Patent ID: 8199254

Claim:
A device for receiving a video signal, which comprises a synchronous signal and a data signal, and separating the synchronous signal in the video signal, the device comprising: a capacitor for receiving the video signal and performing AC coupling according to the video signal to obtain a coupling signal; a level determining circuit for receiving the coupling signal, comparing a voltage level of the coupling signal with a plurality of reference voltages defining a plurality of reference voltage ranges, one of which is a predetermined reference voltage range, and outputting an adjusting signal according to the reference voltage range corresponding to a minimum voltage level of the coupling signal in a predetermined time period; a level adjusting circuit for receiving the adjusting signal and thus adjusting a DC level of the coupling signal until the minimum voltage level of the coupling signal is within the predetermined reference voltage range; a synchronous signal separating circuit for separating the synchronous signal from the coupling signal according to a separating reference voltage when the minimum voltage level of the coupling signal is within the predetermined reference voltage range; an oscillator for providing an operation control signal for the device; and a period control circuit for down-sampling the operation control signal to generate a first period signal and a second period signal, wherein the level determining circuit determines the reference voltage range corresponding to the voltage level of the coupling signal according to the operation control signal and determines the predetermined time period according to the first period signal, and a length of time that the current sources are enabled is determined by an enabling time of the second time period signal.