Slide 1

Agenda
 Body Effect Model
 Reverse and Forward Body Bias

ELEC 301: CMOS VLSI DESIGN

VOLKAN KURSUN


Slide 2

Body Effect Model
 g: Body effect coefficient
– Positive for NMOS
– Negative for PMOS
 ΦF: Fermi potential
– Negative for NMOS
– Positive for PMOS
 VT0: Zero body bias (VSB = 0) threshold voltage

VT  VT 0  g (  2F  VSB  2F )
2qN A Si

g NMOS 
F _ NMOS

Cox

, g PMOS  

2qN D Si
Cox

ni
kT
kT N D

ln
, F _ PMOS 
ln
q
NA
q
ni

ELEC 301: CMOS VLSI DESIGN

VOLKAN KURSUN


Slide 3

NMOS Forward Body Bias
 g: Body effect coefficient, positive for NMOS
 ΦF: Fermi potential, negative for NMOS

 VT < VT0
Negative
Negative

Positive

Negative

VT  VT 0  g (  2F  VSB  2F )

g NMOS

2qN A Si
ni
kT

, F _ NMOS 
ln
Cox
q
NA

ELEC 301: CMOS VLSI DESIGN

VOLKAN KURSUN


Slide 4

NMOS Reverse Body Bias
 g: Body effect coefficient, positive for NMOS
 ΦF: Fermi potential, negative for NMOS

 VT > VT0
Positive
Positive

Positive

Positive

VT  VT 0  g (  2F  VSB  2F )

g NMOS

2qN A Si
ni
kT

, F _ NMOS 
ln
Cox
q
NA

ELEC 301: CMOS VLSI DESIGN

VOLKAN KURSUN


Slide 5

PMOS Forward Body Bias
 g: Body effect coefficient, negative for PMOS
 ΦF: Fermi potential, positive for PMOS

 VT > VT0

Negative

Positive

Negative

Positive

VT  VT 0  g (  2F  VSB  2F )

g PMOS

2qN D Si
kT N D

, F _ PMOS 
ln
Cox
q
ni

ELEC 301: CMOS VLSI DESIGN

VOLKAN KURSUN


Slide 6

PMOS Reverse Body Bias
 g: Body effect coefficient, negative for PMOS
 ΦF: Fermi potential, positive for PMOS

 VT < VT0

Positive

Negative

Negative

Negative

VT  VT 0  g (  2F  VSB  2F )

g PMOS

2qN D Si
kT N D

, F _ PMOS 
ln
Cox
q
ni

ELEC 301: CMOS VLSI DESIGN

VOLKAN KURSUN