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UNIVERSITY OF CALIFORNIA, BERKELEY
College of Engineering
Department of Electrical Engineering and Computer Sciences
EE 105: Microelectronic Devices and Circuits Fall 2009
MIDTERM EXAMINATION #3
11/24/2009
Time allotted: 75 minutes
eR
NAME: Solutrm™
STUDENT ID#:
INSTRUCTIONS:
1. SHOW YOUR WORK. (Make your methods clear to the grader!)
2. Clearly mark (underline or box)-your answers.
3. Specify the units on answers whenever appropriate.
SCORE:1 /16
2 /18
3 116
Total /50
a
(d) [5 pt] What is the definition of cut-off frequency? Find out the expression for cut-off frequency for
the following circuit in terms of MOSFET capacitances and gm.
Vop
Vino M,
Vout
RL
at wheel
Cutotf frequeney ts detned as the freq ony
aia @ [anti
Ag, Pe.
! : Vee
‘ vy, > aa =
In = seg at gs CIV.) 4 vin Yam PL
HHCELI
Vverwt fe
te Se Fe
a
Vos Pr =" 1A dm PL
Gin
Qi, 2in = oe
g 4gat Taek
Ss . tot 2 oa I
[it= saa nn |
(ii)[4 pts} Draw Id vs. Vd for the long channel MOSFET shown in the figure for the specified biasing
conditions. Note that all the voltages are measured with respect to ground which is at zero voltage. In
your plot, you must specify numerical values of ail the relevant voltages. The current values need not be
catculated numerically. Assume Vg=1 V.
Assume Tay
Vf 2ge.N (2.
Vig + 25 + AEHEMCO) gay
Va
Vs=-0.2V |
| ete Ne
ee AAMMLLIILLLEA
nt n*
P-substrate
—-—
Vsubstrate=-0.2 V
(iii)[2 pt] Show qualitatively how the Id-Vd will change if the substrate voltage is modified in the
following way? Assume Vg=1 V.
Say 8 MEO
source yunenor
: ce
yeuerse bowed —
Vs=-0.2V
Vin gues UP
nus
new
/
Sat Mt
P-substrate
nw) ‘i de
Hence Vd ae Vasat
Vsubstrate=-0.4 V a nal
yn
also ew) ie 9
«orth
WW
2.
[18 pt) Operation of MOSFET and basic amplifiers.
1
{a} (2 pt} Considering that 74... * TAL’ explain why channel length modulation does not
affect the long channel MOSFETs.
a fe oE
Ja ocak ca ai (Ut "ie 2
Al ;
“— ee
(6) [2 pt] The equation for current including channel length modulation is usually expressed as:
1 W 2
Ts01 = 3 Coe Ves Ven yk + Ws Foca }
What relationship between A and (Vas-Vosu) is assumed to derive this equation?
AL K (s- \s sat)
(c) [2 pt] Draw the small signal equivalent of a CS amplifier with A « 0.
vii
(d) [4 pt] Consider the following circuit where two short channel MOSFETs of equal length have
been arranged to give an amplifier. Approximate the total gain of this amplifier. Provide a
numerical value.
V, +}
2? Ay = — 9m, (Yo, V0" gins
