# Essay Examples on State University of New York at Cobleskill

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### What is Spectral Purity of an Oscillator Issues

Don’t let the phase noise of a signal source destroy your RF measurements What is spectral purity of an oscillator Spectral purity is the inherent stability of a signal It varies in frequency and time The major measurements of spectral purity are phase noise harmonics and spurs Phase noise is the most important figure of merit of a signal generator In this post you will learn what phase noise is and how it impacts your RF measurements How Big Is the Gap Between Ideal Reality Let's look at ideal and real signals first As shown in Figure 1 below an ideal signal is a perfect sinusoidal waveform in the time domain In the frequency domain it s a single spectral line However in the real world there are always unwanted amplitude and phase fluctuations on the signal Both random amplitude fluctuations and phase fluctuations are added to the ideal sinusoidal waveform equation The waveform has a phase shift and amplitude shift in the time domain In the frequency domain the signal has both amplitude and frequency modulation Figure 1 Equations and waveforms of ideal and real continuous waves Phase noise is a frequency domain view of the noise spectrum around the oscillator signal It describes frequency stability of an oscillator Frequency stability can be broken into two components long term stability and short term stability shown in Figure 2 below Figure 2 Long term frequency stability and short term frequency stability Long term stability is characterized in terms of hours days months or even years Short term stability refers to frequency changes that occur over a period of a few seconds or less There are 2 categories of short term stability Random noise The variation is random and is commonly called phase noise The sources of random noise in a signal include thermal noise amplifier noise and flicker noise in active and passive components Deterministic signals Signals appear as distinct components on the ideal spectrum These signals commonly called spurious signals result from power line frequency or mixers
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