Puzzle 93 of 100

A twisted ring

Goal

Make Q0 and Q1 step through 00, 10, 11, 01 and repeat: on each rising edge of CLK, Q0 takes the inverse of Q1 and Q1 takes Q0.

Die: 30 by 29 squares
Layers: Metal, Polysilicon, Contact, N active, P active, N well, Metal 2, Via
Inputs: CLK, CLKN
Outputs: Q0, Q1
Supply: VDD, VDD
Ground: GND, GND

Go to the solution

New in this puzzle

A ring with a twist

Flip-flops joined in a ring pass a value along on each clock edge. With one inversion in the ring, the ring fills with ones and then with zeros, so two flip-flops step through four states.

Hint

Join QN1 to D0 and Q0 to D1. The two outputs become square waves at a quarter of the clock frequency, a quarter period apart.

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 93, A twisted ring, 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 93, A twisted ring, 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 93, A twisted ring, 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

Metal226 squares
Polysilicon60 squares
Contact40 squares
N active22 squares
P active22 squares
N well90 squares
Metal 2295 squares
Via53 squares
Input padCLK, CLKN
Output padQ0, Q1
Supply padVDD, VDD
Ground padGND, GND
Squares you draw, change, or erase113 squares

About the drawing

The drawing uses 491 of the die's 870 squares.
Part of the drawing is in place when the puzzle opens. To finish it, paint 104 empty squares and change 9 drawn squares.
It forms 16 transistors: 8 N transistors and 8 P transistors. Each one is a place where polysilicon crosses active silicon.
40 contacts join metal to the polysilicon or active silicon under it.
53 vias join metal 2 to the metal under it.

Starting drawing for puzzle 93, A twisted ring, on a numbered grid. — The drawing when the puzzle opens. The dashed outline marks the squares the solution changes.