Various communication systems, such as wireless communication systems of radio frequency (RF), are broadly adopted and play an important role in modern information society. A core technique for modern communication systems is frequency (and/or clock) synthesis, which generates a variable clock of a desired frequency based on a frequency reference clock, such that stability, accuracy, and spectral purity of the variable clock correlate with performance of the frequency reference clock. In a transmitter, the variable clock provided by a local frequency synthesizer can be utilized as a local oscillation carrier for an up-conversion frequency translation from baseband or intermediate-frequency (IF) signals to RF signals. On the other hand, in a receiver, the variable clock provided by a local frequency synthesizer can be adopted as a local oscillation carrier for a down-conversion from RF signals to IF/baseband signals.