The document discusses the Junction Field Effect Transistor (JFET). It describes JFETs as voltage-controlled semiconductor devices with three terminals: the source, drain, and gate. JFETs use either electrons or holes as current carriers. The channel between the source and drain is controlled by the gate, which consists of two heavily doped P-N junctions on either side of the channel. JFETs can be N-channel or P-channel types depending on whether electrons or holes are the majority carriers. The document explains the construction and working principles of JFETs, including how applying a voltage to the gate controls the channel thickness and current flow between the source and drain.

1. Junction Field Effect Transistor
(JFET)
By – Ateeb Khan (S.Y. B.Tech)

2. Content
• Field Effect transistor (FET)
• Junction Field Effect Transistor ( JFET)
• Construction of JFET
• Working of JFET

3. Introduction
The ordinary or bipolar transistor has two main
disadvantage.
• It has a low input impedance.
• It has considerable noise level.
To overcome this problem Field effect transistor (FET)
is introduced because of its:
• High input impedance
• Low noise level than ordinary transistor

4. • Field Effect Transistor is the voltage
controlled device.
JFET
MESFET
MISFET
MOSFET

5. JFET
• Junction Field Effect Transistor is a three terminal
semiconductor device in which current conducted by one
type of carrier i.e. by electron or hole.
• JFET:-

6. Construction
• Source (S): The terminal through which the
majority carriers enter into the channel, is
called the source terminal .
• Drain (D): The terminal, through which the
majority carriers leave from the channel, is
called the drain terminal .
• Gate (G): There are two internally
connected heavily doped impurity regions
to create two P-N junctions. These impurity
regions are called the gate terminal .
• Channel : The region between the source
and drain, sandwiched between the two
gates is called the channel .

7. Types Of JFET
There are two types of JFET
i) n-channel JFET
ii) P-channel JFET

8. Working
• JFET can worked in two conditions
i. When VGS = 0 and VDS >0.
ii. When VGS < 0 and VDS >0

11. Mathematical model
• The current in N-JFET due to a small
voltage VDS (that is, in the linear ohmic
region) is given by treating the channel
as a rectangular bar of material
of electrical conductivity.
ID = bW . qNDµnVDS
L
•where
•ID = drain–source current
•b = channel thickness for a
given gate voltage
•W = channel width
•L = channel length
•q = electron charge = 1.6 x
10−19 C
•μn = electron mobility
•Nd = n-type doping (donor)
concentration.
•VP = pinch-off voltage.

12. Linear region
• In Terms of IDSS

13. Channel Thickness
Constantcurrentregion