Puzzle 48 of 100

A dynamic gate

Goal

While CLK is low, Y must be high. While CLK is high, Y falls when A and B are both high, and then stays low until CLK falls, even if A or B falls first.

Die: 12 by 16 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Inputs: A, B, CLK
Output: Y
Supply: VDD
Ground: GND

Go to the solution

New in this puzzle

Precharge

While CLK is low, a P transistor charges the output node high. When the transistor turns off, the node keeps its charge.

Evaluate

While CLK is high, the N transistors can discharge the node, and nothing can charge it again until CLK falls. The CLK transistor at the bottom of the stack keeps the stack from fighting the precharge.

Guide

Draw a P transistor from VDD to Y with its gate on CLK.
Draw three N transistors in series from Y to GND, with their gates on A, B, and CLK.
Join the P transistor and the top of the N stack to Y.

Hint

Put one P transistor between VDD and Y with its gate on CLK, to charge Y while CLK is low. From Y to GND, put three N transistors in series with their gates on A, B, and CLK, so that Y can fall only while CLK is high.

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 48, A dynamic 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 48, A dynamic 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 48, A dynamic 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

Metal51 squares
Polysilicon42 squares
Contact11 squares
N active14 squares
P active6 squares
N well28 squares
Input padA, B, CLK
Output padY
Supply padVDD
Ground padGND
Squares you draw, change, or erase68 squares

About the drawing

The drawing uses 103 of the die's 192 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 66 empty squares and change 2 drawn squares.
It forms 4 transistors: 3 N transistors and 1 P transistor. Each one is a place where polysilicon crosses active silicon.
11 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 48, A dynamic gate, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.