Structure Description:

Inputs:

A$,$ B$,$ C$,$ D $(4$ input bits$)$

Inverters:

$4$ NOT gates, one for each input, providing A$\text{'},$ B$\text{'},$ C$\text{'},$ and D$\text{'}.$

AND Gates:

$16$ AND gates arranged in a $4$x$4$ grid.

Outputs:

Y$0$ to Y$15(16$ output lines, each corresponding to a specific AND gate$)$

Visualization Guidance:

Imagine a $4$x$4$ grid of AND gates.

Each row represents a combination of A and A$\text{'}.$

Each column represents a combination of B and B$\text{'}.$

Within each cell, place an AND gate with inputs matching the pattern for Y$0$ to Y$15($as described in my previous responses$).$

Connect D and D$\text{'}$ appropriately to the AND gates, following the rule from Figure $1\mathrm{.}8.$

Key Points:

The DCD$4$ decoder doubles the number of AND gates from DCD$3$ and strategically connects them to D and D$\text{'}$ to achieve $16$ unique outputs.

This construction pattern can be extended to create decoders with even more inputs.