what is the internal structure of a OR & AND gate???

Question

I want to know how AND & OR gate works. I mean there internal mechanism. ANd how they produce desired output.

Answer 1

Basically an OR gate can be an array (the number is dependant upon how many input are compared) of diodes. with all the cathodes tied together. If any of the anodes sees a high, then that leg has met the goal and the output is high. If there are 3 inputs and all are low then the output (cathode) is low, but if any input is high then the output is high. So the output is high if input "a" is high OR input "b" is high OR input "c" is high. There is an OR gate. If you reverse the diodes direction, tie the anodes together and throw in a resistor to a source for bias you can create a negative OR gate, or NOR.

An AND gate requires all inputs to be high before the output goes high. There are numerous configurations to build an AND gate, and I'm sure there are easier ways than this, but this is all I can think of off the top of my head. It involves a NPN transistor an op-amp and a resistor. This is a two input AND gate, input "a" is the base of the transistor and input "b" is the non-inverting input to the op-amp. The output is the output of the o-amp, Tie the cathode of the transistor to ground and the anode directly to the inverting input of the op-amp and to the resistor, while the other side of the resistor is tied to the source voltage. As long as the transistor is biased off, no high on input "a" (the base) the source is felt on the inverting leg through the resistor (a high) of the op-amp and the output is always a low. Even if a high is inputted to input "b" (the non-inverting leg), it will never out weigh the source so the output is low. Unless the base (input "a") is high then this basically grounds the inverting leg, now a high on input "b" can out weigh the inverting leg and the op-amp output is a high.