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Questions and Answers
What is the primary characteristic of an IGFET?
What is the primary advantage of a Dual Gate MOSFET?
What is the typical fabrication material for a MESFET?
What is a common application for MESFETs?
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What is the primary drawback of GaAsFET technology?
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What is the primary advantage of HEMT and PHEMT devices?
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What is the typical construction of a MOSFET?
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What is the primary characteristic of a MOSFET that makes it useful in many electronics applications?
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What is the direction of the arrow in a schematic symbol for an N-channel JFET?
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What is a characteristic of JFET operation?
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What is the effect of a negative gate voltage on the channel of a JFET?
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What is the purpose of the two sections of P-type material in a JFET?
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What happens to the channel when the gate voltage reaches a certain threshold?
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What is controlled by the gate-to-source voltage in a JFET?
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What is the common material that connects the source and drain in a JFET?
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What type of device is a JFET?
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What is the concept of the field effect transistor based on?
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What is the function of the gate in a FET?
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What are the two categories of FET based on the type of semiconductor channel?
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What happens when the voltage on the gate is increased in a FET?
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What is a Junction FET (JFET) similar to?
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Where are Field Effect Transistors widely used?
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What is the purpose of selecting the right type of FET in electronic circuit design?
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What is the main difference between a JFET and a MOSFET?
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Study Notes
Insulated Gate FET / Metal Oxide Silicon FET (MOSFET)
- Uses an insulated layer between the gate and the channel, typically formed from a layer of oxide of the semiconductor
- Gate is made of a layer of metal set down on the silicon oxide, which in turn is on the silicon channel
- Widely used in many areas of electronics and particularly within integrated circuits
- Key feature is the exceedingly high gate impedance
Dual Gate MOSFET
- Specialized form of MOSFET with two gates in series along the channel
- Enables performance improvements, especially at RF, when compared to single gate devices
- Provides additional isolation between the input and output, and can be used in applications like mixing/multiplication
Metal Silicon FET (MESFET)
- Normally fabricated using Gallium Arsenide and often referred to as a GaAs FET
- Often used for RF applications where they can provide high gain, low noise performance
- Drawback is the very small gate structure, making it sensitive to damage from static, ESD
HEMT and PHEMT
- High Electron Mobility Transistor and Pseudomorphic High Electron Mobility Transistor
- Developed to enable very high frequency operation
- Although expensive, they enable very high frequencies and high levels of performance to be achieved
JFET
- Unipolar device, differing in operation from a bipolar junction transistor
- Output current controlled by the voltage on the gate
- Gate voltage creates an electrical field, or depletion region, within the device
- Considered a voltage-driven device rather than a current-driven device like the bipolar junction transistor
- Output current controlled by an electrical field created by the input voltage
JFET Operation
- At zero gate voltage, channel height is maximum and channel resistance is minimum, resulting in current flow
- With a slightly positive voltage, the channel height opens further, allowing maximum current flow
- If the gate is made negative with respect to the channel, the diodes become reverse biased and the depletion regions increase
- At a large enough gate-to-source voltage (VGS), the channel is effectively “pinched off” because of the depletion regions touching
FET Basics
- Concept of the field effect transistor is based around the concept that charge on a nearby object can attract charges within a semiconductor channel
- Operates using an electric field effect - hence the name
- FET consists of a semiconductor channel with electrodes at either end referred to as the drain and the source
- Control electrode called the gate is placed in very close proximity to the channel so that its electric charge is able to affect the channel
- Gate of the FET controls the flow of carriers (electrons or holes) flowing from the source to drain
- Semiconductor channel where the current flow occurs may be either P-type or N-type
Field Effect Transistor Types
- Junction FET (JFET)
- Major types of FET that can be covered in the tree diagram
- Each type has its own characteristics and uses in electronic circuit design
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Description
This quiz assesses your understanding of Junction Field-Effect Transistors (JFETs), including their operation, characteristics, and applications. It covers the differences between N-channel and P-channel JFETs, their uses in switching and voltage regulation, and their compatibility with other semiconductor devices.
