1Which of the following is a primary advantage of a Field Effect Transistor (FET) over a Bipolar Junction Transistor (BJT)?
A.FET is a current-controlled device
B.FET has a much lower input impedance
C.FET has a significantly higher input impedance
D.FET relies on both electrons and holes for conduction
Correct Answer: FET has a significantly higher input impedance
Explanation:FETs have a very high input impedance (often in the range of megaohms or higher) compared to BJTs. This prevents the FET from drawing significant current from the preceding stage, minimizing loading effects.
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2How do the charge carriers differ between a FET and a BJT?
A.FET is a bipolar device, BJT is unipolar
B.Both FET and BJT are unipolar devices
C.FET is a unipolar device, BJT is bipolar
D.Both FET and BJT are bipolar devices
Correct Answer: FET is a unipolar device, BJT is bipolar
Explanation:A FET operates using only one type of charge carrier (either electrons or holes), making it unipolar. A BJT uses both electrons and holes for its operation, making it a bipolar device.
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3Which fundamental mechanism controls the output of a Field Effect Transistor?
A.Input current
B.Input voltage
C.Base current
D.Collector voltage
Correct Answer: Input voltage
Explanation:A FET is a voltage-controlled device. The electric field generated by the input voltage at the gate controls the current flowing through the channel.
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4Regarding thermal stability, how does a FET compare to a BJT?
A.FET has a positive temperature coefficient and is less stable
B.FET has a negative temperature coefficient and is more stable
C.BJT is more thermally stable than FET
D.Both have identical thermal stability characteristics
Correct Answer: FET has a negative temperature coefficient and is more stable
Explanation:FETs possess a negative temperature coefficient at high current levels. As temperature increases, mobility decreases and current drops, preventing thermal runaway, which makes FETs more thermally stable than BJTs.
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5Why is a FET generally preferred over a BJT in low-level signal amplifiers, such as in robotic sensor interfaces?
A.FETs produce less electrical noise
B.FETs have higher power consumption
C.FETs require higher driving currents
D.FETs have a lower input resistance
Correct Answer: FETs produce less electrical noise
Explanation:Since FETs operate with only one type of charge carrier and lack the multiple junctions crossing of BJTs, they generate significantly less thermal and shot noise, making them ideal for amplifying weak signals.
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6In the context of Integrated Circuits (ICs), what is a major structural advantage of FETs (particularly MOSFETs) over BJTs?
A.FETs require large coupling capacitors
B.FETs occupy much less area on a silicon chip
C.FETs require multiple complex isolation islands
D.FETs cannot be manufactured on standard silicon
Correct Answer: FETs occupy much less area on a silicon chip
Explanation:FETs, especially MOSFETs, are structurally simpler and smaller than BJTs. They occupy significantly less area on a semiconductor die, allowing for extremely high packing density in digital ICs and microcontrollers.
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7When used as an analog switch or a chopper, what advantage does a FET have over a BJT?
A.It requires a high holding current
B.It has zero offset voltage
C.It has a large saturation voltage drop
D.It acts as an inductor
Correct Answer: It has zero offset voltage
Explanation:Unlike BJTs, which have an inherent offset voltage () even when fully conducting, FETs act essentially as a pure resistor in the ohmic region, resulting in zero offset voltage.
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8What are the three terminals of a Junction Field Effect Transistor (JFET)?
A.Emitter, Base, Collector
B.Anode, Cathode, Gate
C.Source, Drain, Gate
D.Input, Output, Ground
Correct Answer: Source, Drain, Gate
Explanation:The basic JFET has three terminals: Source (where carriers enter), Drain (where carriers leave), and Gate (which controls the channel width).
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9In a standard N-channel JFET, the gate is made of which type of semiconductor material?
A.Intrinsic semiconductor
B.N-type material
C.P-type material
D.Insulating oxide
Correct Answer: P-type material
Explanation:An N-channel JFET consists of an N-type semiconductor bar that acts as the channel, with P-type regions diffused on opposite sides to form the gate.
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10For proper operation of an N-channel JFET in the active region, how must the Gate-Source junction be biased?
