Jongsok Choi M.A.Sc Candidate, University of

Toronto

Overview

TSMC 0.35 um technology Cadence tools Less than 2mm X 2mm die

area Design time = 1 month

Tile based approach Each tile contains a Logic Block,

2 Connections Blocks and a Switch

Box

Pass transistor approach

2

References

Architecture and CAD for Deep-Submicron FPGAs

3

Presentation Outline Schematics

Base Cells – Pass transistor, SRAM, Multiplexer Logic Block – LUT, Set/Reset Logic, D-flipflop Connection Box – Right, Bottom Switch Box Tile 2X2 Programming Circuitry – Row, Column FPGA 4X4 – Programming a multiplier FPGA 32X16 – full schematic

Layouts Base Cells – SRAM, Multiplexer, Pull-up Buffer Logic Block – LUT, Set/Reset Logic, D-flipflop Connection Box – Right, Bottom Programming Circuitry – Row, Column Tile – Single tile, Tile 2X2 FPGA 4X4 – Post-layout simulation of programmed multiplier FPGA 32X16 – floor plan, full layout Clock tree – H-tree implemented Complete layout with Padframe DRC, LVS Results Employed layout techniques and Conclusions

Schematics

5

Base Cells

Schematic Simulation

o Pass transistor

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Highlighted red boxes in the top right hand corner indicate where this cell is used (e.g. Pass transistor is used in the logic element, connection boxes 1 and 2, and the switch block)

Base Cells

Schematic Simulation

o SRAM cell : to program the FPGA with the required functionality

7

Base Cells

Schematic: Simulation

o 2-to-1 Multiplexer

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Base Cells

Schematic

Simulation

Sel2/Sel1 out

11 IN_1

10 IN_2

01 IN_3

00 IN_4

o 4-to-1 Multiplexer: to choose between the four SRAM bits in the LUT

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Logic Block

Top-level Schematic

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Logic Block - LUT Schematic

Simulation

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Logic Block – Set/Reset Logic Schematic:

Simulation When Sram 1, 2 set to ‘1’ => Set= 1 When Sram 1, 2 set to ‘0’ => Reset= 1

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Logic Block – D-Flip Flop

Simulation

Schematic

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Connection Box -Right

Schematic

Simulation Track2 selected when

SRAM set to ‘0’ Track1 selected when

SRAM set to ‘1’

o Functionality: Connect vertical tracks to logic element

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Connection Box -Bottom Top Level Schematic

Output from CB to Tracks Input to CB from

Tracks

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Switch Box

Schematic

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TILE 2x2

V1 V2 V3 V4

H1 H2

H3 H4

Schematic:Each tile has different connections at the switch box Segmented and staggered routing structure for FPGASegment Length of 2

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Programming Circuitry – Programming Column

Schematic

Simulation

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Schematic

Simulation

Programming Circuitry – Programming Row

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FPGA 4x4

Schematic

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FPGA Mapping and Programming bits for a 2 by 2 MultiplierTable shows manually created

bitstream to program the multiplier using 4X4 tiles with programming circuits

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FPGA 4x4

FPGA 4x4

0 1 2 3

0 1 2 30 1 2 3 0 1 2 30 1 2 3

0 1 2 3 0 2 4 6 0 3 6 9

Input 1

Input 2

Bit[3]

Simulation 2 by 2 Multiplier correctly implemented Shows correct output for all possible

inputs

Bit[2]

Bit[1]

Bit[0] Numbers shows total output

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FPGA 32x16 – Full Schematic

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Layouts

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Base Cells

Schematic Layout

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o SRAM cell : to program the FPGA with the required functionality

Base Cells

Schematic Layout

Sel2/Sel1 out

11 IN_1

10 IN_2

01 IN_3

00 IN_4 26

o 4-to-1 Multiplexer: to choose between the four SRAM bits in the LUT

Base Cells

Layout

27

o Pull-up buffer: used to pull the degraded signal back up to VDD

Logic Block

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Top-level Schematic

Logic Block - LUT

Layout

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Schematic

Layout

Logic Block – Set/Reset Logic Schematic

Layout

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Logic Block – D-flipflop

Layout

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Schematic

Logic Block

LUT Set/Reset Buffer_inverter for clock

Pullup Buffer

D-flipflop

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Layout

Connection Box -Right

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Layout

Schematic

Connection Box - Bottom

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Top-level Schematic

Output from Connection box to Tracks

Programming Circuitry – Programming Column

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Layout Schematic

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Programming Circuitry – Programming Column

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Programming Circuitry – Programming Row

Layout

Schematic

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Programming Circuitry – Programming Row

Tile

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Schematic

Tile -Layout

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Logic Element

Right Connection Box

Bottom Connection Box Switch Box

TILE 2x2 - Layout

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FPGA 4x4 - Layout

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FPGA Mapping and Programming bits for a 2 by 2 Multiplier Table shows manually created

bitstream to program the multiplier using 4X4 tiles with programming circuits

FPGA 4x4 - Post Layout Simulation

FPGA 4x4 – Post-Layout Simulation

0 1 2 3

0 1 2 30 1 2 3 0 1 2 30 1 2 3

0 1 2 3 0 2 4 6 0 3 6 9

Input 1

Input 2

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Bit[3]

Bit[2]

Bit[1]

Bit[0]Numbers shows

total output

Post-Layout Simulation 2 by 2 Multiplier correctly implemented Shows correct output for all possible inputs Matches schematic simulations

32x16 Tiles FPGA Floorplan

Program

ming R

ow

4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile

Programming Column

4x4 Tile4x4 Tile

4x4 Tile4x4 Tile

1.52

5 m

m

4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile4x4 Tile

4x4 Tile4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile4x4 Tile

4x4 Tile4x4 Tile

1.52

5 m

m

4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile

4x4 Tile4x4 Tile

4x4 Tile4x4 Tile

1.25 mm

1.525 mm

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FPGA 32x16 - Layout

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Clock Tree

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H-tree structurePerfectly symmetrical in every direction to reduce

clock skew

Complete layout with Padframe

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DRC - Passed

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LVS - Passed

Layout Techniques Employed

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General TechniquesCell pitch of 6um used, layouts optimized for area to

match pitch sizeShared Sources/Drains when possible to minimize areaShared VDD and ground rails between rows

Hierarchical LayoutBigger cells composed of multiple smaller cells Orthogonal metal routing using M3, M4, Local routing

using M1, M2Blocks made to abut well

Wider tracks for power rails to provide enough power Wider horizontal tracks, vertical tracks, and clock tree

for increase drive strength

Conclusions

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Designed a fully functional FPGA Can Implement up to 512 gatesConsists of 8,704 SRAMs148,448 transistors without padframe

Questions

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