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ELEC 5130 - Dai - Fall 2015.pdf
ELEC_5130_-_Dai_-_Fall_2015.pdf
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ELEC 5130 - Dai - Fall 2015.pdf-Midterm Exam I, EL...
ELEC_5130_-_Dai_-_Fall_2015.pdf-Midterm Exam I, ELEC RF Devices
ELEC 5130 - Dai - Fall 2015.pdf-Mid...
ELEC_5130_-_Dai_-_Fall_2015.pdf-Midterm Exam I, ELEC RF Devices
Page 1
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Midterm Exam I, ELEC
RF
Devices
and
Circuits
Thursday, Oct. 1,2015, 12:30am
-1:45pm,
Broun Hall
235,
total score
100 points.
Name:
~
Student
No.:
q
Il
.,
"2. "2.
:}SiY
,
Score:
11
.j.
S
p
Part
A:
Multiple Choice Problems,
30
points
For problem
1
to
6,
one
or
more
of
the given choices
may
be correct, choose ALL the correct
i\
a1lSW€rs
for
a question
for
full
credit. Choosing incorrect answer will carry negative points.
)r
.
/,'
l.i5
oints) What is/are true about linearity?
"o.~.
I
_
,..,
~
~,\
or
a differential pair, gain will be
~d
t high input power.
(
tx
';J
-
.-'-Jy
<:\
(.1-..-
)
2)
g'
eain desensitization occurs
when
a
Singl~~tltsignal
driv:stl1esystent
into nonlinear
•
'4$1\1.1),
\
E2
nd
order inter-modulated tones makes
mo~oub~e_since
they are closer to the fundamental
es.
4)
e 3
rd
order inter-modulated tones makes more trouble since they are closer to the fundamental
~
'~s.
~
/~LThe
~ine~ty
of
the first stage (e.g.,
an
LNA)
of
a receiver has bi
st impact
on
the overall
system lmeanty.
Ans:
__
--'2.=-+,_4-~
_____
_
-1
2.
(5
points) What is/are true related to the BJT
gm
versus MOSFET
gm?
(1) In the active region, the transconductance
ofa
BJT,
i:.3)
(2) In the active
regi~conductance
of
an
MOSFET,
gm
oc~
(3) BJT
has
better
gm
effi ency than
OSFET.
(4)
BJT's
gm
efficiency is p
lOnal to
thermal~.
(5~MOSFET's
gm
efficiency is proportional to
thresh~e.
A'ns:
I,
3
)
l
..
\I'
3.
~ints)
What is/are true comparing a BJT to
an
MQSFFT'J
.
(QlA
BJT has a vertical
!r~sistor
structure, while
an
MOSFET has a lateral transistor structure.
e saturation region, a BJT can be used for amplifier design.
e triode region, a MOSFET can be used as a tunable resistor.
(2
) I
1
Page 2
@n
the weak inversion region, a
MOSFET
follows
an
exponential transfer function.
0)A.
MOSFET transistor has infinite large input impedance at DC.
4.
(5
points) For a
NMOS
transistor operating in the saturation (forward active) region, what
of
the
following conditions are valid:
@)Vgs>Vt
0:.¥ga>Vt
Q)}V
ds
> V gs-
Vt
~~:~:~~s
Vt
Ans:
I'~f~
5.
(5 points) The following bias condition is required to keep
an
npn
BIT
transistor out
of
saturation,
assuming Vbe
(0~.8V
and
0.3V forward bias for base collector
j~~irs
alfowed.
(1)
Vbe >
OmV;
t:!..,Vfb > -300mV; (3)
Vbc>
OmV; (4) Vbc >
80OmV~/ce
> 500mV
Ans:
:
....
6.~5
ints) What is/are true for digital modulations?
1)
SK
has a constant envelope waveform and thus
can
work with a nonlinear power amplifier.
has less abrupt phase
jump
than
OQPSK.
~SK
has narrower spectrum bandwidth than QPSK.
,,(¢))OQPSK avoids simultaneous transitions
of
I
and
Q channels by delaying one
of
the channels
by
~degree.
~
FM
and
PM
have better noise immunity than AM.
Ans:
--~~+-----------------
Part
B: 70
points
7.
(10 points)
The
voltage measured
on
a 50
Ohm
load is expressed as a sinusoidal waveform
Va
=
(O.632V).
sin
20001Zt.
Write the expression
and
calculate the following parameters:
(1)
Peak-to-peak voltage
Vpp=
.2
Vp:=.
.1.
(0.
6~z
)~
[V].
(2)Root-mean-sqUarevoltageVrms=_~Vy(2:;
O.
b~~].
(3) Power
in
Watt
P-
[W],
V;'"
't"
0,
,,~~
t!f~oo
'3
if)
(4)
Power in
dBm
P-
(v
1,
(~
·
w~t;j
)
o--~3b
[dBmJ.
(5) Frequency in
kHz
t'o
~
=-
~O!o;:
/ODoff~@)
2
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