(a) Write the truth table for the combination of the gates shown in the figure.

(b) Explain briefly how a photodiode operates.

Explanation

(a) Truth Table

(b) Photodiode : A photodiode is a special purpose p - n junction diode fabricated with a transparent window to allow light to fall on the diode . It is operated under reverse bias . When a photodiode is illuminated with light (photons) with energy (hv) greater than the energy gap (Eg) of the semiconductor , then electron - hole pair are generated due to absorption of photons . When an external load is connected , current flows . The magnitude of the photocurrent depends on the intensity of incident light.
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