Very-Large-Scale Integration (VLSI) refers to the process of creating an integrated circuit by combining thousands of transistors into a single chip. (reference) Microprocessors are classic examples of VLSI devices. Before VLSI, integrated circuits performed only a limited set of functions; VLSI allows designers to integrate the CPU, memory, and other logic on the same chip. (reference)
• Historical Context – VLSI technology emerged in the 1970s with advances in semiconductor and communication technologies.
• Impact – Integrating many components onto one chip reduces size, power consumption, and cost while increasing performance and reliability.
• Design Flow – A typical VLSI design flow starts with a high-level specification, moves to a behavioral description, then to RTL (Register-Transfer Level) description using hardware description languages, followed by logic synthesis that generates gate-level netlists, and finally physical layout for fabrication.
• Design Hierarchy – Complex circuits are designed using a "divide and conquer" approach: larger functions are split into smaller modules, then implemented and connected. For example, a 16-bit adder can be built from smaller 4-bit adders, which themselves can be built from 1-bit adders.
• Applications – VLSI technology enables high-performance computing, telecommunications, image/video processing, and consumer electronics.
The Static Complementary CMOS structure is a fundamental design approach in digital integrated circuits, known for its robustness and low power consumption. It consists of two key components: a Pull-Up Network (PUN) and a Pull-Down Network (PDN).
The PUN is constructed using PMOS transistors, which conduct when the input signal is low (logic 0), effectively connecting the output to the power supply (VDD).
The PDN is built with NMOS transistors, which conduct when the input is high (logic 1), pulling the output down to ground (GND).
The topologies of the PUN and PDN are complementary (dual) to each other, meaning the structure of one network is the logical inverse of the other. This ensures that only one network is active at a time, preventing static power dissipation.
The Pull-Up Network (PUN) and Pull-Down Network (PDN) in a static complementary CMOS circuit are designed to ensure correct logic functionality while maintaining optimal performance. The general design flow is as follows:
The PDN is constructed based on the Boolean logic function using NMOS transistors.
AND operation → Transistors are placed in series (all inputs must be high to conduct).
OR operation → Transistors are placed in parallel (any high input conducts).