TABLE OF CONTENTS Before looking at the transistor in Chapter 3, it will be helpful to first briefly review the diode, and thereby some of the basic characteristics of the P-N junction, because diode action is an essential ingredient in making current sources and reference voltages. In a circuit's design, this can be induced by using either the forward voltage (V FWD) of a dedicated switching diode or a transistor's base-emitter junction voltage (V BE), or even a JFET's channel diode voltage. In each case the P-N junction is used, either as a stable predictable reference or for compensation purposes.
Early semiconductor diode types were silicon and germanium point contact devices, developed by Dr. Russell Ohl and others at Bell Labs, as well as higher voltage types developed by Dr. Karl Lark-Horovitz and his group at Purdue University. These were developed primarily for the U.S. military and were used in radio, radar, sonar, and other equipment in World War II. Today's silicon junction diodes followed the introduction of the silicon transistor in the early 1960s. Some of the earliest silicon diode manufacturers included Texas Instruments, Fairchild Semiconductor, Transitron, Hughes Semiconductor, and General Electric.
The diode is a two-terminal, single-junction semiconductor device that passes electrical current in only one direction. It is commonly used for rectification, switching, and clamping, as well as in oscillator, varactor, and reference circuits. Small-signal diodes are typically used in relatively small current circuits (less than 100 mA), whereas rectifiers
