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(ELEC102)exampast5.pdf
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12V VDD
11 (30)

RD

ID 0.5mA
VD


VOGiven Vi
VT = 1V VS
VG
K = 0.02mA/V2
Find RD such that Vi = VO ,
and NMOS saturates

i.e. VGS = VDS

QIDS =
K (VGS -
VT )2 =
0.02m(VGS -
1)2 =
0.5mA 0.5m
\
VGS =


+
1 =
6V
0.02m QV =
IR +
V
DD DSD DS
V -
V 12 -
6
DD DS


\
R =
=
=
12kW

D IDS 0.5m
Find VO such that Vi = VDD
i.e. VGS = 12V , hence VGS -VT > VDS and NMOS in triode
2VDS


\
IDS =
2K[( V -
VT )V -
]
GS DS
2
2VDS


=
2(0.02m)[(12 -
1)V -
]
DS 2

V -
V 12 -
V V2
DDDS DS DS
\
IDS =
=
=
0.04m(11VDS -
)
RD 12.5k 2 V2

\
12 -
V =
0.5[11V -
DS ]
DS DS
2 \
12 -
6.5V +
0.25V 2 =
0
DS DS




\
V2 -
26V +
48 =
0
DS DS
\
VDS =
24V or 2V

hence VO = 2V (24 V > VDS is impossible)
= VDS