Analog CMOS Integrated Circuit Design Set 2 - Courses - University ...

I
D
SM
= I
Long Channel Current Equations - 7
• If V DS > V GS – V TH, the transistor is in saturation (active) region,
and the channel is pinched off.
L'
∫ I dx =
D
x=
0
VGS
−VTH
∫WC
μ [ V
V = 0
ox
1 W
I D = μnC
ox ( VGS
−V
2 L'
n
GS
TH
)
−V
( x)
−V
2
TH
EECE 488 – Set 2: Background
SM 10
] dV
• Let’s, for now, assume that L’=L. The fact that
L’ is not equal to L is a second-order effect
known as channel-length modulation.
• Since I D only depends on V GS, MOS transistors in saturation can be
used as current sources.
SM
Long Channel Current Equations - 8
• Current Equation for NMOS:
DS
⎧
⎪0
; if VGS
< VTH
( Cut − off )
⎪
⎪
⎪ W
⎪μ
n ⋅ Cox
⋅ ⋅(
VGS
−VTH
) ⋅V
⎪ L
= ⎨
⎪ W
⎪μ
n ⋅ Cox
⋅ ⋅
⎪ L
⎪
⎪
⎪1
W
2
⋅ μ ⋅ C ⋅ ⋅ ( V −V
)
⎪ n ox
GS TH
⎩2
L
DS
; if V
1 2
[ ( VGS
−VTH
) ⋅V
DS − ⋅VDS
]
2
; if V
GS
GS
> V
> V
EECE 488 – Set 2: Background
, V
; if V
TH
TH
, V
GS
DS
DS
V
> V
TH
GS
GS
, V
DS
−V
TH
−V
TH
< V
GS
−V
( Saturation )
19
) ( Deep Triode)
TH
( Triode)
20