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.