Unit III FET and its Applications 2 Marks Questions and Answers 1. Why do you call FET as field effect transistor? The name “field effect” is derived from the fact that the current is controlled by an electric field set up in the device by an external voltage, applied across gate and source terminals, which reverse bias the junctions. 2. What is a FET? A field effect (FET) is a three terminal semiconductor device in which current conduction takes place by only one type of carriers (either holes or electron) and is controlled by an electric field. 3. Why FET is called an unipolar device? The operation of FET depends upon the flow of majority carriers only (either holes or electrons) so the FET is said to be an unipolar device. 4. Define pinch off voltage? It is the voltage at which the channel is pinched off, i.e. all the free charge from the channel get removed. At Pinch-off voltage V P the drain current becomes constant. 5. Define drain resistance? Drain resistance (rd) is defined as the ratio of small change in drain to source voltage (ΔVds) to the corresponding change in drain current (ΔId) at constant gate to source voltage (Vgs). rd = ΔVds / ΔId at constant gate to source voltage (Vgs) 6. Write down the relationship between various FET parameters? Amplification factor = drain resistance * Transconductance μ = rd * gm 7. Mention the applications of FET. • FET is used as a buffer in measuring instruments, receivers since it has high i/p impedance and low o/p impedance. • FETS are used in RF amplifiers in FM tuners and communication equipment for the low noise level. • Since the device is voltage controlled, it is used as a voltage variable resistor in op-amps and tone controls. • Used as phase shift oscillator because frequency drifts is low. 8. Why the input impedance of FET is more than that of a BJT? The input impedance of FET is more than that of a BJT because the input circuit of FET is reverse biased whereas the input circuit of BJT is forward biased.
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2 marks unit 3files.teceee-in.webnode.in/200000160-2ba8c2ca34/UNIT 3...Why the input impedance in FET is very high in comparison with BJT? JFET have very high input impedance because
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Unit III FET and its Applications
2 Marks Questions and Answers
1. Why do you call FET as field effect transistor?
The name “field effect” is derived from the fact that the current is controlled by an electric
field set up in the device by an external voltage, applied across gate and source terminals, which
reverse bias the junctions.
2. What is a FET?
A field effect (FET) is a three terminal semiconductor device in which current conduction takes
place by only one type of carriers (either holes or electron) and is controlled by an electric field.
3. Why FET is called an unipolar device?
The operation of FET depends upon the flow of majority carriers only (either holes or electrons)
so the FET is said to be an unipolar device.
4. Define pinch off voltage?
It is the voltage at which the channel is pinched off, i.e. all the free charge from the channel get
removed. At Pinch-off voltage VP the drain current becomes constant.
5. Define drain resistance?
Drain resistance (rd) is defined as the ratio of small change in drain to source voltage
(∆Vds) to the corresponding change in drain current (∆Id) at constant gate to source voltage
(Vgs).
rd = ∆Vds / ∆Id at constant gate to source voltage (Vgs)
6. Write down the relationship between various FET parameters?