storage elements ccd line which receives input charge of equivalent magnitude to full charge packets introduced to data processing portions of the device as stated above for a digital charge coupled device data is transmitted in the data processing portion of the device in the form of full charge packets or nominal charge packets if a reference voltage is sought for use in a comparison circuit employing flip flops see copending u s application ser no 448 771 by gunsagar and amelio the reference voltage should lie approximately midway between voltages associated with a full charge packet and a nominal charge packet i e should be about the value of a voltage associated with one half the charge in a full charge packet thus the dedicated ccd line is designed to divide the full charge packet input into a one half charge packet sample the reference voltage generator then produces a voltage associated with each half charge packet sample compares this voltage with an instantaneous reference voltage and through a feedback loop incrementally adjusts the value of the instantaneous reference voltage to make it closer to the voltage associated with the half charge packet sample the comparator circuit used here and described in detail subsequently should be as nearly as possible identical to the comparator circuits for which the reference voltage is generated so as to minimize any mismatching over the range of operation once the instantaneous reference voltage is close to the voltage associated with the sample it may be employed externally as the desired reference voltage the overall.