Duplexer having resonator filters

A duplexer comprising:

• an antenna terminal connected to an antenna;
• a transmit terminal connected to a transmitter configured to send a transmit signal through the antenna terminal;
• a receive terminal connected to a receiver configured to receive a receive signal through the antenna terminal;
• a transmit ladder filter connected between the antenna terminal and the transmit terminal, the transmit filter comprising first through fourth transmit series resonators connected in series between the antenna terminal and the transmit terminal, first through fourth transmit shunt resonators respectively connected between the first through fourth transmit series resonators and a ground voltage, and a cross-coupling capacitor connected between the third transmit shunt resonator and the antenna terminal;
• and a receive ladder filter connected between the antenna terminal and the receive terminal, the receive filter comprising a phase shifter and first through fourth receive series resonators connected in series between the phase shifter and the receive terminal, first through fourth receive shunt resonators respectively connected between the first through fourth receive series resonators and the ground voltage, and a common ground inductor commonly connected between the ground voltage and the third and fourth receive shunt resonators, wherein the cross-coupling capacitor shifts a transmission zero of the transmit signal toward a center frequency of a receive passband of the receive filter.

A duplexer for interfacing a receiver and a transmitter with a common antenna, the duplexer comprising:

• a receive ladder filter connected between the antenna and the receiver, the receive ladder filter comprising receive series resonators and receive shunt resonators, a first receive shunt resonator comprising a first electrode connected between the antenna and a first series resonator and a second electrode connected to ground, a second receive shunt resonator comprising a third electrode connected between the first receive series resonator and a second receive series resonator and a fourth electrode connected to ground, a third receive shunt resonator comprising a fifth electrode connected between the second receive series resonator and a third receive series resonator and a sixth electrode connected to a common ground inductor, and a fourth receive shunt resonator comprising a seventh electrode connected between the third receive series resonator and a fourth receive series resonator and an eighth electrode connected to the common inductor, the common inductor being connected to ground;
• and
• a transmit ladder filter connected between the antenna and the transmitter, the transmit ladder filter comprising transmit series resonators and transmit shunt resonators, a first transmit shunt resonator comprising a first electrode connected between a first transmit series resonator and a second transmit series resonator and a second electrode connected to ground, a second transmit shunt resonator comprising a third electrode connected between the second transmit series resonator and a third transmit series resonator and a fourth electrode connected to ground, a third transmit shunt resonator comprising a fifth electrode connected between the third receive series resonator and a fourth transmit series resonator and a sixth electrode connected to a capacitor node, and a fourth transmit shunt resonator comprising a seventh electrode connected between the fourth transmit series resonator and the transmitter and an eighth electrode connected to ground, wherein the capacitor node is connected to ground through an inductor and to the antenna via a cross-coupling capacitor.