A.Forward biased
B.Reverse biased
C.Unbiased (0V)
D.Alternating bias
Correct Answer: Reverse biased
Explanation:The Gate-Source junction of a JFET must always be reverse-biased to create a depletion region that controls the channel width without drawing significant gate current.
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11What is the physical mechanism by which a JFET controls the current flowing from drain to source?
A.By injecting minority carriers into the base
B.By varying the width of the depletion region in the channel
C.By changing the physical length of the semiconductor crystal
D.By storing charge in a dielectric layer
Correct Answer: By varying the width of the depletion region in the channel
Explanation:Applying a reverse bias to the gate increases the width of the depletion region, which encroaches into the channel and restricts the cross-sectional area available for charge carriers, thereby controlling the current.
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12What is meant by the 'Pinch-off voltage' () in a JFET?
A.The forward voltage required to turn on the gate junction
B.The drain-to-source voltage at which drain current becomes constant
C.The breakdown voltage of the drain-source channel
D.The gate-source voltage at which maximum current flows
Correct Answer: The drain-to-source voltage at which drain current becomes constant
Explanation:Pinch-off voltage () is the specific value of at which the depletion regions from the gate almost touch, causing the drain current () to level off and become nearly constant (saturation).
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13According to Shockley's equation, how is the drain current () of a JFET related to the gate-source voltage ()?
A.
B.
C.
D.
Correct Answer:
Explanation:Shockley's equation defines the transfer characteristic of a JFET as a parabolic relationship: .
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14Under what condition does a JFET exhibit its maximum drain current, known as ?
A.
B. and
C.
D. is highly negative
Correct Answer: and
Explanation: is the Drain-to-Source Saturation Current, which is measured when the gate is shorted to the source () and is equal to or greater than the pinch-off voltage.
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15What is the typical value of the gate current () in a properly biased JFET?
A.Equal to the drain current
B.A few milliamperes
C.Practically zero (in picoamperes or nanoamperes)
D.Exactly half of the source current
Correct Answer: Practically zero (in picoamperes or nanoamperes)
Explanation:Because the gate-source junction is reverse-biased, only a negligible leakage current flows through the gate, making .
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16In which operating region does a JFET behave like a voltage-variable resistor (VVR)?
A.Saturation region
B.Breakdown region
C.Cut-off region
D.Ohmic (Linear) region
Correct Answer: Ohmic (Linear) region
Explanation:In the Ohmic region (where is small, before pinch-off), the JFET channel acts as a resistor whose resistance is controlled by the applied gate-source voltage .
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17What is the relationship between the Pinch-off voltage () and the Gate-to-Source Cutoff voltage () for a JFET?
A.
B. and are independent
C.
D.
Correct Answer:
Explanation:The magnitudes of and are essentially the same, but they refer to different voltages. is a positive value, while is the negative value required to completely cut off the drain current.
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18Why is an N-channel JFET generally preferred over a P-channel JFET in high-frequency applications?
A.N-channel JFETs are cheaper to produce
B.Electrons have higher mobility than holes
C.Holes have higher mobility than electrons
D.N-channel JFETs have a positive pinch-off voltage
Correct Answer: Electrons have higher mobility than holes
Explanation:In an N-channel JFET, the charge carriers are electrons. Since electrons have a significantly higher mobility than holes (the carriers in P-channel devices), N-channel JFETs offer faster switching and better high-frequency response.
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19Due to the symmetrical physical structure of a typical JFET, which two terminals can often be interchanged without drastically altering the device's behavior?
A.Gate and Source
B.Gate and Drain
C.Source and Drain
D.None of the terminals
Correct Answer: Source and Drain
Explanation:Many JFETs have a symmetrical construction where the gate is centered between the source and drain, meaning the source and drain terminals are functionally interchangeable.
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20What does the acronym MOSFET stand for?
A.Metallic Oxide Semiconductor Field Effect Transistor
B.Metal Oxide Semiconductor Field Effect Transistor
C.Magnetic Output Silicon Field Effect Transistor
D.Metal Oxide Silicon Frequency Emitter Transistor
Correct Answer: Metal Oxide Semiconductor Field Effect Transistor
Explanation:MOSFET stands for Metal Oxide Semiconductor Field Effect Transistor, highlighting its construction with a metal gate, oxide insulator, and semiconductor body.
