A 28-GHz Image-Reject Mixer with Active Polyphase Filter for 5G Wireless Applications

A 28-GHz CMOS image-reject mixer (IRM) for 5G applications with an intermediate frequency (IF) of 3.6 GHz is presented. The IRM employs a folded down-conversion mixer for low voltage operation. PMOS as switch stage in IRM requires a lower LO power than NMOS. An active polyphase filter (APPF) with better phase balance than passive polyphase filter (PPPF) is applied to realize improved image rejection at IF. A two-stage PPPF is a better choice to convert the differential LO signals to differential and quadrature signals than APPF. The IRM exhibits 12.5 ± 1.5 dB conversion gain (CG) and the noise figure (NF) is 12.7 dB at IF 3.6 GHz. The maximum image-reject ratio (IRR) at fixed LO 23 GHz is 57 dB. The IRR of better than 40 dB is achieved for the IF from 2 to 4 GHz. The IRM is designed in a 65-nm CMOS technology and only dissipates 15 mW from a 1-V supply voltage.