Oscillators and a method of operating the same are provided, the oscillators include at least one oscillation device including a first magnetic layer having a magnetization direction that is variable, a second magnetic layer having a pinned magnetization direction, and a non-magnetic layer disposed between the first magnetic layer and the second magnetic layer. The oscillation device is configured to generate a signal having a set frequency. The oscillators further include a driving transistor having a drain connected to the at least one oscillation device, and a gate to which a control signal for controlling driving of the oscillation device is applied.