Microelectronics: CMOS Circuits, Device Characteristics, and Applications, Study notes of Electrical and Electronics Engineering

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21) Basic CMOS Circuits

21.1 NMOS Device Characteristics

V DS

V GS

I D

EEE435/591 Microelectronics Spring 2009

21.2 PMOS Device Characteristics

-V DS

-V GS

I D

EEE435/591 Microelectronics Spring 2009

21.3 Device Equations

We usually describe the MOSFET drain current in one of two regimes:

i) Below Saturation [ ]

GS th DS DS

ox D V V V V L

C W

I = − −

( ) GS th DS

ox V V V L

C W

for small V (^) DS

ii) Above Saturation ( )

2

2

GS th

ox D

V V

L

C W

I = −

For circuits we require complementary devices i.e. if a PMOS and NMOS

d i h id ti l bi i (b t f it i ) th th d i

EEE435/591 Microelectronics Spring 2009

device have identical biasing (but of opposite sign) then the same drain

current will flow

ptype th

ntype th

V V

− − =−

And μ n

W

n = μ p Wp ⇒ W p

≈ 2W

n because μ n ~600 cm 2 /Vs and μ p ~300 cm 2 /Vs

21.4 The CMOS Inverter

Vin Vout

EEE435/591 Microelectronics Spring 2009