Logic Gates are the basic building block of all complex digital circuits. You will find them in various families of IC´s TTL and CMOS the most popular, each with many sub-families. They come in packs of 2, 4 or 6 gates per IC. There are occasions when the circuit you are designing requires only one single gate and using an IC occupies too much area in the PCB. Furthermore, if you need a large number of inputs you will need several IC´s and even more PCB area.
Conversely, you can design your own logic gates by combining several diodes and one transistor in a configuration named DTL(diode-transistor logic). This class of gate occupies a small area on the PCB and has an almost unlimited number of inputs (fan-in) by simply adding diodes.The drawback of DTL is the lower speed of operation compared to TTL & CMOS.
Step 1: The NAND Gate
The NAND gate´s output = 0 only when all inputs = 1
Step 2: The NOR Gate
The NOR gate´s output = 1 only when all inputs = 0
Step 3: The NOT Gate
The NOT gate´s output = the inverse of its input
Step 4: Examples of 8-input NAND and 8-input NOR Gates
Step 5: Gate Combinations
By combining NAND, NOR and NOT gates you can configure AND, OR, XNOR and XOR gates.