The initials CMOS stand for Complementary Metal-Oxide Semiconductor. Two elements widely used in semiconductor devices that exhibit both metallic and nonmetallic characteristics are Silicon and germanium. N-type semiconductor material contains more free electrons than pure germanium or silicon crystals. The majority charge carriers in N-type semiconductor material are free electrons. The majority charge carriers in P-type semiconductor material are holes. P-type of semiconductor material contains fewer free electrons than pure germanium or silicon crystals. The name given to an impurity atom that adds holes to a semiconductor crystal structure is acceptor impurity. In Figure E6-1, the schematic symbol for a PNP transistor is Symbol 1. Many MOSFET devices have built-in gate-protective Zener diodes to reduce the chance of the gate insulation being punctured by static discharges or excessive voltages. In Figure E6-2, the schematic symbol for an N-channel dual-gate MOSFET is Symbol 4. The alpha of a bipolar junction transistor is the change of collector current with respect to emitter current. The beta of a bipolar junction transistor is the change in collector current with respect to base current. The names of the three terminals of a field-effect transistor (FET) are fate, drain, source. A FET (Field Effect Transistor) has high input impedance as compared to a bipolar transistor which has low input impedance. FET depletion-mode is when an FET that exhibits a current flow between source and drain when no gate voltage is applied. In Figure E6-2, the schematic symbol for a P-channel junction FET is Symbol 1. The frequency at which a transistor grounded base current gain has decreased to 0.7 of the gain obtainable at 1 kHz is the Alpha cutoff frequency. Gallium arsenide is used as a semiconductor material in preference to germanium or silicon at microwave frequencies. The principal characteristic of a Zener diode is a constant voltage under conditions of varying current. The principal characteristic of a tunnel diode is a negative resistance region. A tunnel diode is capable of both amplification and oscillation. An important characteristic of a Schottky Barrier diode as compared to an ordinary silicon diode when used as a power supply rectifier is that it has less forward voltage drop. A Varactor diode device varies its internal capacitance as the voltage applied to its terminals varies. In Figure E6-3, the schematic symbol for a varactor diode is 1. A common use of a hot-carrier diode is as a VHF / UHF mixer or detector. A metal-semiconductor junction is a type of semiconductor diode. Junction diodes are rated for maximum forward current and PIV. The junction temperature limits the maximum forward current rating in a junction diode. A common use for point contact diodes is as an RF detector. One common use for PIN diodes is as an RF switch. Forward bias is required for an LED to produce luminescence. In Figure E6-3, the schematic symbol for a light-emitting diode is Symbol 5. The recommended power supply voltage for TTL series integrated circuits 5 volts. If the inputs of a TTL device are left open they have a logic-high state. The level of input voltage that is a logic "high" in a TTL device operating with a positive 5-volt power supply is 2.0 to 5.5 volts. The level of input voltage that is a logic "low" in a TTL device operating with a positive 5-volt power-supply is 0.0 to 0.8 volts.
An advantage of CMOS logic devices over TTL devices is lower power consumption.
CMOS digital integrated circuits have high immunity to noise on the input
signal or power supply because
the input switching threshold is about one-half the power supply voltage.
