Oscillators are used in almost all Spread Spectrum, RF and wireless systems -- thus
designers should know something about them. The "Beginner's Box" below
graphically presents the most important design information concerning oscillators. In addition,
we have included a variety of other links to help you learn more about this fascinating subject.
Just click on a link below:
Oscillators are a natural and expected part of the electronic scene. They occur
in many, many applications and make possible circuits and subsystems that perform
very useful functions. Oscillators occur sometimes even when we don't want them --
amplifiers can oscillate if stray feedback paths are present. Without oscillators we
would probably live in a very dull world!
Oscillation occurs when an amplifier is furnished with a feedback path that satisfies
two conditions:
Amplitude Condition -- The cascaded gain and loss through the amplifier / feedback network
must be greater than unity!
Phase Condition -- The frequency of oscillation will be at the point where loop phase
shift totals 360 (or zero) degrees!
In most oscillator circuits, oscillation builds up from zero when power is first applied, under linear
circuit operation. However, limiting amplifier saturation and other non-linear effects end up
keeping the oscillator's amplitude from building up indefinitely. Thus, oscillators are not the
simplest devices in the world to accurately design, simulate or model. There is a real art to
GOOD, STABLE oscillator design. As you learn more about oscillators you will certainly grow to
appreciate them!
Please consult some of the references and links below for more information about oscillators.
BLILEY TECHNOLOGIES, an old-line oscillator
manufacturer with some good introductory articles on various
types of oscillators under the technical resources tabs and the Guide to Products tabs.
CHAOTIC
OSCILLATORS DESIGN WITH PREASSIGNED SPECTRAL CHARACTERISTICS, by Nikolay Maximov, Andrey
Panas and Sergey Starkov, Institute of Radioengineering and Electronics of the Russian
Academy of Sciences — paper from the European Conference on Circuit Theory and Design,
Espoo,Finland, August 28-31,2001
On-Chip Oscillator Design — A neat design note from Zilog, focussing on oscillator theory and
its practical application in design.
NEL Spread Spectrum Technique Measurably Reduces EMI
NEL Frequency Controls, Inc. has introduced a
Spread Spectrum technique designed to modulate the output of a single PLL, spreading the
bandwidth of a synthesized clock and
decreasing the peak amplitudes of its fundamental frequencies and harmonics.
Because FCC regulations on EMI change at speeds above 1 GHz, engineers require frequency
control devices which provide both reliable clock performance and reduced emissions.
The NEL Spread Spectrum technique reduces EMI for the primary clock source, thus also
modulating all other signals being synchronized by the clock. By increasing the
bandwidth to lower the power level at the center frequency, NEL's Spread Spectrum
solution is capable of reducing measured EMI by as much as 12dB.
Ideally suited for use in computers, notebooks and other digital systems, the NEL
Spread Spectrum technique reduces EMI without the need for more costly shielding
or enclosures.
Oscillator Terminology and Considerations From Wenzel Associates, Inc.
Wenzel Associates is a manufacturer of precision crystal oscillators and related radio
frequency devices for the communications, navigation, military, and test equipment markets.
In addition to components, they manufacture a variety of high performance instruments and
subsystems. They have a very interesting website with lots of neat technical information. See
some links below:
