A 100 megabit nine-digit electron tube encoder

A beam deflection tube has been developed which will convert an amplitude modulated signal into a nine-digit binary pulse code modulated signal at sampling speeds in excess of 12 mcs/sec. The tube employs a ribbon beam which is electrostatically deflected over nine columns of apertures in a code plate. This paper describes the tube and the critical tolerances required to achieve a signal-to-noise ratio of 54 db, which is within 3 db of the theoretical limit for a nine-digit encoder. The fabrication techniques which were required to achieve these tolerances are radically different from those used in the encoding tube described at the 1960 Electron Device Meeting. Factors that degrade encoding accuracy include thin oxide films on electrodes and residual gas pressure; techniques for minimizing these effects will be discussed. A secondary emitting target comprised of gold sputtered on a molybdenum substrate, found to be very stable in accelerated aging tests, has been evolved. An output current of 5/µamps per digit is achieved with a peak cathode loading of approximately 100 ma/cm².