CMOS Circuits Basics

Abstract

Although a CMOS chip is a complex object comprising logic, memory, analog, and I/O circuits, significant insight can be gained from the simulated and measured behaviors of circuit elements and small circuit blocks. The basic components and building blocks of digital logic circuits and their electrical properties are described. Circuit simulations are set up with BSIM models for plotting I–V and C–V characteristics of MOSFETs and extracting their key parameters. A methodology to characterize logic gates typically found in a standard cell library is introduced using an inverter as an example. Lookup tables for computing signal delays in combinational logic circuits with different input signal waveforms and load capacitances are generated, highlighting their interdependencies. Delay chains and ring oscillator configurations used for model validation in silicon hardware are described and simulated to extract delay parameters of logic gates. The foundations laid here including Monte Carlo analysis for determining parameter spreads are used throughout the book.