Abstract: A current controlled ring oscillator and a method for controlling the same are provided. The current controlled ring oscillator includes a charge pump (CP), a loop filter (LF), a voltage-current (V-I) converter, and an oscillation unit. The CP is used to provide a charging/discharging current. The LF is coupled to the CP, and is used to provide a control voltage. The V-I converter is coupled to the CP, and is used to convert the control voltage to a control current. The oscillation unit includes a plurality of current controlled delay cells serially connected to one another as a ring, and the oscillation unit is coupled to the V-I converter, and controlled by the control current to generate an oscillation signal.