Signal generation with high output power levels in the mm-wave frequency range represents a challenge in silicon based technologies given the fmax/ft of the transistors and the losses in the passive elements. Recently, Nth harmonic oscillators or N-push oscillators have gained interest owing to their capability to generate signals at frequencies higher than fmax. Furthermore, N-push oscillators provide access to the fundamental frequency signal (f0) in addition to nf0, which can be used for locking to a synthesizer in a phase locked loop, eliminating the need for frequency dividers.
The main advantage of N-push oscillators is the fact that the core oscillators operate at a lower frequency, thus it is easier to realize a wide tuning range core oscillator given the higher quality factor varactors at the fundamental frequency compared to the higher harmonics. However, the tuning range of oscillators at mm-wave frequencies in general is limited due to the low quality factor of MOS varactors. In this talk, we will review circuit and device level techniques to increase the output power and tuning range from mm-wave signal generators. We support our findings with measurement results from fabricated prototypes in SiGe and CMOS technologies.