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Inside Frequency Control

The Secret to Maintaining Low Phase Noise in Oscillator Circuits

Posted by Rob Rutkowski on Feb 20, 2020 9:06:00 AM

Quartz crystal oscillators are the high and mighty option for low phase noise and added frequency stability in circuit design. Yes, simple oscillators like those made with resistor-capacitor (RC) or inductor-capacitor (IC) resonators are fine for some circuits. But if you're dealing with higher performance applications in aerospace, military, and space industries... you're going to want a higher performance crystal oscillator that can maintain low phase noise & strong stability. Otherwise, you'll risk deviating from the very specific (and many times critical) center frequency selected for your design.

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Topics: crystal oscillators, RF Technology, Integrated RF

Ultimate Guide to Understanding Phase Noise

Posted by Bliley Technologies on Feb 20, 2020 9:00:00 AM


Maintaining strong frequency stability in electronic RF circuits by eliminating phase noise is important in many high-end communication applications. This is especially true for precise targeting in radar systems and spectral purity in other communication systems.

Let's take a deep dive into exactly what phase noise and jitter mean. This will help give you a better idea as to why reducing a system's phase noise is significant.

What Is Phase Noise?

Phase Noise  is represented in the frequency domain of a waveform and consists of rapid, short-term, random fluctuations in the phase (frequency). This is caused by time domain instabilities (jitter).
 
Be sure not to confuse phase noise with Jitter. Jitter is a method of describing the stability of an oscillator in the Time Domain. It combines all the noise sources together and shows their effect with respect to time.

In the simplest terms, phase noise describes the stability of an oscillator in the Frequency Domain, while jitter describes stability in the Time Domain.

A Simple 5-Step Path to Understanding Phase Noise

To build an in-depth understanding of phase noise, try using this simple 5 step process. Once you understand the 5 steps, you'll understand what makes phase noise...well... phase noise! 
 
 
"How does Spectral Density connected to Phase Noise in the 5 step process?" you ask? Here's some more details on each step.

Step 1: Spectral Density

Spectral Density is a measure of a signal's power intensity in the frequency domain.  The spectral density provides a useful way to characterize the amplitude versus frequency content of a random signal.

Step 2: When plotting each spectral density point at varied frequency intervals of your choosing (In this case every 1Hz), you're left with a graph that looks like this:

Step 2: Signal Power Density

You are now looking at what is known as the Signal Power Density of the noise. 

Now focus only on the upper sideband of the graph from fstart to fstop, this is called the "Single Side Band".

Step 3: Noise Power Density

We can now refer to the plotted part of the single side band as noise (Anything above the nominal oscillator frequency (Fosc) and not harmonically related can be considered phase noise). The technical term for this part of our graph is Noise Power Density (Step 3). We measure noise power density in dBW (LOG(Watts)) at this point because of the large range which we are looking. 

Step 4: SSB Noise Density

When we combine the single side band and Noise Power Density, we are actually measuring what's called SSB (Single Side Band) Noise Density

Step 5: Phase Noise

Finally, we can look at this in the time domain and we see a "jittery" waveform (see graph), we are looking at "jitter". Because the jitter is much smaller than one complete period (see graph), we can say it is caused by "Phase Fluctuations" (instead of frequency fluctuations). Since these fluctuations are noise, it's actually  phase noise.
 
So...
SSB Noise Density = Phase Noise
...and that's where phase noise comes from! Easy, right?

What Causes Phase Noise?

Phase noise in higher-end applications (such as radar communications, military communications, and space & satcom communications) is typically caused by
  • High vibrations
  • Micro vibrations
  • g forces and acceleration sensitivity
Using an anti-vibration, g-sensitivity crystal oscillator is the best way to eliminate phase noise from all of these potential sources.
 
Here are some common sources of phase noise in crystal oscillators.
 
Random Noise Sources:
Related: Causes and solutions for phase noise in high-end radar and communication systems.

What's Next? Learn How to Achieve Low Phase Noise...

