Provided are voltage controlling assemblies that may be operable as clocks and/or oscillators. A voltage controlling assembly may include a comparator and a variable resistance device connected to one differential signal node of the comparator. The other node may be connected to a capacitor. Alternatively, no capacitors may be used in the assembly. During operation of the voltage controlling assembly, the variable resistance device changes its resistance between two different resistive states. The change from a low to a high resistive state may be associated with a voltage spike at the differential signal node of the comparator and trigger a response from the comparator. This resistance change may have a delay determining an operating frequency of the voltage controlling assembly. Specifically, the variable resistance device in the low resistive state may be kept for a period of time at a certain voltage before it switches into the high resistive state.