A circuit arrangement for controlling a backlight source and an operation method are provided. The circuit arrangement includes a generator. The generator receives a sync signal and generates a pulse width modulation signal synchronous with the sync signal to control the backlight source. The sync signal indicates a frequency of a video including a series of image frames. The sync signal includes a sync period corresponding to a frame of the video. The pulse width modulation signal includes a first waveform pattern in a first sub-period of the sync period and a second waveform pattern in a second sub-period of the sync period. Each of the first waveform pattern and the second waveform pattern includes at least one active pulse. The first waveform pattern is substantially identical to the second waveform pattern.