© Digital Integrated Circuits 2nd Design Methodologies Digital Integrated Circuits A Design Perspective Design Methodologies Jan M. Rabaey Anantha Chandrakasan

© Digital Integrated Circuits2nd Design Methodologies

Digital Integrated Digital Integrated CircuitsCircuitsA Design PerspectiveA Design Perspective

DesignDesignMethodologiesMethodologies

Jan M. RabaeyAnantha ChandrakasanBorivoje Nikolic

December 10, 2002


The Design Productivity ChallengeThe Design Productivity Challenge

Source: sematech97

A growing gap between design complexity and design productivity

58%/Yr. compoundComplexity growth rate

21%/Yr. compoundProductivity growth rate

198

1

10

Log

ic T

ran

sist

ors

pe

r C

hip

(K

)

Pro

du

ctiv

ity (

Tra

ns.

/Sta

ff-M

on

th)

100

1,000

10,000

100,000

1,000,000

10,000,000

1

XX

X XX

X

x

100

1,000

10,000

100,000

1,000,000

10,000,000

100,000,000

10

2.5m

.35m

.10m

198

3

198

5

198

7

198

9

199

1

199

3

199

5

199

7

199

9

200

1

200

3

200

5

200

7

200

9

Transistor/Staff Month


A Simple ProcessorA Simple Processor

MEMORY

DATAPATH

CONTROL

INP

UT

/OU

TP

UT


A System-on-a-Chip: ExampleA System-on-a-Chip: Example

Courtesy: Philips


Impact of Implementation ChoicesImpact of Implementation ChoicesE

nerg

y E

ffic

ienc

y (i

n M

OP

S/m

W)

Flexibility(or application scope)

0.1-1

1-10

10-100

100-1000

None Fullyflexible

Somewhatflexible

Har

dwire

d cu

stom

Con

figur

able

/Par

amet

eriz

able

Dom

ain

-spe

cific

pro

cess

or(e

.g.

DS

P)

Em

bedd

ed m

icro

proc

ess

or


Design MethodologyDesign Methodology

• Design process traverses iteratively between three abstractions: behavior, structure, and geometry• More and more automation for each of these steps


Implementation ChoicesImplementation Choices

Custom

Standard CellsCompiled Cells Macro Cells

Cell-based

Pre-diffused(Gate Arrays)

Pre-wired(FPGA's)

Array-based

Semicustom

Digital Circuit Implementation Approaches


The Custom Approach The Custom Approach

Intel 4004

Courtesy Intel


Transition to Automation and Regular StructuresTransition to Automation and Regular Structures

Intel 4004 (‘71)Intel 4004 (‘71)Intel 8080Intel 8080 Intel 8085Intel 8085

Intel 8286Intel 8286 Intel 8486Intel 8486Courtesy Intel


Cell-based Design (or standard cells)Cell-based Design (or standard cells)

Routing channel requirements arereduced by presenceof more interconnectlayers

Functionalmodule(RAM,multiplier,…)

Routingchannel

Logic cellFeedthrough cellR

ow

s o

f ce

lls


Standard Cell — ExampleStandard Cell — Example

[Brodersen92]


Standard Cell – The New GenerationStandard Cell – The New Generation

Cell-structurehidden underinterconnect layers


Standard Cell - ExampleStandard Cell - Example

3-input NAND cell(from ST Microelectronics):C = Load capacitanceT = input rise/fall time


Automatic Cell GenerationAutomatic Cell Generation

Courtesy Acadabra

Initial transistorgeometries

Placedtransistors

Routedcell

Compactedcell

Finishedcell


A Historical Perspective: the PLAA Historical Perspective: the PLA

x0 x1 x2

ANDplane

x0x1

x2

Product terms

ORplane

f0 f1


Two-Level LogicTwo-Level Logic

Inverting format (NOR-NOR) more effective

Every logic function can beexpressed in sum-of-productsformat (AND-OR)

minterm


PLA Layout – Exploiting RegularityPLA Layout – Exploiting Regularity

f0 f1x0 x0 x1 x1 x2 x2

Pull-up devices Pull-up devices

VDD GNDAnd-Plane Or-Plane


Breathing Some New Life in PLAsBreathing Some New Life in PLAsRiver PLAs A cascade of multiple-output PLAs. Adjacent PLAs are connected via river routing.

