Multi-mode RF front-end circuit

This paper proposes a novel RF front-end circuit for multi-mode/multi-band mobile communication terminals. The RF front-end circuit functions as both a tunable duplexer for a frequency division duplex system and a single-pole double-throw (SPDT) switch with a tunable bandpass filter for a time division duplex system. The circuit comprises two pairs of transmission lines, switches, and variable reactance circuits. The proposed circuit can change transmission and reception frequencies when it functions as a duplexer. The circuit can also tune the center frequency and bandwidth independently when it functions as the SPDT switch with a bandpass filter. This paper shows the characteristics of the proposed circuit at 2.5 GHz, 3.5 GHz, and 4.5 GHz. The results confirm the dual operation of the proposed circuit.