CMP 4202: VLSI System Design Lecturer: Geofrey Bakkabulindi Email: gbakkabulindi@tech. mak. ac. ug
Course Outline 1. Introduction: History and Overview 2. Electronic Properties Of Materials 3. Function Of The Basic Inverter Structure 4. Combinational Logic structures 5. Sequential Logic Structures 6. Semiconductor memories and logic arrays 7. Chip input/output circuits VLSI System Design 2
VLSI Design - Introduction • What is VLSI? – “Very Large Scale Integration” – Defines integration level – 1980 s hold-over from outdated taxonomy for integration levels • Obviously influenced from frequency bands, i. e. HF, VHF, UHF – Sources disagree on what is measured (gates or transistors? ) – #Consider prime numbers e. g 2, 3, 5, 7…as powers of 10 below. • • • 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) VLSI System Design 3
Integration Level Trends Obligatory historical Moore’s law plot VLSI System Design 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, Pi. N) MEMs (piezoelectric integration, accelerometers, gyroscopes, pressure sensors, micro-mirrors) • For CMOS digital design, we only use MOSFET transistors (used as switches) and wires VLSI System Design 5
Chips • Integrated circuits consist of: – A small square or rectangular “die”, < 1 mm thick • Small die: 1. 5 mm x 1. 5 mm => 2. 25 mm 2 • Large die: 15 mm x 15 mm => 225 mm 2 – 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 VLSI System Design 6
VLSI Design • Draw polygons that represent layers deposited on the substrate – More of an art than science Scale: approximately 10 um x 10 um • One 2 -input NAND gate with 4 transistors • Typical microprocessor contains 50 – 200 million transistors (10 -50 million gates) VLSI System Design 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 System Design 8
EDA Tools • Conclusion: – This course is about using design tools to manage design complexity of VLSI systems – Focus on large-scale system design (CAD tools) – CAD tools manage design and verification complexity – 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 largescale design methodology VLSI System Design 9
EDA Tools - Challenges • 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) VLSI System Design 10
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 VLSI System Design 11
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