VLSI is an acronym, it stands for Very Large Scale Integration. An integrated circuit or chip, has millions of transistors that can be connected up to form a circuit. VLSI has a few subcategories:
- Development of the technology itself, for example tech node 16nm.
- Digital design, for example an Intel CPU for desktop computers.
- Analog design, for example an amplifier chip.
- Mixed signal design, for example a stepper motor driver.
Digital IC design uses a cell library from a technology node. It will offer gates and flops, simply put. These are predefined connections of transistors on the chip that implement logic cells like AND, NOT and OR. Digital designs were done via schematic entry, connecting cells together to make boolean logic. The gates and flops were hand connected. When chips started to become more complex, thousands of gates, a syntax was developed to describe the behaviour of a logic function. It is an abstraction layer where the designer has less control over the actual implementation. An EDA tool translates the syntax into cells. And so the HDL, hardware description language, was born.