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Synthesis of an Ultra-precise Time Standard Using Inexpensive Components

IP.com Disclosure Number: IPCOM000014272D
Original Publication Date: 2000-Sep-01
Included in the Prior Art Database: 2003-Jun-19
Document File: 3 page(s) / 101K

Publishing Venue

IBM

Abstract

Disclosed is an apparatus and method for generating a very precise time standard utilizing inexpensive components. Computers, telecommunications equipment, control systems, and many other devices require very precise and accurate time standards. This invention was conceived to solve the problem of providing a very accurate and precise time standard for a computing system, but is applicable to any of the above systems or devices which require a very precise time source or very finely tunable oscillator. A well-known problem of computer systems is that each computer has its own local time standard. These standards are prone to inaccuracy and drift with respect to other external time standards. The traditional solution to this problem is to use a very expensive crystal oscillator, one manufactured and tested to very tight tolerances. For extremely high stability and accuracy this oscillator must be maintained in a strictly controlled temperature environment and typically incorporates a resistive heater and temperature control system. This adds to the cost of the oscillator and wastes energy. This invention takes advantage of the fact that for most crystal oscillators, the variability of the frequency of the output, given a reasonably stable temperature environment, is orders of magnitude less than the manufacturer's guaranteed tolerance between the calibration point and the nominal output frequency.

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Synthesis of an Ultra-precise Time Standard Using Inexpensive Components

Disclosed is an apparatus and method for generating a very precise time standard utilizing inexpensive components.

Computers, telecommunications equipment, control systems, and many other devices require very precise and accurate time standards. This invention was conceived to solve the problem of providing a very accurate and precise time standard for a computing system, but is applicable to any of the above systems or devices which require a very precise time source or very finely tunable oscillator.

A well-known problem of computer systems is that each computer has its own local time standard. These standards are prone to inaccuracy and drift with respect to other external time standards. The traditional solution to this problem is to use a very expensive crystal oscillator, one manufactured and tested to very tight tolerances. For extremely high stability and accuracy this oscillator must be maintained in a strictly controlled temperature environment and typically incorporates a resistive heater and temperature control system. This adds to the cost of the oscillator and wastes energy.

This invention takes advantage of the fact that for most crystal oscillators, the variability of the frequency of the output, given a reasonably stable temperature environment, is orders of magnitude less than the manufacturer's guaranteed tolerance between the calibration point and the nominal output frequency.

The tolerances for the output frequency of crystal oscillators are generally specified in parts per million (PPM). A typical inexpensive crystal oscillator will have an accuracy of approximately 100 PPM, but will demonstrate a stability of better than +/- 1 PPM over a temperature excursion of +/ - 3 degrees Centigrade near room temperature. That is, the difference between the actual output frequency and the calibration point will be within the range of +/- 0.01 % but the amount that the output frequency changes over time will be much less (< +/- 0.0001%).

The central concept of this invention is to take the output of this inexpensive oscillator and divide its frequency by a real 1 (real as used here is a mathematical term meaning a number...