UNIVERSITY OF OSLO
Faculty of mathematics and natural sciences
Examination in
Inf 3410 — Analog Microelectronics
Day of examination: 16. December, 2011
Examination hours:
9.00 – 13.00
This problem set consists of 3 pages.
Appendices:
none
Permitted aids:
All printed and written including calculator
Please make sure that your copy of the problem set is
complete before you attempt to answer anything.
For all questions clearly state you assumptions. You may assume all
transistors to have similar electrical properties.
All questions are weighted with an explicitly marked percentage.
VDD=1.2V
RD
Vout
M1
Vin
Vb
+
_
Figure 1: CMOS amplifier (1)
Problem 1
(5%)
In Figure 1 a single transistor CMOS amplifier is shown. Identity which type
of single transistor amplifier this is and what is considered to be an important
feature for this topology.
Problem 2
(5%)
Draw a small signal equivalent of the amplifier shown in Figure 1 including
body-effect and channel-length modulation.
(Continued on page 2.)
Examination in Inf 3410, 16. December, 2011
Problem 3
Page 2
(5%)
Based on your small-signal equivalent find an equation for low-frequency
transfer function and explain how body-effect is affecting amplifier
performance.
VDD=1.2V
RD
Vout
M1
Vin
RS
Figure 2: Amplifier (2)
Problem 4
(15%)
Another amplifier is shown in Figure 2 and an application restricts maximum
power consumption to 5mW . In order to ensure operation of the MOS
transistor in the saturation region, output voltage should be at least 100mV
above the triode region of operation for the M1 transistor. In addition the
amplifier must have a gain of at least 5. Find appropriate values for RD , RS
and W/L. You may ignore both body-effect and channel-length modulation
and assume µn Cox = 200µA/V 2 and Vthn = 0.5V . Please note the input
signal, Vin , only deliver a small input signal and is unable to provide circuit
biasing.
VDD=1.2V
RD
Vout
M1
Vin
C1
I1
Figure 3: Amplifier (3)
(Continued on page 3.)
Examination in Inf 3410, 16. December, 2011
Problem 5
Page 3
(20%)
In Figure 3 a modified amplifier is shown. Again we want to ensure operation
in the saturation region of the MOS transistor by biasing the M1 transistor
at least 100mV above triode region with a load current of I1 = 1mA. For
simplicity you may ignore body-effect and channel-length modulation and
assume the input capacitor, C1 , to be fairly large. Use µn Cox = 200µA/V 2
and Vthn = 0.5V . Determine an appropriate value for the RD resistor.
Problem 6
(20%)
The amplifier in Figure 3 is expected to have a gain of 4. Using the RD
resistor determined in the question above and the same constants, determine
an appropriate size (W/L) of the M1 transistor.
VDD=1.2V
M2
CL
Vout
Vin
M1
RS
Vb
CS
Figure 4: Amplifier for frequency response analysis
Problem 7
(5%)
In the following you must account for high frequency behavior of the amplifier
shown in Figure 4. As a first step to determine small-signal frequency
response, the capacitors CS and CL indicated in Figure 4 are equivalent,
lumped capacitors. For each of CS and CL determine the major parasitic
capacitances lumped together.
Problem 8
(20%)
Find an equation for the transfer function of the amplifier in Figure 4 using
s-notation. Channel-length modulation and body-effect may be ignored.
Explain which pole is the dominant pole of the transfer function.