Question

Write the truth table for the circuit shown in figure. Name the gate that the circuit resembles.

Answer 1

This is ‘AND’ Gate and its characteristics are as follows:

(1) It has two inputs (A and B) and only one output (Y).

(2) Boolean expression us Y = A·B is read as "Y equals A AND B".

(3) Realization of AND gate

Logical symbol of AND gate

(i) A = 0, 8 = 0

The voltage supply through R is forward biasing diodes D₁ and D₂ (offers low resistance), the voltage V would drop across R. The output voltage at Y = the voltage across diode = 0

(ii) A = 0, B = 1

D₁ = Conducts, D₂ = Not Conducts

The out voltage at Y = The voltage across the diode (D₁) = 0

(iii) A = 1, B = 0 

D₁ = Conducts, D₂ = Not conducts

The out voltage at Y = The voltage across the diode (D₂) = 0

(iv) A = 1, B = 1

None of the diode conducts

The out voltage at Y = Battery voltage = 1

(4) Truth table for ‘AND’ gate

A	B	V0 = A · B
0	0	0
0	1	0
1	0	0
1	1	1