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Unformatted text preview: EEC110B Final Examination 6/14/05 120 points total
This examination is closed book and closed note The ﬁnal page of this examination is a formula sheet that you may tear
off and use during the examination Show all your work on these pages! Excerpts from the UC Davis Code of Academic Conduct:
1. Each student should act with personal honesty at all times. 2. Each student should act with fairness to others in the class. This means, for
example, that when taking an examination, students should not seek an unfair
advantage over classmates through cheating or other dishonest behavior. 3. Students should take group as well as individual responsibility for honorable
behavior. I understand the honor code and agree to be bound by it. Signature NAME (print) M“ This is EXAM A A3 1 20 pts Consider the relaxation oscillator shown below and assume that the operational amplifier is ideal except that it has output swing limits of L+ and L . ,L+ >t Vt?
C :: R3
10 pts (a) Draw one full cycle of the oscillation on the axes provided above and label all peak voltages. Begin with v0 = L+ and vC equal its minimum value at
t: 0. Label the peak values of vC as bL+ and bf and provide an equation
for b. b:— /U.FP ‘ 23
120 QJES 10 pts ,EMM;V\‘\V\3 ‘H/Lc CtPCQ/J? £43 £5? ’Ucté) % 14044.46 A4 (b) Derive an equation for the frequency of oscillation of this circuit in terms
of U, L: and the component values of the resistors and the capacitor. You
may find it useful to recall that the step response of an RC low pass filter is
given by v(t) = VI + (VF “V1 )(1 — e‘t/RC) where VI and VF are the initial and final voltages respectively. Make it clear what you are doing or you will not receive full credit. 3 \\ ‘H/Mc‘r 444e, droolt I": 51MM¢~LPF¢ ’, 7—
UCCT/L> 7‘ bL— + <EbE>(l ‘— a 429) ll
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r; A5 2 25 pts Consider the negative feedback amplifier shown below. This is the circuit almost everyone ended up using for the project. Vcc
R1 RC1 RC2
Q3
Q2
Rs CIN
Q1
v REZ CEZ
s
1) I
/
_ R2 1A —_—— _ 1% R3 COUT
_ v0 10 pts (3) Circle the feedback network on the schematic, draw the appropriate
midband AC unilateral two—port network for it below and provide equations
for all three elements in the twoport model in terms of the components on the
original schematic. Make it clear how you arrive at your equations or you may not receive ﬁill credit. , _ 'U
Q50 (1,6 \ 56— “1i 1 QEAH RF
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.bL ‘ — A6 4 pts (b) Brieﬂy explain what would happen to the operation of the circuit if we
removed RC2, Q2, REZ and C E2 , and tied the base of Q3 directly to the collector of Q1 . The global F$ Loeolcl 44464 be, Posl4‘70¢)_ 1:“ WAGE“ 090+ “4629"” bacccaSc all +146 (Desihue FB)’ “HMO, open/lab? MB 3% AC 85‘.‘,\ woulcl log, lamp 3
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% (I n I, n I, /( Bu) opulcl \OC, \Ax‘ahe/P_ 2 pts (c) Which specification primarily determined the minimum value of I E3 ?
(circle the correct answer): Gain +swing @BW Rout Rm 2 pts (d) Which specification primarily determined the value of R3? (circle the
correct answer): Gain +swing —swing BW Rm 2 pts (e) Which specification primarily determined the maximum value of 1R1?
(circle the correct answer): Gain +swing —swing BW Rm 5 pts (f) Assuming that VE3 is known, and that R3 = RL, derive an equation for the absolute minimum value of I E3 necessary to set v = ~O.5V . Your answer 0min
should be in terms of VE3 and RL . Make it clear how you arrive at your answer or you will not receive full credit. T0 ‘PMA 4445.. Mlnlﬂ/ld/Vl 1:53 ) 129qu Mosl lae, waged b Q QU’Hi‘ 6H}.
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’ 1+ 2 1+1: [1+ £
110. 1103 1105 and a feedback network described by b ( jw) = 0.1 . (3) Draw the Bode magnitude and phase plots for a( jw) 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. (Clams Aif— ' ‘OL’ (wt/5c; o l ’3
B a, D 1 I 0 PM /$c:C_
(c) What is can ? Give the value here and show it on your plot. Exams A476, 2 ~32qu McQ/S
EDéD', m3.2_xn>g“ai/g (d) What is the gain margin, GM? Give the value here and show it on your pIOt' All, (exam—is 2 ”’20 018 (e) What is the phase margin, PM? Give the value here"and show it on your plot.
All awn/us: ”24250 (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. . A9 4 20 pts Consider the DAC constructed with a binary~weighted array of resistors shown below. franc 2 pts (a) How many resistors would be required to implement a 12bit DAC using the architecture shown above (include the feedback resistor in your count)? I 3 2 pts (b) What would the ratio of the largest resistor to the smallest resistor be in
this 12bit DAC? (consider the feedback resistor too) Q __ n
2/2”  Z 6 pts (c) Brieﬂy explain what the main disadvantage of this architecture is and what architecture you would use to overcome this disadvantage. 1116/ (2416 a“: pW/anﬂ'ﬂ f5 U07 [)4fo 4/ a vaq guy/Q, armrm PW KN /€£«¢>Q “tit: We,“ ”(1.4.x ca, [453,5
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#5 VP will C/l/tctméf’, A10 10 pts ((1) Derive an equation for ARO, where ARO is the error in the value of R0 that
would yield a one—LSB error in v0 for the 12—bit DAC. You may find it useful to remember that 1 .~, 1— A for A <<1 . 1+A
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:0 AR : EO All 5 15 pts Consider the amplifier shown below. 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. Be sure to put your final answers in the boxes provided! Assume that VCC = 10 V, V52 =6 V,
R1275 k9, R2 =2.5 k9, RE2 = 100 9. and RL =50 9.. v0 5 pts (3) Find the lower swing limit of this amplifier, vOmin , assuming that it is set by Q2 cutting off (I want a NUMBER). Put your answer in the box provided
3 Z n ANS to the right. 5 pts 5 pts A12 (b) Find the lower swing limit of this amplifier, v0 min, assuming that it is set by Q1 saturating and that Q1 has infinite beta and V = 0.2 V (I want a CEsat NUMBER). Put your answer in the box provided to the right. (c) Find the upper swing limit of this amplifier, Vain“, assuming that Q2 has infinite beta (I want a NUMBER). Put your answer in the box provided to the right.
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(Aha/l a1 C’LJJFS 63$; 4‘ :0 79 032': vac, V51? UBpoJ since, =00) \/ = fi. A13 10 pts 1’3 ‘79me
Brieﬂy explain the main advantage(s) and disadvantage(s) of using‘élegative feedback in a multi—stage amplifier. GleloaJ haéccpoc, FE McLKe$ ‘H/u: OVCFQH ql‘n
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D A14 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:
1C2 =10 mA, 1C1: 1mA, 1R1: 100 “A, VBl : 2 V, and VBZ : 3 V. Only your final answers will be graded and you may safely ignore base currents.
PUT YOUR ANSWERS IN THE BOXES PROVIDED. 8014A. 2014!). ,Vkﬂu 1’ 501m 301m 314a 23hr LIBOJk ...
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 Spring '08
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