Video signal processing circuit and computer system

Abstract

A video signal processing circuit, in which a horizontal synchronizing signal is separated from an input analog video signal by a synchronism separating circuit, whether a “H” period of the horizontal synchronizing signal continues for more than a prespecified period of time or not is checked by a synchronizing signal monitoring counter, and power supply to an A/D converter is controlled thereby according to a result the confirmation.

1. A video signal processing circuit comprising:
 an A/D converter converting an input analog video signal to a digital video signal in response to a power supply;  
 a synchronism separating unit separating a synchronizing signal from said input analog video signal;  
 a monitoring unit monitoring a disturbance of the synchronizing signal and time for which the disturbance continues; and  
 a power supply unit supplying power to said A/D converter, wherein said power supply unit stops the power supply to said A/D converter when the time for which the disturbance continues exceeds a predetermined time period that is shorter than the time period for which a normal horizontal synchronizing signal continues.  
 
     
     
       2. A computer system connected to an external device and executing image processing according to an analog video signal inputted from the external device comprising:
 a video signal processing circuit generating a digital video signal according to an analog video signal inputted from the external device;  
 an image processing circuit executing image processing according to a digital video signal generated by said video signal processing circuit; and  
 a power supply unit supplying power within the computer system, wherein said video signal processing circuit comprises:  
 an A/D converter converting an input analog video signal to a digital video signal in response to a power supply,  
 a synchronism separating unit separating a synchronizing signal from said input analog video signal,  
 a monitoring unit monitoring a disturbance of the synchronizing signal and time for which the disturbance continues, and  
 a power supply unit supplying the power to said A/D converter, wherein said power supply unit stops the power supply to said A/D converter when the time for which the disturbance continues exceeds a predetermined time period that is shorter than the time period for which a normal horizontal synchronizing signal continues.  
 
     
     
       3. A method comprising:
   converting a video signal at an A/D converter in response to a power supply;        separating a synchronizing signal from the video signal;        monitoring a disturbance of the synchronizing signal and time for which the disturbance continues; and        stopping the power supply to the A/D converter when the time for which the disturbance continues exceeds a predetermined time period that is shorter than the time period for which a normal horizontal synchronizing signal continues.