For the logic circuit and input waveforms shown in the source figure, input A is high from t = 0 to 2 s. Input B is high from t = 0 to 1 s, low from 1 to 2 s, and high again from 2 to 3 s. Which description gives the output waveform Y?

Question

G1 Physics · Accepted Answer

From the circuit shown in the source figure, the upper AND gate produces A·B. Because of the inversion at the lower input path, the lower AND gate produces Ā·B. These two outputs are combined so that the resulting Boolean expression is Y = A·B + Ā·B. Factor B: Y = (A+Ā)B. Since A+Ā = 1, we obtain Y = B. Therefore the output waveform is exactly the same as input B. The given B waveform is high from 0 to 1 s and again from 2 to 3 s. Hence Y is high over those same intervals. Correct option: B.