Transistors and Combinational Logic

Question 1

What types of storage elements are used in sequential logic?

Answer 1

Storage elements include latches, flip-flops, and registers

Question 2

What roles do inputs and outputs play in logic circuits?

Answer 2

Inputs are the values fed into a circuit, while outputs are the resulting values produced by the circuit’s logic

Question 3

What is the function of a multiplexer (MUX)?

Answer 3

MUX selects one input out of several inputs to connect to the output based on control signals

Question 4

How can we create a NAND gate using CMOS technology?

Answer 4

By combining n-type and p-type transistors in a specific configuration to achieve the NAND function

Question 5

How do we construct basic logic structures using MOS transistors?

Answer 5

By combining individual MOS transistors to form logic gates that implement simple Boolean functions

Question 6

How does an n-type transistor operate compared to a p-type transistor?

Answer 6

An n-type transistor conducts when a high voltage is applied to its gate, while a p-type transistor conducts when the gate is at 0V

Question 7

How is a decoder implemented in combinational logic?

Answer 7

A decoder takes n inputs and produces 2^n outputs, with exactly one output being true for each input combination

Question 8

What distinguishes sequential circuits from combinational circuits?

Answer 8

Sequential circuits have memory elements and their output depends on both current and previous inputs, while combinational circuits rely only on current inputs

Question 9

What is the importance of having a closed circuit for electron flow?

Answer 9

A closed circuit allows electrons to flow; without it, the circuit remains open and non-functional

Question 10

How do we implement a logic function using a PLA?

Answer 10

By programming the connections from AND gate outputs to OR gate inputs based on the desired logic function

Question 11

What are the two types of MOS transistors?

Answer 11

n-type and p-type MOS transistors

Question 12

What is the purpose of a full adder in binary addition?

Answer 12

A full adder computes the sum of three bits: two significant bits and a carry bit, producing a sum and carry out

Question 13

How does the truth table of a full adder work?

Answer 13

The full adder truth table shows all combinations of inputs and their corresponding sum and carry outputs

Question 14

What is the logical function of a NAND gate?

Answer 14

The NAND gate outputs false (0) only when both inputs are true (1); otherwise, it outputs true (1)

Question 15

How many control bits are required for a MUX with N inputs?

Answer 15

A multiplexer with N inputs requires log2(N) control bits

Question 16

What is CMOS technology and how does it utilize both n-type and p-type transistors?

Answer 16

CMOS technology uses both n-type and p-type transistors to create efficient and low-power logic gates

Question 17

What is the function of the R-S latch in digital circuits?

Answer 17

An R-S latch stores a single bit of information and has two control inputs, Set (S) and Reset (R)

Question 18

What is the function of the gate in a MOS transistor?

Answer 18

The gate controls the connection between the source and drain; applying voltage can either allow or stop current flow

Question 19

What are the basic building blocks of combinational logic?

Answer 19

Basic building blocks include decoders, multiplexers, full adders, and programmable logic arrays (PLAs)

Question 20

How do transistors act as switches in circuits?

Answer 20

Transistors control the flow of electrons, allowing for information flow similar to how a switch controls electrical circuits

Question 21

What is a programmable logic array (PLA) and how is it structured?

Answer 21

A PLA consists of an array of AND gates followed by OR gates, allowing for flexible implementation of logic functions

Question 22

Why are simultaneous S and R inputs of a latch forbidden?

Answer 22

Simultaneous S and R inputs can cause metastability, leading to unpredictable behaviour of the latch outputs

Question 23

Buffer logic gate

Answer 23

If the input is 1, then the output is q; if the input is 0, then the output is 0

Question 24

AND logic gate

Answer 24

Output is 1 only when both inputs are 1

Question 25

OR logic gate

Answer 25

For the output to be 1, at least one input must be 1

Question 26

XOR logic gate

Answer 26

Output is 1 if the inputs are different but 0 if the inputs are the same

Question 27

Inverter or NOT logic gate

Answer 27

If the input is 1, then the output is 0; if the input is 0, then the output is 1

Question 28

NAND logic gate

Answer 28

AND gate with the circle of a NOT gate at the output, output is false if both inputs are true, otherwise, the output is true

Question 29

NOR logic gate

Answer 29

A combination OR gate followed by an inverter; its output is true if both inputs are false, otherwise, the output is false

Question 30

XNOR logic gate

Answer 30

XOR gate followed by an inverter; its output is true if the inputs are the same and false if the inputs are different