Analysis of high-order sub-harmonically injection-locked oscillators

High-order subharmonically injection-locked oscillators have recently been proposed for low phase-noise frequency generation, with carrier-selection capabilities. This work focuses on the analysis of this frequency-synthesis procedure, with emphasis on the oscillator capability to discriminate the input tones, under the variation of a tuning voltage. The oscillator is described with an analytical envelope-domain formulation, leading to an expression for the oscillator phase shift with respect to the input source. The average of this phase shift is shown to evolve in a continuous manner in the distinct synchronization bands obtained versus the tuning voltage. Then, the subsynchronized operation at a high frequency ratio (N = 30) is considered, showing the applicability of envelope-domain simulations under various Fourier decompositions and sampling rates. The synchronization bands are obtained through the phase averaging technique. The analysis has been applied to a prototype at 2.7 GHz that has been manufactured and measured.