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Unformatted text preview: ECE ECE145C (undergrad) and ECE218c (graduate) MidTerm Exam. Nov 7, 2002 Do not open exam until instructed to.
Open book Use any and all reasonable approximations (5% accuracy is fine. ) , AFTER STATING
THEM. f/ééﬂ/I. Name: Problem 1, xx points You will be working on the, circuit below:
2 K K/ To the left is the device model . Recall that C Che = Champ, + gmrf. Let us take Cje=17 fF,
beta=infinity, chi=2.6 fF, chx=0 fF, Rbb=30
Ohms, Rex=6.67 Ohms, and tau_f=0.44 ps.
The transistor, has 3 um"2 emitter area We are once again analyzing one stage in a
cascade of amplifiers. This always involves
g me'e' bookkeeping headaches, so for clarity the
probem will be exactly defined as below. Flc1 Rc2 RC1 03a 03b 32 The arrows indicate connections between points. To simplify the problem to the point at
which it can be worked on an exam, Qla/b and Q3a/b will use highly simplified models,
wherin the transistor is given infinite beta, zero Rex and Rbb, and zero ch. IQ RC1 RC2 RC1 Part a, xx points
DC bias. 01 R02 RC1 R02 20 ’4 7f
20 :V
ﬂ, 2 07 /ag0_/L
0/7SAﬂ
Kl _ ‘ {cad
/. (A/ Vgen has a DC level chosen so that the base of Q1 is at the same DC voltage as the base
and the collector of Q2 (all are at 750 mV). 20 is 50 Ohms. Isl is 1.5 mA, 152 is 3 mA.
Find Rcl Rc2, and the DC voltages at all nodes within the circuit. Draw all DC node voltages and branch currents directly on the circuit diagram. Rf is 300 Ohms. Part b, xx points
Midband gains Find the differential voltage gain of the circuit, which we will here define a
2  (Vow /V ), where Vout is the AC voltage at the collector of Q3a. Show gen intermediate results indicated. , M S
transconductance of Qla= Z 8 q transimpedance of Q2a= voltage gain of the Qla/Q2a combination: + 7 2’ 5
Z 9 7
27/. {1/ voltage gain of Q3a= overall voltage gain: S *** the Part 0, xx points
device models Please enter the device arameter values below. If you plan to use degenerated models (absorbing Rex) for Q2, please draw the resulting
transistor equivalent circuit and indicate element values below. al J ﬁg! 1 Ce «+ 7/7 r/Fv f4 {01¢ﬂ/4f/ / Oz“ 2‘74f Part (1, xx points
high frequency analysis RC1 RC2 RC1 Please note that the overall circuit simplifies considerably because (I) we can use halfckt
models for differential operation and (2) the simplied model of Q1 results in Cbel being
part of a completely separate network from the remainder of the problem. Using MOTC, find the following: . . . . : S
charging t1me constant assomated w1th Cbela = Z 7’ éﬂ’z" W a 7%/ resulting pole frequency in the transfer function = 275 Hz,
(not rad/sec) ***** first—order time constant associated with CbeZa: 3 r“ (ﬂ X 30 ’ {’4‘ '7 /' 0 7/ 4¢74
firstorder time constant associated with Gobi/2a: Z 8 7'4 V f? f/k " /’ Zz/j <%,Zé J  7' 5
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Part e, xx points Please make a quantitative bode plot of the transfer function (lab 1 both axes, draw pole frequencies in the right places, an slopes correctly)
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/ / 0 /ﬂ0 Va/Ae 4g Q:M *9 “'4 : ,1 (—1" I] ~ a / I . or 441/ Jutlo/ ' 9 WM /é'—/’@ Problem 2, xx points Our transistor model is now much simpler,
with a transistor ft of 300 GHz: 1 Cbe ngbe The circuit has all transistors biased at 1 mA each. Rxx is 52 Ohms. Rc2 has a 300 mV
DC drop across it. 1”: a. z 44‘
Acﬂc/ /,¢¢4 /I¥J 4/ 4‘49 A/h 7//2 ; 3:?::/z
/
ﬂit; W7d¢/hf~/{ If /4Z, 5 2 .1. = /’/.7:/
2,.
7 /  Z 3/,4/giaafc/t
Z 2. 2 ML WA; #0:“ a ll Part a, xx goints
DC bias Draw all DC node voltages and branch currents on the circuit diagram below ...
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This note was uploaded on 08/06/2008 for the course ECE 145 taught by Professor Rodwell during the Fall '07 term at UCSB.
 Fall '07
 RODWELL

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