We began with the basic concepts of electricity: voltage, current, resistance, and capacitance. Voltage is electrical force, current is the intensity of the flow of electrical charge, resistance restricts current flow, and capacitance represents an ability to store electrical charge. Ohm's law

`(`

`=`

`)`

and the charge-capacitance-voltage equation
`(`

`=`

`)`

describe the
relationships among these electrical quantities.Next we examined how to build useful logic functions from the primitive electrical components at our disposal: resistors, diodes, and transistors. We started with primitive diode-resistor logic. This has the serious drawbacks that it is not easy to cascade and an inverter cannot be built in the logic. The introduction of the transistor changed all this, and the resulting diode-transistor logic was a popular implementation technology in the 1950s and 1960s. More recently, it has been replaced by the more efficient transistor-transistor logic.

We also covered an important class of transistor structures, the field effect MOS

`(`

metal-oxide-silicon`)`

transistors.
Logic gates constructed from such transistors are much simpler to analyze than
bipolar transistors. MOS switching structures are covered in more detail in
Chapter 4.Other forms of high-speed bipolar logic gates, such as current mode logic

`(`

CML`)`

and emitter-coupled
logic `(`

ECL`)`

, are beyond the scope of our presentation
here. See the reference to Wakerly's book in the next section if you are
interested in learning more about these.Some of the more detailed aspects of TTL logic are described in Sections 2.5.2, 3.5.1, and 3.5.2. Section 2.5.2 discusses the packaging of TTL gates into convenient building blocks called integrated circuits. Sections 3.5.1 and 3.5.2 cover the detailed technical specification of the electrical performance of TTL logic gates, as well as methods for correctly computing the gate fan-outs and power consumption.

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