Abstract: An in-depth investigation of oscillation modes in an oscillator based on a distributed amplifier is presented. It shows that instability problems reported in previous papers are intrinsic to the circuit nonlinear dynamics. The undesired phenomena include discontinuous jumps when continuously varying the tuning voltage, quasi-periodicity, or two incommensurable self-generated oscillations, and nonuniqueness of the mode, meaning that the same frequency can be achieved by several combinations of tuning voltages. The numerical bifurcation analysis of the circuit reveals a complicated dynamical structure that explains the mechanisms leading to the reported undesired behaviors. Special attention is paid to the presence of complicated bifurcation scenarios leading to quasi-periodic behavior and a chaotic regime. The results of this theoretical investigation are confirmed by independent numerical simulations through time-domain integration and qualitatively predict the experimental observations. Then, a stabilization procedure based on the introduction of resistors is presented, evaluating its impact on the oscillation amplitude and the uniqueness of the desired oscillation modes obtained when tuning the bias voltages.

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