CSCE 612: VLSI System Design

1. CSCE 612: VLSI System Design Instructor: karan

2. VLSI Design • What is VLSI? • “Very Large Scale Integration” • Defines integration level • 1980s hold-over from outdated taxonomy for integration levels • Obviously influenced from frequency bands, i.e. HF, VHF, UHF • Sources disagree on what is measured (gates or transistors?) • SSI – Small-Scale Integration (0-102) • MSI – Medium-Scale Integration (102-103) • LSI – Large-Scale Integration (103-105) • VLSI – Very Large-Scale Integration (105-107) • ULSI – Ultra Large-Scale Integration (>=107)

3. Integration Level Trends Obligatory historical Moore’s law plot

4. Integrated Circuits/MEMs • Today, VLSI refers to systems impl. w/integrated circuits • Integrated circuit refers mostly to general manufacturing technique • micro/nano-scale devices on a semiconductor (crystalline) substrate • Formed using chemical/lithography processing • What kind of devices / structures? • transistors (bipolar, MOSFET) • wires (interconnects and passives) • diodes (junction, LEDs, VCSELs, MSM, photoconductor, PiN) • MEMs (piezoelectric integration, accelerometers, gyroscopes, pressure sensors, micro-mirrors) • For CMOS digital design, we only use MOSFET transistors (used as switches) and wires

5. Chips • Integrated circuits consist of: • A small square or rectangular “die”, < 1mm thick • Small die: 1.5 mm x 1.5 mm => 2.25 mm2 • Large die: 15 mm x 15 mm => 225 mm2 • Larger die sizes mean: • More logic, memory • Less volume • Less yield • Dies are made from silicon (substrate) • Substrate provides mechanical support and electrical common point

6. VLSI Design • Draw polygons that represent layers deposited on the substrate • More of an art than science • One 2-input NAND gate with 4 transistors • Typical microprocessor contains 50 – 200 million transistors (10-50 million gates) Scale: approximately 10 um x 10 um

7. VLSI Design • Manual layout design is obviously not practical • Design complexity: • Manually drawing layout for a billion transistors would take too long • Even if we could… • How to verify (test) designs for functionality, speed, power, etc.? • Complexity scales faster than actual design • How to reuse designs? • How to create human-readable designs? • How to speed-up design process? • These problems form a great deal of work • Electronic Design Automation (EDA) • a.k.a. CAD • Advancing EDA technology, physical fabrication technology, advanced designs, and IP form bulk of work (and money) in VLSI

8. EDA Tools • Conclusion: • This course is about using design tools to manage design complexity of VLSI systems • Only way to learn tools: practice and work with tools individually • Must teach IC fundamentals, but prevent course from becoming semiconductor theory, analog electronics, circuits, or digital logic course • Target large-scale integration and EDA • Reach good balance between fundamental IC theory and automated large-scale design methodology • 80-90% of course time will be spent in lab • Tutorials will provide basic knowledge • Must learn the tools on your own (assisted by instructor)

9. Course Overview • This course is called “VLSI System Design” • Focus on large-scale system design (CAD tools) • CAD tools manage design and verification complexity • What we have… • Latest, most advanced CAD tools in the EDA industry • Three primary players • Synopsys, #258 ($1.2 billion revenue) • Cadence Design Systems, #259 ($1.1 billion revenue) • Mentor Graphics, ? • Comparison: Microsoft #95 ($36.8 billion), Intel #102 ($34.2 billion) • Fabrication award for 500 nm CMOS fabrication process • AMI C5N process with academic design kit (NCSU CDK) • 1.5 mm x 1.5 mm die size, multiple dies, packaging

10. EDA Tools • Big companies, lots of money, 40 years of integrated circuit design experience, conferences, journals, powerful PCs… what’s the problem? • IC CAD tools are difficult to use • Written by electrical engineers (not professional programmers) • Incredibly buggy • Not documented • Rely on ancient, outdated file formats for interoperability • Still mostly rely on command-line interfaces • Utilize outdated, primitive, buggy APIs for GUIs • Inherently required to solve hard problems • Place components, route wires • Must utilize advanced heuristics that are only as good as fabrication process technology information and user input (garbage-in, garbage-out)

11. EDA Tools • Cadence tools • “IC-Tools” => IC5141 package (Linux) • Collection of tools managed by Design Framework II (dfII) • Virtuoso schematic/layout editor • Analog Environment • Spectre simulator • Diva DRC, EXT, LVS • Other Cadence tools • SignalStorm => TSI42 package (Linux) • Abstract Generator => DSMSE54 (Solaris) • First Encounter => SOC42 package (Linux) • Synopsys • Design Compiler (Linux) • Mentor • HDL Designer (Linux)

12. What EDA Tools Can Do • Manual layout vs. EDA is like: • Manual transmission vs. automatic transmission • HTML programming vs. Frontpage • Assembly code programming vs. compiled high-level language • Manual layout for small, optimized designs will always be superior • EDA techniques for larger-scale designs will always be superior (verification, reusability, NRE, etc.) • Goal: do careful, manual design of smaller components (cells) and use EDA to combine them for large-scale design

13. What EDA Tools Can Do • “My” Design Flow process info, cell abstracts Abstract Generation Cadence AbGen Circuit Sim Cadence IC-Tools Digital cell library design Cadence IC-Tools Characterization Cadence SignalStorm char. info Design Specification Standard Cell Library Behavioral VHDL Design Mentor HDL Designer Synthesis Synopsys Design Analyzer Place-and-Route Cadence First Encounter VHDL Verilog Behavioral Simulation Mentor ModelSim Cell Timing Simulation Mentor ModelSim Interconnect Timing Simulation Mentor ModelSim

14. Course Organization • Course will be divided into units • Introduction: IC design and fabrication fundamentals • Lectures • Assignments from textbook • CMOS circuit design, layout, and simulation • Tutorial: Cadence IC-Tools • Design projects • Development of standard cell library • Cell library development • Tutorial: Cadence SignalStorm and Abstract Generator • Report on cell library • VHDL Design • Lectures on VHDL • Tutorial: Mentor HDL Designer • Design project • Logic Synthesis • Tutorial: Synopsys Design Analyzer • Place-and-route • Tutorial: Cadence First Encounter • Course project • Teams? • Design? • Fabrication?