Puzzle 41 of 100

A transmission gate

Goal

Make Y follow A at full level while C is high, and keep its last level while C is low. CN is always the inverse of C.

Die: 12 by 12 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well
Inputs: C, A, CN
Output: Y

New in this puzzle

A weak high

An N transistor passes a low level fully, but it passes a high only partway, because it turns off as its far side rises toward its gate voltage. A P transistor does the opposite: it passes a high fully and a low only partway.

Transmission gate

An N transistor and a P transistor between the same two nodes, with opposite gate signals, turn on and off together. Each passes the level the other passes poorly, so the pair passes both levels fully.

Guide

Choose N Well and paint the outlined block under the N switch.
Choose P Active and paint the middle row of the well.
Place a contact on each end of the P active silicon.
Place a contact above CN, then paint polysilicon from it up across the P active silicon and one square past it.
Join each end of the P switch to the end of the N switch above it.

Hint

The N switch passes a low fully but a high only partway. Add a P switch between the same two nodes with its gate on CN, because a P switch passes a high fully. Together the two switches are a transmission 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 41, A transmission 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 41, A transmission 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 41, A transmission 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

Metal21 squares
Polysilicon9 squares
Contact6 squares
N active5 squares
P active5 squares
N well15 squares
Input padC, A, CN
Output padY
Squares you draw, change, or erase20 squares

About the drawing

The drawing uses 38 of the die's 144 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 20 empty squares.
It forms 2 transistors: 1 N transistor and 1 P transistor. Each one is a place where polysilicon crosses active silicon.
6 contacts join metal to the polysilicon or active silicon under it.

Starting drawing for puzzle 41, A transmission gate, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.