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21What acts as the insulating layer between the gate and the channel in a MOSFET?
A.Air gap
B.Silicon dioxide ()
C.Undoped intrinsic silicon
D.Polytetrafluoroethylene (PTFE)
Correct Answer: Silicon dioxide ()
Explanation:A very thin layer of Silicon dioxide () acts as a dielectric insulator, physically separating the gate from the semiconductor channel.
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22Because of its insulated gate construction, a MOSFET is also commonly referred to as what?
A.IGFET
B.BJT
C.UJT
D.SCR
Correct Answer: IGFET
Explanation:MOSFETs are frequently called Insulated-Gate Field-Effect Transistors (IGFETs) because the gate is electrically isolated from the main current-carrying channel.
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23How does the input impedance of a MOSFET generally compare to that of a JFET?
A.MOSFET has a lower input impedance than JFET
B.MOSFET and JFET have identical input impedances
C.MOSFET has a higher input impedance than JFET
D.MOSFET has zero input impedance
Correct Answer: MOSFET has a higher input impedance than JFET
Explanation:Because of the insulating layer, the gate of a MOSFET is completely isolated from the channel. This gives MOSFETs an exceptionally high input impedance ( to ), typically higher than that of a reverse-biased JFET.
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24Which type of MOSFET operates completely with NO physical channel existing when the gate-source voltage is zero?
Explanation:An Enhancement-type MOSFET (E-MOSFET) is 'normally off'. It lacks a physical channel at zero gate bias; a channel must be electrically induced by applying a sufficient gate voltage.
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25In an Enhancement MOSFET, what is the 'Threshold Voltage' ()?
A.The maximum voltage the gate oxide can withstand before breaking down
B.The minimum gate-source voltage required to create a conducting channel
C.The voltage at which the drain current reaches zero
D.The voltage applied to the substrate terminal
Correct Answer: The minimum gate-source voltage required to create a conducting channel
Explanation:The Threshold Voltage () is the critical gate-source voltage at which an inversion layer is formed, thereby establishing a conductive channel between the source and drain.
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26In an N-channel E-MOSFET, applying a positive voltage (greater than ) to the gate forms a channel by which process?
A.Depleting holes and accumulating electrons to form an inversion layer
B.Injecting minority carriers from the drain
C.Causing an avalanche breakdown in the substrate
D.Creating a heavily doped P-type region
Correct Answer: Depleting holes and accumulating electrons to form an inversion layer
Explanation:A positive gate voltage repels the majority carriers (holes) in the P-type substrate and attracts minority carriers (electrons) to the surface directly beneath the oxide, forming an N-type 'inversion layer' which acts as the channel.
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27Which type of MOSFET can operate in BOTH depletion and enhancement modes?
A.E-MOSFET
B.D-MOSFET
C.Only N-channel MOSFETs
D.Only P-channel MOSFETs
Correct Answer: D-MOSFET
Explanation:A Depletion-type MOSFET (D-MOSFET) has a physically implanted channel. It can be operated in depletion mode (reducing channel carriers) or enhancement mode (increasing channel carriers) depending on the polarity of .
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28What is the fourth terminal often found in the structural diagram of a MOSFET, which is usually internally connected to the source?
A.Emitter
B.Collector
C.Base
D.Body (or Substrate)
Correct Answer: Body (or Substrate)
Explanation:A MOSFET inherently has four terminals: Gate, Source, Drain, and Body (Substrate). In most discrete MOSFETs, the Body is internally tied to the Source to maintain a fixed reference potential.
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29The extremely thin layer in a MOSFET makes it highly susceptible to damage from which of the following?
A.Low frequency magnetic fields
B.Electrostatic Discharge (ESD)
C.Visible light exposure
D.Acoustic noise
Correct Answer: Electrostatic Discharge (ESD)
Explanation:The thin oxide layer has a low breakdown voltage. Static electricity from human handling can easily exceed this voltage and permanently puncture the oxide layer, ruining the device.
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30Which of the following describes the fundamental structure of CMOS (Complementary MOS) technology?
