VLSI

• Acronym of VLSI– Very-Large-Scale Integration

• A VLSI contains more than a million or so switching devices or logic gates

• Early in the first decade of the 21st century, the actual number of transistors has exceeded 100 million

• A piece of silicon (a chip) is typically about 1 centimeter on a side

VLSI

• Very Large Scale Integration– design/manufacturing of extremely small,

complex circuitry using modified semiconductor material

– integrated circuit (IC) may contain millions of transistors, each a few m in size

– applications wide ranging: most electronic logic devices

Integrated Circuits• Digital logic is implemented using transistors in

integrated circuits containing many gates.– small-scale integrated circuits (SSI) contain

10 gates or less– medium-scale integrated circuits (MSI)

contain 10-100 gates– large-scale integrated circuits (LSI) contain

up to 104 gates– very large-scale integrated circuits (VLSI)

contain >104 gates

Integrated Circuits

• Improvements in manufacturing lead to ever smaller transistors allowing more per chip.– >107 gates/chip now possible; doubles every 18

months or so• Variety of logic families

– TTL - transistor-transistor logic– CMOS - complementary metal-oxide semiconductor– ECL - emitter-coupled logic– GaAs - gallium arsenide

IC Product

• Processors– CPU, DSP, Controllers

• Memory chips– RAM, ROM, EEPROM

• Analog– Mobile communication,

audio/video processing• Programmable

– PLA, FPGA• Embedded systems

– Used in cars, factories– Network cards

• System-on-chip (SoC)

Images: amazon.com

Choice of Technology

• Two distinct types of technology are fabricated in silicon based upon– BJT (Bipolar Junction Transistor)– MOS (Metallic Oxide Semiconductor)

• Since processing of these technologies is very different, it is impractical to mix them up within a chip

Choice of MOS and BJT

• MOS logic occupies much smaller area of silicon than the equivalent BJT logic

• MOS technology has a much higher potential packing density

• A MOS logic circuit requires appreciably less current and hence less power than its bipolar counter part

• However, bipolar circuits operate faster than MOS circuits

• Even so, the speed-power product for MOS logic compares favorably with that of BJT logic

Choice of MOS and BJT

• The structure of an MOS transistor is much simpler than that of bipolar devices and this makes manufacturing process easier

• This in turn should result in fewer faults occurring in fabrication (high yield)

• Dynamic logic circuits cannot be implemented in bipolar technology

• Thus in terms of area, power dissipated, yield and flexibility MOS technology is superior to BJT

Moore’s Law

• Moore’s Law:– The number of transistors on an integrated

circuit will double every 18 months• The level of integration of silicon technology as

measured in terms of number of devices per IC• This comes about in two ways – size reduction of

the individual devices and increase in the chip or dice size

Moore’s LawMoore’s Law

Source: Intel web page (www.intel.com)

VLSI Design Flow

module AddAccm (A, B, clk, out, reset); input[15:0] B; output[15:0] A,out; Input clk, reset; reg[15:0] Ar, Br, out;

always @(posedge clk or posedge reset) begin if (reset = = 1) begin Ar=0; Br=0; end else begin Br = B; Ar = out; end end always @(Ar or Br) out = Ar + Br;endmodule layout

RTL

Placed & Routed

netlist

VLSI Hierarchy in Design

Cost increases

Complexity increases

Verification Effort increases

Gates

System

Silicon

Transistors

Blocks