Browse Prior Art Database

OSCILLATOR WITH CURRENT CONTROLLED CMOS FREQUENCY/DUTY CYCLE CONTROLLED OSCILLATOR

IP.com Disclosure Number: IPCOM000007419D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2002-Mar-25

Publishing Venue

Motorola

Related People

Shayan Zhang: AUTHOR [+2]

Abstract

In the design of VLSI circuits and systems the need frequently arises for signals having prescribed standard waveforms with specified characteristics like amplitude, frequency and duty cycle. These stand- ard waveforms, which include sinusoidal, square, tri- angular, pulse, and etc., can be generated in Signal Generators. A ring oscillator with adjustable fre- quency and duty cycle is a basic building block for various types of Signal Generators.

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MO7VROLA Technical Developments

OSCILLATOR WITH CURRENT CONTROLLED CMOS FREQUENCY/DUTY CYCLE CONTROLLED OSCILLATOR

by Shayan Zhang and Joseph J. Nahas

1. INTRODUCTION

  In the design of VLSI circuits and systems the need frequently arises for signals having prescribed standard waveforms with specified characteristics like amplitude, frequency and duty cycle. These stand- ard waveforms, which include sinusoidal, square, tri- angular, pulse, and etc., can be generated in Signal Generators. A ring oscillator with adjustable fre- quency and duty cycle is a basic building block for various types of Signal Generators.

  Systems in which standard signals are required include: 1) computer and control systems where clock pulses are needed for timing; 2) communication sys- tems where signals of a variety of waveforms are utilized as information carriers and 3) test and meas- urement systems where signals are employed for testing and characterizing electronic materials, devices and circuits.

  The origination of this work is motivated in the requirement of designing a Metallization Test Struc- ture Driver [l] for VLSI technology development. The Metallization Test Structure Driver is designed to drive current pulses into metal test structures to test for current induced electromigration under non-DC conditions. A key element ofthe test struc- ture is a DC-controlled CC0 (Current Controlled Oscillator) with a built-in variable frequency and duty cycle which could be continually adjusted. Frequency and duty cycle are two important factors for model- ing AC and pulsed-DC electromigration effects [2, 3, 41. This document describes the basic concept, the physical insight, the design details, and the sim- ulation results ofa CC0 circuit compatible with dig- ital CMOS processes.

2. OVERVIEW

  The CC0 is designed to enable the Metallization Test Structure Driver to provide the AC driving cur- rent of various frequencies and duty cycle. The CC0

uses an odd number of CMOS inverters, with a dif- ferential amplifier and current mirrors inserted in series with certain stages ofthe inverters, connected in a closed ring. Both the frequency and the duty cycle are controlled by the inverter biasing current and voltage. The hequency can be varied from lMHz to 600MHz continuously. The duty cycle control range is from 10% to 90% continuously. Only two DC input control signals are required for the he- quency and duty cycle control.

2.1 BASIC CONCEPT

  The frequency and duty cycle of a ring oscillator with N identical inverters is related to the average driving current of each inverter as: (See Appendix
A) where W/L, g, and Id are the width-to-length ratio, transconductance, and bias current, respectively, of each MOS transistors of the inverters. C is the effective output capacitance of each inverter stage. The bias current is the drain saturation current when the gate input voltage equals the inverter threshold voltage. The duty cycle is derived under the condi- tion th...