Understanding Logic Gates - The brains behind Digital Electronics

In the world of digital electronics, everything runs on 0s and 1s. And the magic behind processing these binary values? Logic Gates. From microprocessors to memory chips, every digital device you use is built using these basic building blocks.

Primary Logic Gates:

  • They are called "primary" because they are the basic building blocks of digital electronics.
  • These gates perform the most fundamental logical operations

⮞ AND Gate:(Multiplication-like)


  • The output is 1 only if both inputs are 1.
  • Boolean Expression: Y = A·B

⮞ OR Gate:(addition-like)

  • The output is 1 if any one or both inputs are 1.
  • Boolean Expression: Y = A + B

⮞ NOT Gate:(inversion)

  • It inverts the input.
  • Boolean Expression: Y = A̅  

Why Primary?

Because all other complex circuits and logic functions are ultimately built from combinations of these three basic gates. They are the "first" layer of logic.


Note: NOT gate acts only on a single input.

Universal Logic Gates:

  • They are called "universal" because you can use only one type of them to build any logic circuit.
  • NAND and NOR gates are universal.

Using only NANDs or only NORs, you can make AND, OR, NOT, and any other logic circuit.

⮞ NAND Gate (NOT + AND):

  • It is the complement of the AND gate.
    Boolean Expression: Y = 

⮞ NOR Gate (NOT + OR)

  • It is the complement of the OR gate.
  • Boolean Expression: Y =

Why Universal?

Because they are powerful enough to "universally" implement any logic function without needing other gates.

Both NAND and NOR gates are called universal gates because any digital logic circuit can be built using only these gates.

Derived(Secondary) Logic Gates:

  • They are called "derived" because they are created by combining primary gates.
  • These are secondary gates formed from the basic ones

⮞ XOR Gate (Exclusive OR):

  • Output is 1 if only one input is 1.
  • Boolean Expression: Y = A̅B + AB̅

⮞ XNOR Gate (Exclusive NOR):

  • Output is 1 if both inputs are the same (either both 0 or both 1).
  • Boolean Expression: Y = AB + A̅B̅

⮞ NAND gate (NOT + AND)

⮞ NOR gate (NOT + OR)

Why Derived?

Because you derive them (create them) using primary gates.

  • Primary = Basic ingredients (like flour, sugar, salt)
  • Derived = Recipes made using the ingredients (like cake, cookies)
  • Universal = A super ingredient (like magic powder!) from which you can make any recipe alone!

Boolean Algebra and Expression Simplification:

Boolean Algebra is used to simplify complex expressions and reduce the number of gates in a circuit.


Some important laws:

            A + AB = A (Absorption Law)

            A(A + B) = A (Absorption Law)

            A + A = A

            A · A = A


Tip:

For more than three variables, you can use K-Maps (Karnaugh Maps) to make minimization faster and easier — a vital skill for logic designers!


In Short:

  • AND, OR, NOT are the primary gates.
  • NAND and NOR are the universal gates.
  • XOR and XNOR are derived gates.
  • Boolean algebra helps simplify and optimize designs.
  • Truth tables define how a gate behaves for each input combination.


Coming up next in the Digital Series: Number Systems Conversion - stay tuned to hobitronics.blog

Comments

  1. GummyBear28 April 2025 at 02:40

    As NAND as well as NOR gates are both universal and derived as we get it from NOT + AND , NOT+OR , but leaving gates (eg) in CMOS technology , we can implement NAND , NOR logic using pull up and pull down network .... then can it still be a derived gate or will that behave as a basic gate?

    ReplyDelete
    Replies
    1. Hobitronics28 April 2025 at 02:55

      In CMOS technology, NAND and NOR behave as basic gates because they are directly implemented using pull-up and pull-down networks, even though functionally they are derived (NOT + AND/OR) in Boolean logic.

      Delete

Post a Comment

Popular posts from this blog

Decoding the Invisible: Your Journey into Communication Systems Begins Here!

Image
From WhatsApp texts to satellite signals—communication systems are the invisible threads weaving our world together.  And now, you’re about to understand how it all works. 🌐 Why Communication Systems Matter? Ever paused and wondered how your voice travels across continents in seconds? Or how your phone knows you're streaming that YouTube video in HD with zero lag? Welcome to the magic of communication systems —the lifeline of our connected world. From basic AM radios to 5G networks, and from Morse code to high-speed fiber optics, communication systems have evolved massively. Today, they're at the heart of: 📱 Smartphones and Internet 🛰️ Satellite Navigation 📶 Wireless Networks and IoT 💬 Instant Messaging and Cloud Computing 🌍 Global Broadcasting and Live Streaming 🚀 What to Expect in the Hobitronics Communication Series? Basics Demystified:  Signals, bandwidth, modulation, transmission lines—made simple and visual. Analog vs Digital:   Understand h...
Read more

Current Conduction in Semiconductors: Drift and Diffusion Explained

Image
Current conduction in semiconductors , unlike in metals, is influenced not only by electric fields but also by how charge carriers —electrons and holes—are distributed spatially . Two primary mechanisms govern this conduction: ✅ Drift Current – Carrier motion under the influence of an electric field ✅ Diffusion Current – Carrier motion due to concentration gradients These two mechanisms are fundamental in the operation of key electronic components such as diodes, transistors, and solar cells . 1. Drift Current – Motion Under an Electric Field When an electric field (E) is applied across a semiconductor, it exerts a force on mobile charge carriers— electrons and holes . This causes them to accelerate and generate a net flow of charge , which we call drift current . Drift Current Formula: Where: q = charge of an electron (1.6 × 10⁻¹⁹ C) n = carrier concentration (per m³) μ = mobility of carriers (m²/V·s) E = applied electric field (V/m) What Happens Without a...
Read more

