NOT GATE | LOGIC GATES | VERILOG | FPGA

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This video provides an overview of logic gates, focusing on the NOT gate, and demonstrates its implementation using Verilog and an FPGA board.

Logic Gates and Binary Values
Logic gates are the building blocks of all digital electronics.
They are electronic circuits that have one or more inputs and only one output.
Logic gates work on binary values, which are 0 and 1.
0 means off, low, or false.
1 means on, high, or true.
Logic gates are categorized into three types:
Basic Logic Gates: NOT gate, AND gate, OR gate.
Universal Logic Gates: NAND gate, NOR gate.
Exclusive Logic Gates: XOR gate, XNOR gate.
There are a total of seven types of logic gates.
The NOT Gate (Inverter)
The NOT gate is also known as an inverter or negation.
Its logical operation is to give the opposite value of the input.
If the input is 0, the output is 1.
If the input is 1, the output is 0.
If the input is 'A', the output is 'A bar' (negation of A).
The symbol for a NOT gate typically consists of a triangle with a circle in front of it.
Propagation Delay
The change from input to output occurs with some delay.
This time delay is known as Propagation Delay ($T_{PD}$).
Propagation delay is the time taken for the input to propagate to the output.
NOT Gate Implementation

The NOT gate's function is verified using a truth table and explained through two common transistor technologies:
CMOS Technology (Complementary Metal-Oxide-Semiconductor): CMOS logic gates are built using a combination of PMOS (P-type MOSFET) and NMOS (N-type MOSFET) transistors.
When the input is 0, the PMOS turns on, and the VCC (value 1) goes to the output.
When the input is 1, the NMOS turns on, and the ground (value 0) goes to the output.
NPN Transistor:
When the input is 0, the NPN transistor is in the cutoff region (open circuit), and VCC is connected to the output (value 1).
When the input is 1, the NPN transistor is in the saturation region (short circuit), and the ground is connected to the output (value 0).
Connecting NOT Gates
Two (Even Number) NOT Gates in a Loop: This configuration is known as a buffer.
The circuit is bistable and holds the input value, making it a basic memory element (e.g., a basic latch or flip-flop).
It is also known as a bistable multivibrator.
Three (Odd Number) NOT Gates in a Loop:
This configuration is not stable.
It generates a square wave.
It is known as a square wave generator, an astable multivibrator, a free-running circuit, a ring oscillator, or a clock generator.
FPGA Implementation (Verilog)

The video details the steps for implementing a NOT gate on an FPGA board using the Xilinx Vivado software and the Verilog hardware description language:
Create a Design Source (Verilog Code): The NOT gate logic is defined using the assign keyword and the negation operator (~) in Verilog.
Create a Simulation Source (Testbench): A testbench is written to virtually verify the design by applying inputs and checking the outputs.
Run Behavioral Simulation: The simulation is run to ensure the logic gate functions correctly.
Add Constraint File (.XDC): This file maps the logical ports (input 'in' and output 'out') in the Verilog code to the physical pins (F4 for input switch, F10 for output LED) on the FPGA board.
Run Synthesis, Implementation, and Generate Bitstream: These steps prepare the design for the hardware.
Program the Device: The bitstream is loaded onto the FPGA board.
Physical Verification: The final demonstration confirms the NOT gate function: when the input switch is OFF (0), the output LED is ON (1), and when the input switch is ON (1), the output LED is OFF (0).