Component variability as a limit in digital electronics

摘要

Commercially successful electronic computers have been built with vacuum tubes and with transistors as active devices. Attempts to build computers with circuits based on other kinds of solid state devices have failed in spite of being the focus of large, well-funded efforts. The tunnel diode was invented shortly after the transistor and was the earliest of these. Josephson junctions and resonant tunneling devices also attracted massive investments as possible but unsuccessful alternatives to transistor based logic. What happened? Why did large development efforts devoted to these novel technologies fail? The answer is found in their inability to deal with the variability inevitably found in nominally identical parts. Transistors and vacuum tubes act as switches that form logic signals from standards that are distributed and recognizable throughout a system, signals that do not depend on the switching device that produced them. High gain is needed to emulate switches and is only obtained by using the attractive force between positive and negative charges as a gate to control current.