Understanding Masking, Enabling, and Disabling of Logic Gates

Image
In digital electronics, logic gates are the basic building blocks of all digital systems. But did you know that we can control whether a gate actively participates in a circuit using masking , enabling , and disabling techniques? These are crucial concepts, especially when working with multiplexers , tri-state buffers , and control logic . Let’s break it down in simple terms. What is Masking in Logic Gates? Masking is a method of controlling the output of a logic gate by using a specific input value (often 0 or 1) to “mask” or block the effect of another input. It's widely used in data handling , interrupt systems , and bitwise operations . Example: AND Gate Masking Let A = input signal Let B = mask Output = A AND B If B = 1 → Output = A (no masking) If B = 0 → Output = 0 (signal is masked) Example: OR Gate Masking Let A = input signal Let B = mask Output = A OR B If B = 0 → Output = A (no masking) If B = 1 → Output = 1 (signal is masked) This is especia...
Read more

SOP vs POS in Boolean Algebra

Image
What is SOP (Sum of Products)? SOP is a series of AND terms added together (ORed) . Each product term represents a unique combination where the output is 1. Example : F(A, B, C) = A \cdot B' \cdot C + A' \cdot B \cdot C F ( A , B , C ) = A ⋅ B ′ ⋅ C + A ′ ⋅ B ⋅ C Used in : Combinational logic, digital gates, circuit simplification. What is POS (Product of Sums)? POS is a series of OR terms multiplied together (ANDed) . Each sum term represents a condition where the output is 0. Example : F ( A , B , C ) = ( A + B + C ′ ) ⋅ ( A ′ + B + C ) Used in : Logic minimization, designing circuits from false outputs.   SOP vs POS: Key Differences Canonical vs Non-Canonical Forms Canonical forms are ideal for deriving expressions directly from truth tables. How to Derive SOP and POS from a Truth Table Example Truth Table: SOP (Use F = 1 rows): Row 2: A=0 , B=1 → A'·B Row 3: A=1 , B=0 → A·B' SOP = A'·B + A·B' POS (Use F = 0 rows): Row...
Read more

Where Does the Conduction Band Exist?

Image
Understanding the Origin of Conduction and Valence Bands in Semiconductors In every semiconductor textbook, we read about the "valence band" and the "conduction band." But have you ever paused to ask— where exactly do these bands come from? Are they part of an atom? Do they exist naturally? Or do they arise from something deeper? Let’s break this concept down and explore the true origin of the conduction band in solids—especially semiconductors. “The Conduction Band Exists Inside an Atom”- Does it? This is a very common misunderstanding — that individual atoms have conduction bands. But here’s the truth: A single, isolated atom does not have a conduction band. Instead, atoms have discrete energy levels , like steps on a staircase. Electrons in atoms can only occupy these specific levels— no continuous band of energies exists. What Happens When Atoms Come Together? Now here’s where the real magic begins. When many atoms combine to form a solid , their outerm...
Read more

From Chaos to Clean Circuits: K-Maps Make Logic Easy

Image
Welcome back to the Hobitronics Digital Electronics Series ! Today, we’re diving into one of the most powerful logic simplification tools: the Karnaugh Map (K-Map) . If you want cleaner circuits, fewer logic gates, and optimal Boolean expressions—this post is for you. What is a Karnaugh Map? A Karnaugh Map (K-Map) is a grid-based method used to simplify Boolean algebra expressions without complex algebraic steps. It visually organizes truth table outputs (1s and 0s). Makes it easier to group terms that can be combined. Minimizes logic circuits, saving gates and power. Why Use K-Map? Simplifies expressions : Groups adjacent 1s to reduce the number of terms. Reduces hardware complexity : Minimizes logic gates required in the final circuit. Eliminates redundancy : Removes unnecessary or repeated logic components. Easy visualization : Makes logical groupings clearer than manipulating equations. Prime Implicants and Variants 1. Prime Implicant (PI) : A group of 1s (or minter...
Read more

Carrier Lifetime & Current Flow in Direct vs Indirect Bandgap Semiconductors Explained

Image
Semiconductors aren’t just about electrons jumping between bands—they’re also about how long they live in those excited states and how they move to generate current. In this post, we explore the key idea of carrier lifetime , the nature of electrons and holes , and why direct and indirect bandgap materials behave very differently. What is Carrier Lifetime? Carrier lifetime is the average time an electron-hole pair exists before recombination . In direct bandgap semiconductors , the conduction band minimum and valence band maximum align. Recombination is easy and fast, emitting photons. Carrier lifetime is short . In indirect bandgap semiconductors , the conduction band and valence band do not align. Recombination is slower, requiring phonons (vibrations) to assist. Carrier lifetime is longer . This is why LEDs use direct bandgap materials —quick recombination emits light. Whereas indirect bandgap materials like silicon are better for solar cells, where longer carrier lifetime...
Read more

Understanding Signals and Modulation

Image
Communication systems rely on signals to transmit  information  effectively. These signals vary based on  frequency  and  origin , shaping how data is conveyed and interpreted. Types of Signals Signals can be categorized based on their frequency range: Low-Frequency Signals  (Below 300 Hz): Found in seismic waves and brain signals. Mid-Frequency Signals  (300 Hz – 30 kHz): Includes human voice, music, and standard audio transmissions. High-Frequency Signals  (30 kHz – 300 GHz): Used in television, satellite communication, and radar systems. Common Signal Sources and Their Frequency Ranges: Introduction to Modulation Transmission of signals over  long  distances comes with challenges such as  interference  and  signal degradation . This is where modulation plays a crucial role. What is Modulation? Modulation is the technique of altering a signal to ensure effective transmission. It involves modifying a carrier wave accordin...
Read more