Presentation on logic gates andits applications
History of logic gates The first logic gates were developed around 1837 and were of mechanical form. For most of that century, these gates went through much development until Nikola Tesla developed circuit-based logic in 1898. Furthermore, Boolean algebra was introduced to circuit analysis during the mid-19th century and shaped the way people interpret this logic today
There are many different types of logic in electronics, where gates are made up of many different devices such as diodes, relays transistors, and most importantly, integrated circuits (ICs).
Variations of logic gatesOne of the biggest decisions to make when dealing with Boolean logic is deciding which gates to use to compare your logic inputs. Here is a breakdown of different types of logic gates including their output truth tables when two Boolean inputs exist:
AND GateThe AND gate compares in a waythat the output is high only if both inputsare high.
OR Gate The OR gate will have a high output for all input cases except when both inputs are low.
NOT gate (inverter)The output Q is true when the input A is NOT true,the output is the inverse of the input: Q = NOT A A NOT gate can only have one input. A NOT gate isalso called an inverter.
NAND gate (NAND= Not AND) This is an AND gate with the output inverted, as shown by the o on the output. The output is true if input A AND input B are NOT both true: Q = NOT (A AND B) A NAND gate can have two or more inputs, its output is true if NOT all inputs are true.
NOR gate (NOR = Not OR) This is an OR gate with the output inverted, as shown by the o on the output. The output Q is true if NOT inputs A OR B are true: Q = NOT (A OR B) A NOR gate can have two or more inputs, its output is true if no inputs are true.
EX-OR (EXclusive-OR) gateThe output Q is true if either input A is true OR input B istrue, but not when both of them aretrue: Q = (A AND NOT B) OR (B AND NOT A) This is like an OR gate but excluding both inputs beingtrue. The output is true if inputs A and B are DIFFERENT. EX-OR gates can only have 2 inputs.
EX-NOR (EXclusive-NOR) gateThis is an EX-OR gate with the output inverted, as shownby the o on the output. The output Q is true if inputs A and B are the SAME (bothtrue or bothfalse): Q = (A AND B) OR (NOT A AND NOT B) EX-NOR gates can only have 2 inputs.
Applications Simple application of NAND gate The application discussed here is that of a door closing system of an automobile. A car needs to be so designed that the driver gets a visual indication if any of the doors of the car is open so that it helps to avoid accident and injury to the passengers. Assuming there are two doors (just for simplicity, it works for more doors as well) where this system is fitted, the circuit can be designed using a NAND gate as follows
You can see from the figure that when any of the switches is open due to the door position, the NAND gate energies the lamp inside the car, hence warning the driver. A Car Door Open Warning System using a NAND Gate
This truth table gives us the behaviour oflamp inside the car when any one the doorsare opened
Some more examples Below is the logic gate for a simple house alarm. The alarm protects the front and back doors and six windows. Once the alarm is set if any of the doors or windows are opened the alarm will sound.