Question

The device shown here is most likely a _________.

• A. Comparator
• B. Multiplexer
• C. Inverter
• D. Demultiplexer

Hint:

To quickly tell routing devices apart in block diagrams: - Multiplexer (Data Selector): Many inputs $\rightarrow$ One output. - Demultiplexer (Data Distributor): One input $\rightarrow$ Many outputs. - Decoder: Binary input code $\rightarrow$ Single active output line (often structurally identical to a DEMUX where the data input serves as an enable control).

Answer 1

The Correct Option is D

Concept: Combinational digital components are characterized by how they route and process data based on their input, output, and control configurations:
• Multiplexer (MUX): Takes multiple input lines and routes a selected one to a single output line ($N$-to-$1$ device).
• Demultiplexer (DEMUX): Takes a single input line and routes it to one of several output lines ($1$-to-$N$ device) based on the states of its select lines.

Step 1: Analyzing the Provided Schematic Structure
Let us evaluate the pin layout shown in the diagram:
• Left side inputs: There is a single data input pin labeled $D$, and two binary control lines labeled $S_0$ and $S_1$. There is also an active-low enable pin labeled $\overline{\text{EN}}$ (indicated by the inversion bubble).
• Right side outputs: There are four distinct output pins labeled $Y_0, Y_1, Y_2,$ and $Y_3$, each featuring an active-low inversion bubble.

Step 2: Checking the Pin Ratio
The device takes one single data input source ($D$) and splits it across four potential output lines ($Y_0$ to $Y_3$). This configuration represents a $1$-to-$4$ distribution network. The specific output destination is selected using the two control lines ($S_1S_0$):
• $S_1S_0 = 00 \rightarrow$ Route input $D$ to output $Y_0$
• $S_1S_0 = 01 \rightarrow$ Route input $D$ to output $Y_1$
• $S_1S_0 = 10 \rightarrow$ Route input $D$ to output $Y_2$
• $S_1S_0 = 11 \rightarrow$ Route input $D$ to output $Y_3$ This $1$-input-to-$2^n$-outputs structural behavior defines a Demultiplexer.

Step 3: Disproving alternative choices

• Comparator: Compares two multi-bit binary numbers to determine if they are equal or if one is greater, outputting a simple true/false status signal.
• Multiplexer: Routes one of many inputs to a single output line, which is the exact inverse of this diagram.
• Inverter: A simple single-input, single-output gate that outputs the logical complement of its input.