Circuits: VLSI

Puzzle 35 of 100

Exclusive OR

Goal

Make Y high while A and B differ. The compound gate and two inverters are drawn: connect them.

Die
22 by 20 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

Inputs and their inverses

A compound gate fed with the inputs and their inverses can compute functions that no plain gate can. The exclusive OR of A and B is not(A and B, or not A and not B).

Hint

Y is low while A and B are both high, or both low. Feed A and B to the inverters and to one pair of gate lines of the compound gate, and the inverter outputs to the other pair. A line can pass above the VDD rail or below the GND rail to get around the cells.

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 35, Exclusive OR, 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 35, Exclusive OR, 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 35, Exclusive OR, 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

  • Metal139 squares
  • Polysilicon92 squares
  • Contact27 squares
  • N active15 squares
  • P active30 squares
  • N well42 squares
  • Input padA, B
  • Output padY
  • Supply padVDD
  • Ground padGND
  • Squares you draw, change, or erase67 squares

About the drawing

  • The drawing uses 229 of the die's 440 squares.
  • Part of the drawing is in place when the puzzle opens. To finish it, paint 60 empty squares and change 7 drawn squares.
  • It forms 12 transistors: 6 N transistors and 6 P transistors. Each one is a place where polysilicon crosses active silicon.
  • 27 contacts join metal to the polysilicon or active silicon under it.
Starting drawing for puzzle 35, Exclusive OR, on a numbered grid.
The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.