Automatic white balance adjusting circuit in color image display

摘要

A detector circuit detects a voltage corresponding to the leakage current that flows through the cathode electrode of a color display during a vertical blanking period of a video signal. The voltage detected is held in a first sample-and-hold circuit. Meanwhile, a reference signal corresponding to the reference black level is input during a part of the vertical blanking period of the video signal. A voltage corresponding to the leakage current that flows through the cathode electrode of the color display during the part of the vertical blanking period is detected by the detector circuit and then held in a second sample-and-hold circuit. The voltage held in the first sample-and-hold is subtracted from the voltage held in the second sample-and-hold circuit. A comparator circuit compares the difference between these voltages with a reference voltage. The result of the comparison controls a cutoff adjustment circuit for adjusting a DC level of the video signal.