Impact of ultra-low phase noise oscillators on system performance

June 02, 2015 //By Ramon M. Cerda and Gerd Reinhold
Impact of ultra-low phase noise oscillators on system performance
Ramon M. Cerda, Crystek Crystals Corporation and Gerd Reinhold, Produktmartketing FCP, WDI AG, consider the impact of ultra-low phase noise oscillators on system performance.

Introduction
To an electrical engineer, in an ideal word there would be no noise. But what is noise? What is electrical noise? Or more to the point of this paper: What is phase noise? As engineers, we know intuitively that low noise in a system is better than high noise. However, we must somehow quantify this noise in units and terms that we can all be in agreement with – and we will. We will also examine the difference in phase noise performance of commodity vs. low-cost, high-performance crystal oscillators. Understanding the cost performance trade-offs between oscillators is important to a system design. Many times we see two competitive systems separated widely in performance, but NOT in price. The oscillator phase noise characteristics will dominate the entire system performance and spending a few more dollars on the oscillator can turn a mediocre system into a superb system.

However, an engineer can easily over-specify the oscillator, and hence the key is to understand exactly how the oscillator phase noise (or jitter) limits the system performance. To help with this understanding, a tutorial on phase noise and jitter is in order.

Phase Noise and Jitter in Oscillators – A tutorial
In an oscillator, phase noise is the rapid random fluctuations in the phase component of the output signal. The equation of this signal is:

Where:    A 0 = nominal peak voltage
    f 0  = nominal fundamental frequency
    t = time
    Δø(t) = random deviation of phase from nominal – “phase noise”

Above, Δø(t) is the phase noise, but A 0 will establish the signal-to-noise ratio. Figure 1 illustrates this.

Figure 1: The signal to noise ratio is a function of A 0

The Noise Floor
Noise signals are stochastic and, in a broad sense, noise can be characterized as any undesired signal that interferes with the main signal to be processed or generated. It can disturb any physical

Design category: 

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