Silicon, Circuits, and the Digital Revolution

SCEN103 Final Exam             NAME:______________________

May 23, 2000

For full credit, work must be shown, including formulas used and algebraic and numerical steps. Answers must include units.

1. (1 pt.)
Here is a tip from one of the student project pages this term:

If cleaned with CD cleaner cloth, always wipe radially, NEVER wipe circularly around disk.

From your understanding of CD tracking and alignment and the "scratch resistance" demonstration in class, explain why this statement may have merit.

2. (2 pts.) Contact!
Preface: IBM developed EBCDIC (Extended Binary Coded Decimal Interchange Code), an eight-bit scheme, for its larger operating systems in the mid 1960's. It is used for text files in IBM's OS/390 operating system, still in use by many corporations for their legacy applications and databases. UNIX-based computers instead use the industry standard code for text, ASCII.
Question: The following sequence of bits is arriving from somewhere just beyond a neighboring star.
1100 1001 1100 0010 1101 0100 0110 0000 1001 0101 1001 0110 1010 0011 0101 1010

The radio astronomer realizes that the sequence doesn't make sense in ASCII, so decides to try to decode it using EBCDIC. What does the message say?

Recode the message using ASCII for retransmission in binary.
----  ---- ----  ---- ----  ---- ----  ---- ----  ---- ----  ---- ----  ---- ----  ----

3. (3 pts.) An eXtraORdinary CMOS circuit

Fill in the following table to determine the logical function of this two-input gate. (Note that 'NOT'ted inputs have been provided and that interconnections of the inputs to a common point have been eliminated to keep the circuit schematic as simple as possible.)

A
B
1
2
3
4
5
6
7
8
output
    on/off on/off on/off on/off on/off on/off on/off on/off  
0
0
                 
0
1
                 
1
0
                 
1
1
                 

How many additional transistors would it take to create the two 'NOT'ted inputs?

4. (2 pts.) Illuminate me!
A refrigerator (600 W) and a toaster oven (1400 W) are successfully operating from a standard kitchen circuit protected for 20 A. How much power remains available for lighting?

5. (2 pts.) Group term projects
Answer one of the following questions.

  1. What is gene therapy and how is it used to fight diseases
  2. Modem stands for modulator-demodulator. What is being modulated in a modem and how does it represent a digital signal?
  3. What do the letters stand for in MP3? Why does the MP3 format take up less space than the CD format?
  4. What does DTMF stand for and how is it used to encode keystrokes on a touch-tone phone?
  5. How is information storage and retrieval different on a CD-RW from a conventional CD ROM?
  6. Which U.S. space program first made extensive use of on-board digital computing? What were the objectives of this program?
  7. What are the advantages of HDTV over traditional TV?
  8. How many keys are used in asymmetric encryption? How do they work?

6. (2 pts.)
Explain how donor doping make silicon a better conductor using simple concepts of electronic band structure. Include an appropriate sketch.

7. (4 pts.)
Answer the following questions about the following circuit.

  1. Which resistor has the largest voltage across it?
  2. Which resistor has the largest current through it?
  3. What is the current through the battery?
  4. How much power does the battery deliver?

8. (4 pts.) Gates Galore
In class we investigated the 2-input XOR gate by constructing the truth table for the following combination of OR, NAND, and AND gates.

Construct the truth table for the 3-input XOR gate by considering the following combination of two 2-input XOR gates

A
B
C
1
2
D
0
0
0
     
0
0
1
     
0
1
0
     
0
1
1
     
1
0
0
     
1
0
1
     
1
1
0
     
1
1
1
     
 

Finally, prove that the following combination of gates is equivalent to a 3-input XOR gate by completion of the truth table below and comparison with the above table.

A
B
C
3
4
5
6
7
8
D
0
0
0
             
0
0
1
             
0
1
0
             
0
1
1
             
1
0
0
             
1
0
1
             
1
1
0
             
1
1
1
             


SCEN103 Comments, suggestions, or requests to ghw@udel.edu.
"http://www.physics.udel.edu/~watson/scen103/colloq2000/exams/final-00s.html"
Last updated May 24, 2000.
© George Watson, Univ. of Delaware, 2000.