Methods and apparatus for supplying radio frequency (RF) power to a process chamber. An RF generator is configured with a capability to operate with an RF power output independent of a reference frequency or synchronize the RF output power to the reference frequency. A clock ramp is used to change an RF power output frequency of the RF output power to match the reference frequency when the frequencies are in an unlocked state. When the RF power output frequency reaches the reference frequency, the RF power output can be locked to the reference frequency.