COMBINATIONAL LOGIC

10/16/98


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Table of Contents

COMBINATIONAL LOGIC

Overview

Combinational vs. Sequential Logic

Static CMOS Circuit

Static CMOS

NMOS Transistors in Series/Parallel Connection

PMOS Transistors in Series/Parallel Connection

1’s, 0’s, and CMOS

Complementary CMOS Logic Style Construction (cont.)

Example Gate: NAND

NAND Gate Layout

Another NAND Layout

Example Gate: NOR

Example Gate: COMPLEX CMOS GATE

Construction of Complex Gates

Example Procedure

Bridge Networks

Dual Graphs and Networks

Systematic Gate Layout

Issues

4-input NAND Gate

Standard Cell Layout Methodology

Two Versions of (a+b).c

Graphs & Paths

Logic Graph

Consistent Euler Path

Layout Procedure

Example: x = ab+cd

Variations (1)

Variations (2)

Variations (3)

Properties of Complementary CMOS Gates

Properties of Complementary CMOS Gates

Transistor Sizing

Propagation Delay Analysis - The Switch Model

What is the Value of Ron?

Numerical Examples of Resistances for 1.2mm CMOS

Analysis of Propagation Delay

Design for Worst Case

Influence of Fan-In and Fan-Out on Delay

tp as a function of Fan-In

Fast Complex Gate - Design Techniques

Fast Complex Gate - Design Techniques (2)

Fast Complex Gate - Design Techniques (3)

Fast Complex Gate - Design Techniques (4)

Source & Drain Capacitances

Example: Full Adder

A Revised Adder Circuit

Ratioed Logic

Ratioed Logic

Active Loads

Load Lines of Ratioed Gates

Pseudo-NMOS

Pseudo-NMOS NAND Gate

Improved Loads

Improved Loads (2)

Example

Pass-Transistor Logic

NMOS-only switch

Solution 1: Transmission Gate

Resistance of Transmission Gate

Pass-Transistor Based Multiplexer

Transmission Gate XOR

Delay in Transmission Gate Networks

Elmore Delay (Chapter 8)

Delay Optimization

Transmission Gate Full Adder

(2) NMOS Only Logic: Level Restoring Transistor

Level Restoring Transistor

Solution 3: Single Transistor Pass Gate with VT=0

Complimentary Pass Transistor Logic

4 Input NAND in CPL

Dynamic Logic

Example

Transient Response

Dynamic 4 Input NAND Gate

Reliability Problems — Charge Leakage

Charge Sharing (redistribution)

Charge Redistribution - Solutions

Clock Feedthrough

Clock Feedthrough and Charge Sharing

Cascading Dynamic Gates

Domino Logic

Domino Logic - Characteristics

np-CMOS

np CMOS Adder

Manchester Carry Chain Adder

CMOS Circuit Styles - Summary

Author: kaat

Email: mbhate@ece.uci.edu

Home Page: http://www.eng.uci.edu/~ece151