PRE-CHARGE

PR

E-

CH

AR

GE

PRE-CHARGE

PR

E-C

HA

RG

E

BUFFER

BUFFER

BU

FF

ER

BU

FF

ER

PRE-CHARGE

PR

E-C

HA

RG

E

BUFFER

BU

FF

ER

PRE-CHARGE

PR

E-

CH

AR

GE

BUFFERB

UF

FE

R

• No placement and routing needed. • Output buffers and the input buffers

of the next stage are shared.

Courtesy B. Brayton


Experimental ResultsExperimental Results

Layout of C2670

Network of PLAs, 4 layers OTC

River PLA,2 layers no additional routing

Standard cell, 2 layers channel routing

Standard cell,3 layers OTC

0.2

0.6

1

1.4

0 2 4 6 area

dela

y

SC N PLA R PLA

Area: RPLAs (2 layers) 1.23 SCs (3 layers) - 1.00, NPLAs (4 layers) 1.31 DelayRPLAs 1.04SCs 1.00 NPLAs 1.09 Synthesis time: for RPLA , synthesis time equals design time; SCs and NPLAs still need P&R.

Also: RPLAs are regular and predictable


MacroModulesMacroModules

25632 (or 8192 bit) SRAMGenerated by hard-macro module generator


““Soft” MacroModulesSoft” MacroModules

Synopsys DesignCompiler


““Intellectual Property”Intellectual Property”

A Protocol Processor for Wireless


Semicustom Design FlowSemicustom Design Flow

HDLHDL

Logic SynthesisLogic Synthesis

FloorplanningFloorplanning

PlacementPlacement

RoutingRouting

Tape-out

Circuit ExtractionCircuit Extraction

Pre-Layout Simulation

Pre-Layout Simulation

Post-Layout Simulation

Post-Layout Simulation

StructuralStructural

PhysicalPhysical

BehavioralBehavioralDesign Capture

Des

ign

Iter

atio

nD

esig

n It

erat

ion


The “Design Closure” ProblemThe “Design Closure” Problem

Courtesy Synopsys

Iterative Removal of Timing Violations (white lines)


Integrating Synthesis with Integrating Synthesis with Physical DesignPhysical Design

Physical SynthesisPhysical Synthesis

RTL (Timing) Constraints

Place-and-RouteOptimization

Place-and-RouteOptimization

Artwork

Netlist with Place-and-Route Info

MacromodulesFixed netlists


Pre-diffused(Gate Arrays)

Pre-wired(FPGA's)

Array-based

Late-Binding ImplementationLate-Binding Implementation


Gate Array — Sea-of-gatesGate Array — Sea-of-gates

rows of

cells

routing channel

uncommitted

VDD

GND

polysilicon

metal

possiblecontact

In1 In2 In3 In4

Out

UncommitedCell

CommittedCell(4-input NOR)


Sea-of-gate Primitive CellsSea-of-gate Primitive Cells

NMOS

PMOS

Oxide-isolation

PMOS

NMOS

NMOS

Using oxide-isolation Using gate-isolation


Example: Base Cell of Gate-Isolated GAExample: Base Cell of Gate-Isolated GA

n-well

contact

21GND2019181716151413121110987654321VDD

m2m1polyp-diffn-diffp-well

contact forisolator

continuousn-diff strip

continuousp-diff strip

From Smith97


Example: Flip-Flop in Gate-Isolated GAExample: Flip-Flop in Gate-Isolated GA

CLK

D

Q

GND

VDD

Q

CLR

From Smith97


Sea-of-gatesSea-of-gates

Random Logic

MemorySubsystem

LSI Logic LEA300K(0.6 m CMOS)

Courtesy LSI Logic


The return of gate arrays?The return of gate arrays?

metal-5 metal-6

Via-programmable cross-point

programmable via

Via programmable gate array(VPGA)

