Logic gates are the basic building blocks of digital circuits and perform logical operations. The main logic gates are AND, OR, and NOT. An AND gate outputs 1 only if all its inputs are 1. An OR gate outputs 1 if any of its inputs are 1. A NOT gate inverts its single input. Logic gates are constructed from diodes, transistors, and resistors on a silicon chip and their inputs and outputs represent either 1 or 0, true or false. Combination gates like NAND and NOR are derived from basic logic gates and their truth tables define the output for all possible input combinations.

1. LOGIC GATES

2. WHAT ARE LOGIC GATES?
The Logic Gate is the simplest
integrated circuit (IC). They are
called logic gates because the circuits
act like gates in a fence.
The gate is either open or closed
depending on the conditions set.

3. THE BASIC LOGIC GATES
AND : acts in the same
way as two switches are
placed in series.
X equals A and B
X= A.B
OR: operates like a
circuit with two
switches placed in
parallel.
X equals A or B
X= A+B
NOT: acts in the same way
as a transistor. It is an
INVERTER.
A with a bar is read as Not A

4. LOGIC GATES consist of diodes, transistors
and resistors assembled in a silicon chip.

5. LOGIC GATES SYMBOL AND TRUTH TABLES
At any given time, every terminal may have an input
or output of 1(high) or 0 (low). In most logic
gates, the low state is approx. 0 volt, while the
high state is 5 volts or 6 volts in some.

6. Take Note:
The inputs and outputs of logic gates are either 1
or 0 which stands for Yes or No; True or False; or
high or low voltages respectively.

7. OTHER TYPES OF LOGIC GATES
These are the simplest combination gates
derived from the basic logic gates.
NAND gate is a combination
of AND and NOT gate.
NOR gate is an OR and
NOT gate combination.

8. OTHER TYPES OF LOGIC GATES
TRUTH TABLES

9. TRY THIS! A system of AND gates
with 5 inputs
A
B
C
D
E
What is the final output in X if A = 1 and
B = 0, C = 0, D = 1 and E = 1 ?
X

10. TRY THIS!
A = 1 and B = 0, What is the final
output at X?
X

11. A system of combination of gates.
A
B
C
D
Determine the output in X if A and B are
both 1 and C and D are both 0?
X

12. TRY THIS!

13. TRY THIS!

14. LOGIC GATES SUMMARY