1. FET ( Field Effect Transistor)
Few important advantages of FET over conventional Transistors
Unipolar device i. e. operation depends on only one type of charge carriers (holes or electrons)
Voltage controlled Device (gate voltage controls drain current)
Very high input impedance ( )
Source and drain are interchangeable in most Low-frequency applications
Low Voltage Low Current Operation is possible (Low-power consumption)
Less Noisy as Compared to BJT
No minority carrier storage (Turn off is faster)
Self limiting device
Very small in size, occupies very small space in ICs
Low voltage low current operation is possible in MOSFETS
Zero temperature drift of out put is possible.

2. Types of Field Effect Transistors (Classifications)
JFET
MOSFET (IGFET)
n-Channel JFET
p-Channel JFET
FET
Enhancement MOSFET
Depletion MOSFET
n-Channel EMOSFET
n-Channel DMOSFET
p-Channel DMOSFET
p-Channel EMOSFET

3. The Junction Field Effect Transistor (JFET)
Figure: n-Channel JFET.

4. JFET SYMBOLS Gate Drain Source Gate Drain Source Gate Drain Source
n-channel JFET
n-channel JFET
(Offset-gate symbol)
p-channel JFET

5. Figure: n-Channel JFET and Biasing Circuit.
Biasing the JFET
Figure: n-Channel JFET and Biasing Circuit.

6. Operation of JFET at Various Gate Bias Potentials
Figure: The nonconductive depletion region becomes broader with increased reverse bias.
(Note: The two gate regions of each FET are connected to each other.)

7. Operation of a JFET Drain - N Gate P P + + - DC Voltage Source - N +

8. Figure: n-Channel FET for vGS = 0.
Simple Operation and Break down of
n-Channel JFET
Figure: n-Channel FET for vGS = 0.

9. N-Channel JFET Characteristics and Breakdown
Break Down Region
Figure: If vDG exceeds the breakdown voltage VB, drain current increases rapidly.

10. Figure: Transfer (or Mutual) Characteristics of n-Channel JFET
Transfer (Mutual) Characteristics of
n-Channel JFET
IDSS
VGS (off)=VP
Figure: Transfer (or Mutual) Characteristics of n-Channel JFET

11. Biasing Circuits used for JFET
Fixed bias circuit
Self bias circuit
Potential Divider bias circuit

12. JFET (n-channel) Biasing Circuits
For Fixed Bias Circuit
Applying KVL to gate circuit we get
and
For Self Bias Circuit
Where, Vp=VGS-off & IDSS is Short ckt. IDS

13. JFET Biasing Circuits Count…
or Fixed Bias Ckt.

14. JFET Self (or Source) Bias Circuit
This quadratic equation can be solved for VGS & IDS

15. The Potential (Voltage) Divider Bias

16. A Simple CS Amplifier and Variation in IDS with Vgs

17. FET Amplifier Configurations and Relationships:v + _ G V DD 1 SS 2
Common Drain (CD) Amplifier (also called “source follower”) L o D S
Note: The biasing circuit is the same for each amp.