Tunable oscillator derived from Colpitts structure with simply controllable condition of oscillation and synthetic inductor based on current amplifier and voltage differencing transconductance amplifier

Our contribution discusses modification of well-known Colpitts LC oscillator to fully electronically controllable type utilizing adjustable current amplifier and inductance simulator based on voltage differencing transconductance amplifier (VDTA) instead of common bipolar transistor and passive metal coil. Implementation of current amplifier allows independent and direct control of oscillation condition, simplifies design (capacitors can have equal values because condition is not dependent on them) and used inductance equivalent based on VDTA allows linear control of frequency of oscillation and quadrature outputs with unchangeable amplitudes during the tuning process. Theory was verified by PSpice simulations and experimental measurement.