The document presents information on MOSFET operation and characteristics. It discusses that MOSFETs are widely used in electronics as switches and for auto intensity control of street lights. It describes the basic construction of MOSFETs, noting they have an insulating layer of SiO2 and a polysilicon gate. The two main types of MOSFETs are introduced as enhancement type and depletion type. Key characteristics of enhancement type MOSFETs are described, including that drain current increases with increasing gate-source voltage above a threshold.

1. PRESENTING ON MOSFET OPERATION
&CHARECTERISTICS
Rafsan Rafin Khan.
Chittagong University Of Engineering & Technology

3. FET
• USED AS SWITCH.
• WIDELY USED IN ELECTRONICS DEVICE.
• AUTO INTENSITY CONTROL OF STREET LIGHT
BY MOSFET
 Voltage control device.
 Three terminal device.
 Unipolar Devices
 Field effect relates to the depletion region
formed on the channel in FET
 Faster then BJT
 Low voltage device.

4. FET
BASICALLY TWO TYPES -
1. JUNCTION FIELD EFFECT TRANSISTOR (JFET)
2. METAL OXIDE SEMICONDUCTOR FIELD EFFECT TRANSISTOR
(MOSFET).

5.  MOSFET
 No P-N junction structure.
 Insulator SiO₂ is used.
 Polycrystalline Silicon material is used for the
gate material.

6.  Construction :
1. No direct connection to the Gate terminal and
the
Channel.
2. SiO₂ is the insulating layer that
create very high input impedance.
3. For insulated gate its also
called IGFET
4. In some cases Substrate is internally
connected to the source terminal.

7. TYPES OF MOSFET-
•1… ENHANCEMENT TYPE MOSFET
•2…DEPLATION TYPE MOSFET

8. Enhancement
Type MOSFET

9. Depletion Type MOSFET

10.  BASIC OPERATION OF ENHANCEMENT TYPE
MOSFET……
 The induced channel allow to pass
electrons from source to drain
 More wide channel means more
flow of electron.
 More gate to source volt means
more current.
P-type N-Channel
MOSFET

11.  The gate and channel act as a parallel
plate capacitor.
 The gate voltage must be greater then
zero.
 The positive potential at gate will
pressure the holes in the p- substrate to
leave the area.
 Electrons will attract to the positive
potential.
 If gate voltage increase the concentration
of electrons near the siO2 surface
increase rapidly.
 Gate voltage when cross the threshold
voltage then the current pass rapidly.
Threshold voltage(VGST ) -The minimum positive
voltage between gate and source to induce n-channel.

12. N-type P-channel
Enhancement type MOSFET

13. CHARACTERISTICS OF ENHANCEMENT
TYPE
• VGS always positive
• As VGS increases Id
increases
• Increasing VDS ,keeping
VGS constant, then ID
goes to saturation .

14.  VDS=VGS-VT
 For fixed value of VT , higher the value of VGS
higher the saturation level of VDS
 For value of VGS less then the threshold voltage,
the drain current is zero .
 Also When VGS =VT the current will zero.
 VDG=VDS-VGS
 When VDG is fixed and greater then VDS, then
increasing VDS will create the channel to pinch off.

15. VT>VGS –cut off region.
VGS-VT>VDS>0 – linear region.
VDS>VGS-VT – saturation region.

16. OPERATION AND CHARACTERISTICS OF
DEPLETION TYPE MOSFET
N channel depletion
type MOSFET

17. DEPLETION TYPE MOSFET
P channel depletion
type MOSFET

18. OPERATION :
 If the gate to source voltage is zero the current
will pass through the implemented gate
 But if this volt is positive the MOSFET will run
as enhancement type.
 Negative volt of VGS will run the circuit as
depletion type.
 But negative type voltage limit will not exceed
the pinch off level.
 If the negative voltage touch pinch off point
then the current flow will stop.

19. P-CHANNEL DEPLETION TYPE MOSFET

20. Characteristics :

21. Discussion Characteristic between two types of MOSFET :
 If Gate voltage is positive and
more then threshold voltage,
then Enhancement Type &
depletion type will not show
the same characteristic.