A communications apparatus is provided. A first wireless communications module provides a first wireless communications service and communicates with a first communications device in compliance with a first protocol. A second wireless communications module provides a second wireless communications service and communicates with a second communications device in compliance with a second protocol. A clock source is shared by the first and the second communications modules and provides a reference clock to the first and the second communications modules. The first wireless communications module detects a request from the second wireless communications module for activating the clock source, determines whether the reference clock has been stably generated by the clock source, and adjusts an electrical characteristic of the clock source to facilitate the reference clock output from the clock source to achieve a target frequency when the reference clock has not been stably generated.