Question

If V_A and V_B are the input voltages (either 5V or 0V) and V_o is the output voltage then the two gates represented in the following circuit (A) and (B) are:-

(1) AND and OR Gate

(2) OR and NOT Gate

(3) NAND and NOR Gate

(4) AND and NOT Gate

Answer 1

Correct answer is 2.

If A = B = 0, there is no potential anywhere here

V₀ = 0

If A = 1, B = 0, Diode D₁ is forward biased, here

V₀ = 5V

If A = 0, B = 1, Diode D₂ is forward biased hence

V₀ = 5V

If A = 1, B = 1, Both diodes are forward biased

hence V₀ = 5V

Truth table for I^st

^{\(\therefore\)} Given circuit is OR gate

For II^nd circuit

V_B = 5V, A = 1

V_B = 0V, A = 0

When A = 0, E – B junction is unbiased there is no current through it

^{\(\therefore\)} V₀ = 1

When A = 1, E – B junction is forward biased V₀ = 0

^{\(\therefore\)} Hence this circuit is not gate.