There is provided an oscillator which includes a current source, a capacitor coupled between the current source and a reference ground, a first switch coupled to the capacitor in parallel, an error amplifier, a comparator and a one-shot circuit. The error amplifier is coupled to the capacitor and configured to generate a regulation voltage based on a reference voltage and the voltage across the capacitor. The comparator is configured to compare the voltage across the capacitor with the regulation voltage and generate a comparison signal. The one-shot circuit is coupled to the comparator, wherein based on the comparison signal, the one-shot circuit generates a trigger signal to control the first switch.