Optimum Conditions for Efficient Second-Harmonic Power Generation in mm-Wave Harmonic Oscillators
Aboozar Ghorbani-Nejad, Amir Nikpaik, Abdolreza Nabavi, Amir Hossein Masnadi Shirazi, Shahriar Mirabbasi, Sudip Shekhar
Abstract
Based on the polyharmonic distortion (PHD) method, we present an approach to find the optimum conditions for efficient second-harmonic signal generation in millimeter-wave (mm-wave) harmonic oscillators that also maximize their DC-to-RF efficiency. These conditions include magnitude and phase of voltages at the gate and drain of the core transistors at both fundamental and second-harmonic signal components as well as the DC bias point to generate the maximum achievable second-harmonic power. We also establish that the steady-state oscillation at the fundamental frequency is a crucial criterion to obtain such conditions. The maximum achievable power and efficiency obtained from the proposed approach are independent of the harmonic oscillator topology and hence can be regarded as a reference for comparing different design techniques and structures. According to the proposed design procedure, the optimum conditions for an nMOS transistor acting as the active core of a 200-GHz harmonic oscillator are found and a second-order harmonic oscillator topology that can fulfill the optimum conditions is proposed. The oscillator is designed and fabricated in a 65-nm CMOS process and achieves peak DC-to-RF efficiency of 6.05%. The peak output power at 1.2-V supply is 2.9 dBm at 203 GHz.