Lecture #5 FET Biasing & AC Analysis Instructor: Dr. Ahmad El-Banna N

ov

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2014

J-601-1448 Electronic Principals

Integrated Technical Education Cluster At AlAmeeria‎

© A

hmad

El-B

anna

Agenda

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Construction and Characteristics

FET Biasing

Design and Troubleshooting

JFET small signal Model

FET Amplifier Networks

Practical Applications

Note! Same concepts of the BJT, so we will just overview the FET transistors.

CONSTRUCTION AND CHARACTERISTICS

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Construction

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• One of the most important characteristics of the FET is its high input impedance.

• FETs are more temperature stable than

BJTs, and FETs are usually smaller than BJTs, making them particularly useful in integrated-circuit (IC) chips.

Construction..

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N-channel

Characteristics & Equations

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Depletion-Type MOSFET

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• There is no direct electrical connection between the gate terminal and the channel of a MOSFET.

• It is the insulating layer of SiO2 in the MOSFET construction that accounts for the very desirable high input impedance of the device.

Depletion-Type MOSFET

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Other MOSFETS

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• VMOS AND UMOS POWER MOSFETs • CMOS

• MESFET

FET BIASING

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FIXED-BIAS CONFIGURATION

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Example

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Voltage-Divider Bias

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Example

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DESIGN AND TROUBLESHOOTING

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Design Example

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Troubleshooting

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The level of VDS is typically between 25% and 75% of VDD .

The continuity of a network can be checked simply by measuring the voltage across any resistor of the network.

JFET SMALL SIGNAL MODEL

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JFET small signal Model

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Fixed-Bias Configuration

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phase shift of 180° between input and output voltages.

VOLTAGE-DIVIDER CONFIGURATION

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FET AMPLIFIER NETWORKS

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Design FET Amplifier Network

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Summary Table

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Cascaded Configuration

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PRACTICAL APPLICATIONS 27

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Three-Channel Audio Mixer

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Motion Detection System

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• For more details, refer to:

• Chapter 6,7,8, Electronic Devices and Circuits, Boylestad.

• The lecture is available online at:

• https://speakerdeck.com/ahmad_elbanna

• For inquires, send to:

• ahmad.elbanna@feng.bu.edu.eg

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