PHYS345 Second Midterm Exam, December 2, 1999

1.
1. Implement this truth table using the fewest number of gates.
5 dual-inputs from boxing ones followed by DeMorgans: (B+A)'+(D+C)'+(A+C)'
4 dual-inputs by considering distributive property: {(B+A)'+[C+(D.A)]'}'
There are numerous other expressions which work too...

2. Construct a truth table proof to demonstrate that A'.B + A.B' = A XOR B
The proof is in the pudding.

3. What is the current through the input resistor?     0.2 mA toward the virtual ground

What is the current into the inverting terminal?     zero!

What is the current through the feedback resistor?     0.2 mA away from the virtual ground

What is the current through the load resistor?     2 mA toward the op amp output

What is the current through the output of the amplifier? Source (out) or sink (in)?     The output is sinking 2.2 mA

2.

Complete the circuit diagram so that it works as desired; that is, set up the D input of flip-flop 0.     D0 = Q'0

3.

Complete the state diagram to show the behavior of this 2-bit counter for E disabled.
repetitive cycling through the sequence 00, 10, 01 with 11 excluded and not entering

Complete the state diagram to show the behavior of this 2-bit counter for E enabled.
repetitive cycling through the sequence 11, 01, 10 with 00 excluded and not entering

4. (20 points)

1. What voltage gain (in dB) is needed?     34 dB

2. What attenuation (in dB) was added?     -6 dB

5. (20 points)

1. Design a differentiator circuit that will have a gain of 25 dB for a 100 mV signal at 200 Hz.     1.0mF input capacitor and 14.1k feedback resistor

2. What is the input impedance seen by the signal for your circuit?     -j 790 ohm

3. What is the improvement in the signal-to-noise ratio?     10.5 dB

"http://www.physics.udel.edu/~watson/phys345/exams/mid2-99f-ans.html"
Last updated December 8, 1999.
Copyright George Watson, Univ. of Delaware, 1999.