公开(公告)号：DE3574650D1

公开(公告)日：1990-01-11

申请号：DE3574650

申请日：1985-06-24

Applicant: IBM

Inventor： HO CECIL TZECHOR ,  WILMAN JOHN GILBERT

IPC: H01J37/147 ,  H01J37/305 ,  H01L21/027 ,  H04N3/26

Abstract: A high speed focus control circuit for an electron beam projection system. The circuit includes a conventional digital to analog converter, comprising a register for storing an n-bit digital value, and n current drivers, each of which provides a current which is proportional to the associated bit weighted value. Rather than summing the currents from all n current drivers and driving a single focus coil, each current driver is connected to one of n individual coils, wound on a common bobbin. This reduces circuit capacitance and permits higher switching speed.