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Chapter 1

 
Introduction
An improved understanding of oscillator phase noise is needed for the improvement of oscillator
performance.  Such an understanding will help future electrical engineers cope with the expected
dramatic rise in the amount of wireless communication traffic (Baberg, 2000; Kouznetsov &
Meyer, 2000).  As demands on the capacity of a system grow, more users will be required to fit in
a given bandwidth.  To accomplish this, the bandwidth of each user must be decreased.  Oscillator
phase noise, however, contributes to an increase of the bandwidth of each user, therefore limiting
the number of users in a given frequency band (Robins, 1982).
Oscillators are a vital part of any radio-frequency (RF) hardware.  They are necessary for
frequency synthesis, operation of phase-locked loops, and mixing, and typically several oscillators
exist in any given receiver or transmitter.  Phase noise of each oscillator in a system is additive
and has negative effects on frequency stability, bit-error rate (BER) and adjacent channel signals
(Robins, 1982; Siweris, 1985).
The roots of phase noise lie in the noise sources of the transistor (or other active device) used
in the oscillator.  Shot noise, burst noise, partition noise, thermal noise and
 noise are the major transistor noise sources. All of these noise sources, except thermal noise, exist only when
current is flowing in the device and can be controlled to some extent by controlling the current
duty cycle.  The basic process creating oscillations is by feedback using a resonant circuit with
period current pulses charging the tuned circuit.  Between charging pulses, the transistor conducts
zero current and is considered 'off.'  Phase noise is produced depending on the shape of the
current pulse when the transistor is 'on.'  If the current is a relatively narrow pulse, existing for
very short time, there will be less phase noise produced than with a wider and longer pulse.  From
the engineer's perspective, the narrow pulse provides less contribution to creating time shifts in
the energy storage when lined up with the output waveform peak. Making the designer's job
easier is that only pulse width need be considered in design because the feedback process
automatically synchronizes the current pulse with the output waveform peak.  The pulse width
can be designed into an oscillator using nonlinear design techniques, thus gaining control over
transistor noise sources affecting phase noise.
Using nonlinear design methods based on the circuit principles in the text Communication
Circuits: Analysis and Design by Kenneth K. Clarke and Donald T. Hess (1971), it is possible to
control the current pulse width in the oscillator transistor.  Pulse-width control is accomplished by
varying the drive voltage of an active device.  Other benefits of designs based on the principles of
Clarke and Hess include the ability to set harmonic levels, output power, and oscillation frequency
with reasonable precision..
To examine the relationship between phase noise and current pulse width, Hewlett-Packard
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