In what application is gallium arsenide used as a semiconductor material?
AnswerIn microwave circuits
Gallium arsenide is useful at very high frequencies because of its semiconductor properties, so the pool associates it with microwave circuits.
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E6 · Circuit Components
Amateur Extra · correct answers only, in question-pool order.
Which of the following semiconductor materials contains excess free electrons?
AnswerN-type
N-type semiconductor material is doped so electrons are the majority carriers, giving it an excess of free electrons.
Why does a PN-junction diode not conduct current when reverse biased?
AnswerHoles in P-type material and electrons in the N-type material are separated by the applied voltage, widening the depletion region
Reverse bias pulls majority carriers away from the PN junction, widening the depletion region and greatly reducing current flow.
What is the name given to an impurity atom that adds holes to a semiconductor crystal structure?
AnswerAcceptor impurity
An impurity that creates holes in a semiconductor crystal is called an acceptor impurity.
How does DC input impedance at the gate of a field-effect transistor (FET) compare with that of a bipolar transistor?
AnswerAn FET has higher input impedance
The insulated or reverse-biased gate structure of an FET draws very little DC current, so an FET generally has much higher DC input impedance than a bipolar transistor.
What is the beta of a bipolar junction transistor?
AnswerThe change in collector current with respect to the change in base current
Bipolar transistor beta is current gain: the change in collector current divided by the corresponding change in base current.
Which of the following indicates that a silicon NPN junction transistor is biased on?
AnswerBase-to-emitter voltage of approximately 0.6 volts to 0.7 volts
A silicon NPN transistor that is forward biased on typically has about 0.6 to 0.7 volt from base to emitter.
What is the term for the frequency at which the grounded-base current gain of a bipolar junction transistor has decreased to 0.7 of the gain obtainable at 1 kHz?
AnswerAlpha cutoff frequency
The alpha cutoff frequency is where grounded-base current gain has fallen to about 0.7 of its low-frequency value.
What is a depletion-mode field-effect transistor (FET)?
AnswerAn FET that exhibits a current flow between source and drain when no gate voltage is applied
A depletion-mode FET conducts between source and drain even with zero gate voltage applied.
In Figure E6-1, which is the schematic symbol for an N-channel dual-gate MOSFET?
Answer4
In Figure E6-1, symbol 4 is the N-channel dual-gate MOSFET.
In Figure E6-1, which is the schematic symbol for a P-channel junction FET?
Answer1
In Figure E6-1, symbol 1 is the P-channel junction FET.
What is the purpose of connecting Zener diodes between a MOSFET gate and its source or drain?
AnswerTo protect the gate from static damage
MOSFET gates are vulnerable to electrostatic overvoltage. Zener diodes connected between the gate and source or drain clamp excessive voltage and protect the gate.
What is the most useful characteristic of a Zener diode?
AnswerA constant voltage drop under conditions of varying current
A Zener diode is useful because, in its operating region, it maintains a nearly constant voltage over a range of current.
Which characteristic of a Schottky diode makes it a better choice than a silicon junction diode for use as a power supply rectifier?
AnswerLower forward voltage drop
A Schottky diode has a lower forward voltage drop than a conventional silicon PN-junction diode, reducing conduction loss in rectifier service.
What property of an LED's semiconductor material determines its forward voltage drop?
AnswerBand gap
The semiconductor band gap determines the photon energy and therefore the forward-voltage behavior associated with an LED material.
What type of semiconductor device is designed for use as a voltage-controlled capacitor?
AnswerVaractor diode
A varactor diode is operated so its junction capacitance varies with applied reverse voltage, making it a voltage-controlled capacitor.
What characteristic of a PIN diode makes it useful as an RF switch?
AnswerLow junction capacitance
A PIN diode has very low junction capacitance when reverse biased, helping it isolate RF signals effectively in switching applications.
Which of the following is a common use of a Schottky diode?
AnswerAs a VHF/UHF mixer or detector
Schottky diodes switch quickly and have useful high-frequency behavior, making them common as VHF/UHF mixers and detectors.
What causes a junction diode to fail from excessive current?
AnswerExcessive junction temperature
Excessive forward current overheats the diode junction. If the junction temperature becomes too high, the device can fail.
Which of the following is a Schottky barrier diode?
AnswerMetal-semiconductor junction
A Schottky barrier diode uses a metal-semiconductor junction rather than a conventional PN junction.
What is a common use for point-contact diodes?
AnswerAs an RF detector
Point-contact diodes are useful at RF because their small junction and low capacitance make them effective detectors.
In Figure E6-2, which is the schematic symbol for a Schottky diode?
Answer6
In Figure E6-2, symbol 6 is the Schottky diode.
What is used to control the attenuation of RF signals by a PIN diode?
AnswerForward DC bias current
A PIN diode's RF resistance can be controlled with forward DC bias current, allowing it to act as a variable RF attenuator.
