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Unformatted text preview: A3 1 20 pts Consider the small—signal highfrequency AC equivalent circuit for an ampliﬁer i
shown below. Find an approximate equation for cocH using either open— or short
circuit time constants, Whichever is appropriate. Do NOT use the Miller
approximation. Explain how you arrive at your answer or you will not receive full
credit. More room is available on the next page. l
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5043 Hm; Lll‘ﬁul‘l’ as shown . A4 Additional space for problem 1. ﬁnal 22;): 03:. +141: $915+ $5~>uﬁ2a 4+M$¢srm 4.0 gmL +446, dramk shown a Q h V”
K as _' ,——~ A5 2 10 points Consider the cascode ampliﬁer shown below. VCC
5 pts (a) Draw the smallsignal low R E g R
frequency AC equivalent 1 C Cour
circuit. Ignore rb and r0 in both CB *—i V transistors and label all model A ﬁi HQZ RL elements (you do not need to — provide equations for them). R2 g 1—
Use the hybrid7t model for Q1 and the Tmodel for Q2. W\/  E . [:Q1 5 pts A6 (b) Draw the smallsignal highfrequency AC equivalent circuit. Ignore 7’01 a r02 and rbz and label all model elements (you do not need to provide equations for
them). Use the hybrid7: model for Q1 and the Tmodel for Q2. A7 3 25 points Consider the ampliﬁer shown below. We want to design this circuit to achieve a
maximum symmetric swing of 2 volts at the output. Assume that VCC = 10 V. VCC V0 5 pts (a) Assuming (just for this part of the problem) that ﬂ; is inﬁnite, what is the
maximum DC bias voltage we can use at the collector of Q1? Explain how you arrive at your answer or you will not receive full credit. r I' l  \ {32"‘0; =§ (8)2" WC?) $0 PP Qt (ya—PS 0Q?)
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{2957 70c $44.37? 39 2V (U5; ) pol/dc, A8 5 pts (b) Assuming (just for this part of the problem) that V51 = 2 V and VCESAT = 0.2 V,
What is the minimum DC bias voltage we can use at the collector of Q1? Explain how you arrive at your answer or you will not receive full credit. A m, U mg» lac, ma, +3 Mm. Clam 107
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4+ 2U, ‘30) Knot/Q 0C4 é; VE‘+\[CE _4 223V A SAT 0‘ Min : Lilav Cl M A9 15 pts (c) Derive an equation for the absolute minimum DC bias current that must be
used in Q2 as a function of RE and RL. Explain how you arrive at your answer or you will not receive full credit.
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Iain/win — 2‘ A10 4 20 points Consider the negative feedback
ampliﬁer block diagram shown at
right. 4 pts (3) Derive the equation for the closed loop gain of this system, A f = §£ , in i terms of a and b. Make what you are doing clear or you will not receive full SD: (153$: a($;~‘3,c): alsrbgé) $D<Hal7> :Gkgc‘ credit. ‘ “so I a
A?“ $5 Maia §g>
V 4 pts (b) Derive an equation for the error signal, Se, in terms of a and b. Make what you
are doing clear or you will not receive full credit. San SLV$¢ 1 gé’bgo Z "alﬁga ( A11 12 pts (c) Assume that the forward ampliﬁer v0
has the largesignal static transfer
characteristic shown at right and that b = 0.2. Draw the resulting closed—loop
largesignal static transfer characteristic
on the axes below. Label all slopes and
breakpoints. Explain how you
determine the slopes and breakpoints
for your plot or you will not receive full credit. ...
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 Spring '08
 Spencer
 pts, Grid bias, Biasing, ac Equivalent Circuit

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