EXCLUSIVE-NOR Gate - 5.5.1.7 | 5. Logic Families - Part D | Digital Electronics - Vol 1
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Interactive Audio Lesson

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Introduction to XNOR Gate

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0:00
Teacher
Teacher

Today, we're diving into the EXCLUSIVE-NOR gate, also known as the XNOR gate. Can anyone tell me what the primary function of this gate is?

Student 1
Student 1

Is it used for comparing two inputs to see if they're the same?

Teacher
Teacher

Exactly! The XNOR gate outputs a true signal when both inputs are equalβ€”either both true or both false. To help remember this, we can use the phrase 'both agree, output's glee.'

Student 2
Student 2

What about the truth table? What does it look like?

Teacher
Teacher

Great question! Let's break that down. When both inputs are low, the output is high. When both inputs are high, the output is also high. And if one is high and the other low, the output is low. This is critical for understanding digital logic!

Circuit Implementation

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Teacher
Teacher

Now, let's look at how the XNOR gate is implemented in a CMOS configuration. Can anyone tell me what MOSFETs are used here?

Student 3
Student 3

I think it uses both P-channel and N-channel MOSFETs, right?

Teacher
Teacher

Correct! The complementary arrangement of these MOSFETs allows for efficient operation. Remember, this allows low power dissipation in static conditions and enhances performance. Can anyone summarize the logic arrangement?

Student 4
Student 4

Sure! It's about using NAND and OR gates to achieve equality, and then we invert it at the end.

Teacher
Teacher

Perfect! Now, let's reinforce this with a phrase: 'Equal inputs, XNOR outputs.' This can help you remember their relationship.

Applications of XNOR Gate

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Teacher
Teacher

What can we say about the practical applications of the XNOR gate?

Student 2
Student 2

I've heard they're used in equality checkers in digital circuits.

Teacher
Teacher

Absolutely! They're essential in digital error detection and correction. So, how can we remember their importance?

Student 1
Student 1

Maybe we could say, 'XNOR equals, thus it secures!' to emphasize its role in ensuring correct logic.

Teacher
Teacher

Excellent! That's a memorable way to encapsulate its purpose in digital logic. Let’s summarize this session: XNOR gates compare inputs, ensuring accuracy in crucial applications.

Introduction & Overview

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Quick Overview

The EXCLUSIVE-NOR (XNOR) gate is a digital logic gate that outputs true or HIGH only when its two inputs are equal.

Standard

The EXCLUSIVE-NOR gate is implemented in CMOS technology and features a configuration that allows the output to be true when both inputs are the same. It is the complement of the EXCLUSIVE-OR gate. Understanding its circuit diagram and truth table is essential for logical computations in digital systems.

Detailed

EXCLUSIVE-NOR Gate

The EXCLUSIVE-NOR (XNOR) gate is a fundamental digital logic device used to determine equality between two binary inputs. In CMOS (Complementary Metal Oxide Semiconductor) technology, it is implemented using an arrangement of MOSFETs that allows for efficient operation with low power dissipation. The gate has two noteworthy configurations: the logic diagram and the internal schematic.

Truth Table

The output of the XNOR gate can be expressed using the Boolean equation:

  • Y = (A AND B) OR (NOT A AND NOT B)

This can be summarized in its truth table:
- When both A and B are 0, Y = 1
- When both A and B are 1, Y = 1
- When A = 0 and B = 1, Y = 0
- When A = 1 and B = 0, Y = 0

Circuit Implementation

The CMOS implementation consists of a configuration of P-channel and N-channel MOSFETs. Together, they create an effective logical operation where the output retains the equality of the inputs. This feature is crucial in various applications, such as digital signal processing and error detection, ensuring the efficient operation of complex digital circuits.