What is the function of hysteresis in a comparator?
AnswerTo prevent input noise from causing unstable output signals
Comparator hysteresis creates separate switching thresholds for rising and falling inputs, preventing small amounts of noise from repeatedly toggling the output.
What happens when the level of a comparator’s input signal crosses the threshold voltage?
AnswerThe comparator changes its output state
When the comparator input crosses its threshold voltage, the comparator changes output state.
What is tri-state logic?
AnswerLogic devices with 0, 1, and high-impedance output states
Tri-state logic provides three possible output conditions: logic 0, logic 1, and a high-impedance disconnected state.
Which of the following is an advantage of BiCMOS logic?
AnswerIt has the high input impedance of CMOS and the low output impedance of bipolar transistors
BiCMOS combines CMOS input characteristics with bipolar output capability, giving high input impedance and low output impedance.
Which of the following digital logic families has the lowest power consumption?
AnswerCMOS
Among the listed digital logic families, CMOS has the lowest power consumption.
Why do CMOS digital integrated circuits have high immunity to noise on the input signal or power supply?
AnswerThe input switching threshold is about half the power supply voltage
CMOS logic thresholds are typically near the middle of the supply range, giving substantial noise margin before an unintended input change is interpreted as a new logic state.
What best describes a pull-up or pull-down resistor?
AnswerA resistor connected to the positive or negative supply used to establish a voltage when an input or output is an open circuit
A pull-up or pull-down resistor connects a signal to a supply rail so the line assumes a defined voltage when no active device is driving it.
In Figure E6-3, which is the schematic symbol for a NAND gate?
Answer2
In Figure E6-3, symbol 2 is the NAND gate.
What is used to design the configuration of a field-programmable gate array (FPGA)?
AnswerHardware description language (HDL)
Field-programmable gate arrays are configured using a hardware description language such as VHDL or Verilog.
In Figure E6-3, which is the schematic symbol for a NOR gate?
Answer4
In Figure E6-3, symbol 4 is the NOR gate.
In Figure E6-3, which is the schematic symbol for the NOT operation (inversion)?
Answer5
In Figure E6-3, symbol 5 is the NOT or inverter function.
What is piezoelectricity?
AnswerA characteristic of materials that generate a voltage when stressed and that flex when a voltage is applied
Piezoelectric materials convert between mechanical stress and electrical voltage: stressing the material generates voltage, and applying voltage causes mechanical deformation.
What is the equivalent circuit of a quartz crystal?
AnswerSeries RLC in parallel with a shunt C representing electrode and stray capacitance
A quartz crystal is modeled as a series RLC branch in parallel with a shunt capacitance representing the electrodes and stray capacitance.
Which of the following is an aspect of the piezoelectric effect?
AnswerMechanical deformation of material due to the application of a voltage
One side of the piezoelectric effect is mechanical deformation caused by applying an electric voltage.
Why are cores of inductors and transformers sometimes constructed of thin layers?
AnswerTo reduce power loss from eddy currents in the core
Laminating magnetic cores into thin layers breaks up circulating eddy-current paths and reduces core power loss.
How do ferrite and powdered iron compare for use in an inductor core?
AnswerFerrite cores generally require fewer turns to produce a given inductance value
Ferrite generally has higher permeability than powdered iron, so fewer turns are required to obtain the same inductance.
What core material property determines the inductance of an inductor?
AnswerPermeability
Core permeability determines how strongly the core supports magnetic flux and therefore has a major effect on inductance.
Which of the following materials has the highest temperature stability of its magnetic characteristics?
AnswerPowdered iron
Among the listed materials, powdered iron has the highest temperature stability of its magnetic characteristics.
What devices are commonly used as VHF and UHF parasitic suppressors at the input and output terminals of a transistor HF amplifier?
AnswerFerrite beads
Ferrite beads are commonly placed at transistor-amplifier terminals to add loss and impedance at VHF/UHF parasitic frequencies.
What is a primary advantage of using a toroidal core instead of a solenoidal core in an inductor?
AnswerToroidal cores confine most of the magnetic field within the core material
A toroidal core forms a closed magnetic path, confining most of the magnetic field within the core material.
Which type of core material decreases inductance when inserted into a coil?
AnswerBrass
A brass core acts as a conductive, nonmagnetic slug that can reduce the inductance of a coil.
What causes inductor saturation?
AnswerOperation at excessive magnetic flux
An inductor core saturates when magnetic flux becomes excessive and the core can no longer respond proportionally to additional magnetizing force.
Why is gallium arsenide (GaAs) useful for semiconductor devices operating at UHF and higher frequencies?
AnswerHigher electron mobility
Gallium arsenide offers high electron mobility, which supports high-speed device operation at UHF and microwave frequencies.
