Adaptive load for coupler in broadband multimode multiband front end module

A radio-frequency (RF) system comprising:

• a first directional coupler having a first input port, a first output port, a first coupled port, and a first isolated poet, the first directional coupler configured to receive a first RF signal within a first frequency band at the first input port and to provide the first RF signal on the first output port;
• a second directional coupler having a second input port, a second output port, a second coupled port, and a second isolated port, the second directional coupler configured to receive a second RF signal at the second input port and to provide the second RF signal at the second output port, the second RF signal being within a second frequency band different from the first frequency band, the second coupled port being connected to the first isolated port;
• a power amplifier module connected to the first input port of the first directional coupler and to the second input port of the second directional coupler and configured to provide the first and second RF signals;
• power detection circuitry connected to the first coupled port of the first directional coupler;
• and
• a termination circuit connected to the second isolated port of the second directional coupler and configured to provide a shared termination impedance for the first and second directional couplers selected to optimize combined performance of the first and second directional couplers over the first and second frequency bands, the termination circuit including a first inductor, a first capacitor, and a resistor connected in parallel to form a parallel RLC circuit, and the termination circuit further including a second inductor and a second capacitor, the parallel RLC circuit being connected in series with and between the second inductor and the second capacitor, the shared termination impedance being a complex impedance.

A wireless device comprising:

• a transceiver configured to process a plurality of RF signals in a corresponding plurality of frequency bands;
• an antenna in communication with the transceiver configured to transmit the plurality of RF signals;
• a plurality of directional couplers each having an input port configured to receive one of the RF signals in a respective one of the plurality of frequency bands and an output port configured to provide the one of the RF signals to the antenna, the plurality of directional couplers each further including a main transmission line extending between the input port and the output port and a coupled transmission line, the coupled transmission lines of the plurality of directional couplers being connected together in series to provide a daisy-chain of the plurality of directional couplers;
• a power amplifier module connected to the input port of each directional coupler in the daisy-chain and configured to provide the plurality of RF signals;
• power detection circuitry connected to a coupled port of a first directional coupler in the daisy-chain;
• and
• a termination circuit connected to an isolated port of a last directional coupler in the daisy-chain and configured to provide a shared termination impedance for the plurality of directional couplers that is selected to optimize combined performance of the plurality of directional couplers over the plurality of frequency bands, the termination circuit including a first inductor, a first capacitor, and a resistor connected in parallel to form a parallel RLC circuit, and the termination circuit further including a second inductor and a second capacitor, the parallel RLC circuit being connected in series with and between the second inductor and the second capacitor.