An 8 Way Power Combined 28GHz Direct Downconversion for 5G RF Beamformers

A passive eight-way power combined 28GHz mm-wave Gilbert cell I-Q Mixer in a 45nm bulk CMOS process is reported in this work for 5G RF beamformers. The 8:1 novel lumped quarter wave combiner/splitter utilizes transformer coupling to achieve a post layout efficiency of 67%, with a 2X reduction in area when compared to an only spiral inductor based implementation. With an isolation between ports greater than-22 dB, the amplitude and phase mismatch are kept within 0.3dB and 3 degrees respectively. Post-layout EM simulations of the I-Q mixer utilizing a current bleed technique predict a gain of 9dB, an OIP3 of +9dBm and a noise figure of 9.9dB at a power consumption of 17mW in an active area of only 0.39mm2. The I-Q mismatch is limited to half a dB in amplitude and 0.5 degree in phase, leading to an RSB <-40dBc. To ensure a compact realization, two key layout modification strategies implemented over a conventional mm-wave Gilbert cell are also discussed.