Current Sources and Voltage References

47

Chapter 4

Using BJTs to Create Current Sources

Today’s silicon planar, epitaxial, bipolar junction transistors are but distant cousins of

the early transistors invented at Bell Labs. Transistors have been the subject of hun-

dreds of millions of dollars worth of research over the years, yet today we can buy

them for pennies. As with the early development of the Internet by the U.S. Defense

Advanced Research Projects Agency (DARPA), so it was with the support of the U.S.

Department of Defense, particularly by the Air Force, that fueled the early R&D work

into both the transistor and the integrated circuit. Airplanes, rockets, and missiles have ...