In a controlled oscillator having a resonator (2) and at least one amplifier (1) with positive feedback, the oscillation signal, which is present at the resonator (2), is fed to an analogue-to-digital converter (21). The analogue-to-digital converter (21) supplies numerical information on the amplitude and/or the phase of the oscillation signal to a control circuit (22). The control circuit (22) emits at least one control signal for setting the phase and/or the amplitude of the oscillation of the oscillator. For producing the control signal the control circuit (22) may be associated with a table of parameters (24). The output of the control circuit (22) is formed by a digital-to-analogue converter (23). In one embodiment, the oscillator is a push-pull oscillator having two transistors (34) as amplifiers, which are connected to a controllable current source (7). The control circuit (22) in this case controls the operating points of the amplifiers (34) via a bias at the base connections of the transistors (34) and via the current through the controllable current source (7). In order to start the oscillator, the base potentials of the transistors (34) are set such that they are asymmetrical.