Question

Which of the following is a sequential logic circuit?

• A. Full adder
• B. Multiplexer
• C. Flip-flop
• D. Decoder

Hint:

If a circuit has memory (stores past information), it is sequential. If output depends only on current inputs, it is combinational.

Answer 1

The Correct Option is C

Concept: Digital logic circuits are broadly classified into two types:
• Combinational Circuits: Output depends only on present inputs. These circuits do not have memory. Examples include adders, multiplexers, and decoders.
• Sequential Circuits: Output depends on both present inputs and past states (memory). These circuits contain storage elements like flip-flops. A flip-flop is the fundamental building block of sequential circuits, as it can store one bit of information and retain its state until changed by input signals.

Step 1: Understanding each option
• Full Adder: A full adder performs binary addition of three inputs (A, B, Carry-in) and produces Sum and Carry-out. It does not store any previous value. Hence, it is a combinational circuit.
• Multiplexer: A multiplexer selects one of many inputs based on selection lines and forwards it to the output. It performs selection only based on current inputs, so it is also a combinational circuit.
• Flip-flop: A flip-flop can store a binary value (0 or 1). Its output depends not only on current input but also on its previous state. Therefore, it is a sequential circuit.
• Decoder: A decoder converts binary input into one of many outputs. It has no memory element and depends only on present inputs. Hence, it is a combinational circuit.

Step 2: Final conclusion Among all the given options, only the flip-flop has memory and exhibits sequential behavior. \[ \therefore \text{Correct answer is (C) Flip-flop} \]