1.1 Introduction

Current sources and voltage references both depend on inherent characteristics of the transistor, either the bipolar junction transistor (BJT) or the field-effect transistor (FET), in order to operate properly. It seems only fitting then, in beginning this book, that we first take a brief trip back in time, and trace a history of how and when some of these products originated.

Actually, current sources and voltage references both predate the integrated circuit by several decades. Current sources were originally created by simply using resistors or by using resistors together with vacuum tubes. However, their combination did not provide much accuracy or stability. In the 1940s and '50s, it was common to see vacuum tube voltmeters (VTVMs) and other instrumentation based on the tube. Before being used within integrated circuits, or designed as commercial IC products, voltage references took the form of bulky and expensive laboratory standards. These included the Weston cell, the Clark cell, as well as some types of batteries. Those types of laboratory standards were used for decades. The best-known standard cell was the Weston cell, which produced a constant voltage output of 1.019 volts and was virtually independent of temperature change. The Weston cell utilized an H-shaped glass container and was powered by unique chemical actions. Great care was needed not to tip or knock over the cell or to load the output with any appreciable current, because it would temporarily cease operation. Recovery time could take days or even weeks. Both types of...