| 摘要 |
PURPOSE:To set automatically both the luminance and the contrast at the optimum state for a picture system using an A/D converter, by supplying the output of a peak holding circuit for the upper and lower limits of a video signal in the form of the reference voltage of the A/D converter. CONSTITUTION:The video signal is supplied through an input terminal 1 to an A/D converter as well as to the peak holding circuits 2 and 3. Thus the upper and lower limits of the video signal are held, and the output voltage is supplied to the converter 4 as the reference value. The video signal is supplied to a terminal 17 of the converter 4 and then the plus inputs of the voltage comparators 18, 19 and 20 respectively. The upper and lower limit reference voltages are supplied to the terminals 21 and 22, and the potentials divided by the resistance 23-26 are supplied to the minus inputs of the comparators 18-20. The outputs of the comparators 18-20 are converted into the 2-bit digital signals by an encoder 27 and delivered to the output terminals 29 and 30 to be converted into the picture digital signals having high stability and high reproducibility. |
