Stacked common-gate Colpitts oscillators with transformer-coupled load

We present three variants of the common-gate Colpitts oscillator which can be useful in wireless power transfer (WPT) systems since they have integrated transformer-coupled loads. The proposed oscillators were systematically obtained by analyzing all possible four-element common-gate Colpitts oscillator configurations. Their third-order characteristic equations are derived, and the oscillation start-up condition and frequency of oscillation are then found. Circuit simulations and experimental results are presented to verify the theoretical analysis.