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VLSI

VLSI. Acronym of VLSI V ery- L arge- S cale I ntegration A VLSI contains more than a million or so switching devices or logic gates Early in the first decade of the 21 st century, the actual number of transistors has exceeded 100 million

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VLSI

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  1. VLSI • Acronym of VLSI • Very-Large-Scale Integration • A VLSI contains more than a millionor 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 1centimeter on a side

  2. 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 mm in size • applications wide ranging: most electronic logic devices

  3. 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

  4. 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

  5. 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

  6. 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 isimpractical to mix them up within a chip

  7. 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, bipolarcircuits operate faster than MOS circuits • Even so, the speed-power product for MOS logic compares favorably with that of BJT logic

  8. 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 flexibilityMOS technology is superior to BJT

  9. 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

  10. Moore’s Law Source: Intel web page (www.intel.com)

  11. VLSI Design Flow RTL 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 netlist Placed & Routed layout

  12. System Blocks Gates Transistors Silicon VLSI Hierarchy in Design Cost increases Complexity increases Verification Effort increases

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