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Detailed overview of different types of latches and flip flops, their characteristics, and how they function within sequential circuits. ​

Objectives

  • Introduction to memory elements
  • Explanation of various types of latches and flip-flops
  • Characteristics tables for different flip-flops

Introduction

  • Combinational circuits depend on the current input and lack memory.
  • Sequential circuits depend on both current input and past output, incorporating memory elements.
  • Sequential circuits consist of combinational logic and memory elements.

Types of Sequential Circuits

  • Synchronous: Output changes at specific times, memory elements affected at discrete instants.
  • Asynchronous: Output changes at any time based on input.

Memory Elements

  • Flip-flops: Memory elements that change state on clock signals, typically a square wave.
  • Triggering Types:
    • Pulse-triggered: Includes latches, ON = 1, OFF = 0.
    • Edge-triggered: Includes flip-flops, triggered by positive or negative edge of the clock signal.

S-R Latch

  • Active-HIGH S-R Latch: Uses NOR gates, has SET and RESET states.
  • Active-LOW S’-R’ Latch: Uses NAND gates, has SET and RESET states.
  • Characteristics tables provided for both types.

D Latch

  • Eliminates invalid state of S-R latch.
  • When enable (EN) is HIGH, Q follows D input.
  • Characteristics table provided.

Flip-Flops

  • Suitable for synchronous logic circuits.
  • Use clock signals to control state changes.
  • Edge-triggered Flip-Flops: Change state at clock edges (positive or negative).

Types of Flip-Flops

  • S-R Flip-Flop: Comprises NAND latch, pulse-steering circuit, and pulse transition detector.
  • D Flip-Flop: Single input D, Q follows D at clock edge.
  • J-K Flip-Flop: No invalid state, includes toggle state.
  • T Flip-Flop: Complementing flip-flop, can be made using J-K or D flip-flop.

Characteristics Tables

  • Provided for S-R, D, J-K, and T flip-flops, detailing their behavior based on inputs and clock signals.

This document provides a detailed overview of different types of latches and flip-flops, their characteristics, and how they function within sequential circuits.

Flip Flops – Lesson 7

Engineering Institute of Technology