In one embodiment, an apparatus includes a first circuit of a digitally controlled oscillator (DCO). The first circuit has a loss component. A second circuit is coupled to the first circuit and configured to transform a positive impedance into a negative impedance in series with a negative resistance. The negative impedance includes an adjustable reactive component used to adjust a frequency of an output signal of the DCO. An equivalent reactance seen by the first circuit is less than a reactance of the adjustable reactive component.