A new tunable RF front-end circuit for advanced 4G handsets

A large number of frequency bands have been included in mobile phone handsets and in their RF front end circuit, RF paths have been increasing and the configuration has been becoming a complex more and more. A new tunable RF front-end circuit for single RF chain architecture is proposed in this paper. A tunable duplexer composed of wideband circulator and SAW based tunable filters for TX and RX, and a tunable low RX noise power amplifier have been developed. RX band noise level in FDD system is studied. Those devices are fabricated for the operation in the low frequency band of 669-960MHz which fractional bandwidth is 31.5%. Experimental results in Band 5 and Band13 show 40dB isolation of the tunable duplexer and 10dB noise level improvement of the tunable low RX noise PA, which achieve target value of 50dB suppression of RX band noise. This results show promising possibility of simple RF front-end of future mobile handsets.