Question 4
(a) Define logic gate.
(b) Give one example each of:
(i) standard logic gate;
(ii) alternative logic gate.
(c) using P and Q as inputs and R as output:
(i) draw the logic symbol for an XOR logic gate;
(ii) construct the truth table for XOR logic gate.
(d) List two uses of a logic gate.
Observation
The expected answers were:
- Logic gate is an elementary building block of a digital circuit with the two binary conditions i.e;
low (0) or high (1) which is a representation of different voltage levels.
OR
Logic gate is a logical circuit device in digital devices with one or more inputs but only one output channel.
(b) (i) AND logic gate, OR logic gate and NOT logic gate.
(ii) NAND logic gate, XNOR, NOR logic gate and XOR logic gate.
(c) (i)
XOR Logic gate symbol
(ii) Truth Table for XOR logic gate
INPUT |
OUTPUT |
|
P |
Q` |
R |
0 |
0 |
0 |
0 |
1 |
1 |
1 |
0 |
1 |
1 |
1 |
0 |
(d) Uses of Logic Gate
- Logic gates are used as building blocks of digital electronic hardware.
- Logic gates are used in the construction of simple comparator.
- Logic gates are used for decision making.
- It is used in constructing alarms
- It is used in push-button lock circuit
- It is used in traffic light controller
- It is used in light-activated burglar
- It is used in safety thermostat, an automatic watering system
- It is used in the Arithmetic and Logic Unit (ALU)
- It is used to build digital and complex integrated circuits
- It is used in error checking in FM transmission.
- It is used in Micro-controller circuits.
The question required candidates to define logic gate; give examples of logic gates and draw a logic gate.
It was reported that candidates showed poor knowledge of logic gate and a good number of them failed to draw a logic gate.