ECWT: Antenna Switch Linearity Requirements for GSM/WCDMA Mobile Phone Front-Ends

Abstract

The design of the RF front-end part in modern cellular phones is becoming increasingly complex and demanding due to increasing number of frequency bands and modes that the phone needs to operate in. One of the main components of the RF front-end is the antenna switch that selects which TX/RX path is connected to the antenna. This paper considers the linearity requirements for antenna switches used to switch full-duplex WCDMA signals. The most demanding linearity requirement for WCDMA is shown to be the RX out-of-band blocking performance. The out-of-band blocking problem is shown to be caused by the three dominating intermodulation distortion (IMD) mechanisms of the switch. The switch IMD performance is also shown to depend on the relative phase shift between switch and duplexer. Two measurement setups are shown with measured results.