Sequential Circuits

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Arjit Sharma
01 Min

Sequential circuits are logic circuits with memory . Their output depends not only on current inputs but also on the history of inputs.

Key Characteristics -

  • Use feedback loops to store state
  • Require a clock signal for timing (in synchronous systems)
  • Built using flip-flops and latches

Types of Sequential Circuits

1. Latches

Simplest memory elements, storing 1 bit and built using NOR or NAND gates.

  • SR Latch: Stores 1 bit using Set (S) and Reset (R) inputs

SR-Latch

2. Flip-Flops

Clocked version of latches where data changes only on clock edge (e.g., rising or falling).

  • Types:
    • SR Flip-Flop: Like an SR latch but clock-controlled.
    • D Flip-Flop: Stores the input bit on clock edge
    • JK Flip-Flop: Versatile, no invalid state
    • T Flip-Flop: Toggles output on each clock pulse

3. Registers

Group of flip-flops used to store multi-bit values. They are synchronized by clock, used in processors for temporary data storage

4. Counters

Circuits that count clock pulses in sequence. There are multiple types like Up Counter, Down counter etc

5. Finite State Machines (FSMs)

Models that manage sequences by transitioning between states. These are defined by -

  • States: Defined conditions (e.g., “idle,” “active”).
  • Inputs/Outputs: Determine transitions and results.
  • Transition Logic: Rules for moving between states.

Example - A traffic light controller cycling through “red”, “green” and “yellow”.

Conclusion

These circuits are essential for building CPUs, timers, memory controllers, and any logic that must respond to sequences over time.

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