exam2_fall2009

exam2_fall2009 - Prof. Sam Palermo ECEN 325 Exam #2...

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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 constant-voltage-drop 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 , 7; Drole "11451" 19¢: 54—044 K215“: ova 3k '1 vow +o.‘7v ~Iov um —:ov + Lm s 0 5K VowT gK + gk IO! U JT 5 7?.“ W a ° 772V ' - f0 5 (UV -(7'724 r0.7b’) “MW 53/94 ID= BIA/MA The following circuit has a small-signal AC signal, VLAC, in series with a DC voltage. b) Find the DC output voltage, VO‘DC, DC diode current ID, and small-signal diode rd (10 points) 0) Find the small-signal 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 small-signal 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 small-signal 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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exam2_fall2009 - Prof. Sam Palermo ECEN 325 Exam #2...

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