An 8 Way Power Combined 28GHz Direct Downconversion Receiver 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 a spiral inductor-only implementation. With an isolation between ports greater than -22 dB, the amplitude and phase mismatch of the power combiner 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 of the receiver is 0.5 dB in amplitude and 0.5 degree in phase, leading to an RSB $\lt -40$dBc. To ensure compact realization, two key layout improvements over a conventional mm-wave Gilbert cell are also discussed.