Which of the following device packages is a through-hole type?
AnswerDIP
A DIP, or dual in-line package, is a traditional through-hole IC package with pins inserted through circuit-board holes.
Which of the following materials supports the highest frequency of operation when used in MMICs?
AnswerGallium nitride
Among the listed materials, gallium nitride supports the highest frequency of MMIC operation.
Which is the most common input and output impedance of MMICs?
Answer50 ohms
Most RF MMICs are designed for standard 50-ohm input and output systems.
Which of the following noise figure values is typical of a low-noise UHF preamplifier?
Answer0.5 dB
A noise figure around 0.5 dB is typical of a good low-noise UHF preamplifier.
What characteristics of MMICs make them a popular choice for VHF through microwave circuits?
AnswerControlled gain, low noise figure, and constant input and output impedance over the specified frequency range
MMICs are popular because they provide controlled gain, low noise figure, and relatively constant input and output impedance across their specified frequency range.
What type of transmission line is often used for connections to MMICs?
AnswerMicrostrip
Microstrip is commonly used to connect MMICs because short controlled-impedance traces can be formed directly on the circuit board.
How is power supplied to the most common type of MMIC?
AnswerThrough a resistor and/or RF choke connected to the amplifier output lead
Many common MMICs receive DC bias through a resistor and/or RF choke connected to the amplifier output lead while RF is coupled separately.
Which of the following component package types have the least parasitic effects at frequencies above the HF range?
AnswerSurface mount
Surface-mount packages have very short leads and compact geometry, so they introduce the least parasitic inductance and capacitance of the listed package types above HF.
What circuit-board area advantage does surface-mount technology offer at RF?
AnswerSmaller circuit area.
The official E6E10 source lists smaller circuit area as one RF advantage of surface-mount technology compared with through-hole construction.
What circuit-trace advantage does surface-mount technology offer at RF?
AnswerShorter circuit board traces.
The official E6E10 source lists shorter circuit-board traces as an RF advantage of surface-mount technology.
What parasitic-component advantage does surface-mount technology offer at RF?
AnswerComponents have less parasitic inductance and capacitance.
The official E6E10 source identifies reduced parasitic inductance and capacitance as an RF advantage of surface-mount components.
What is a characteristic of DIP packaging used for integrated circuits?
AnswerTwo rows of connecting pins on opposite sides of package (dual in-line package)
DIP means dual in-line package: two parallel rows of connecting pins on opposite sides of the package.
Why are DIP through-hole package ICs not typically used at UHF and higher frequencies?
AnswerExcessive lead length
Through-hole DIP leads are relatively long, and at UHF those leads introduce too much unwanted inductance and capacitance.
What absorbs the energy from light falling on a photovoltaic cell?
AnswerElectrons
According to the Extra pool, electrons absorb the energy from light falling on a photovoltaic cell, enabling the cell to produce electrical output.
What happens to photoconductive material when light shines on it?
AnswerResistance decreases
Illumination creates additional charge carriers in photoconductive material, so its resistance decreases.
What is the most common configuration of an optoisolator or optocoupler?
AnswerAn LED and a phototransistor
The most common optoisolator pairs an LED with a phototransistor, transferring a signal optically while maintaining electrical isolation.
What is the photovoltaic effect?
AnswerThe conversion of light to electrical energy
The photovoltaic effect is the conversion of light energy into electrical energy.
Which of the following describes an optical shaft encoder?
AnswerA device that detects rotation by interrupting a light source with a patterned wheel
An optical shaft encoder uses a patterned wheel to interrupt or pass light as the shaft turns, converting rotation into pulses or position information.
Which of these materials is most commonly used to create photoconductive devices?
AnswerCrystalline semiconductor
Crystalline semiconductor material is commonly used for photoconductive devices because its conductivity changes when light creates charge carriers.
What is a solid-state relay?
AnswerA device that uses semiconductors to implement the functions of an electromechanical relay
A solid-state relay uses semiconductor devices to perform the switching function of an electromechanical relay without moving contacts.
Why are optoisolators often used in conjunction with solid-state circuits that control 120 VAC circuits?
AnswerOptoisolators provide an electrical isolation between a control circuit and the circuit being switched
Optoisolators let a low-voltage control circuit operate a 120 VAC circuit while maintaining electrical isolation between the two sides.
What is the efficiency of a photovoltaic cell?
AnswerThe relative fraction of light that is converted to current
The pool defines photovoltaic efficiency as the relative fraction of incident light converted to current.
What is the most common material used in power-generating photovoltaic cells?
AnswerSilicon
Silicon is the most common semiconductor material used in power-generating photovoltaic cells.
What is the approximate open-circuit voltage produced by a fully illuminated silicon photovoltaic cell?
Answer0.5 volts
A fully illuminated silicon photovoltaic cell produces approximately 0.5 volt open circuit.