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Unformatted text preview: PHYS3360/AEP3630 Electronic Circuits FINAL EXAM
2:00 — 4:30PM, May 17, 2011 Name : Signature:
Lab Section # and TA: Total number of pages: 11 Score: Part Possible Score
I oints Read this ﬁrst! 0 This examination is closed books and closed notes. Show all work and explain your
results. I Unless stated otherwise, try to give a numerical answer to all questions in addition to an
analytical expression. You may use a simple calculator. All other electronic devices are
prohibited. Use the provided space after each question for your answers. If you need more
room for a problem, write "over" and continue on the back. Cross out anything that should
not be considered part of your answer. 0 Make sure you have all 11 pages. 0 By signing this exam you certify that you adhere to the Cornell academic integrity code. 0 Good luck! Page 1 of I] Part I: Multipleanswer questions 14 (20 points — 5 points each) Please sappiy your answer in the boxed area. No partiai credit is awarded. 1. A sinusoidal signal is being sampled with frequencyﬁ and
the sampled waveform has an apparent frequency of 0.1 jg.
What is (are) the possible frequency (frequencies) of the original signal? Choose all that apply.
(A) 11.}? (B) 2.2 )2 (C) 3.3;; (D) 991} (E) None of the above. Which of the following are effective in eliminating electric
noise due to low frequency (60Hz) magnetic interference?
Choose all that apply. (A) Thin aluminum enclosure of the circuit. (B) Using twisted pair. (C) Using low resistance wires. (D) Using optoisolators to break large area loops. (E) Running wires close to grounded conducting plates. on inputs X and Y: Z = X 69 Y? Choose all that apply. . Which of the following performs an equivalent to XOR operation Page 2 of l l 4. Which of the following is true about the transistor connected as shown
below? Assume that the baseemitter voltage drop is 0.6V and B = 100,
+12V +12V E
0 (A) The transistor is in cut01°F. (B) The transistor is in active mode.
(C) The transistor is in saturation. 61st aUHVL
V5 :: LIV (Volt . 3 «sme . (Law  = 1.5m Page 3 of l l Part II: MOSFET ampliﬁer (20 points) You do need to Show your work. The following circuit uses two identical nchannel enhancement mode MOSFETS, e.g. K] = K2 = K
= SOmMV2 and threshold voltage VII = V12 = Vy = 2V. Power supply voltage Vdd = +12V. (Recall
that the drainsource current in a MOSFET is given by K[2(V(_}5 — VﬁVDs — V052] for ohmic and
K(Vc,5 — V02 for saturation regimes respectively). Va 0, Vh—I 01 (a) Find Qpoint values for drainsource current for each of the transistors, IDSI and 11332, and the
output voltage Vmu when the input voltage Vin = 5V. In which of the three possible regimes
(cutoff, ohmic or saturation) are each of the two MOSFETS Q1 and Q2? 2:; VGS< V1 , =7 muff ‘
elsz «3+ V‘Ds < Veg r VT , 3) Ol‘MC
ollwruﬂc ‘=) mek Q’l 3 VGM = VM, V1591 : Von}:
(27,. Vets); Valet—Void: , V‘bsz L‘Vers,_.
Nata: Vbcz7VGs5V‘r Wags ASSW at“; both MoSFﬁTS m M Ma duck ' VGS«.VG$2>VT 3 EVHA Q13. Sad”. = (c) Find the values min(Vin) and max(Vm) that a signal supplied to Vin should stay within to
produce undistorted output at Vow. Which of the two transistors is responsible for maria/m)? "DISMth ocowr i} allay Q. or 01 an M ahﬂ 0F ome (M.
521. 51L VM<VT ‘9 wink al Voukr—VAAVN‘CVMVT'M Vm > VA“ V" , =7 okmtc
Z 627,. VGSZLVM< VT 12.7 01.65%
MAG}; Cow mark M Wit ‘fl/ws) I Mm (Vhai=\/T:2V i and
W = W :1“. e Q1‘CSPMSIL‘Q
l 7. s Page 5 of l l Part 111: ND Converter (20 points) You do need to Show your work.
