Podcast
Questions and Answers
A ______ type of FET has a positive or negative value of Gate to Source voltage (VGS)
A ______ type of FET has a positive or negative value of Gate to Source voltage (VGS)
depletion
Typically, JFETs can only have ______ values for Gate to Source voltage (VGS)
Typically, JFETs can only have ______ values for Gate to Source voltage (VGS)
negative
Complementary ______ is made up of two MOSFETs, one p-channel and one n-channel, in a single substrate
Complementary ______ is made up of two MOSFETs, one p-channel and one n-channel, in a single substrate
MOS
Metal ______ FET (MESFET) is more recently developed than MOSFET and junction FET
Metal ______ FET (MESFET) is more recently developed than MOSFET and junction FET
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______ Arsenide (GaAs) MESFET uses GaAs instead of Silicon as the substrate
______ Arsenide (GaAs) MESFET uses GaAs instead of Silicon as the substrate
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The drain current is zero for levels of gate to source voltage less than the ______ level VGSth
The drain current is zero for levels of gate to source voltage less than the ______ level VGSth
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FETs are ______ devices which could be used in applications wherein bipolar junction transistors are used.
FETs are ______ devices which could be used in applications wherein bipolar junction transistors are used.
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FET is a ______ controlled device, whereas BJT is a current controlled device.
FET is a ______ controlled device, whereas BJT is a current controlled device.
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FETs are classified as ______ devices because current flow is only dependent on either electron flow or hole flow.
FETs are classified as ______ devices because current flow is only dependent on either electron flow or hole flow.
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FETs have a very high ______ impedance compared to BJTs.
FETs have a very high ______ impedance compared to BJTs.
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The gate of a Junction Field Effect Transistor (JFET) is ______ biased.
The gate of a Junction Field Effect Transistor (JFET) is ______ biased.
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FETs could also be classified as ______ and IGFET (Insulated Gate Field Effect Transistor).
FETs could also be classified as ______ and IGFET (Insulated Gate Field Effect Transistor).
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MOSFET is also known as ______ Gate FET or ______.
MOSFET is also known as ______ Gate FET or ______.
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Unlike JFET, ______ MOSFET is able to operate with positive and negative values of VGS.
Unlike JFET, ______ MOSFET is able to operate with positive and negative values of VGS.
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Silicon dioxide is used as an ______ material in MOSFET.
Silicon dioxide is used as an ______ material in MOSFET.
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When VGS is equal to Vp (VGS (off)), ID is equal to ______ A.
When VGS is equal to Vp (VGS (off)), ID is equal to ______ A.
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The region for positive VGS is called ______ region.
The region for positive VGS is called ______ region.
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Enhancement Type MOSFET is ______ by Shockley's equation.
Enhancement Type MOSFET is ______ by Shockley's equation.
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Study Notes
FET Basics
- A Field Effect Transistor (FET) is a three-terminal device that can be used in applications where bipolar junction transistors are used.
- FET is a voltage-controlled device, unlike a BJT which is a current-controlled device.
- FET is a unipolar device, meaning current flow is only dependent on either electron flow (n-channel) or hole flow (p-channel).
- FET has a very high input impedance (1 Mohm to hundreds of Mohm or higher) compared to BJTs.
Types of FETs
- Junction Field Effect Transistor (JFET): Gate is insulated, and typically can only have negative values of Gate to Source voltage (VGS).
- Metal Oxide Semiconductor Field Effect Transistor (MOSFET) or Insulated Gate FET (IGFET): Schottky Barrier, can operate with positive and negative values of VGS.
- Metal Semiconductor Field Effect Transistor (MESFET): uses GaAs instead of Silicon as the substrate, and it uses Schottky barriers at the Gate instead of silicon-dioxide insulating material.
FET Characteristics
- Turn-on delay (tdl): time for device to start switching on after input signal is applied.
- Rise Time (tr): time for device to reach on level after starting to switch on.
- Turn-off delay (td2): time for device to start switching off after input is applied.
- Fall time (tf): time for device to fall to off condition after starting to switch off.
- Saturation Level: the greater the value of VGS, the greater the saturation level for VDS.
MOSFET
- More sensitive to static electricity.
- One of the most important devices in ICs.
- Can operate with positive and negative values of VGS.
- Substrate is internally connected to the Source, or has a separate terminal called Substrate (SS).
- Silicon dioxide (SiO2) is an insulating material where the gate is connected to, and also acts as a dielectric, opposing electric field.
FET Operation
- When VGS is equal to Vp (VGS (off)), ID is equal to 0 A.
- When VGS is equal to 0 V, ID is equal to IDSS.
- The region for positive VGS is called enhancement region because in this region, Drain current is increased (“enhanced”).
- The region for negative VGS is called depletion region because in this region, Drain current is lessened due to the recombination of electrons.
Zener Diodes
- Two zener diodes placed back to back can be installed between the gate and the source to prevent excessive voltages from being applied across the two terminals.
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Description
Test your understanding of MOSFET switching characteristics, including turn-on delay, rise time, turn-off delay, and fall time. Learn how to prevent excessive voltages across the gate and source terminals.
