AND-OR-INVERT and OR-AND-INVERT Gates - 5.5.1.8 | 5. Logic Families - Part D | Digital Electronics - Vol 1
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5.5.1.8 - AND-OR-INVERT and OR-AND-INVERT Gates

Practice

Interactive Audio Lesson

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Introduction to AND-OR-INVERT Gate

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0:00
Teacher
Teacher

Today, we'll explore the AND-OR-INVERT gate. This gate is an essential component in digital circuit design. Can anyone describe what they think it might do?

Student 1
Student 1

I think it combines the operations of AND and OR!

Teacher
Teacher

Exactly! It performs an AND operation on two sets of inputs and then inverts the result. Its output can be expressed as Y = (AB) + (CD)'. Can anyone explain what this means in practical terms?

Student 2
Student 2

It means if either A and B are true or C and D are true, the output will be false!

Teacher
Teacher

Very close! It’s when both (A and B) and (C and D) yield true that the result is false. Let's summarize: The output will be zero when either pair of inputs equals one or both pairs equal one.

Circuit Design for AND-OR-INVERT

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Teacher
Teacher

Now let's look at how we can implement an AND-OR-INVERT gate using MOSFETs. Who can explain the role of N-channel and P-channel MOSFETs in this circuit?

Student 3
Student 3

N-channel ones connect to ground, and P-channel to VDD, right?

Teacher
Teacher

Exactly! This configuration allows us to manage the conduction paths. Can someone describe what happens when the output is high?

Student 4
Student 4

When the output is high, it means that both required inputs aren't true together!

Teacher
Teacher

Correct! That demonstrates the interplay between alternating high and low signals and switching actions within the circuits. Great job summarizing!

OR-AND-INVERT Gate Fundamentals

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Teacher
Teacher

Now, let’s shift gears to the OR-AND-INVERT gate. What is its analogous structure to the AND-OR-INVERT gate?

Student 1
Student 1

It should also use N and P MOSFETs but focus on OR first and then AND?

Teacher
Teacher

You got it! It processes the inputs somewhat in reverse, where the Boolean equation is expressed as Y = (A + B)'(C + D)'. What can we conclude when the output equals one?

Student 2
Student 2

It means that both input pairs must be false, right?

Teacher
Teacher

Correct! Both pairs failing will allow connection paths to maintain a high output. Excellent work!

Introduction & Overview

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Quick Overview

This section explores the functionality and implementation of AND-OR-INVERT and OR-AND-INVERT gates in CMOS technology, including their Boolean expressions and circuit designs.

Standard

The section details the AND-OR-INVERT and OR-AND-INVERT gates, explaining how their outputs can be described by specific Boolean expressions. It also delves into the internal circuit schematics, demonstrating how these gates are constructed using N-channel and P-channel MOSFETs.

Detailed

In this section, we discuss two advanced logic gates known as AND-OR-INVERT (AOI) and OR-AND-INVERT (OAI) that are utilized in CMOS technology. The outputs of these gates can be mathematically expressed using Boolean algebra:

AND-OR-INVERT Gate

The output Y is expressed as:
Y = (AB) + (CD)' (5.3)
For the output to be 0:
1. Either A+B=1 or C+D=1
2. Both A+B and C+D = 1.
The circuit ensures that when this condition is met, there exists a conduction pathway from ground to the output, validating the logical expression.

Conversely, if both A+B and C+D result in 0, the circuit maintains a high output.

OR-AND-INVERT Gate

This gate outputs Y as:
Y = (A + B)'(C + D)' (5.4)
The internal schematics highlight the connection of N-channel MOSFETs for AND operations and P-channel MOSFETs for OR operations. This section is critical as it demonstrates both the operational principles of these gates and their practical implementations in circuit designs.

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AND-OR-INVERT Gate Overview

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Figure 5.43 shows the internal schematic of a typical two-wide, two-input AND-OR-INVERT gate.
The output of this gate can be logically expressed by the Boolean equation
Y =(AB + CD) (5.3)

Detailed Explanation

The AND-OR-INVERT gate is a complex logic gate that combines AND and OR operations, followed by an inversion. It takes four inputs, A, B, C, and D, and its output Y is defined by the equation Y = (AB + CD). This means that for the output to be 1 (logic HIGH), either the AND operation (A AND B) must be true or the other AND operation (C AND D) must be true. This interplay of logic operations allows for versatile control in complex logic circuits.

Examples & Analogies

Imagine a light switch that can be turned on by either of two separate ways: pressing one of two buttons (A and B) or pulling one of two levers (C and D). The light will only turn on if at least one of those methods is activated. If both sets of controls are inactive, the light remains off. This is similar to how the AND-OR-INVERT gate operates; it checks multiple conditions to determine whether to output a signal.

Conditions for Logic '0' Output

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From the above expression, we can say that the output should be in a logic β€˜0’ state for the following input conditions:
1. When either A + B = logic β€˜1’ or C + D = logic β€˜1’
2. When both A + B and C + D equal logic β€˜1’.

