Circuits: VLSI

Puzzle 36 of 100

A multiplexer

Goal

Make Y follow B while S is high, and A while S is low. The inverter for S and an output inverter are drawn.

Die
19 by 18 squares
Layers
Metal, Polysilicon, Contact, N active, P active, N well
Inputs
A, B, S
Output
Y
Supply
VDD
Ground
GND

Go to the solution

New in this puzzle

A select line

S enables one pair and its inverse enables the other, so only one input reaches the output at a time. The pair that is turned off cannot affect Y.

Hint

Draw a gate of two pairs that is low while S and B are both high, or while the inverse of S and A are both high. Its output is the inverse of the chosen input, so it feeds the output inverter. S can reach its second gate line by passing under the GND rail.

Solution

This is the game's reference drawing for the puzzle. It meets the goal and passes the design rules. Other drawings can pass as well.

Top View of the solved die for puzzle 36, A multiplexer, with the Side View below it.
Top View of the solved die, captured from the game. Paths that carry a high level at the moment shown are lit. The Side View below cuts through the row between the dashed lines.
The game window in Isometric View with the solved die for puzzle 36, A multiplexer, the guide, and the scope.
The whole game window in Isometric View. The scope on the right compares each output with its target band, and the message above it confirms that the drawing passes.
Solution drawing for puzzle 36, A multiplexer, drawn on a numbered grid with every layer in its game color and pattern.
The solution on the grid. Squares are numbered from the top left corner, so you can count them. The dashed outline marks the squares you draw, change, or erase; the rest is drawn when the puzzle opens.

Legend

  • Metal115 squares
  • Polysilicon90 squares
  • Contact26 squares
  • N active15 squares
  • P active30 squares
  • N well38 squares
  • Input padA, B, S
  • Output padY
  • Supply padVDD
  • Ground padGND
  • Squares you draw, change, or erase108 squares

About the drawing

  • The drawing uses 202 of the die's 342 squares.
  • Part of the drawing is in place when the puzzle opens. To finish it, paint 103 empty squares and change 5 drawn squares.
  • It forms 12 transistors: 6 N transistors and 6 P transistors. Each one is a place where polysilicon crosses active silicon.
  • 26 contacts join metal to the polysilicon or active silicon under it.
Starting drawing for puzzle 36, A multiplexer, on a numbered grid.
The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.