2. TRUE or FALSE? A semiconductor is a metal that can be manipulated to be either a
good or a bad conductor of electricity.
3. TRUE or FALSE? A circuit is a collection of transistors (and possibly other electronic
devices) wired together to produce a particular behavior.
4. TRUE or FALSE? NMOS and PMOS were two competing companies that manufactured
microchips in the early 1960s.
5. TRUE or FALSE? If there is no electrical current on the input wire to a NOT gate, then
there will be current on its output wire.
6. TRUE or FALSE? The sum of the binary numbers 101
7. TRUE or FALSE? A flip-flop is a circuit that serves to store a single bit.
8. TRUE or FALSE? Jack Kilby and Robert Noyce are credited with independently
inventing the integrated circuit.
9. TRUE or FALSE? The main reason that workers wear protective clothing when
manufacturing integrated circuits is to protect them from exposure to dangerous
10. TRUE or FALSE? Moore’s Law dictates that integrated circuitry must be manufactured
out of silicon, as opposed to other semiconductors such as germanium.
11. Name three different technologies that, over the years, have served as electrical switches
in computers. How were these technologies similar, and how were they different? What
advantages or disadvantages did each provide?
Electromagnetic relays, vacuum tubes, and transistors all served as electrical switches,
controlling the flow of electricity via a control wire. Relays were different from the other
two in that they were physical switches that opened and closed to disconnect and connect
the flow of electricity along a wire. Vacuum tubes and transistors required no moving
parts, but differed in their makeup and performance. Vacuum tubes were large, required
lots of energy, produced lots of heat, and tended to burn out frequently. Transistors,
since they were solid pieces of metal, were smaller, required less energy, and durable.
12. Electricians commonly wear rubber shoes and gloves to protect themselves when
working with live wiring. Would this suggest that rubber is an efficient or inefficient
conductor of electricity? Explain your answer.
Rubber is a poor conductor, and is often used as insulation to protect workers from
13. Describe the difference between an NMOS transistor and a PMOS transistor.
A positively doped metal-oxide semiconductor (PMOS) transistor contains silicon doped
with impurities that make it conduct electricity, but it can be made nonconductive by
applying current to a separate control wire. Conversely, a negatively doped metal-oxide
semiconductor (NMOS) transistor contains silicon doped with impurities that make it
nonconductive, but it can be made conductive by applying current
14. It is possible to develop truth tables for logic circuits, just as we did for individual gates.
For example, the following logic circuit combines an AND gate and an OR gate.
Complete the corresponding truth table by calculating the output value for each set of
to determine the overall output.]
2 and 12 is 1102.
0 0 0 | 0
0 0 1 | 1
0 1 0 | 0
0 1 1 | 1
1 0 0 | 0
1 0 1 | 1
1 1 0 | 1
1 1 1 | 1
OR gates are in reversed positions. Complete the corresponding truth table by calculating
the output value for each set of inputs.
0 0 0 | 0
0 0 1 | 0
0 1 0 | 0
0 1 1 | 1
1 0 0 | 0
1 0 1 | 1
1 1 0 | 0
1 1 1 | 1
2 and 10112? Show the steps you used to calculate
rather than half-adders.
When adding the two numbers bit by bit, you must include the carry that might come from the
previously added bits. As a result, each addition has three potential bit values that must be added
– requiring a full adder.
18. What is the total number of gates required to build a 4-bit adder? Assuming two transistors per
NOT gate (as in Figure 16.8) and four transistors per AND and OR gate (as in Figures 16.9 and
16.10, respectively), what is the total number of transistors in the circuitry of the 4-bit adder?
As shown in Figure 16.15, a 4-bit adder can be constructed using 4 full-adders. Each full-adder
is built out of 2 half-adders and an OR gate, totaling 8 half-adders and 4 OR gates. Since each
half-adder is built out of 2 AND gates, an OR gate, and a NOT gate, the total for a 4-bit adder is:
16 AND gates, 12 OR gates, and 8 NOT gates. Thus, the total number of transistors is (16*4) +
12*4 + 2*8 = 64 + 4 2 AND gates, an OR gate, and a NOT gate, the total for a 4-bit adder is: 16
AND gates, 12 OR gates, and 8 NOT gates. Thus, the total number of transistors is (16*4) +
12*4 + 2*8 = 64 + 48 + 16 = 128.
19. Describe how a flip-flop is able to retain the last bit value assigned to it.
A flip-flop stores a bit whose value can be set to 1 by applying current to one input wire and then
reset to 0 by applying current to another input wire. This behavior is achieved within the
circuitry via a feedback loop, which causes the output of the circuit to circle back and refresh the
20. Does it make any sense for both of a flip-flop’s input wires to carry current at the same time?
What would happen within the circuit if this were to happen?
It does not make sense to send a current along both the Set and Reset lines at the same time,
since their purposes are contradictory (Set sets the stored bit to 1, Reset resets the bit to 0). If
current was sent along both control lines, then a race condition would occur, and the bit would
either be set and then immediately reset (if the current along the Set line travels through the
circuitry faster) or else reset and then immediately set .
21. In what way is integrated-circuit manufacturing similar to photography?
To achieve precision on such a small scale, integrated-circuit manufacturing relies heavily on
techniques normally associated with photography. Similar to photographic development, lightsensitive
chemicals (photoresist) are used to coat the semiconductor material on the chip. The
pattern of transistors that is to be layered onto the chip is printed on a mask, and ultraviolet light
is filtered through the mask. Once exposure is completed, the photoresist that was not exposed
and the soft layer of semiconductor below are etched away, leaving only the desired pattern of
semiconductor material on the surface of the chip
22. Can Moore’s Law continue to hold forever? That is, can technology continue to advance at its
current rate indefinitely, causing the number of transistors that fit on a microchip to double every
12 to 18 months? Explain.
Clearly, there are physical limits to how many transistors can fit on a microchip. Each transistor
must take up some finite space and leave room for connections between the transistors. Current
research is being performed in developing quantum computers whose components are the size of
atoms, which would represent the limits of miniaturization. However, there is still room for
improvements in transistor density using current technology, and most experts predict that
Moore’s Law will continue to hold for many years to come.