Circuits: VLSI

Puzzle 12 of 100

P transistors need a well

Goal

Make Y follow A only while C is low.

Die
12 by 8 squares
Layers
Metal, Polysilicon, Contact, N active, P active, N well
Inputs
C, A
Output
Y

Go to the solution

New in this puzzle

P active silicon and the N well

A P transistor is the opposite switch: it conducts while its polysilicon is low. P active silicon must lie inside an N well.

Guide

  1. Choose N Well and paint a block five squares wide and three tall in the middle of the die.
  2. Paint metal from A and from Y up to the edge of the well.
  3. Choose P Active and paint the middle row of the well.
  4. Place a contact on each end of the P active silicon.
  5. Place a contact under C, then paint polysilicon from it down across the P active silicon and one square past it.
  6. Watch the scope. Y follows A only while C is low.

Hint

A P transistor conducts while its gate is low. P active silicon must sit inside an N well, so paint the well first and the P active silicon over it.

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 12, P transistors need a well, 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 12, P transistors need a well, 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 12, P transistors need a well, 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.

Legend

  • Metal11 squares
  • Polysilicon5 squares
  • Contact3 squares
  • P active5 squares
  • N well15 squares
  • Input padC, A
  • Output padY

About the drawing

  • The drawing uses 25 of the die's 96 squares.
  • The die starts empty, so you draw every square.
  • It forms 1 transistor: 1 P transistor. Each one is a place where polysilicon crosses active silicon.
  • 3 contacts join metal to the polysilicon or active silicon under it.