Understanding Combinational Circuits: Multiple Inputs to Single Output

This question asks us to identify a specific type of combinational circuit. Combinational circuits are digital logic circuits whose output depends solely on the current combination of their inputs. They don't have memory elements like flip-flops, meaning their past states don't influence the current output.

The core function we're looking for is a circuit that takes multiple inputs and processes them to produce a single output. Let's examine the options provided:

Analyzing Circuit Functions

• Multiplexer (MUX):
  • A multiplexer is often called a 'data selector'.
  • It features multiple data input lines (e.g., \(I_0, I_1, I_2, I_3\)) and typically one or more select lines (control lines).
  • Based on the binary code applied to the select lines, the multiplexer chooses one of the multiple input lines and directs its data to a single output line.
  • Therefore, a multiplexer effectively converts multiple inputs into a single output based on control signals. This perfectly matches the question's description.
• Demultiplexer (DEMUX):
  • A demultiplexer performs the opposite function of a multiplexer.
  • It takes a single input line and routes it to one of several possible output lines.
  • The selection of the output line is controlled by select lines.
  • Since it converts a single input to multiple outputs, it does not fit the question's criteria.
• Decoder:
  • A decoder takes a binary input code (e.g., \(n\) bits) and activates one of \(2^n\) unique output lines.
  • For example, a 2-to-4 decoder has 2 input bits and 4 output lines. Only one output line is active (e.g., HIGH) for each unique combination of the 2 input bits.
  • While it has multiple inputs (the binary code) and multiple outputs, it doesn't convert multiple inputs to a *single* output in the way described. Its primary function is to decode an input code into a specific output line activation.
• Counter:
  • A counter is a sequential circuit, not a combinational circuit.
  • It uses memory elements (like flip-flops) to store its current state.
  • Counters are designed to change state in response to clock pulses or other inputs, typically counting events or clock cycles.
  • This functionality is fundamentally different from converting multiple inputs to a single output based purely on the present inputs.

Conclusion on Circuit Type

Based on the analysis, the Multiplexer is the combinational circuit specifically designed to select one from multiple inputs and route it to a single output line, controlled by select inputs.

Therefore, the correct answer is the Multiplexer.