Detailed Explanation

For the AND-OR-INVERT gate to output a logic '0', it requires specific input conditions. If either the combination of inputs A and B or inputs C and D yield a true (logic '1') condition, the output will be '0'. This means the circuit will find a path to ground, preventing the output from being high. Essentially, the AND-OR-INVERT only activates its output when both AND combinations are false; otherwise, it will not. Therefore, having at least one input from both AND groups set to true will ensure the output remains low.

Examples & Analogies

Think of a security alarm system with two zones (A + B and C + D). The alarm will not sound (output is LOW) if either of the zones is triggered (e.g., someone crosses into the area) or both zones are compromised. Only when both zones remain quiet will the alarm remain off, akin to making sure every condition for activity is inactive before allowing the output.

Conditions for Logic '1' Output

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This implies that:
1. Either A or B or both are in a logic β€˜0’ state.
2. Either C or D or both are in a logic β€˜0’ state.

Detailed Explanation

For the output of the AND-OR-INVERT gate to be high (logic '1'), the input conditions must lead to both AND groups (A + B and C + D) yielding false values. Specifically, A and B must produce a false condition, and similarly, C and D must also yield a false condition. If either or both elements of these pairs are in a logic '0' state, ground cannot connect through to the output, allowing the circuit to produce a high output instead.

Examples & Analogies

Imagine a two-door entry system to a safe. The safe will only unlock (output '1') if both doors are closed (indicating that their corresponding conditions do not allow access). So, if one door is closed and the other is open, or if both doors are open, the safe remains locked. Only when both are closed will it openβ€”this mirrors the AND conditions controlling the output's state effectively.

OR-AND-INVERT Gate Overview

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The OR-AND-INVERT gate can also be implemented in the same way. Figure 5.44 shows a typical internal schematic of a two-wide, two-input OR-AND-INVERT gate.
The output of this gate can be expressed by the Boolean equation
Y = (A + B)(C + D) (5.4)

Detailed Explanation

The OR-AND-INVERT gate combines two OR operations, followed by an AND operation, and then inverts the output. The relationship here is that Y = (A + B)(C + D), meaning the output is high (logic '1') when both combinations of OR operations yield true. Essentially, the circuit first checks each pair of inputs to see if either of them is non-zero and only then determines the final output by ANDing these results together.

Examples & Analogies

Think of a party invitation that requires two separate guest lists. For the event to happen (output '1'), at least one guest from list A or B needs to attend, and simultaneously, at least one from list C or D should also show up. The final decision to throw the party depends on having enough guests from both lists – this is similar to how the OR-AND-INVERT gate functions by combining inputs in a way that depends on both sets being active.

Definitions & Key Concepts

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Key Concepts

  • AND-OR-INVERT Gate: Implements an AND operation followed by an OR and then an INVERSION.

  • OR-AND-INVERT Gate: Implements an OR operation followed by an AND and then an INVERSION.

  • CMOS Technology: Utilizes N-channel and P-channel MOSFETs for constructing logic gates.

Examples & Real-Life Applications

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

Examples

  • In a practical scenario, if A=0, B=0, C=1, D=0 for the AND-OR-INVERT gate, the output Y will be Y = (00) + (10)' = 0 + 1 = 1. Thus, the output is high.

  • For the OR-AND-INVERT gate, if A=1, B=1, C=0, D=1, Y = (1 + 1)' * (0 + 1)' = 0 * 1 = 0. Therefore, the output Y is low.

Memory Aids

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

🎡 Rhymes Time

  • A gate called AND-OR, gives outputs galore; When A and B are true, Y will be zero, you see!

πŸ“– Fascinating Stories

  • Imagine two friends A and B trying to enter a party where C and D wait outside. The party is off if both pairs show up. Only when one is absent can the fun begin!

🧠 Other Memory Gems

  • Remember AOI: A And B, O Or C, I Inversion.

🎯 Super Acronyms

Memory aid for AND-OR-INVERT is 'AOI'.

Flash Cards

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Glossary of Terms

Review the Definitions for terms.

  • Term: ANDORINVERT Gate

    Definition:

    A logic gate that performs both AND and OR operations, followed by an inversion.

  • Term: ORANDINVERT Gate

    Definition:

    A logic gate that performs OR operations first followed by an AND, and then inverts the result.

  • Term: CMOS

    Definition:

    Complementary Metal-Oxide-Semiconductor; a technology for constructing integrated circuits.

  • Term: Nchannel MOSFET

    Definition:

    A type of MOSFET that conducts when a positive voltage is applied to the gate.

  • Term: Pchannel MOSFET

    Definition:

    A type of MOSFET that conducts when a negative voltage is applied to the gate.

  • Term: Boolean Expression

    Definition:

    A mathematical representation of logical variables and operations.