Circuits: VLSI

Puzzle 27 of 100

A and not B

Goal

Make Y high only while A is high and B is low.

Die
15 by 15 squares
Layers
Metal, Polysilicon, Contact, N active, P active, N well
Inputs
A, B
Output
Y
Supply
VDD
Ground
GND

Go to the solution

New in this puzzle

An inverted input

An inverter in front of a gate input changes which level of that input the gate responds to. Many functions are a familiar gate with one input inverted.

Hint

Invert one of the inputs first. A NOR gate gives a high output only while both of its inputs are low. Connect the inverse of A to one NOR input and connect B directly to the other.

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 27, A and not B, 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 27, A and not B, 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 27, A and not B, 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

  • Metal69 squares
  • Polysilicon37 squares
  • Contact16 squares
  • N active8 squares
  • P active16 squares
  • N well52 squares
  • Input padA, B
  • Output padY
  • Supply padVDD
  • Ground padGND
  • Squares you draw, change, or erase100 squares

About the drawing

  • The drawing uses 128 of the die's 225 squares.
  • Part of the drawing is in place when the puzzle opens. To finish it, paint 98 empty squares and change 2 drawn squares.
  • It forms 6 transistors: 3 N transistors and 3 P transistors. Each one is a place where polysilicon crosses active silicon.
  • 16 contacts join metal to the polysilicon or active silicon under it.
Starting drawing for puzzle 27, A and not B, on a numbered grid.
The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.