JEE Main 2022 · 25 July · morning · Single correct · +4 / −1
In the circuit, the logical value of A=1 or B=1 when potential at A or B is 5 V and the logical value of A=0 or B=0 when potential at A or B is 0 V.
The truth table of the given circuit will be :
- (a) A, B, Y; 0, 0, 0; 1, 0, 0; 0, 1, 0; 1, 1, 1
- (b) A, B, Y; 0, 0, 0; 1, 0, 1; 0, 1, 1; 1, 1, 1
- (c) A, B, Y; 0, 0, 0; 1, 0, 0; 0, 1, 0; 1, 1, 0
- (d) A, B, Y; 0, 0, 1; 1, 0, 1; 0, 1, 1; 1, 1, 0
Answer and solution
Answer (a) A, B, Y; 0, 0, 0; 1, 0, 0; 0, 1, 0; 1, 1, 1
Solution
Physics sir · 3 steps
Any input at 0 V turns its diode on and drags Y down to 0 V, so Y is high only when both inputs are high.
- Read the diodes. Each diode has its anode on the Y side and its cathode at the input. The junction Y is pulled up towards +5 V through R, so a diode conducts only when its input sits below Y.
- Input at 0 V. If A or B is at 0 V, that diode is forward biased. It conducts, and Y is clamped to about 0 V. The drop of 5 V appears across R.
A B Diodes Y 0 0 D₁ and D₂ on 0 1 0 D₂ on 0 0 1 D₁ on 0 1 1 both off, no current in R 1 - So. With both inputs at 5 V, neither diode has a forward voltage across it. No current flows through R, so Y stays at 5 V. This is an AND gate, which is option (a).
The idea to keep. In a diode gate, find where the resistor pulls the output. If it pulls up to +V with the diodes pointing towards the inputs, you have AND. If it pulls down to ground with the diodes pointing towards Y, you have OR.
Answer from the NTA final answer key. Solution by PrepWiser.