[Pileggi02]

Exploits regularity of interconnect


Prewired ArraysPrewired ArraysClassification of prewired arrays (or field-programmable devices): Based on Programming Technique

Fuse-based (program-once) Non-volatile EPROM based RAM based

Programmable Logic Style Array-Based Look-up Table

Programmable Interconnect Style Channel-routing Mesh networks


Fuse-Based FPGAFuse-Based FPGA

antifuse polysilicon ONO dielectric

n+ antifuse diffusion

2 l

From Smith97

Open by default, closed by applying current pulse


Array-Based Programmable LogicArray-Based Programmable Logic

PLA PROM PAL

I 5 I 4

O0

I 3 I 2 I 1 I 0

O1O2O3

Programmable AND array

ProgrammableOR array I5 I4

O0

I3 I2 I1 I0

O1O2O3

Programmable AND array

Fixed OR array

Indicates programmable connection

Indicates fixed connection

O0

I3 I2 I1 I0

O1O2O3

Fixed AND array

ProgrammableOR array


Programming a PROMProgramming a PROM

f0

1 X 2 X 1 X 0

f1NANA

: programmed node


More Complex PALMore Complex PAL

From Smith97

programmable AND array (2i 3 jk) k macrocells

j -wide OR array

j

macrocell

productterms

D Q

A

1

j

B

CLK

OUT

C i i inputs

i inputs, j minterms/macrocell, k macrocells


2-input mux 2-input mux as programmable logic blockas programmable logic block

FA 0

B

S

1

Configuration

A B S F=

0 0 0 00 X 1 X0 Y 1 Y0 Y X XYX 0 YY 0 XY 1 X X 1 Y1 0 X1 0 Y1 1 1 1

XYXY

XY


Logic Cell of Actel Fuse-Based FPGALogic Cell of Actel Fuse-Based FPGA

A

B

SA Y

1

C

D

SB

1

S0S1

1


Look-up Table Based Logic CellLook-up Table Based Logic Cell

Out

ln1 ln2

Me

mory In Out

00 00

01 1

10 1

11 0


LUT-Based Logic CellLUT-Based Logic Cell

Courtesy Xilinx

D4

C1....C4

xxxxxx

D3

D2

D1

F4

F3

F2

F1

Logicfunction

ofxxx

Logicfunction

ofxxx

Logicfunction

ofxxx

xx

xx

4

xxxxxx

xxxxxxxx

xxx

xxxx xxxx xxxx

HP

Bitscontrol

Bitscontrol

Multiplexer Controlledby Configuration Program

x

xx

x

xx

xxx xx

xxxx

x

xxxxxx

xx

x

xx

xxx

xx

Xilinx 4000 Series

Figure must be updated


Array-Based Programmable WiringArray-Based Programmable Wiring

Input/output pinProgrammed interconnection

InterconnectPoint

Horizontaltracks

Vertical tracks

Cell

M


Mesh-based Interconnect NetworkMesh-based Interconnect NetworkSwitch Box

Connect Box

InterconnectPoint

Courtesy Dehon and Wawrzyniek


Transistor Implementation of MeshTransistor Implementation of Mesh



Hierarchical Mesh NetworkHierarchical Mesh Network

Use overlayed meshto support longer connections

Reduced fanout and reduced resistance



EPLD Block DiagramEPLD Block Diagram

MacrocellPrimary inputs

Courtesy Altera


Altera MAXAltera MAX

From Smith97


Altera MAX Interconnect ArchitectureAltera MAX Interconnect Architecture

LAB2

PIA

LAB1

LAB6

tPIA

tPIA

row channelcolumn channel

LAB

Courtesy Altera

Array-based(MAX 3000-7000)

Mesh-based(MAX 9000)


