Patent ID: 6246448
Filing Date: 2001-06-12
Classification: H01J,H04N

Abstract:
A purity adjustment device for a video display appliance having a cathode ray tube (CRT), comprising:an initial value determining section for determining a first voltage corresponding to an earth magnetic field of a specified place where a purity of a picture displayed on the CRT present white;an earth magnetic field detecting coil for detecting the earth magnetic field of a present place where the video display appliance is located, and producing a second voltage corresponding to the detected earth magnetic field;a comparing section in which the first voltage from the initial value determining section and the second voltage from the earth magnetic field detecting coil are superimposed together, and compared to an input reference voltage to produce a third voltage that is amplified to produce an output;an amplifying section for amplifying an output of the comparing section and producing an amplified voltage as a purity compensation voltage; anda purity coil for producing a magnetic field for controlling a position of electron beams scanned on a screen of the CRT in accordance with the purity compensation voltage provided from the amplifying section.