Digital logic and electronic circuits derive their functionality from electronic switches called
transistors . Roughly speaking, the transistor can be likened to an electronically controlled valve whereby energy applied to one connection of the valve enables energy to flow between two other connections. By combining multiple transistors, digital logic building blocks such as AND gates and flip-flops are formed. Transistors, in turn, are made from semiconductors . Consult a periodic table of elements in a college chemistry textbook, and you will locate semiconductors as a group of elements separating the metals and nonmetals. They are called semiconductors because of their ability to behave as both metals and nonmetals. A semiconductor can be made to conduct electricity like a metal or to insulate as a nonmetal does. These differing electrical properties can be accurately controlled by mixing the semiconductor with small amounts of other elements. This mixing is called doping . A semiconductor can be doped to contain more electrons (N-type) or fewer electrons (P-type).
Examples of commonly used semiconductors are silicon and germanium. Phosphorous and boron are two elements that are used to dope N-type and P-type silicon, respectively.
A transistor is constructed by creating a sandwich of differently doped semiconductor layers. The two most common types of transistors, the bipolar-junction transistor (BJT) and the
field-effect transistor (FET) are schematically illustrated in Fig. 2.1. This figure shows both the silicon structures of these elements and their graphical symbolic representation as would be seen in a circuit diagram. The BJT shown is an NPN transistor, because it is composed of a sandwich of N-P-N doped silicon. When a small current is injected into the base terminal, a larger current is enabled to flow from the collector to the emitter . The FET shown is an N-channel FET; it is composed of two N-type regions separated by a P-type substrate. When a voltage is applied to the insulated gate terminal, a current is enabled to flow from the drain to the source .
It is called N-channel, because the gate voltage induces an N-channel within the substrate, enabling current to flow between the N-regions. diode, which is formed simply by a
junction of N-type and P-type silicon. Diodes act like one-way valves by conducting current only
from P to N. Special diodes can be created that emit light when a voltage is applied.
ppropriately enough, these components are called light emitting diodes , or LEDs. These small lights are manufactured by the millions and are found in diverse applications from telephones to traffic lights.
transistors . Roughly speaking, the transistor can be likened to an electronically controlled valve whereby energy applied to one connection of the valve enables energy to flow between two other connections. By combining multiple transistors, digital logic building blocks such as AND gates and flip-flops are formed. Transistors, in turn, are made from semiconductors . Consult a periodic table of elements in a college chemistry textbook, and you will locate semiconductors as a group of elements separating the metals and nonmetals. They are called semiconductors because of their ability to behave as both metals and nonmetals. A semiconductor can be made to conduct electricity like a metal or to insulate as a nonmetal does. These differing electrical properties can be accurately controlled by mixing the semiconductor with small amounts of other elements. This mixing is called doping . A semiconductor can be doped to contain more electrons (N-type) or fewer electrons (P-type).
Examples of commonly used semiconductors are silicon and germanium. Phosphorous and boron are two elements that are used to dope N-type and P-type silicon, respectively.
A transistor is constructed by creating a sandwich of differently doped semiconductor layers. The two most common types of transistors, the bipolar-junction transistor (BJT) and the
field-effect transistor (FET) are schematically illustrated in Fig. 2.1. This figure shows both the silicon structures of these elements and their graphical symbolic representation as would be seen in a circuit diagram. The BJT shown is an NPN transistor, because it is composed of a sandwich of N-P-N doped silicon. When a small current is injected into the base terminal, a larger current is enabled to flow from the collector to the emitter . The FET shown is an N-channel FET; it is composed of two N-type regions separated by a P-type substrate. When a voltage is applied to the insulated gate terminal, a current is enabled to flow from the drain to the source .
It is called N-channel, because the gate voltage induces an N-channel within the substrate, enabling current to flow between the N-regions. diode, which is formed simply by a
junction of N-type and P-type silicon. Diodes act like one-way valves by conducting current only
from P to N. Special diodes can be created that emit light when a voltage is applied.
