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Georgia Institute of Technology School of Electrical and Computer Engineering
Midterm-1 Exam
ECE-6414 Spring 2015
Monday, Feb. 23, 2015 Duration: 50min
First name ______________________ Last name____________________________
ID number _______________________________________
This is a close-book, close-note exam. However, you can bring up to two sheets of equations
with you. For this exam no computer access is permitted.
Show your work and reasoning for partial credits. Remember to write you name on each page.
Please consider the following honor pledge. “I have neither given nor received any
unauthorized assistance on this exam.”
Signature ________________________________________
Assume κ = 1, BJT: VEB = nUTLn(IC/IS), where UT = Thermal voltage, IS = saturation current
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First name ______________________ Last name_____________________________
The circuit on the left (L) shows a common source output stage with error amplifiers, while the
one on the right (R) shows a class-AB common drain output stage.
Assumptions: The error amplifiers’ input impedance is infinite but their gain is finite = A.
VthN = |VthP| = Vth, kp(W/L)1 = kn(W/L)2 = k(W/L)
(a) What are three advantages of (L) over (R)? [5]
(b) What are three advantages of (R) over (L)? [5]
(c) How does the left circuit (L) work (briefly)? [5]
(d) What type of feedback is used in (L)? What type of amplifier is it? [5]
(e) Find the open-loop parameters: AOL, β, Ri, and Ro for (L). [20]
(f) Find the closed-loop parameters: ACL, Rin, and Rout for (L). [20]
(g) Draw the small signal model for the left circuit (L). [10]
(h) Using the small signal model in (g) verify the calculations in part (f). [10]
(i) What is the output swing of this circuit? [5]
(j) What topologies do you choose for the upper and lower error amplifiers in (L) to have rail
to rail input voltage range? [5]
(k) In a large signal analysis, find the difference between Vi and Vo in (L) if the offset
voltages are zero (VOSP = VOSN = 0V).
(l) In a large signal analysis, find the difference between Vi and Vo in (L) if the offset
voltages are not zero but A >> 1 (optional).
(L) (R)