A.It uses two N-channel E-MOSFETs in series
B.It pairs an N-channel and a P-channel MOSFET on the same substrate
C.It combines a BJT with a MOSFET
D.It uses only Depletion-type MOSFETs
Correct Answer: It pairs an N-channel and a P-channel MOSFET on the same substrate
Explanation:CMOS technology integrates complementary symmetrical pairs of P-type and N-type enhancement MOSFETs, which leads to extremely low static power consumption.
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31Which structural modification is commonly used in 'Power MOSFETs' to allow them to handle high currents and voltages in robotic motor drives?
Explanation:Power MOSFETs usually employ a vertical structure (where current flows vertically through the silicon die) rather than a lateral structure, which maximizes the cross-sectional area for current flow and improves heat dissipation.
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32In the schematic symbol for an Enhancement-type MOSFET, how is the channel represented to indicate that it is 'normally off'?
A.A solid, continuous straight line
B.A broken or dashed line between source and drain
C.A solid circle encompassing the transistor
D.An arrow pointing away from the gate
Correct Answer: A broken or dashed line between source and drain
Explanation:The broken line in the E-MOSFET symbol represents that the channel is not physically continuous or present at zero gate bias. (A D-MOSFET uses a solid line).
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33Which equation accurately represents the transfer characteristic of an Enhancement MOSFET in the saturation region?
A.
B.
C.
D.
Correct Answer:
Explanation:For an E-MOSFET in saturation, the drain current is given by , where is a device constant and is the threshold voltage.
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34What happens to a D-MOSFET when ?
A.The device is completely cut off
B.The device breaks down
C.A significant drain current, , flows through the physical channel
D.The input impedance drops to zero
Correct Answer: A significant drain current, , flows through the physical channel
Explanation:Since a D-MOSFET has a built-in channel, an appreciable drain current () will flow even when is zero, provided there is a voltage across the drain and source.
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35In an N-channel D-MOSFET, operating in the 'depletion mode' requires what polarity of gate-source voltage ()?
A.Positive
B.Negative
C.Zero
D.Alternating
Correct Answer: Negative
Explanation:To operate an N-channel D-MOSFET in depletion mode (reducing channel conductivity), a negative must be applied to repel electrons from the channel.
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36What is represented by the 'Output Characteristics' (or Drain Characteristics) of a FET?
A.A plot of versus for a constant
B.A plot of versus for various constant values of
C.A plot of versus for a constant
D.A plot of Input impedance versus Frequency
Correct Answer: A plot of versus for various constant values of
Explanation:Output characteristics describe the output behavior of the device: plotting output current () against output voltage () for stepped values of the input control voltage ().
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37What does the 'Transfer Characteristic' curve of a JFET illustrate?
A.The relationship between Drain current () and Gate-Source voltage () at constant
B.The relationship between Drain current () and Drain-Source voltage () at constant
C.The response of the transistor to varying temperatures
D.The variation of output resistance with drain voltage
Correct Answer: The relationship between Drain current () and Gate-Source voltage () at constant
Explanation:The transfer characteristic shows how the input voltage () 'transfers' to control the output current ().
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38What is the general shape of the transfer characteristic curve of a JFET?
A.Linear
B.Exponential
C.Parabolic
D.Sinusoidal
Correct Answer: Parabolic
Explanation:Because the transfer equation is based on Shockley's equation (), the curve forms a part of a parabola.
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39Which parameter is defined as the slope of the Transfer Characteristic curve ()?
A.Drain resistance ()
B.Amplification factor ()
C.Transconductance ()
D.Input impedance ()
Correct Answer: Transconductance ()
Explanation:Transconductance (), also called forward transadmittance, is the ratio of change in drain current to the change in gate-source voltage, representing the gain of the FET.
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40How is the dynamic drain resistance () of a FET calculated from its output characteristics?
A. at constant
B. at constant
C. at constant
D. at constant
Correct Answer: at constant
Explanation:Drain resistance is the reciprocal of the slope of the output characteristic curve in the saturation region, evaluated as the change in output voltage divided by the change in output current.
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41Which relationship correctly links Amplification factor (), Transconductance (), and Drain resistance () in a FET?
