Design of injection-locked oscillator circuits using an HBT X-parameters™-based model

A load independent X-parameters-based heterojunction bipolar transistor (HBT) model has been used for the first time in the design and behaviour prediction of injection-locked oscillator circuits. This model has been extracted from load-pull measurements with a large-signal network analyser and, in order to obtain a high oscillator RF power, targeting a load impedance close to the optimum one for HBT maximum output power. A methodology is given to obtain robust injection-locked oscillator circuits with a high-synchronisation bandwidth. Several injection-locked oscillator prototypes have been designed and fabricated, and their measurements compared with the simulations obtained using the X-parameters model. Satisfactory results were obtained when the prototypes were operated as free-running and synchronised oscillators.