EECS 140, Fall 91
Quiz 2
D. O. Paderson
H. Chang
OPEN BOOK: Present the essence of your solution for each problem on the front of a page. The back sides
of the pages may be used for computations but will not be evaluated. Do not use blue books.
Problem #1
1. A two-stage amplifier is shown in Figure Q2.1. Values of the BJT parameters for the two devices are given
in the figure.
a. For VA = oo and Re = 0, estimate the frequency response of the overall voltage gain, Av = vo/vs.
b. How is the frequency response changed if VA = 100V?
(Use approximations to arrive at a conclusion.)
c. How does the product of the low-frequency gain and the -3dB bandwidth change as Re is increased from
zero to 10ohms?
note: this problem refers to Figure Q2.1 which is a circuit diagram
Problem #2
2. A feedback amplifier is shown in Figure Q2.2. Bias levels and circuitry are assumed present to produce the
specified collector currents, Ic = 1mA.
a. Establish whether the overall feedback is positive or negative.
b. With respect to the output node vo1, what is the value of the open-loop gain, aL?
c. What is the value of the open-loop gain aL with respect to the output node vo2?
d. Estimate the value of the output resistance seen from vo1 and from vo2.
note: this problem refers to Figure Q2.2 which is a circuit diagram
Problem #3
3. A feedback amplifier is modeled as in Figure Q2.3.
a. Sketch the locii of the natural frequencies of the closed-loop amplifier as the amplifier gain value, avo, is
increased from zero.
b. For Rf = 100k, what value of avo is required to achieve a maximally flat magnitude response for the
closed-loop gain, Av(s)?
c. If the value of avo is fixed at -100, and if aLo is varied by changing Rf, what value of Rf is needed to
achieve the MFM response?
note: this problem refers to Figure Q2.3 which is a circuit diagram
EECS 140, Quiz 2, Fall 91 (delete this example: CS 150, Midterm #2, Fall 1994)
EECS 140, Fall 91 Quiz 2 D. O. Paderson H. Chang(e.g., Professor J. Wawrzynek) 1
