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EE 3110 Microelectronics I
Practice Test (Midterm Exam 2 2014)
Subject: MOSFETs
Instructions:
1) ALWAYS SHOW YOUR WORK!
2) Put a box or circle around your answers.
3) Open Notes, Open Book, Closed Multisim/LTSpice, Closed Internet. Any type of
calculator is allowed.
4) Numbers in the parentheses on the right indicate points for that particular
problem.
Name: ________________________________________________________
Date: _______________
Problem
Points
1 (Transistor and its operation)
/32
2 (VTC)
/8
3 (Find ID and VD)
/20
4 (Current Mirror)
/10
5 (CS Amplifier)
/20
6 (CS Amplifier)
/10
6 (CG Amplifier)
/10
Total
/100
Weber State University
EE3110 Microelectronics I
Suketu Naik
2
PROBLEM 1 (16)
Consider the transistor shown on the right.
(a) Name the transistor and label the nodes (i.e. G for Gate, D for Drain, S for Source) (2):
(b) Draw ID vs VDS characteristics for this device (8).
Assume that the overdrive voltage VOV = 0.5 V, Early voltage VA= 50 V, and maximum
saturation current ID = 10 mA. Clearly label (write numbers) the transition points (e.g. -VA, VOV,
IDSAT) on the plot. Draw the approximate boundaries between different regions of operation (i.e.
Triode, Saturation) and label the regions appropriately.
(c) In terms of the application of the device, why do we operate it in the Triode region and in the
Saturation region (Hint: look at the slope of the curve in each region) (2)?
Weber State University
EE3110 Microelectronics I
Suketu Naik
3
(d) Draw the cross section of the device (which shows the three terminals, the induced channel,
and the substrate) and write the pertinent equation for the current ID for each of the following
portion of the ID vs VDS plot. Use λ to indicate channel length modulation.
Triode Region: Linear Operation
Cross section (3)
Equation (2): _______________________________________________________________
Triode Region: Bent Curve
Cross section (3)
Equation (2): ________________________________________________________________
Weber State University
EE3110 Microelectronics I
Suketu Naik
4
Saturation Region: Constant Current Source
Cross section (3)
Equation (2): ________________________________________________________________
Saturation Region: Channel length modulation
Cross section (3)
Equation (2): ________________________________________________________________
Weber State University
EE3110 Microelectronics I
Suketu Naik
5
PROBLEM 2 (8): Consider the amplifier shown below. Here VDD = 15 V, RD = 10 kΩ, kn = 1
mA/V2, and Vtn = 0.5 V.
(a) Draw the Voltage Transfer Characteristic (VTC) curve. Find the coordinates of the two end
points of the saturation region (linear portion), A and B. Label these points on the plot (4).
(b) Suppose that the amplifier is biased with an overdrive voltage VOV = 1.5 V. Find the
coordinates of the bias point Q on the VTC curve (4).
Weber State University
EE3110 Microelectronics I
Suketu Naik
6
PROBLEM 3 (20): In the circuits below, find the current (ID) and voltages (VD) as labeled.
Here VDD = 10 V, VSS = -10 V, kn = kp = 1 mA/V2, Vtn = 1 V, Vtp = -1 V. Ignore channellength modulation.
Weber State University
EE3110 Microelectronics I
Suketu Naik
7
PROBLEM 3 (Continued...)
Weber State University
EE3110 Microelectronics I
Suketu Naik
8
PROBLEM 4 (10): A PMOS based current mirror circuit with two PMOS transistor P1 and P2 is
shown below. Here VDD = 2.5 V, kp = 0.5 mA/V2, Vtp = -1.2 V. You can assume that W/L ratio
is identical for the two transistors and that both the transistors are operating in saturation region.
Ignore channel-length modulation.
Design the circuit (find R1 and R2) that results in VD1 (DC voltage at the drain of P1) = 1 V.
Weber State University
EE3110 Microelectronics I
Suketu Naik
9
PROBLEM 5 (20): A common-source amplifier circuit is shown below. Here VDD = 5 V, VSS =
-5 V, kn = 1.08 mA/V2, Vtn = 0.8 V, VA = 50 V, Rsig = RG = 100 kΩ, RL=100 kΩ, and
CG=CD=CS=100 μF. Assume that the DC bias current ID = 1 mA.
Design the circuit: (a) perform DC analysis and find RS, (b) use small-signal model, perform AC
analysis and find RD (don’t forget to include ro) if the overall voltage gain GV is required to be
-8 V/V.
(a) DC analysis:
Weber State University
EE3110 Microelectronics I
Suketu Naik
10
(b) AC analysis (small-signal model) :
Weber State University
EE3110 Microelectronics I
Suketu Naik
11
PROBLEM 6 (10): Please choose between either of the problems (see page 13).
A PMOS based common-source amplifier circuit is shown below. Here VDD = 2.5 V, kp = 6.7
mA/V2, Vtp = -0.7 V, Rsig = 500 Ω, RL = 10 kΩ, and CG=CD=CS=100 μF. The transistor has
very large |VA|.
(a) Perform DC analysis and find RS to bias the transistor at ID = 0.3 mA. Note: RG1= 100 kΩ.
and RG2= 50 kΩ .
(b) Draw the small-signal model and find the overall gain, GV if RD = 1 kΩ.
Weber State University
EE3110 Microelectronics I
Suketu Naik
12
Weber State University
EE3110 Microelectronics I
Suketu Naik
13
PROBLEM 6 (10): Please choose between either of the problems (see page 11).
Consider the NMOS Common-Gate amplifier below. Here VDD = 10 V, VSS = -10 V, RS = 200
kΩ, kn = 1.08 mA/V2, Vtn = 0.8 V, Rsig = 50 Ω, RL = 10 kΩ, and CD=CS=100 μF. Assume gm =
1 mA/V and RD = 15 kΩ. You can also assume that as you look down from the source terminal
towards Rs and Vss, very large resistance is present. Ignore channel length modulation.
Find Rin, Ro, and overall voltage gain GV (Hint: use T-model). What does the overall voltage
gain become for Rsig = 1 kΩ? 10 kΩ? 100 kΩ?
Weber State University
EE3110 Microelectronics I
Suketu Naik
14
Weber State University
EE3110 Microelectronics I
Suketu Naik