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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)

Midterm-1 Solution (ECE-6414)Thursday, February 19, 2015 9:10 PM

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