Circuits: VLSI

Puzzle 26 of 100

A strong NAND

Goal

Y now drives a large load. Widen the transistors so that both edges are at least as fast as the target.

Die
13 by 17 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

Width in series

Transistors in series share one path, and the current of the pair is limited by both. To match one transistor two squares wide, two in series need four squares each.

Hint

Two N transistors in series pass about half the current of one, so each needs twice the width of a single pull-down. Each P transistor pulls Y up on its own.

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 26, A strong NAND, 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 26, A strong NAND, 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 26, A strong NAND, 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

  • Metal74 squares
  • Polysilicon32 squares
  • Contact22 squares
  • N active32 squares
  • P active32 squares
  • N well66 squares
  • Input padA, B
  • Output padY
  • Supply padVDD
  • Ground padGND
  • Squares you draw, change, or erase54 squares

About the drawing

  • The drawing uses 157 of the die's 221 squares.
  • Part of the drawing is in place when the puzzle opens. To finish it, paint 31 empty squares and change 23 drawn squares.
  • It forms 4 transistors: 2 N transistors and 2 P transistors. Each one is a place where polysilicon crosses active silicon.
  • 22 contacts join metal to the polysilicon or active silicon under it.
Starting drawing for puzzle 26, A strong NAND, on a numbered grid.
The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.