Puzzle 40 of 100

A smaller exclusive OR

Goal

Make Y high while A and B differ. The die has room for two rows of cells that share the GND rail.

Die: 13 by 26 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Inputs: A, B
Output: Y
Supply: VDD, VDD
Ground: GND

New in this puzzle

Fewer transistors

The output of one gate can be an input of a compound gate. A NOR gate gives the AND of the inverses of A and B in one step, so it replaces two inverters and a pair of transistors.

Hint

The NOR of A and B is high while both are low, so Y is low while A and B are both high, or while their NOR is high. Draw a NOR gate in the upper row and feed it to a compound gate in the lower row. A and B pass under the GND rail from one row to the next.

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 40, A smaller 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 40, A smaller 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 40, A smaller 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

Metal92 squares
Polysilicon65 squares
Contact21 squares
N active12 squares
P active24 squares
N well80 squares
Input padA, B
Output padY
Supply padVDD, VDD
Ground padGND
Squares you draw, change, or erase154 squares

About the drawing

The drawing uses 188 of the die's 338 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 149 empty squares and change 5 drawn squares.
It forms 10 transistors: 5 N transistors and 5 P transistors. Each one is a place where polysilicon crosses active silicon.
21 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 40, A smaller exclusive OR, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.