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.
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