A successiveapproximation ADC has an input range of 010 V and a conversion time of 1 its. (a) How many hits must the converter have in order to be able to resolve changes in the value of
a DC input of 0.05 V? (b) What must the clock frequency of the converter assuming that one bit can be set per each
clock tick? Tow = nAJcak , or M55. :1 2mg]
Aidk (c) Suppose that the input is a sine wave that swings between 0 and 10 V. At what frequency
will the “effective bits” of the converter drop to 4? In other words, at what frequency will
the change in the input during the conversion be equivalent to the resolution obtained with a
4bit converter? 15m : YE can Matt)
2
:32): 'A‘E=fo7r3cbt may d’i’ Max msl Page 6 of l l (d) Next, you decide to use this AD converter as a DC voltmeter, which averages many
samples of the input voltage vm in order to reduce the uncertainty in the measured value due
to noise. If the input signal consists of a 2.05V DC voltage and a 0.5V rms noise voltage, roughly how many samples must be averaged to reduce the uncertainty in the DC value of
vin to ~50mV? To (than Vail/WU)le milk by KID would (atrium [Chem Page 7 of l l Part IV: Warble Alarm (Lab Manual Problem 10.4) (20 points) You do need :0 Show your work. The circuit shown below produces a sirenlike noise. The 555 on the left oscillates at a low frequency and controls the frequency of the 555 on the right. The 555 on the right oscillates at two
different audio frequencies and drives the speaker through the coupling capacitor Cour. Rm = RA; = 10 k9, RB. = 1M0, R32 = 3.9 141,1112 = 4? kQ,C1= 0,47 uF, C2 = 0.1 hr, and Com =10 pF. VCCS'U'QV VCC o RST
555 T TRIG THHS
I GND OUT I Vourm fan. 'Eb COD?
SPEAKER @ % (a) Derive the formula for oscillation period with the 555 in the astable conﬁguration and
calculate the frequency of the 555 on the left, f] (in Hz). For the basic internal structure of
the 555 timer refer to the schematic below. Page 8 of l l t
“W “’4: %‘“=Vcc+(‘’‘é~vcc)eiafw
(OUT:HI) '
‘9 ‘lCH'’ 642mmth C.
L
TDISC 0N Jivcc'; O‘l (23W; '0) 6 lecl
(om—ac) (b) When vouvll is low (0V) calculate the frequency of the 555 on the right, fza (in Hz). (Hint:
Mr. Thevenin might have something interesting to contribute to the solution). Mum ; Rm: as; + Rn. "KAI =~ l2.1kSZ V V 9‘” \l 9‘“ Jim.
TH CL mum: W“ KitIRAQ V 'DlSC on; C2 outcanch ham 23,; “lo WM
Ytﬂwﬂuﬁs 0,; Vowr1 , 1.2. {L :L 251(1 ZDISC 0H3: C1 claung 4* VTk‘H’W RTkﬁz.
VVCQ
‘tHT—Rn‘czehO/‘m 2, “W” (C) When vmm is high (9V) calculate the frequency of the 555 on the right, ﬂu, (in Hz). “* M mm MA M 2“: G06“;
25= 933 Hz Problem V. Waveform Generator (20 points) You do need to Show your work. (a) Sketch the output voltage Your of the circuit below along with the CLK signal as a function of
time for at least one complete period before the pattern starts to repeat itself. Assume an ideal
opamp, and OISV logic levels. S ccif each vOUy volta 6 level on the lot. Fl Page H) of l ] (b) What is the period of voul pattern (in ms) if CLK frequency is 10 kHz? _ lé
‘6 SW5 " T' 10000 n; (c) If R = 10 k9, what is the maximum current the flipﬂops need to be spec’ed at to generate a
stable 5V output? _ Sv
Jar use 2 Imx “31' Iwax 2 Page 1] ofl] ...
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