Revision: MOS Transistors
(DC and AC Analysis)
Prob.1: Find Vout for Vin = 1V, 4V, and 8V for the shown circuit, assuming VDD = 10V,
VT= 2 V and K=0.5mA/V2 (Ans. 10 V, 5 V, 0.659 V)
VDD
R=5K
Vout
Vin
M
Prob.2: Find the DC operating point (IDS,VDS, VGS and mode of operation) for the shown
circuit assuming VDD = 10V, VT= 1 V and K =1 mA/V2
(Ans. IDS=0.5mA, VDS=4.5V, VGS=2 V, Sat. mode) .
VDD
10M
R=5K
M
10M
6K
Prob.3: Find the DC operating point (IDS,VDS, VGS and mode of operation) for the shown
circuit assuming VDD = 10V, VT= -1 V and K =1 mA/V2
(Ans. IDS=0.125mA, VDS=5.5V, VGS= - 0.5 V, Sat. mode).
VDD
32K
10M
4K
Prob.4: For the PMOS transistor shown, VT = -2 V, µ p cox = 8µA / V 2 and L =10um.
Find W of the transistor, and the value of R in order to establish a drain current of 0.1 mA
and voltage Vout = 7 V
(Ans. W=250 um, R= 70K).
10V
Vout
R
Prob. 5: Design the circuit in Fig.1 to obtain a current of ID = 80 µA. Find the value
required for R and find the DC voltage VD. Let the NMOS transistor have VT =0.6V,
µ n C ox = 200µA / V 2 , L = 0.8 µm and W = 4 µm
(Ans. R= 25K, VD= 1V).
VDD = 3V
ID
R
VD
Fig.1
Prob.6: Consider the circuit of Fig.1 which is designed in Problem 4 (to which you
should refer before solving this problem). Let the voltage VD be applied to the gate
of another transistor M2 as shown in Fig.2. Assume that M2 is identical to M1. Find
the drain current and mode of operation of M2.
VDD = 3V
(Ans. ID2 =80µA, Sat).
VDD = 3V
20 Kohm
R
VD
M1
Fig.2
M2
Prob.7: For the CS configuration shown, calculate the voltage gain, the input resistance
and the output resistance. Given µ n C ox = 0.1mA / V 2 , W/L = 4, VT=1 V, λ = 0.01 V-1.
[Hint: Before AC analysis, you must do DC analysis such that AC model parameters (gm
and rds) can be calculated].
15 V
2K
vout
5K
vin
2M
4 mA
-15V
Prob.8: For the CD configuration shown, calculate the voltage gain, the input resistance
and the output resistance. Given µ n C ox = 0.1mA / V 2 , W/L = 1, VT=1.5 V, λ = 0.02 V-1.
15 V
10 K
vin
vout
1M
1 mA
1K
-15V
Prob.9: For the CG configuration shown, calculate the
voltage gain, the input
2
resistance and the output resistance. Given µ n C ox = 0.1mA / V , W/L = 8, VT=1 V, λ = 0.01
V-1.
15 V
1K
vout
5K
1K
vin
-15V
Prob. 10: Consider the common source amplifier shown. Determine the small signal
voltage gain, input resistance and the output resistance Assuming that the transistor has
1
VT = 1.5 V, K=0.25 mA/V2, V A = = 50V and assuming the coupling capacitors to be
l
sufficiently large so as can be neglected.
VDD = 15V
RD = 10 Kohm
10 Mohm
vout
RL = 10 Kohm
vin
Rin
Rout