Integrated circuits are sets of electronic components that are interconnected. Active components supply energy and include vacuum tubes and transistors. Passive components absorb energy and include resistors, capacitors, and inductors.
Vacuum tubes or electron tubes are glass or ceramic enclosures that contain metal electrodes for producing, controlling, or collecting beams of electrons. A diode has two elements, a cathode and an anode. The application of energy to the cathode frees electrons which migrate to the anode. Electrons only flow during one half-cycle of an alternating (AC) current. A grid inserted between the cathode and anode can be used to control the flow and amplify it. A small voltage can cause large flows of electrons that can be passed through circuitry at the anode end.
Special purpose tubes use photoelectric emission and secondary emission, as in the television camera tube that emits and then collects and amplifies return beams to provide its output signal. Small amounts of argon, hydrogen, mercury, or neon vapors in the tubes change its current capacity, regulate voltage, or control large currents. The finely focused beam from a cathode-ray tube illuminates the coating on the inside of the television picture tube to reproduce images.
Transistors are made of silicon or germanium containing foreign elements that produce many electrons or few. N-type semiconductors produce a lot of electrons, and p-type semiconductors do not. Combining the materials creates a diode, and when energy is applied, the flow can be directed or stopped depending on direction. A triple layer with either n-p-n or p-n-p creates a triode, which, again can be used to amplify signals. The field-effect transistor or FET superimposes an electric field and uses that field to attract or repel charges. The field can amplify the current much like the grid does in the vacuum tube. FETs are very efficient because only a small field controls a large signal. A controlling terminal or gate is called a JFET or junction FET. Addition of metal semiconductors, metal oxides, or insulated gates produce other varieties of transistor that enhance different signal-transmitting aspects.
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