The correct basic Boolean logic schematic symbols shown in Figure E6-5 are summarized in the following table,
The electron beam in a vidicon is deflected by varying electromagnetic fields. Persistance in a cathode ray tube (CRT) is the length of time the image remains on the screen after the beam is turned off. An electrostatic CRT deflection is better when high-frequency waves are to be displayed on the screen. If a cathode ray tube (CRT) is designed to operate with an anode voltage of 25,000 volts, if the anode voltage is increased to 35,000 volts the image size will decrease. Exceeding the anode voltage design rating can cause a cathode ray tube (CRT) to generate X-rays. A charge-coupled device (CCD) samples an analog signal and passes it in stages from the input to the output. It is commonly used as an analog-to-digital converter. A charge-coupled device (CCD) in a modern video camera stores photogenerated charges as signals corresponding to pixels. A liquid-crystal display (LCD) is a type of display that uses a crystalline liquid to change the way light is refracted. The principle advantage of liquid-crystal display (LCD) devices over other types of display devices is that they consume less power. The material property that determines the inductance of a toroidal inductor with a 10-turn winding is core permeability. The usable frequency range of inductors that use toroidal cores, assuming a correct selection of core material for the frequency being used, is from less than 20 Hz to approximately 300 MHz. One important reason for using powdered-iron toroids rather than ferrite toroids in an inductor is that powdered-iron toroids generally have better temperature stability. Another reason is that ferrite toroids generally require fewer turns to produce a given inductance value. A primary advantage of using a toroidal core instead of a solenoidal core in an inductor is that toroidal cores contain most of the magnetic field within the core material. 43 turns. would be required to produce a 1-mH inductor using a ferrite toroidal core that has an inductance index (A L) value of 523 millihenrys/1000 turns. 35 turns. would be required to produce a 5-microhenry inductor using a powdered iron toroidal core that has an inductance index (A L) value of 40 microhenrys/100 turns. Ferrite beads are commonly used as VHF and UHF parasitic suppressors at the input and output terminals of transistorized HF amplifiers. A filter with 2.4 kHz at -6 dB bandwidth would be a good choice for use in a SSB radiotelephone transmitter. A filter with 6 kHz at -6 dB bandwidths would be a good choice for use with standard doublesideband AM transmissions. One aspect of the piezoelectric effect is the physical deformation of a crystal by the application of a voltage. A crystal lattice filter is a filter with narrow bandwidth and steep skirts made using quartz crystals. The technique used to construct low-cost, high-performance crystal ladder filters is to measure crystal frequencies and carefully select units with a frequency variation of less than 10% of the desired filter bandwidth. The relative frequencies of the individual crystals are factors that have the greatest effect in helping determine the bandwidth and response shape of a crystal ladder filter. A monolithic microwave integrated circuit (MMIC) is an amplifier device that consists of a small pill-type package with an input lead, an output lead and 2 ground leads. The characteristic impedance of circuits in which almost all MMICs are designed to work is 50 ohms. The typical noise figure of a monolithic microwave integrated circuit (MMIC) amplifier is approximately 3.5 to 6 dB. The microstrip construction technique is used when building an amplifier for the microwave bands containing a monolithic microwave integrated circuit (MMIC). Plastic packages are the most common type used for inexpensive monolithic microwave integrated circuit (MMIC) amplifiers. The operating bias voltage normally supplied to the most common type of monolithic microwave integrated circuit (MMIC) is through a resistor and/or RF choke connected to the amplifier output lead. The supply voltage the monolithic microwave integrated circuits (MMIC) amplifiers typically require is 12 volts DC.
Photoconductivity is the increased conductivity of an illuminated semiconductor.
The conductivity of a photoconductive material increases
when light shines on it.
Photoconductivity will cause the resistance
of a crystalline solid to change.
Electrons absorb the energy from light falling on a photovoltaic cell.
The material most affected by photoconductivity is a crystalline semiconductor. Cadmium sulfide will exhibit the greatest photoconductive effect when illuminated by visible light. Lead sulfide will exhibit the greatest photoconductive effect when illuminated by infrared light. Gallium arsenide photovoltaic cell have the highest efficiency. The most common configuration for an optocoupler is an LED and a phototransistor. An optoisolator is an LED and a phototransistor. Optoisolators provide a very high degree of electrical isolation between a control circuit and a power circuit making them suitable for use with a triac to form the solid-state equivalent of a mechanical relay for a 120 V AC household circuit. Optoisolators are often used in power supplies because they have very high impedance between the light source and the phototransistor. An optical shaft encoder is an array of optocouplers whose light transmission path is controlled by a rotating wheel. Silicon is the most common type of photovoltaic cell used for electrical power generation. The approximate open-circuit voltage produced by a fully-illuminated silicon photovoltaic cell is 0.5 V. |