Lecture #2 1

CSE45435 – VLSI Design

 

Lecture #2

Please note the change in Office Hours

Office hours: Monday 3.00 - 5.00 Tuesday 11.30 - 1.00

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Trends in Microprocessor Technology

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Evolution in Complexity

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Silicon in 2010

Die Area: 2.5x2.5cmVoltage: 0.6 VTechnology: 0.07m

Density Access Time(Gbits/cm2) (ns)

DRAM 8.5 10DRAM (Logic) 2.5 10SRAM (Cache) 0.3 1.5

Density Max. Ave. Power Clock Rate(Mgates/cm2) (W/cm2) (GHz)

Custom 25 54 3Std. Cell 10 27 1.5

Gate Array 5 18 1Single-Mask GA 2.5 12.5 0.7

FPGA 0.4 4.5 0.25

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WHY MONOLITHIC INTEGRATION OF A LARGE NUMBER OF FUNCTIONS ON A SINGLE CHIP?

Demand for higher computing power Low cost Small size More circuitry more transistors Dense packing requirement with limited die size

(less than 1.5cm on a side)

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Why build integrated Circuit?

Why build integrated Circuit? IC Technology is driving the whole innovative devices an

d systems which effected the way we live.Print a circuit, like printing a picture ICs are much smaller consume less power than discrete component easier to design and manufacture more reliable than discrete system can design more complex system cost no longer dependent on # of devices

Fast growth of electronic industry.

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VLSI applications VLSI applications

Electronic system in cars Digital electronics control VCRs Transaction processing system, ATM Personal computers and Workstations Medical electronic systems Laptops, cellphones, PDAs etc….

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The advantages of digital I Cs over discrete compone

nts

The advantages of digital I Cs over discrete compone

nts Size

much smaller both transistor and wires. leads to smaller parasitic resistances, capacitances and ind

uctances

Speed communication within the chips are much faster than betw

een the chips on a PCB - High speed of circuits on chip due to smaller size

Power Consumption Logic operation within the chip consumes much less power

S maller size -- > smaller parasitic capacitances and resistan

ce

-- > require less power to drive the circuit

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Advantages of IC at Syst em Level

Advantages of IC at Syst em Level

Smaller Physical Size can make small electronic appliances. ie. Por

table TV, handheld cellular telephone…

Lower Power Consumption reduces total power consumption of a whole

electronic circuit. cheaper power supply which leads to a simpl

er cabinet for power supply. Less heat,cooling fans may no longer be necessary.

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Advantages of IC at Syst em Level (cont.)

Advantages of IC at Syst em Level (cont.)

Reduced Cost Reduction in number of components.

Power Supply requirement.

Cabinets

The cost of building a whole system is reduced eventhough IC s cost more.

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Integrated Circuit Manufacturing

Integrated Circuit Manufacturing

Technology Select technology to build a complex system

in the fastest possible way.

Economics IC plant is very expensive. $1billion or more. II II I IIII II IIIIII II II IIIIIIIII

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Moore’s Law

1960In s,Gordon Moore: Co-founder of INTEL predicted IIII III IIIIII II IIIIIIIIIII IIIII IIII III

onentially (DIIIII every 18 months). Exponential improvement in technology is a natural trend: steam engines, dynamos, automobiles etc.

ln (#dev)

year

good

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Good News

Since the cost of the printing process (called wafer fabrication) was growing at a modest rate, it implied that the cost per function was dropping exponentially. At each new generation, each gate costs about 1/2 what it did 3 years ago. Shrinking an existing chip makes it cheaper!

yearyear

diecost

ln(cost/function)

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Bad News Although the cost of manufacturing

IC's remained approximately constant, the design cost did not. In fact, while designer productivity has improved with time, it has not increased at the same rate as the complexity of the chips.

So the cost of the chip design is growing exponentially with the complexity of the circuit. Integrating a system on a piece of silicon has an attractive manufacturing cost, but frightening design cost and risk. Need to build very complex stuff.

In addition, the number of custom IC designers was (and is) fairly limited. Even if you were willing to take the risk, where would you find the people to do the design?

year

ln(design cost/function)

year

ln(design cost)

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Design Technology

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VLSI Technology

- 1 . Schottky TTL (Transistor transistor logic)

A

B

C= A * B

Vcc

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VLSI Technology

2.ECL (Emitter coupled logic)

C= A + B

Vcc

C= A + B

A B

-V EE

NOR

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3.MOS (Metal Oxide semiconductor)

VLSI Technology

VDD

C = A + BBA

NOR

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VLSI Technology

4. CMOS (Complementary MOS)

VDD

C = A + BA

B

NOR

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Most Prominent Technology - CMOS 

   Smaller sized transistors  Lower power consumption Zero static power

  Dynamic power increases with switching 

But SLOW compared to others 

Compromise - BiCMOS Technology

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Manufacturing Steps

1.  Circuit schematic - transistor circuit diagram

 2.  Layout generation

- rectangular patterns for transistors and interconnect

 3. Mask generation 4. Chip fabrication

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Challenges faced

Defects in wafer·    use minimum die area

 Reduce cost

·    use minimal layout area  Increase speed

·    use efficient interconnect patterns – ( long and winding paths reduce speed)

Short design timeHigh market competition

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Abstractions and Disciplines How to Deal with 109

Transistors? Digital abstraction

signals are 1 or 0 Switch abstraction

MOSFETs as simple switches

Gate abstraction Unidirectional elements Separable timing

Synchronous abstraction Race free logic Function does not depend

on timing

Partition the problem(Use hierarchy) Module is a box with

pins apply recursively

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Design Abstraction Levels

n+n+S

GD

+

DEVICE

CIRCUIT

GATE

MODULE

SYSTEM

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What is on an Integrated Circuit? Actually only two types of things:

Conducting layers which form the wires on the IC. There are many layers of wires (used to have 1

layer of metal, now advanced processes have 5-7 metal layers). Wires have electrical properties like resistance and capacitance.

(Requires insulators and contacts between layers.)

Transistors (the free things that fit under the wires).There are a few kinds of transistors. In this course

we will study MOS ICs, so we will work with MOS transistors. These transistors can be thought of as voltage controlled switches. The voltage on one terminal of the transistor determines whether the other two terminals are connected or not.

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MOSFET Fundamentals

N-channel Metal Oxide Semiconductor Field-Effect Transistor

NMOS Transistor

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The MOS Capacitor

Negative Voltage To Metal

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Small Positive Voltage To Metal

The MOS Capacitor

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+ ++

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The MOS Capacitor

Less Positive

n

More Positive Much More Positive

n << Ions

V < VT

n Ions

V VT

n >> Ions

V > VT

VT Minimum Voltage for Inversion

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++ + ++ +

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NMOS Transistor

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PMOS Transistor