The gain of an amplifier in a receiver operating in a cellular communication system is controlled by determining one or more gain variability metrics, which are then used to produce first and second threshold values. A frequency difference between a current carrier frequency and a target carrier frequency is ascertained and then compared to the threshold values. Target gain setting production is based on comparison results: If the frequency difference is larger than the first threshold, a full automatic gain control algorithm is performed; if the frequency difference is smaller than the first threshold and larger than the second threshold, an optimized automatic gain control algorithm is performed, wherein the optimized automatic gain control algorithm uses a current gain setting as a starting point; and if the frequency difference is smaller than both the first and second thresholds, the current gain setting is used as the target gain setting.

A buzzer driving system includes a filter circuit and a driving circuit. The filter circuit is configured to filter an audio playback signal and output an analog playback signal. The driving circuit is electrically connected to the filter circuit and configured to output a driving voltage to the buzzer based on the analog playback signal. The driving system generates the driving voltage in an analog form to enhance the output audio quality of the buzzer.