An Area-Efficient Reconfigurable Compact Multi-Band Directional Coupler in RF SOI CMOS Technology

In this paper, a reconfigurable directional coupler covering a wide range of operating frequency is presented. Excessive insertion loss at high frequencies of an inherently high-pass weakly coupled electrically short coupler limits the range of operating frequencies. In the proposed design, the effective coupling strength between the primary and pick-up coils can be switched, thus reducing the coupling coefficient at higher frequencies. An area-efficient physical design is adopted by reusing the area inside the primary coil, occupying a core area of 0.072mm2. The device is implemented in a 90 nm RF SOI CMOS switch technology. The designed directional coupler shows a coupling coefficient between 25 dB and 20 dB from 900 MHz to 2.8GHz. Insertion loss at 2.8GHz is improved from 0.253dB to 0.185dB. Directivity of more than 25dB can be reached from 700 MHz to 3.25 GHz with the on-chip matching termination.