Puzzle 21 of 100

A NAND gate

Goal

Make Y low only while A and B are both high. For every other pair of inputs Y is high.

Die: 13 by 12 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Inputs: A, B
Output: Y
Supply: VDD
Ground: GND

New in this puzzle

Transistors in series

Two transistors in a row along one strip conduct only while both of them are on. The silicon between them needs no contact.

Transistors side by side

Two transistors that join the same two nodes conduct while either of them is on. In a NAND gate the P pair shares its middle contact, which is the output.

Guide

Choose N Well and paint the outlined block under VDD, then paint P active silicon along the strip inside it.
Paint two polysilicon lines down across the P active silicon and on toward GND. Each line forms a P transistor where it crosses.
Paint N active silicon across both lines just above GND. The two N transistors it forms are in series.
Place the outlined contacts, and join the outer P contacts to VDD and the left N contact to GND.
Bring A and B along metal to the contacts beside their polysilicon lines. Metal passes over polysilicon without joining it.
Join the middle P contact to the right N contact, and run that line to Y.

Hint

Put two P transistors side by side between VDD and Y, so that either input can pull Y high. Put two N transistors in a row between Y and GND, so that Y falls only while both conduct. Each input's polysilicon line forms one P gate and one N gate.

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 21, A NAND gate, 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 21, A NAND gate, 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 21, A NAND gate, 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

Metal62 squares
Polysilicon22 squares
Contact10 squares
N active8 squares
P active16 squares
N well44 squares
Input padA, B
Output padY
Supply padVDD
Ground padGND
Squares you draw, change, or erase85 squares

About the drawing

The drawing uses 111 of the die's 156 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 85 empty squares.
It forms 4 transistors: 2 N transistors and 2 P transistors. Each one is a place where polysilicon crosses active silicon.
10 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 21, A NAND gate, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.