AN826 データシートの表示（PDF） - Microchip Technology

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AN826

Crystal Oscillator Basics and Crystal Selection for rfPICTM and PICmicro® Devices

Microchip Technology 

GLOSSARY

Accuracy - The degree of conformity of a measured or

calculated value to its definition or with respect to a

standard reference.

Aging - The systematic change in frequency over time

because of internal changes in the oscillator. Aging is

the frequency change with time when factors external

to the oscillator such as environment and power supply

are kept constant.

Calibration - The process of identifying and measuring

time or frequency errors, offsets, or deviations of a

clock/oscillator relative to an established standard.

Drift - The linear (first-order) component of a system-

atic change in frequency of an oscillator over time. Drift

is due to aging plus changes in the environment and

other factors external to the oscillator.

Frequency - The rate at which a periodic phenomenon

occurs over time.

Offset - The difference between the measured value

and the defined value.

Precision - The degree of mutual agreement among a

series of individual measurements.

Quality Factor (Q) - The ratio of energy stored in a

reactive component (such as a capacitor or inductor) to

the energy dissipated. Equal to the reactance divided

by the resistance.

Reproducibility - With respect to a set of independent

devices of the same design, it is the ability of these

devices to produce the same value. With respect to a

single device, it is the ability to produce the same value

and to put it into operation repeatedly without adjust-

ments.

Resolution - The degree to which a measurement can

be determined. The smallest significant difference that

can be measured with a given instrument.

Stability - Statistical estimate of the [frequency] fluctu-

ations of a signal over a given time interval.

- Short term stability - usually involves mea-

surement averages from a few tenths of a

second to 100 seconds.

- Long term stability - usually involves mea-

surement averages beyond 100 seconds.

Synchronization - The process of measuring the dif-

ference in time of two time scales such as the output

signals generated by two clocks. In the context of tim-

ing, synchronization means to bring two clocks or data

streams into phase so that their difference is zero.

Tolerance - The maximum allowable frequency devia-

tion from the specified frequency. It is specified in parts

per million (PPM) at a specific temperature, usually +25

degrees C.

AN826

FURTHER READING

There are several excellent tutorials on frequency con-

trol devices at the IEEE Ultrasonics, Ferroelectrics and

Frequency Control web site. The URL is

http://www.ieee-uffc.org

Several crystal manufacturers have application notes

about crystal and crystal oscillator operation. Refer to

the individual crystal manufacturers’ web sites.

REFERENCES

[1] B. Razavi, RF Microelectronics, Prentice Hall PTR,

Upper Saddle River, NJ, 1998.

[2] The ARRL Handbook for Radio Amateurs, ARRL,

Newington, CT, 2001 (published annually).

[3] R. W. Rhea, Oscillator Design and Computer Sim-

ulation, 2nd edition, Noble Publishing, Atlanta, GA,

1995.

[4] T. H. Lee, The Design of CMOS Radio-Frequency

Integrated Circuits, Cambridge University Press,

New York, NY, 1998.

[5] M. E. Frerking, Crystal Oscillator Design and Tem-

perature Compensation, Van Nostrand Reinhold

Company, New York, 1978.

[6] R. J. Matthys, Crystal Oscillator Circuits, Revised

Edition, Krieger Publishing Company, Malabar, FL,

1992

© 2002 Microchip Technology Inc.

DS00826A-page 11

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