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Unformatted text preview: Prof. Sam Palermo ECEN 325 Exam #2 November 5, 2009 Texas A&M University
Department of Electrical and Computer Engineering ECEN 325 — Electronics
Fall 2009 Exam #2 Instructor: Sam Palermo  Please write your name in the space provided below 0 Please verify that there are 4 pages in your exam 0 You may use w double—sided page of notes and equations for the exam
0 Good Luck! Prof. Sam Palermo ECEN 325 Exam #2 November 5, 2009 Problem 1 (30 points) For all the circuits below, use the constantvoltagedrop diode model (VD=0.7V), Vth=25.9mV, and
n=l. a) Find VOUT and ID (10 points) I ,D e’ ,3 ,QiVé/«ga b {4364) '0 10K
am ——> VOW : 10V( [00% —=‘ 6.€7l/,
OUT 174/0? (ansfﬁoﬁ‘ i
10V 10kQ ,
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ova
3k '1 vow +o.‘7v ~Iov um —:ov + Lm s 0
5K VowT gK + gk IO!
U JT 5 7?.“
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'  f0 5 (UV (7'724 r0.7b’) “MW 53/94 ID= BIA/MA The following circuit has a smallsignal AC signal, VLAC, in series with a DC voltage. b) Find the DC output voltage, VO‘DC, DC diode current ID, and smallsignal diode rd (10 points) 0) Find the smallsignal AC transfer function vo‘Ac(s)/vlgAC(s) (10 points)
1 kn V0,tot=V0.DC+Vo.AC [5 Wave/sa— la/a 56‘!) Va 5 /O[// 19”]: WNW 01346, MuS'r A¢ Foi’wa/d 322564 [K VMU+ VM— ’7V:O Sven—r: [K lk $35M “0.7V 0 [K ._———— : Sig/l ID: rd=ﬁ57ﬂ
0,50! I I ‘l’ 5553! 115;;
2 Prof. Sam Palermo ECEN 325 Exam #2 November 5, 2009 Problem 2 (35 points)
Assume for problem 2 that the transistor B=150, VBE=0.7V, and Vth=25.9mV. a) Calculate the DC values for Vc, VB, VB, 1C, 13, and IE. Compute the AC small signal parameters gm, r“, re. (18 points) IOU
10v 5v LS“ 133., we. Ic= mm lDOK 4'15
113: l22 A _RL ska LS“ /
7 IE: EV  0.7 V V' TE 1 “W5? = lttthvc= 7021/ 2 2.3% +— KO“
VB: 5,6?1/ ”“ 1if: , 2:0
1.4kﬂ Lg: — A I : IE a... V =
v4: love 1.5kZ/HQMA) t ’7’ /“ J C ’9 E 2,?‘((/ 5 7,03\/ _ Tc, 2 M% / Aegm/l gm: Vr: = /,?M(/,gz)=2.°mv M rn= (ﬁe/(A
Va= VFHDW‘ ZMV re= 130/2 ' /‘ z 3193. s L
e j: )3, 0
b) Sketch the small—signal model of the circuit. Assume that the capacitors act as AC shorts and
that the transistor’s ro is inﬁnite (can be neglected). (11 points) W] id. E5547, am, i c) Calculate the small signal gain AV=VO/Vi, the input resistance Rm, the output resistance Rout.
(6 points) A c  Mia/m ,<76.4’”%>(/swsa
v 05M ,eEl _ 2 + 76,+M%:/0Q/0 AV: _/O"V/V l + ,6; s
X 0 q Rm= léék/L
Rf“? : RB/M/n’ * 0?“) £3]: WON/[£96k # /§/(zoo)j Rm: (’S’k/L Prof. Sam Palermo ECEN 325 Exam #2 November 5, 2009 Problem 3 (35 points)
Assume for problem 3 that the transistor [3:150, VBE=0.7V, and Vlh=25.9rnV.
a) Calculate the DC values for VC, VB, IC, 13, and IE. Compute the AC small signal parameters gmrmre. (8 pointS) 1W ML é Va _ 1C: aﬂigm/l
IB= £1944
15: 0324/14
Vc= 074W
VB: 0,71/
gm: ?§.4M’4/y
In: 4,2k/L
42M; ésvﬁ: re= 2530,11,
: 281022. b) Sketch the smallsignal model of the circuit. Assume that the capacitors act as AC shorts and
that the transistor’s r0 is inﬁnite (can be neglected). (15 points) ‘ marital W C 75 W / c) Using the smallsignal model in (b), derive an expression for the small signal gain Av=v.,/vi in
terms of RF, RC, RL and the transistor small signal parameters (variables only, no numbers).
Then compute Av with the parameters from part (a). (12 points) , 024]? + 70 i <7;
KU/ﬂ a, Q; 4’ 6r“? ’ Rangp Av Expression: : “lsw (Ma/M) “4’8” ’7
: w 354’”% ‘ 7332 i(/d"'///M//‘%) ...
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