Е-Публикации
Технически университет - София

Abstract: This work presents a reliability-oriented design methodology for LC oscillators, focusing on Colpitts configurations implemented by a bipolar transistor. A nonlinear steady-state analytical framework is used as a practical design tool to determine the resonant tank parameters, loop gain conditions, and the dependence of oscillation amplitude on the operating conditions. Based on this analysis, a systematic sizing procedure is developed, in which the LC tank is designed and statistically characterized prior to amplifier and bias selection. The influence of component tolerances, temperature variation, supply voltage deviation, and load changes is quantified through statistical Monte Carlo analysis. To overcome the amplitude instability observed in the classical Colpitts topology, an automatic gain control (AGC) block is introduced that directly regulates the transistor transconductance, eliminating the need for individual amplitude adjustment. The simulation results demonstrate that, while the conventional Colpitts oscillator exhibits output amplitude variations of approximately ±30% under realistic parameter deviations, the proposed AGC-enhanced design limits worst-case amplitude variation to within ±10% using only standard tolerance components. A hardware prototype was developed to experimentally validate the methodology over wide variations in resonant tank parameters, amplifier bias conditions, and external load. The combined analytical, statistical, and experimental results confirm that the proposed approach simplifies the design process, improves robustness, and enables predictable, trimming-free oscillator operation suitable for mass-produced electronic systems.

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