Clock generation devices and methods

A clock generation device provided for a transmitter is provided and comprises a clock generator, a calculator and a first phase locked loop (PLL) circuit. The clock generator generates a first clock signal. The calculator calculates a frequency difference between the first and second clock signals. The first PLL circuit generates an output clock signal according to a first reference clock signal related to the first clock signal, and a frequency of the output clock signal is changed according to the frequency difference. The transmitter transmits data according to the output clock signal.