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Unformatted text preview: A3 1 30 pts Consider the oscillator shown below and assume that the operational ampliﬁer is
ideal (which means that it has inﬁnite bandwidth). The transfer function H( f),
which is vp/vo, is also shown below. 101 102 103 104 105 106 107 108 109 101010111012 o 1 f
 VG+ 20v‘ _J— _J—w M‘_—_
e 4o
16 Magnitude _60 V. ,, ,,
R1 R2 ((113) 80
i W 9 WW I
100
v,, _ —120r
V0 270
v + 130
P
90
Phase 0
H(f) (Degrees)
~90
180
270
5 pts (21) At what frequency is it possible for this circuit to oscillate? Ignore the block
labeled G on the schematic for this part. (only your answer will be graded)
7f \ a ‘H ) CXA M B
:2 Q : M H
D ‘% 73 to M H & 10 pts (b) What is the minimum value of R2 necessary for oscillations to occur if R1 is
IkQ? Ignore the block labeled G on the schematic for this part. Make it clear what
you are doing or you will not receive full credit. (more room is available on the
next page if you need it) [win]: 7‘; a Ammo $9 44114} 4445" imp Sada will
be 1. A = H gem => tagaer W» Q‘LMM 7’ £><AMI3 Mawl— _—.5 {2 .29?er lac: A4 5 pts (0) What will the frequency of oscillation be if the op amp contributes 90° of
phase to the loop? Ignore the blockvlabeled G on the schematic for this part. (only your answer will be graded) éxA M \3 A a 100 KHz» \MHg 10 pts (d) What will be the peak magnitude of the oscillation at v0 if the block labeled G
in the schematic has the transfer characteristic shown below? Use the value you found for R2 in part (b). Make it clear what you are doing or you will not receive fullcredit.
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(Heal : gvgb \/ 15 pts A5 30 pts / Consider the g RC negative feedback RS CW Rm H—KQZ ampliﬁer shown. W Q‘ Almost everyonevs ’— used a circuit :5 $223 :: CE similar to this on T T R com the project and it W o V0
was the circuit Rx shown in the R” g RL solution. ? T (3) Draw the smallsignal midband AC equivalent circuit using the appropriate unilateral twoport model for the feedback network (circle the feedback network
on the schematic above). Use R; = RS + Rm and R2 = RL + Ram in your circuit and call v; the voltage across R2. Consider v; to be the output variable that is fed back. Give equations for the elements in the two—port model of the feedback network in terms of the components shown on the schematic (you do not need to
derive the equations). A6 15 pts (b) Assume that solving for the DC bias point of this circuit reveals: V31 = 1.7 V,
V52 = 1.8 V and V32 = 2.5 V, with Rf: 2 k9, R152 = 200 Q, Rout = 50 Q and
RL = 50 Q. Derive a value for vomin. Make, state and check the validity of any
reasonable assumptions you make (I do not expect an exact answer). I do want a
number, but you must show your equations. Make it clear what you are doing or you will not receive full credit. 7\=\ Wm“ M beamed. be a. Morale?) or QL wing 51:9
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QEZ "F Lgv av REL+EOG++ EL)( 3 pts 3 pts 3 pts 3 pts 3 pts 5 pts A7 20 pts Consider a negative feedback ampliﬁer with a forward ampliﬁer described by , 106
auw)‘ 1+2 1+ 2 1+2
110 1104 1106 and a feedback network described by b (jw) = 0.1 . (a) Draw the Bode magnitude and phase plots for a(ja)) on the axes on the following page. Also draw the magnitude of 1/ b ( jw) on the same plot. (b) What is (0180 ? Give the value here and show it on your plot. ; I EXAMS;
'0 M504 103 {WI/<2, (c) What is mu ? Give the value here and show it on your plot. 13‘ axﬁm Fri F:
to “ML/<3 52x16” rad/s (d) What is the gain margin, GM? Give the value here and show it on your plot. 0 aa a” ‘3’ “2.048 (e) What is the phase margin, PM? Give the value here and show it on your plot. 9 O EJAM. B 2,2_.9'° (f) If you added a new dominate pole to this ampliﬁer, what would you need to set the pole frequency to in order to achieve a 45° PM? Give the value here and show
how you obtained it on your plot. Degrees 0 45 ~90 l35 180 225 270 103 .‘ﬁiifku&bck4“ ‘ t 102 101 100 11 102 103 104 105 06 107 108 co ‘L 20 0 ,
103 102 101 100 101 102 103 > 1.4 105 106 107 108
O W W— 45
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Degrees 18O —225 ] 270 v —— —v —~ 2‘ A9 4 15 pts Consider the R—2R ladder shown below. You may use the space provided to work
out your answers to this problem, but you do NOT NEED TO SHQW YQUR WORK because only your ﬁnal answers will graded. Be sure to put your ﬁnal
answers in the boxes provided! Assume that VB 2 16 V, R z 8 k9, and 2R=16k£2. r VB :zzu 35¢ 5mm E V3 R V4 21? + iv» W» W» W» w» i
212%»? 2R 5 pts (a) What is V3 (I want a NUMBER)? Put your answer in the box provided to the right.
V3 ' \LL. 1 ‘3; w. Ye.
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Va 1 o. 2,\/
5 pts (b) What is [4(1 want a NUMBER)? Put your answer in the box provided to the
right.
T : “TL—i : A10 5 pts (c) Brieﬂy explain what the main advantage of an R—ZR ladder is when compared
to using a binaryweighted array of resistors. VOA.“ Ck [0;an ’m€;6LCK‘Ccl. awma 1 ‘HAC [$665+
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5P?“ (A, VQMJCE“: aw 53¢? a. F" d All 5 15 pts Consider the successive approximation analogto—digital converter shown below
and assume that a standard binary search is used. The table below the ﬁgure shows the operation of the converter one clock cycle at a time as it performs a
conversion on an input voltage VI = 2.5 V, with VFS = 8 V for the threebit DAC. You are to ﬁll in the six missing values in the table (VCOMP is either High or Low). You may use the space provided to work out your answers to this problem, but
you do NOT NEED .TO SHOW YOUR WORK because only your ﬁnal answers
will graded. Put your ﬁnal answers IN THE TABLE PROVIDED. Successive
Approximation
Register OUT A12 10 pts Consider the ampliﬁer circuit shown below and assume that VCC = 5 V. Find the values of all of the resistors so that the following bias point is achieved: Only your ﬁnal answers will be graded and you may safely ignore base currents.
PUT YOUR ANSWERS IN THE BOXES PROVIDED. VCC 1" Ear—é,ka ngéAKJL $9558ng ...
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 Spring '08
 Spencer

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