Field-Programmable Gate ArraysField-Programmable Gate ArraysFuse-basedFuse-based

I/O Buffers

P rogram/Test/Diag nostics

I/O Buffers

I/O B

uffe

rs

I/O B

uffe

rs

Vertical ro utes

Rows o f logic m odule s

Routing channels

Standard-cell likefloorplan


Xilinx 4000 Interconnect ArchitectureXilinx 4000 Interconnect Architecture

2

12

8

4

3

2

3

CLB

8 4 8 4

Quad

Single

Double

Long

DirectConnect

DirectConnect

Quad Long GlobalClock

Long Double Single GlobalClock

CarryChain

Long

12 4 4

Courtesy Xilinx


RAM-based FPGA RAM-based FPGA

Xilinx XC4000ex

Courtesy Xilinx


A Low-Energy FPGA (UC Berkeley)A Low-Energy FPGA (UC Berkeley)

Array Size: 8x8 (2 x 4 LUT)

Power Supply: 1.5V & 0.8V

Configuration: Mapped as RAM

Toggle Frequency: 125MHz

Area: 3mm x 3mm


Larger Granularity FPGAsLarger Granularity FPGAs

1-mm 2-metalCMOS tech

1.2 x 1.2 mm2

600k transistors

208-pin PGA

fclock = 50 MHz

Pav = 3.6 W @ 5V

Basic Module: Datapath

PADDI-2 (UC Berkeley)


Design at a crossroadDesign at a crossroad

System-on-a-ChipSystem-on-a-Chip

RAM

500 k Gates FPGA+ 1 Gbit DRAMPreprocessing

Multi-

SpectralImager

Csystem+2 GbitDRAMRecog-

nition

Ana

log

64 SIMD ProcessorArray + SRAM

Image Conditioning100 GOPS

Embedded applications where cost, performance, and energy are the real issues!

DSP and control intensive Mixed-mode Combines programmable and

application-specific modules Software plays crucial role


Addressing the Design Complexity IssueAddressing the Design Complexity IssueArchitecture ReuseArchitecture Reuse

Reuse comes in generationsGeneration Reuse element Status

1st Standard cells Well established

2nd IP blocks Being introduced

3rd Architecture Emerging

4th IC Early research

Source: Theo Claasen (Philips) – DAC 00


Architecture ReUseArchitecture ReUse

Silicon System Platform Flexible architecture for hardware and software Specific (programmable) components Network architecture Software modules Rules and guidelines for design of HW and SW

Has been successful in PC’s Dominance of a few players who specify and control architecture

Application-domain specific (difference in constraints) Speed (compute power) Dissipation Costs Real / non-real time data


Platform-Based DesignPlatform-Based Design

A platform is a restriction on the space of possible implementation choices, providing a well-defined abstraction of the underlying technology for the application developer

New platforms will be defined at the architecture-micro-architecture boundary

They will be component-based, and will provide a range of choices from structured-custom to fully programmable implementations

Key to such approaches is the representation of communication in the platform model

““Only the consumer gets freedom of choice;Only the consumer gets freedom of choice;designers need freedomdesigners need freedom fromfrom choice”choice”

(Orfali, et al, 1996, p.522)(Orfali, et al, 1996, p.522)

Source:R.Newton


Berkeley Pleiades ProcessorBerkeley Pleiades Processor

• 0.25um 6-level metal CMOS

• 5.2mm x 6.7mm

• 1.2 Million transistors

• 40 MHz at 1V

• 2 extra supplies: 0.4V, 1.5V

• 1.5~2 mW power dissipationInterface

Reconfigurable

Data-path

FPGA

ARM8 Core


Heterogeneous Programmable PlatformsHeterogeneous Programmable Platforms

Xilinx Vertex-II Pro

Courtesy Xilinx

High-speed I/O

Embedded PowerPcEmbedded memories

Hardwired multipliers

FPGA Fabric


SummarySummary

Digital CMOS Design is kicking and healthy Some major challenges down the road

caused by Deep Sub-micron Super GHz design Power consumption!!!! Reliability – making it workSome new circuit solutions are bound to emerge

Who can afford design in the years to come? Some major design methodology change in the making!


