Imec, Murata and Huawei showcased a stand-alone multiband electrical-balance duplexer in 0.18µm SOI CMOS at Mobile World Congress in Barcelona, Spain. This type of duplexer is a promising alternative to the fixed frequency surface-acoustic wave (SAW) filters implemented in mobile phones providing transmit-to-receive (TX-to-RX) isolation. SAW duplexers are integrated into mobile phones to suppress TX-to-RX signal transfer and avoid unwanted frequency components in the RF signal. As SAW duplexers are functioning at a fixed frequency, more and more SAW duplexers would be needed so that mobile phones can support the ever growing amount of bands adopted by operators. Due to their frequency flexibility, electrical-balance duplexers are paving the way to an integrated multiband solution for TX-to-RX isolation in front end modules in mobile phones.
This new 1.9 to 2.2 GHz duplexer (1.75 mm2) is implemented on a 0.18µm RF silicon-on-insulator (SOI) CMOS technology. It enables high quality integrated passive devices and high power duplexer operation (27 dBm TX output). It achieves excellent linearity (more than +70 dBm IIP3 in both TX and RX), which is comparable to conventional passive SAW filters. This prevents the duplexer from generating nonlinear distortion in the presence of external jammer signals at specific sensitive frequencies and its own large TX signal. The duplexer achieves low insertion losses, at less than 3.7 dB TX and 3.9 dB RX, and has isolation characteristics competitive with state of the art SAW duplexers. It uses a single ended topology to avoid common mode leakage issues that could cause the RX to compress for high power TX input signals. Marking an industry first achievement reported upon at the International Solid State Circuits Conference (ISSCC), Feb. 22 to 26, it is the first electrical balance duplexer reported to be linear enough to avoid RX de sensitization due to inter and cross modulation between the TX and typical 3GPP-defined jammers.
