arm circuit includes:
• a first series arm resonator defined by an acoustic wave resonator having a resonant frequency in the pass band of the first filter;
• and
• a second series arm resonator defined by an acoustic wave resonator that is electrically connected in parallel to the first series arm resonator and that has a resonant frequency located on a higher frequency side of a frequency at a high frequency end of the pass band of the first filter.

A multiplexer comprising:

• a common terminal;
• a first filter that is an acoustic wave filter electrically connected to the common terminal and that has a pass band;
• and
• a second filter that is electrically connected to the common terminal and that has a pass band on a higher frequency side of the pass band of the first filter;
• wherein the first filter includes:
• a first input/output terminal;
• a second input/output terminal;
• a series arm circuit provided on a path connecting the first input/output terminal and the second input/output terminal;
• another series arm circuit including an acoustic wave resonator provided on the path;
• and
• a parallel arm circuit electrically connected to a node on the path and ground;
• in the parallel arm circuit or the series arm circuit, a frequency at which an impedance is locally minimum is defined as a resonant frequency, and a frequency at which an impedance is locally maximum is defined as an anti-resonant frequency, a frequency at which an impedance of a resonator is locally minimum is defined as a resonant frequency, and a frequency at which an impedance of the resonator is locally maximum is defined as an anti-resonant frequency,
• and the parallel arm circuit has a resonant frequency located on a lower frequency side of a frequency at a low frequency end of the pass band of the first filter;
• the series arm circuit includes:
• a first series arm resonator defined by an acoustic wave resonator having a resonant frequency in the pass band of the first filter;
• and
• a second series arm resonator defined by an acoustic wave resonator that is electrically connected in parallel to the first series arm resonator and that has a resonant frequency located on a higher frequency side of a frequency at a high frequency end of the pass band of the first filter;
• the series arm circuit is electrically connected to the first input/output terminal without the another series arm circuit being interposed there between;
• the first input/output terminal is electrically connected to the common terminal without any acoustic wave resonator being interposed there between;
• the another series arm circuit has one or more resonant frequencies and one or more anti-resonant frequencies, and a value obtained by dividing a frequency difference between an anti-resonant frequency located at a lowest frequency and a resonant frequency located at a lowest frequency of the series arm circuit having the one or more resonant frequencies and the one or more anti-resonant frequencies by the resonant frequency located at the lowest frequency is defined as a band width ratio of the series arm circuit;
• the parallel arm circuit has one or more resonant frequencies and one or more antiresonant frequencies, and a value obtained by dividing a frequency difference between an antiresonant frequency located at a lowest frequency and a resonant frequency located at a lowest frequency of the parallel arm circuit having the one or more resonant frequencies and the one or more anti-resonant frequencies by the resonant frequency located at the lowest frequency is defined as a band width ratio of the parallel arm circuit;
• a value obtained by dividing a frequency difference between an anti-resonant frequency of a series arm resonator and a resonant frequency of the series arm resonator by the resonant frequency is defined as a band width ratio of the series arm resonator;
• and
• a band width ratio of the first series arm resonator is wider than both a band width ratio of the another series arm circuit and a band width ratio of the parallel arm circuit.