NEGATIVE TO POSITIVE INVERTING DEVICE

摘要

PURPOSE:To automatically set up the black level of the optimum positive signal by detecting the peak value of a negative video signal and determine the black level of a positive signal to be inversed on the basis of the peak value. CONSTITUTION:A peak value is detected from an output signal of a gamma correction circuit 7 and held by a peak detection holding circuit 12. The electric potential passes through a buffer of an FETQ4 in a pedestal regulating circuit 13 and DC level shifted amplified by a transistor TR5 to be applied to the base of a TRQ 3 in a pedestal adding circuit 9. Variable resistance VR1 and VR2 are regulated so that the optimum pedestal level is always maintained even if the input signal is changed from 0 to the allowable maximum value. The resistance VR1 and VR2 determine the bias level and response sensitivity for the change of the input signal respectively. Even if the peak level of the original negative signal is changed, the appropriate black level of each positive signal can be automatically set up.