Abstract: Voltage controlled oscillator provided with a resonant network, an amplifier and a reactive network, all incorporated in an oscillator loop, the reactive network having one or more reactive components whose values depend on a control signal fed to a control input, so that the oscillator frequency can be regulated with said control signal. A control loop is provided between the resonant network and the reactive network, with which control loop the difference is determined between a measure of the imaginary part of the impedance or admittance of the resonant network and the control signal acting as reference quantity. The imaginary part of the impedance or admittance of the reactive network is regulated with said difference. The control loop contains a derivation circuit for deriving said measure and a differential amplifier, to one input of which the output signal of the derivation circuit is fed and to the other input of which the control signal is fed.