Hisao Hayafuji

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.

A study on low Rx-band noise power amplifier for reconfigurable RF front-end circuit

RF paths in mobile phone have been increasing and the configuration has been becoming a complex year by year. A new tunable RF front-end circuit for a single RF chain architecture was proposed. That solution needs the tunable low RX-band noise power amplifier(LNPA) in order to reduce the noise at a RX input port of a transceiver IC in cooperation with the tunable duplexer in FDD system handsets. In this paper, a principle of LNPA is described and it is shown that an interstage filter is effective compared with other circuit configulations. The required characteristics for the interstage filter in LNPA are studied and the RX band attenuation of the interstage filter is calculated with employing equations using noise figure and gain parametaers. It is found that the RX-band noise floor of LNPA is determined by the noise level of a back stage amplifirer Q2, when the interstage filter RX band attenuation is more than 25dB. LNPA is fabricated to clarify the operation and less than -140dBm/Hz which is the target value of the system can be obtained. This results show the promising possibility of Tunable LNPA for simple RF front-end for future mobile handsets.