A.
B.
C.
D.
Correct Answer:
Explanation:The amplification factor indicates the maximum voltage gain possible and is calculated as the product of transconductance and dynamic drain resistance.
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42What mathematical equation describes the relationship between the transconductance at a specific and the maximum transconductance for a JFET?
A.
B.
C.
D.
Correct Answer:
Explanation:By taking the derivative of Shockley's equation with respect to , we obtain a linear relationship for transconductance: .
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43On the output characteristics of a JFET, what happens when the Drain-Source voltage () increases excessively into the 'Breakdown Region'?
A.The drain current drops to zero
B.The gate oxide layer ruptures
C.An avalanche breakdown occurs, causing drain current to increase sharply
D.The device becomes perfectly resistive
Correct Answer: An avalanche breakdown occurs, causing drain current to increase sharply
Explanation:If exceeds the breakdown voltage rating of the FET, avalanche breakdown occurs at the reverse-biased gate-channel junction, leading to a rapid and potentially destructive increase in drain current.
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44What defines the 'Pinch-off Locus' on a JFET's output characteristics graph?
A.The vertical line where
B.The boundary curve separating the Ohmic region from the Saturation region
C.The horizontal line representing maximum
D.The region of thermal runaway
Correct Answer: The boundary curve separating the Ohmic region from the Saturation region
Explanation:The pinch-off locus is a parabolic curve on the output characteristics connecting all points where (magnitude-wise), marking the transition from the resistive ohmic region to the constant-current saturation region.
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45In the transfer characteristics of an Enhancement MOSFET, where does the curve intersect the axis?
A.At
B.At (Pinch-off voltage)
C.At (Threshold voltage)
D.It never intersects the axis
Correct Answer: At (Threshold voltage)
Explanation:For an E-MOSFET, the drain current is zero until the gate voltage reaches the threshold voltage . Therefore, the transfer curve starts (intersects the axis) at .
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46How does 'Channel Length Modulation' affect the output characteristics of a MOSFET in the saturation region?
A.It causes the current to drop to zero
B.It makes the output curves perfectly horizontal
C.It introduces a slight positive slope to the output curves instead of them being perfectly flat
D.It causes an immediate avalanche breakdown
Correct Answer: It introduces a slight positive slope to the output curves instead of them being perfectly flat
Explanation:Similar to the Early effect in BJTs, as increases in saturation, the effective channel length decreases, causing the drain current to increase slightly. This gives the output characteristics a finite, non-zero slope.
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47If you plot the transfer characteristic of a D-MOSFET, the curve extends through which quadrants relative to ?
A.Only positive values of
B.Only negative values of
C.Both positive and negative values of
D.Only
Correct Answer: Both positive and negative values of
Explanation:Because a D-MOSFET can operate in both depletion mode (e.g., negative for N-channel) and enhancement mode (positive for N-channel), its transfer curve spans across the y-axis, covering both polarities of .
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48What parameter is calculated using the formula ?
A.Maximum amplification factor
B.Minimum channel resistance
C.Maximum transconductance at
D.Threshold voltage
Correct Answer: Maximum transconductance at
Explanation:The maximum transconductance of a JFET occurs when . By evaluating the derivative of Shockley's equation at , we find .
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49In the linear (ohmic) region of a MOSFET, how does primarily behave with respect to ?
A. is completely independent of
B. increases exponentially with
C. has a nearly linear, proportional relationship with
D. decreases as increases
Correct Answer: has a nearly linear, proportional relationship with
Explanation:At very low values of (well below pinch-off or saturation), the MOSFET channel acts like a simple resistor, yielding a linear relationship between and .
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50Why are FETs widely used in robotic sensory systems requiring high fidelity?
A.They inherently produce digital outputs
B.Their high input impedance ensures the sensor circuit is not loaded heavily
C.They act as step-up transformers for DC voltages
D.They can operate without a power supply
Correct Answer: Their high input impedance ensures the sensor circuit is not loaded heavily
Explanation:Robotic sensors (like piezoelectrics or photodetectors) often output extremely weak signals. The very high input impedance of a FET prevents the drawing of significant current from the sensor, thus preserving the signal fidelity.