Insert F - Design synthesisInsert F - Design synthesis


Circuit synthesisCircuit synthesis derivation of the transistors schematics from logic

functions- complementary CMOS

- pass transistor- dynamic

- DCVSL (differential cascode voltage switch logic)

transistor sizing - performance modeling using RC

equivalent circuits - layout generation synthesis not popular due to designers reluctance


Logic synthesisLogic synthesis

state transition diagrams, FSM, schematics, Boolean equations, truth tables, and HDL used

synthesis - combinational or sequential - multi level, PLA, or FPGA

logic optimization for - area, speed , power- technology mapping


Logic optimizationLogic optimization

Expresso - two level minimization tool (UCB)

state minimization and state encoding MIS - multilevel logic synthesis (UCB)

Example : S = (AB) Ci

Co= AB + ACi + BCi


Logic optimizationLogic optimizationMultilevel implementation of adder generated by MIS II cell library from University of Mississippi


Architecture synthesisArchitecture synthesis

behavioral or high level synthesis optimizing translation e.g. pipelining Cathedral and HYPER tools HYPER tutorial and synthesis example:

http://infopad.eecs.berkeley.edu/~hyper


Architecture synthesis exampleArchitecture synthesis example


Architecture synthesisArchitecture synthesis


Emerging TechnologiesEmerging Technologies

Complementary Orthogonal Complementary Orthogonal Stacked MOS - Stacked MOS - COSMOSCOSMOS Stack two MOSFETs under a common gate Improve only hole mobility by using strained SiGe channel

– pMOS transconductance equal to nMOS

Reduce parasitics due to wiring and isolating the sub-nets

Conventional CMOS

Complementary Orthogonal

Stacked MOS

Savas Kaya

Technology BaseTechnology Base Strained Si/SiGe layers

Built-in strain traps more carriers and increases mobility– Equal+high electron and hole mobilities (Jung et al.,p.460,EDL’03)

SOI (silicon-on-Insulator) substrates active areas on buried oxide (BOX) layer Reduces unwanted DC leakage and AC parasitics

Mizuno et al., p.988, TED’03

Cheng et al., p.L48, SST’04

COSMOS StructureCOSMOS Structure Single common gate: mid-gap metal or poly-SiGe Ultra-thin channels: 2-6nm to control threshold/leakage

Strained Si1-xGex for holes (x0.3) Strained or relaxed Si for electrons

Substrate: SOI

COSMOS Structure - 3D View ICOSMOS Structure - 3D View I Single gate stack: mid-gap metal or poly-SiGe

Must be engineered for a symmetric threshold

In units of m

COSMOS Structure - 3D View IICOSMOS Structure - 3D View II Conventional self-aligned contacts

Doped S/D contacts: p- (blue) or n- (red) type Inter-dependence between gate dimensions:

W

L

nMOS

L

W

pMOS


COSMOS Gate ControlCOSMOS Gate Control A single gate to control both channels

High-mobility strained Si1-xGex (x0.3) buried hole channel

– High Ge% eliminates parallel conduction and improves mobility

– Lowers the threshold voltage VT

Electrons are in a surface channel Requires fine tuning for symmetric operation

0

0.5

1

1.5

2

2.5

0

0.5

1

1.5

2

2.5

3

-1.2 -0.8 -0.4 0 0.4 0.8 1.2

electronsholes

Vgate [V]

nVT

= 1011

[cm-2

]


3D Characteristics: 40nm Device 3D Characteristics: 40nm Device

Symmetric operation No QM corrections

– Lower VT Features in sub-threshold

operation– Related to p-i-n parasitic

diode included in 3D

COSMOS Inverter COSMOS Inverter

Top view Peel-off top views

No additional processing Just isolate COSMOS layers and establish proper contacts Significantly shorter output metallization

3D TCAD Verification3D TCAD Verification Inverter operation verified in 3D

40nm COSMOS NOT gate driving CL=1fF

load

ApplicationsApplications Low power static CMOS:

Should outperform conventional devices in terms of speed– Multiple input circuit example: NOR gate

Area tight designs : FPGA, Sensing/testing, power etc. ?

Documents

© Digital Integrated Circuits 2nd Design Methodologies Digital Integrated Circuits A Design Perspective Design Methodologies Jan M. Rabaey Anantha Chandrakasan