1.1: Introduction

1.1.1: First, a Little History

Just as the late eighteenth through nineteenth centuries are known as the industrial age due to the rise of mechanization, the twentieth century can be referred to as the beginning of the electronic age. The first half of the century was dominated by electronic vacuum tubes that made possible devices such as radio, television, radar and long distance telephone. The technology of the vacuum tube was displaced mid-century by the introduction of solid-state semiconductors. The first working prototype transistor was invented at Bell Labs in 1947 by John Bardeen, Walter Brattain and William Shockley. This device, properly referred to as a point contact transistor, was quickly superseded by the bipolar junction transistor, a major topic of this text.

Commercial production of the transistor and related devices improved the performance of existing applications and made possible a range of new ones. Semiconductors proved to be smaller, lighter, more reliable and less expensive to build than their vacuum tube counterparts. The last 30 or so years of the century saw the rapid expansion of the integrated circuit where numerous transistors are combined in a single device. Initially such a device may have contained the equivalent of a dozen or so individual semiconductor devices, but today that number has grown to the billions¹. This extreme density has given rise to now common-place applications such as cell phones, GPS devices, laptop computers, tablets and our global communications infrastructure.

The science writer, Arthur C. Clarke, once observed that “Any sufficiently advanced technology is indistinguishable from magic”. Indeed, although today the typical citizen living in an industrialized country makes use of numerous electronic devices each day (sometimes without even being aware of it), they typically have scant knowledge of how these devices “work their magic”. Obviously there is no magic, only the application of scientific principles mixed with human ingenuity. Further, just as it is true that many more people can use a cell phone than design one, it is also true that there is a greater need for people who can design, manufacture and maintain devices based on semiconductors than for people who design the semiconductors themselves. The scope of this text, then, focuses on the operation and application of semiconductor devices rather than the design of the semiconductors themselves.

1.1.2: Variable Naming Convention

One item that often confuses beginning students of almost any subject is nomenclature. Before we begin our discussion of semiconductor devices it is important that we decide upon a consistent naming convention. Throughout this text we will be examining numerous circuits containing several passive and active components. We will be interested in a variety of parameters and signals. In order to keep confusion to a minimum we will use the following conventions in our equations for naming devices and signals.

\(R\)	Resistor (DC, or actual circuit component)
\(r\)	(AC equivalent, where phase is 0 or ignored)
\(C\)	Capacitor
\(L\)	Inductor
\(Q\)	Transistor (Bipolar or FET)
\(D\)	Diode
\(V\)	Voltage (DC)
\(v\)	Voltage (AC)
\(I\)	Current (DC)
\(i\)	Current (AC)

Table \(\PageIndex{1}\)

Resistors, capacitors and inductors are differentiated via a subscript that usually refers to the active device to which it is connected. For example, \(R_E\) is a DC bias resistor connected to the emitter of a transistor while \(r_C\) refers to the AC equivalent resistance seen at a transistor’s collector. \(C_E\) refers to a capacitor connected to a transistor’s emitter lead. Note that the device related subscripts are always shown in upper case, with one exception: If the resistance or capacitance is part of the device model, the subscript will be shown in lower case to distinguish it from the external circuit components. For example, the AC dynamic resistance of a diode would be called \(r_d\). If no active devices are present or if several items exist in the circuit, a simple numbering scheme is used, such as \(R_1\). In very complex circuits a specific name will be given to particularly important components, as in \(R_{source}\).

Voltages are normally given a two-letter subscript indicating the nodes at which it is measured. \(V_{XY}\) is the DC potential from node X to node Y while \(v_{XY}\) indicates the AC signal appearing across node X to node Y. A single-letter subscript, as in \(V_X\), indicates a potential relative to ground (in this case from node X to ground). The exceptions to this rule are power supplies, that are given a double letter subscript indicating the connection point (\(V_{CC}\) is the collector power supply), and particularly important potentials that are directly named, as in \(v_{in}\) (AC input voltage) and \(V_{R2}\) (DC voltage appearing across \(R_2\)). If an equation for a specific potential is valid for both the AC and DC equivalent circuits, the uppercase form is preferred (this makes things more consistent with circuits that are directly coupled, and thus can amplify both AC and DC signals). Currents are named in a similar way but generally use a single subscript referring to the measurement node (\(I_X\) is the DC current flowing through a conductor into or out of node X). All other items are directly named. By using this scheme, you will always be able to determine whether the item expressed in an equation is a DC or AC equivalent, its approximate circuit location, and other factors about it.

References

¹It is worth noting that the construction of an integrated circuit does not involve the creation and interconnection of millions or billions of single discrete transistors. Instead, the manufacturing process builds all of the transistors simultaneously, rather like a layer cake.