The term "Three legged NOT gate" is a playful, informal way to refer to a specific logic gate symbol that often causes confusion among beginners in digital electronics. While the standard NOT gate is represented by a single input and a single output, the "three legged" version features an additional input, leading to questions about its function and purpose. This article delves into the meaning behind this symbol and its role in digital circuits.
Understanding the "Three Legged" NOT Gate
The "three legged" NOT gate, also known as an inverted buffer, is not a distinct gate type like AND, OR, or XOR. Instead, it's a representation of a NOT gate combined with a buffer. To understand this concept, we need to break down the components individually:
The NOT Gate: The Basics
The NOT gate, as its name suggests, performs the logical negation operation. It takes a single input, and its output is the logical inverse of that input. This means:
- If the input is HIGH (logical 1), the output is LOW (logical 0).
- If the input is LOW (logical 0), the output is HIGH (logical 1).
The Buffer: A Signal Amplifier
A buffer is a simple logic gate that essentially replicates its input onto its output. It acts like a signal amplifier, strengthening the signal without changing its logical value. In other words:
- If the input is HIGH (logical 1), the output is also HIGH (logical 1).
- If the input is LOW (logical 0), the output is also LOW (logical 0).
Combining NOT and Buffer: The "Three Legged" Representation
Now, imagine combining a NOT gate and a buffer in series. The output of the NOT gate becomes the input to the buffer. This arrangement effectively creates a "three legged" representation, with:
- Input 1: The input to the NOT gate.
- Input 2: The input to the buffer, which is connected to the output of the NOT gate.
- Output: The output of the buffer, which represents the final output of the entire circuit.
Why Use the "Three Legged" Representation?
This combined representation might seem unnecessary at first, but it serves a specific purpose in circuit design. The buffer component adds several advantages:
- Signal Strength: The buffer can amplify the signal from the NOT gate, making it more robust and able to drive larger loads.
- Isolation: The buffer acts as an isolator, preventing the NOT gate's output from being affected by the load connected to the final output.
- Output Enable: In some circuits, the input to the buffer can be used as an output enable signal. This allows for selective control over whether the final output is driven or not.
Understanding the Symbol
The "three legged" NOT gate symbol is a visual representation of this combined logic:
[Insert image of "three legged" NOT gate symbol here]
The symbol typically consists of a standard NOT gate symbol (a small circle with an input and output) with an additional input connected to the output of the NOT gate. This additional input represents the input to the buffer.
Practical Applications of the "Three Legged" NOT Gate
While the "three legged" representation is not a separate logic gate, it finds applications in various digital circuits:
- High-Speed Circuits: The buffer's signal strengthening capability can improve the performance of circuits operating at high speeds.
- Output Buffering: The buffer is commonly used to isolate outputs and prevent loading effects on previous stages in a circuit.
- Output Enable Control: The buffer's input can be used as an enable signal, allowing for controlled activation or deactivation of the output.
Conclusion
The "Three Legged" NOT gate symbol, while not a distinct gate type, represents a useful combination of a NOT gate and a buffer. This representation offers advantages like signal amplification, isolation, and output enable control, making it a valuable tool in digital circuit design. By understanding its components and purpose, engineers can effectively utilize this symbol and its inherent capabilities in their circuits.