An oscillator is provided that includes at least one capacitor, at least one comparator, and at least one device for charging or discharging the at least one capacitor. The capacitor is coupled to the comparator. The comparator compares the voltage on the capacitor with a reference voltage, and activates the device so as to command the charging or the discharging of the capacitor. The oscillator also comprises a circuit for supplying a preset voltage to the comparator when the device commands the charging of the capacitor, so that the comparator compares the reference voltage diminished by the preset voltage with the voltage on the capacitor, or the voltage on the capacitor added to the preset voltage with the reference voltage.