JPS5640328A - Electric charge transfer type digital/analogue converting unit - Google Patents

Abstract

PURPOSE:To enhance the set precision of a weight coefficient and make the unit small-size, by setting the weight coefficint as the ratio of areas of divided electrodes of the charge transfer element. CONSTITUTION:Electrodes 21-27 are charge detecting electrodes to detect transfer charge of each delay stage and form one delay stage of charge coupling device CCD together with plural electrodes, which are not divided, between respective charge detecting electrodes. Through the value of the weight coefficient is determined by the ratio of areas of two divided electrodes, the length of respective charge detecting electrodes in the charge transfer direction is fixed here. When length of electrodes 21, 23, 25 and 27 on the channel are denoted as 1N, 1S, 12, and 11 respectively and each electrode is divided to satisfy expression (2), the weight coefficient of D/A is obtained. The charge quantity is determined by the level of input pulses. The charge quantity stored in capacity 33 is the sum of charge quantities induced in respective electrodes, and change components of the output voltage of the operational amplifier become the analogue output of D/A.