A communication device comprises a processor; and a diplexer comprising a low pass filter passing signals with frequency below a first frequency threshold, the low pass filter having a first input and a first output, and a second filter being one of a high pass filter and a band pass filter passing signals with frequency above a second frequency threshold, the second filter having a second input and a second output; and a switch controllable by the processor for connecting the second input to a termination in a first state and connecting the second input to the first input in a second state responsive to a control signal from the processor, wherein the first output is coupled to the second output and the first input is configured to receive an input signal having a frequency range covering at least the first frequency threshold.

A resonant element includes first, second, and third plane electrodes, a first via electrode defining a first inductor, a second inductor, and a third inductor. The first via electrode connects the first plane electrode and the second plane electrode, and each of the second inductor and the third inductor connects the first plane electrode and the third plane electrode. The third plane electrode defines a first capacitor together with the second plane electrode, the second inductor includes second via electrodes, and the third inductor includes third via electrodes. Each of the second via electrodes and the third via electrodes is a columnar conductor extending in the extending direction of the first via electrode.

The present disclosure provides a radio frequency duplexer circuit and a radio frequency substrate. The radio frequency duplexer circuit includes a first terminal, a second terminal, a third terminal, a low-pass filter, and a high-pass filter. The low-pass filter includes N first filter sub-circuits coupled in series and a first tuning sub-circuit. Among the N first filter sub-circuits coupled in series, a first end of a 1.sup.st first filter sub-circuit is coupled to the first terminal, and a second end of a N.sup.th first filter sub-circuit is coupled to the second terminal. The high-pass filter includes M second filter sub-circuits coupled in series and a second tuning sub-circuit. Among the M second filter sub-circuits coupled in series, a first end of a 1.sup.st second filter sub-circuit is coupled to the first terminal, and a second end of a M.sup.th second filter sub-circuit is coupled to the third terminal.

A package for a tunable filter is disclosed. In an embodiment, the tunable filter includes a substrate having a first interconnection plane and a semiconductor device assembled on the substrate in a first component plane, the semiconductor device electrically connected to the first interconnection plane and containing tunable passive components. The filter further includes a control unit arranged in the first component plane, a dielectric layer arranged above the first component plane, a second component plane arranged on the dielectric layer and discrete passive devices arranged in the second component plane and interconnected with the semiconductor device, wherein the tunable passive components are tunable by the control unit.

A multilayer triplexer includes a first coil connected between a common terminal and a first filter, a second coil connected between the common terminal and a second filter, and a third coil connected between the common terminal and the third filter. The first coil, the second coil, and the third coil each include a coil conductor pattern between ones of substrate layers of a multilayer body. The coil conductor pattern of the first coil, the coil conductor pattern of the second coil, and the coil conductor pattern of the third coil do not overlap each other when the multilayer body is seen through in a direction in which the substrate layers are stacked on one another.

A branching filter includes a first filter provided between a common port and a first signal port, and a second filter provided between the common port and a second signal port. The branching filter further includes a connection path and a first capacitor. The connection path includes a first inductor, and connects the common port and the first filter. The first capacitor is provided between the connection path and the ground. The second filter is connected to the connection path. The first capacitor is connected to the first inductor at a first branch point located at any position in the first inductor.

RF communications circuitry, which includes a first RF filter structure and RF detection circuitry, is disclosed. The first RF filter structure includes a first group of RF resonators, which include a first pair of weakly coupled RF resonators coupled to a signal path of a first RF signal. One of the first group of RF resonators provides a first sampled RF signal. The RF detection circuitry detects the first sampled RF signal to provide a first detected signal. The first RF filter structure adjusts a first filtering characteristic of the first RF filter structure based on the first detected signal.

A tunable duplexer circuit is described, wherein the frequency response as well as bandwidth and transmission loss characteristics can be dynamically altered, providing improved performance for transceiver front-end applications. The rate of roll-off of the frequency response can be adjusted to improve performance when used in duplexer applications. A method is described where the duplexer circuit characteristics are optimized in conjunction with a specific antenna frequency response to provide additional out-of-band rejection in a communication system. Dynamic optimization of both the duplexer circuit and an active antenna system is described to provide improved out-of-band rejection when implemented in RF front-end circuits of communication systems. Other features and embodiments are described in the following detailed descriptions.

A radio frequency duplexer with a first directional coupler configured to divide an input reception signal into a first auxiliary reception signal and a second auxiliary reception signal, where the first auxiliary reception signal and the second auxiliary reception signal comprise signal components at a reception frequency, a first filter configured to filter the first auxiliary reception signal to obtain a third auxiliary reception signal, a second filter configured to filter the second auxiliary reception signal to obtain a fourth auxiliary reception signal, where pass bands of the first and the second filters comprise the reception frequency, a second directional coupler configured to combine the third auxiliary reception signal with the fourth auxiliary reception signal to obtain an output reception signal.

Multiplexing circuitry is disclosed that includes filtering circuitry, which provides a first transfer function between a common port and a first port and a second transfer function between the common port and a second port. The first transfer function and second transfer function provide a first passband and a second passband, respectively. The first transfer function also has a stopband provided within the second passband of the second transfer function due to the filtering circuitry including a first parallel resonant circuit provided in series in a first filter path being weakly coupled to a second parallel resonant provided in shunt with respect to a second filter path. The weak coupling between the first parallel resonant circuit and the second parallel resonant circuit thus naturally provides a stopband in the first transfer function within the second passband of the second transfer function.