Enhancing Spectral Range and Power of Chaos in Colpitts Oscillator by Diode-Varactor Based Capacitive Nonlinearity in LC-Tank

The paper presents a simple modification in the feedback network of standard Colpitts oscillator for the generation of high frequency chaos with enhanced power. The modification consists of replacing one capacitor in the voltage divider arm of the feedback LC-tank of standard Colpitts circuit by a pair of back-to-back connected varactor diodes. The voltage dependent capacitance of the varactor diode pair varies nonlinearly with the output voltage, which generates nonlinear feedback signal. This combined with input I-V nonlinearity of the amplifier generates high frequency chaotic output with enhanced power. The spectral band gets extended up to 5 GHz and the power increases approximately by two times. The present work is a simulation study based on the nonlinear dynamics of the Colpitts circuit. The analysis includes calculations of fixed points, Lyapunov stability, bifurcation diagrams, phase portraits and frequency spectrum by Fourier transform. Simulation results are for comparing the chaotic behaviors before and after modification.