The Art Of Electronics

An AND gate has two or more inputs and a single output. The definition of AND gate states that if one of the inputs is 0 the output will be 0. The figure below shows the structure of the AND gate. For a two-input AND gate, the relationship between input and output is shown in the truth table below. You will notice that if any-one of the input is 0 then the output is 0. Now let us try to understand how you can build AND gate using diodes. But first, you must understand the basic principle on which the diode works. Look at the figure of the diode below. If you apply some positive voltage V(in) which is greater than Vth (Breakdown voltage of diode) at point A then the diode will act as a closed switch or it will be forward biased. Thus the diode will start conducting. On the other hand, if you apply some negative voltage V(in) which is less than Vth, the diode will not conduct and will act as an open switch. This is called reverse biased. Having understood the wor...

An OR gate has two or more inputs and a single output. The definition of OR gate states that if one of the inputs is '1' the output will be '1'. The figure below shows the structure of the OR gate. For a two-input OR gate, the relationship between input and output is shown in the truth table below. You will notice that if any-one of the input is 1 then the output is 1. Now let us try to understand how you can build OR gate using diodes. But first, you must understand the basic principle on which the diode works. Look at the figure of the diode below. If you apply some positive voltage V(in) which is greater than Vth (Breakdown voltage of diode) at point A then the diode will act as a closed switch or it will be forward biased. Thus the diode will start conducting. On the other hand if you apply some negative voltage V(in) which is less than Vth, the diode will not conduct and will act as an open switch. This is called reverse biased. Having und...