Lecture-01.2.2 - A Switch Genealogy | 19th Century...

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Unformatted text preview: A Switch Genealogy | 19th Century. Mechanical turn switch: This device provides a model for the operation of the electronic switches used in modern com- puters. Activated by a simple twisting motion, this basic switch goes into the on position when the metal contact element (red) is rotated to close the circuit between contact points, allow- ing current (green) to continue. Other types of switches look considerably different (right), but their function is the same. 1906. Triode electron tube: Also called vacu- um tubes, many thousands of these devices were required to run early computers. A posi- tive charge to the grid encourages negatively charged electrons to surge across the vacuum between the cathode {a wire filament) and the anode (a metal plate), completing a circuit and enabling current to pass through. When negatively charged, the grid repels electrons and keeps the circuit broken. 1948. Junction transistor: in this pea-sized switch, current is turned on and off by the inter- action of three specially treated, or “deped,” layers of germanium. The emitter and the col- lector are doped to provide extra electrons, the base to provide extra ”holes,” or positive charge carriers. A positive charge (red) to the base enables electrons and holes to move,- the electron carries current (green) from the emitter to the collector to complete the circuit. 1959. Planar transistor: ldentical in principle to the junction transistor at left, the planar tran- sistor is a mere 1/200 of an inch long. As shown in this cross-sectional view, a positive electric charge to the base perm its passage of current from the emitter to the collector. The planar process allowed dozens of transistors, together. with resistors and capacitors, to be formed al I the same time on one side ofa silicon chip; ...
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