Combinational vs Sequential Circuits
Combinational vs Sequential Circuits
1. Combinational Circuits
Definition:
Circuits where the output depends only on the current inputs at any given time.
Key Feature:
No memory or feedback elements; they do not store past input information.
Examples:
Adders (e.g., Half Adder, Full Adder)
Multiplexers
Decoders
Encoders
Comparators
Behavior:
The output changes immediately when the inputs change.
Implementation:
Built using logic gates (AND, OR, NOT, NAND, etc.)
2. Sequential Circuits
Definition:
Circuits where the output depends on both current inputs and past history (previous inputs).
Key Feature:
They contain memory elements like flip-flops or latches to store state information.
Examples:
Counters
Shift Registers
Finite State Machines
Memory devices (RAM)
Behavior:
The output depends on the sequence of inputs over time, not just the current input.
Implementation:
Combination of logic gates + memory elements (flip-flops/latches).
Comparison Table
Feature Combinational Circuits Sequential Circuits
Memory None Has memory elements
Output depends on Present inputs only Present inputs and past states
Timing No clock needed Usually synchronized with a clock signal
Complexity Simpler More complex
Examples Adders, MUX, Decoder Counters, Registers, State Machines
Summary
Combinational circuits: output = function of inputs now.
Sequential circuits: output = function of inputs and history (stored state).
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