A control generator is provided, comprising: a summer configured to add a ramping phase adjustment signal and a basic phase adjustment signal to generate a combined phase adjustment signal based on the combined phase adjustment signal; a look-up table configured to generate first through Nth digital phase and frequency adjustment signals; and first through Nth digital to analog converters configured to convert the first through Nth digital phase and frequency adjustment signals to first through Nth analog phase and frequency adjustment signals in accordance with first through Nth clock signals, respectively. wherein N is an integer greater than 1.