Scribd
Upload
102 views34 pages

Outline Outline: - Channel Length Modulation Pmos Role of Substrate Temperature Effects Channel Length Modulation

This document discusses MOSFET devices and characteristics. It outlines topics including channel length modulation, PMOS operation, the role of the substrate, and temperature effects. It also recaps NMOS operation in cutoff, linear, and saturation modes. Specific MOSFET characteristics are examined, such as drain current versus drain-source voltage for different gate voltages. The effects of channel length and temperature on device operation are described. Finally, CMOS transistor operation is briefly introduced.

Uploaded by

Amandeep Gupta
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
102 views34 pages

Outline Outline: - Channel Length Modulation Pmos Role of Substrate Temperature Effects Channel Length Modulation

This document discusses MOSFET devices and characteristics. It outlines topics including channel length modulation, PMOS operation, the role of the substrate, and temperature effects. It also recaps NMOS operation in cutoff, linear, and saturation modes. Specific MOSFET characteristics are examined, such as drain current versus drain-source voltage for different gate voltages. The effects of channel length and temperature on device operation are described. Finally, CMOS transistor operation is briefly introduced.

Uploaded by

Amandeep Gupta
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 34

Outline

Channel Length Modulation


PMOS
Role of Substrate
Temperature Effects

2/12/2015

Recap
NMOS Operation in
Cut off ,Linear and Saturation mode
Related Equations

2/12/2015

MOSFET

When VGS=0 V and VDS =1 V

When VGS=0 V and VDS =3 V

When VGS=2 V and VDS =0 V

When VGS=2 V and VDS =1 V

When VGS=5 V and VDS =0 V

When VGS=5 V and VDS =1 V

When VGS=10 V and VDS =10 V

Effect of Channel Length


Modulation

Effect of Channel Length


Modulation

Linear/Triode Region
MOS transistor can be modelled as linear resistor
r whose value is controlled by v
DS

2/12/2015

DS

13

Large Signal equivalent Model (saturation)

Since the drain current independent of drain voltage, ,the


saturated mosfet behaves as ideal current source whose value
is controlled by vGS

and L
The effect of channel-length
length modulation is less for a longlong
channel MOSFET than for a short-channel
short
MOSFET.

iD - vDS Characterstics (Channel Length Modulation)

Effect of L on channel length Modulation

2/12/2015

17

iD - vDS Characterstics (Channel Length Modulation)

Chapter 4
MOS field-Effect
Effect Transistors (MOSFETs)
Modelling
Channel
Length Modulation
Figre 4.17

NMOS Transistor

Conduction characteristics for nMOS


transistor
Enhancement - mode
Devices are cutoff with zero gate bias voltage
Apply
Apply +ve voltage to gate to make channel

Depletion - mode
G

Devices conduct with zero gate bias voltage


Channel exists. Apply -ve
ve voltage to turn off

Conduction characteristics for nMOS


transistor

D
G

n
S

(assuming
fixed Vds)
Depletion - mode
Enhancement - mode
Devices are cutoff with zero gate bias voltage
Apply +ve voltage to gate to make channel

Devices conduct with zero gate bias


voltage
channel exists. Apply -ve voltage to
turn off

PMOS Transistor

Chapter 4

MOS field-Effect
Effect Transistors (MOSFETs)

PMOS Transistor - Symbolic Representation


Figure 4.18

Conduction characteristics for


pMOS transistor

(assuming fixed Vds)

HomeWork
Voltage and Current Equations for PMOS in
Linear and Saturation mode

2/12/2015

26

Role of substrate
In many applications the source terminal is connected to
the substrate terminal B which results in the PN junction
between the substrate and the induced channel having
zero (cutoff) bias

2/12/2015

27

Role of substrate
The reverse bias voltage will widen the depletion region
.This in turn reduces the channel depth

To return to its former state -------has to be increased


VGS
2/12/2015

28

Role of substrate
The effect of V on the channel can be most
convinently represented as a change in the
threshold voltage Vt
SB

Vto - threshold voltage for VSB = 0


- Fabrication process
2/12/2015

29

Role of substrate

If V changes then there is incremental change in


V , which in turn results in incremental change in i
even though v is constant
SB

GS

The body (substrate ) controls i thus the body acts


as another gate for the MOSFET , a phenomenon
known as Body Effect
D

2/12/2015

30

Temperature Effects

2/12/2015

EEE C424/ECE C313

31

Temperature Effects

2/12/2015

EEE C424/ECE C313

32

Breakdown and input Protection

2/12/2015

EEE C424/ECE C313

33

Chapter 4

MOS field-Effect
Effect Transistors (MOSFETs)
Figure 4.9

CMOS Transistor

You might also like