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EXCLUSIVE-NOR Logic Implementation

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An EXCLUSIVE-NOR gate is implemented using the logic diagram of Fig. 5.42(a). As is evident from the figure, the output of this logic arrangement can be expressed by
\[\text{Y} = A \cdot \overline{B} + \overline{A} \cdot B = \text{EX-NOR function} \ (5.2)\]

Detailed Explanation

The EXCLUSIVE-NOR gate is a fundamental logic gate in digital electronics that produces a true output (1) only when the two binary inputs are either both true (1) or both false (0). The formula provided demonstrates this behavior: when both inputs A and B are the same (either 0 and 0 or 1 and 1), the output Y will be true. Understanding this code representation helps in designing circuits that use this gate, indicating when two inputs are in agreement.

Examples & Analogies

Think of the EXCLUSIVE-NOR gate like a pair of friends who only agree if they both feel the same way about something. If both friends are happy or both are sad, they agree on their feelings (output is true). But if one is happy and the other is sad, they disagree (output is false).

Internal Schematic of EXCLUSIVE-NOR Gate

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Figure 5.42(b) shows the internal schematic of a two-input EX-NOR gate. MOSFETs Q1-Q4 constitute the NAND gate. MOSFETS Q5 and Q6 simulate ORing of A and B, and MOSFET Q7 provides ANDing of the NAND output with ORed output. Since MOSFETs Q8-Q10 make up the complement of the arrangement of MOSFETs Q5-Q7, the final output is inverted. Thus, the schematic of Fig. 5.42(b) implements the logic arrangement of Fig. 5.42(a) and hence a two-input EX-NOR gate.

Detailed Explanation

The inner workings of the EXCLUSIVE-NOR gate are a combination of several MOSFETs working together in tandem. MOSFETs Q1 to Q4 form a NAND gate, while Q5 and Q6 create the logical OR of the inputs A and B. This means that if either A or B is high, they will output a 1. The output from the NAND gate and the output from the OR gate are then combined using another MOSFET (Q7) which allows passing of the signal only if the previous signals dictate so. Finally, the output is inverted (by Q8, Q9, and Q10) to convert the NAND/OR output to the EXCLUSIVE-NOR output, providing the expected logical behavior.

Examples & Analogies

Imagine a voting panel where you need a majority for a decision to be made. Each panel member can either vote 'yes' or 'no.' If both panel members vote 'yes' or both vote 'no,' the final decision is made (the gate's output is true). However, if one votes 'yes' and the other votes 'no,' the proposal is rejected (output is false). The arrangement of votes is akin to how transistors are arranged in the gateβ€”working together to reach a logical conclusion.

Definitions & Key Concepts

Learn essential terms and foundational ideas that form the basis of the topic.

Key Concepts

  • XNOR Gate: Outputs true when both inputs are equal.

  • CMOS Technology: Allows for low power dissipation and high integration of logic gates.

  • Truth Table: Displays the output states for all input combinations of the XNOR gate.

Examples & Real-Life Applications

See how the concepts apply in real-world scenarios to understand their practical implications.

Examples

  • If both inputs are '1', the XNOR output is '1'; if one input is '0' and the other is '1', the output is '0'.

  • The XNOR gate is often used in circuits to check for equality between two binary numbers in digital computing.

Memory Aids

Use mnemonics, acronyms, or visual cues to help remember key information more easily.

🎡 Rhymes Time

  • XNOR's delight, same inputs that ignite!

πŸ“– Fascinating Stories

  • Imagine two friends shaking hands, they smile when they match, but frown when they don't. That's how XNOR behaves with its inputs.

🧠 Other Memory Gems

  • Remember: EQUAL = TRUE with XNOR!

🎯 Super Acronyms

XNOR = eXclusive NOT OR, reinforcing equality!

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: Complementary Metal Oxide Semiconductor (CMOS)

    Definition:

    A technology for constructing integrated circuits using complementary and symmetrical pairs of p-type and n-type MOSFETs.

  • Term: EXCLUSIVENOR (XNOR) Gate

    Definition:

    A digital logic gate that outputs true only when the inputs are equal.

  • Term: MOSFET

    Definition:

    A type of field-effect transistor commonly used in CMOS technology.

  • Term: Truth Table

    Definition:

    A mathematical table used to determine the output of a logic gate based on various input combinations.