DESIGN AND CONSTRUCTION OF FET AMPLIFIER
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Abstract
FET amplifier is an amplifier which uses one or more field-effect transistors (FETs). The main advantage of an FET used for amplification is that it has very high input impedance and low output impedance.
FET Amplifier is designed to deliver appreciable power to the load. Audio Power amplifiers may be called upon to supply power ranging from a few watts in an audio amplifier to many hundreds or thousands of watts to a load (speaker). In audio amplifiers the load is usually the dynamic impedance presented to the amplifier by a loudspeaker, and the function is to maximize the power delivered to the load over a wide range of frequencies. The power amplifier in a radio transmitter operates over a relatively narrow band of frequencies with the load essentially constant impedance.
CHAPTER ONE
INTRODUCTION
The field-effect transistor (FET) is a transistor that uses an electric field to control the shape and hence the electrical conductivity of a channel of one type of charge carrier in a semiconductor material. FETs are also known as unipolar transistors as they involve single-carrier-type operation. The FET has several forms, but all have high input impedance. While the conductivity of a non-FET transistor is regulated by the input current (the emitter to base current) and so has a low input impedance, a FET’s conductivity is regulated by a voltage applied to a terminal (the gate) which is insulated from the device. The applied gate voltage imposes an electric field into the device, which in turn attracts or repels charge carriers to or from the region between a source terminal and a drain terminal. The density of charge carriers in turn influences the conductivity between the source and drain.
FET amplifier uses one or more field-effect transistors (FETs). The main advantage of an FET used for amplification is that it …READ MORE
1.2 OBJECTIVE OF THE PROJECT
The main objective of this work is to design and construct an audio power amplifier using FET as the power transistor.
1.3 APPLICATION OF THE PROJECT
Important applications include public address systems, theatrical and concert sound reinforcement systems, and domestic systems such as a stereo or home-theatre system. Instrument amplifiers including guitar amplifiers and electric keyboard amplifiers also use audio power amplifiers. In some cases, the power amplifier for an instrument is integrated into a single amplifier “head” which contains a preamplifier, tone controls, and electronic effects. In other cases, musicians may create a setup with separate rack mount preamplifiers, equalizers, and a power amplifier …READ MORE
1.4 SIGNIFICANCE OF THE PROJECT
FET amplifiers are less noisy compared to BJT amplifiers as the operation of the device depends on majority carriers and no recombination currents are required for its operation.
The amplifier exhibit high input resistance typically of the order of mega ohms. In JFET this is due to reverse biasing both the junctions of JFET thereby reducing drastically the conductance of channel. In MOSFET this is aggravated due to silicon dioxide layer provided…READ MORE
1.5 LIMITATIONS OF PROJECT
1. FET amplifier theoretically are ideal voltage amplifiers with high input resistance and low output resistance. But it is seldom used in amplifier circuits due to its low gain bandwidth product compared to Bipolar Junction Transistors.
2. Faster switching times can be achieved in BJT amplifier compared to FET amplifier by preventing the devices from going into hard saturation. In FET internal junction capacitance’s are responsible for higher delay times.
3. The performance of FET deteriorates as frequency increases due to feedback by
