All Basic Gates (NOT, AND, OR)
NOT Gate:
Basic Memory Element: Using a feedback loop with NOT gates, a basic memory element can be aerated. It is called a bistable multivibrator.
If A = 0, 0 is in a stable state and
If A = 1, 1 is in a stable state.
But, an astable multivibrator creates a random sequence of 0s and 1s. (Depending on i/p)
If there are ‘n’ NOT gates connected in a feedback path and n = Odd; if represents the propagation delay of one NOT gate, then
Important note:
1) If the number of NOT gates is odd in a feedback path ⇒ Astable multivibrator
2) If the number of NOT gates is even in a feedback path ⇒ Bistable multivibrator
Example 1:
Consider the following circuit with a propagation delay of 100 ps (PS = pico second) = seconds) ( of each NOT gate is loops). Calculate the time period and frequency.
Solution:
Example 2:
Consider the following circuit. Calculate the time period.
Solution:
Time period and frequency depend on the number of NOT gates involved in feedback only. Other gates will cause delay only.
∴ Time period = (3 X 10 X 2) = 60 s
AND Gate:
AND gate follows Commutative and associative law.
1) AB = BA
2) A(BC) = (AB)C
Enable input of AND Gate:
During enable situation AND gate act as a buffer.
Disable input of AND gate
Question:
What should be the output of the circuit if z represents the floating input of AND gate?
Solution:
Floating input is always enable i/p for AND gate, which is 1. (So, z = 1)
So, the output is 0.
OR Gate:
OR gate follows Commutative and associative law.
1) A+B = B+A
2) A+(B+C) = (A+B)+C
Just in the inverse logic as shown in AND,
i) Enable i/p of OR Gate= 0 (behaves as a buffer)
ii) Disable i/p of OR gate = 1
Contributed by