Calculations of Image Lag in Vidicon-Type Camera Tubes. I. Beam Discharge Lag and Total Image Lag, Including Photoconductive Lag

Abstract

Image lag in vidicon-type camera tubes is analyzed, taking scanning processes with a low-velocity electron beam into consideration. As the beam landing characteristics, not only usual form of ib=Ibexp (av) but also newly invented one of ib=Ib/{1+exp (-av)} are employed. The latter shows much better agreement to the measured characteristics than the former, but the difference between them is negligible at the regions where image lags become troublesome. First, by expressing target surface potentials and target output currents in exponential forms, the relationship between them is obtained analytically and presented graphically as the target surface potential curves under steady state conditions. Then, the fundamental expressions for beam discharge lag or capacitive lag are obtained for both rise and decay by applying the above-mentioned relationship to transient cases. Finally, the total image lag, including photoconductive lag, is analyzed. From the results obtained by computer calculation, the general features of image lag and the lower limit of image lag are known.