Differential and common mode stability analysis of differential mm-wave CMOS amplifiers with capacitive neutralization

In this paper differential mode and common mode stability analysis of differential transformer-coupled CMOS mm-wave amplifiers with capacitive neutralization is investigated. Simulation of a differential amplifier implemented with a complete PSP transistor model shows that capacitive neutralization can improve the differential stability. In common mode however, the differential pair becomes potentially unstable over a wider frequency range. A robust common mode resistive stabilization technique, which ensures complete stability of the amplifier, is also discussed and analyzed. The analysis and stabilization techniques were successfully applied to stabilize a common mode unstable integrated F-band 45 nm CMOS amplifier. Measurements confirm the stabilization of the amplifier and a differential gain of 16 dB at 110 GHz is achieved.