Achieving low phase noise in a crystal oscillator is critical to achieving high-performance. Therefore, it's important to understand an in-depth look at phase noise. Instantly download our free visual guide to the impact of phase noise on various applications.
 
Now that you know all about phase noise and jitter, you might find it useful to learn about the  best output signal type in your oscillators.
Download our visual guide to the effects of phase noise
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Topics: engineering, crystal oscillators

Common Misconceptions About Crystal Oscillator Stability

Posted by Bliley Technologies on Feb 2, 2020 10:14:00 AM

RF engineers would love to get their hands on ideal crystal oscillator circuits. That is, a quartz crystal oscillator that transmits at the designated frequency for the entire life of the device without any frequency deviation. Unfortunately, that ideal circuit world is a mathematical fantasy.

There are many factors that contribute to quartz oscillator stability and frequency drift issues. To prevent these problems as much as possible, having a firm understanding of precise frequency stability will help give you the tools to keep your applications performing optimally. But there's another problem...

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Topics: crystal oscillators, RF Technology

Is a Swept Quartz Crystal Necessary in your Timing Application?

Posted by Rob Rutkowski on Dec 11, 2019 8:45:00 AM

What is a Swept Quartz Crystal?

Like many other things, radiation can impact a crystal oscillator's frequency. This is because radiation physically alters the quartz crystal inside the oscillator (changes position of weakly bound compensators that change the elastic constants of quartz). In some cases, radiation can even impact the crystal series resonance. The increase of resonance can be serious enough to cause the oscillator to stop oscillating if the crystal isn't radiation resistant. When a quartz crystal is manufactured to be radiation resistant, the crystal is referred to as a swept quartz crystal.

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Topics: crystal oscillators, RF Technology

7 Key Factors of Crystal Oscillator Circuit Design

Posted by Rob Rutkowski on Nov 21, 2019 10:26:42 AM

There are 7 key factors of understanding successful crystal oscillator circuit design. These include

  1. Series circuit
  2. Load Capacitance
  3. Parallel Circuit
  4. Drive Level
  5. Frequency vs mode
  6. Design Considerations
  7. Negative Resistance
In this post, we're going to cover the basics of oscillator design and each of the 7 key components of great crystal oscillator circuit design.
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Topics: crystal oscillators

Warning! EFC Over-Specification May Be Costing You (Do this instead!)

Posted by Rob Rutkowski on Oct 2, 2019 11:14:09 AM

What if I told you that specifying more Electronic Frequency Control (EFC) than you need could actually be hurting you pocketbook? Well, it very well may be! Paying attention to whether your supplier is using AT cut vs SC cut crystals will help you save money in the long run with OCXOs.

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Topics: crystal oscillators, Clocks & Crystals, RF Technology

What The Heck is an OCXO Oscillator? (Facts & Functionality)

Posted by Rob Rutkowski on Aug 20, 2019 8:20:00 AM

Ahh the mysterious OCXO. What the heck is an OCXO anyway? What's it good for? When should you use one in your electronic system design? These questions and more will all be answered in this post.

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Topics: crystal oscillators, Clocks & Crystals

How to use Electronic Frequency Control to Enhance Crystal Oscillator Design

Posted by Rob Rutkowski on May 14, 2019 8:45:00 AM

Want to know what's better than a crystal oscillator? A crystal oscillator combined with Electronic Frequency Control (EFC). Of course, it really comes down to your specific application and what requirements you're looking for to determine if EFC would be a good addition to your crystal oscillator circuit design, and if so, which method is best for you.

There are 4 options to choose from when selecting an Electronic Frequency Control method for your crystal oscillator. These 4 options are

  1. Pulse Width Modulation & Low Pass Filter
  2. Reference RF Signal & Phase Locked Loop (PLL)
  3. Voltage Divide
  4. Digital-to-Analog Converter (DAC)

In this post, let's take a closer look at each option and compare the pros and cons between them.

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Topics: crystal oscillators, RF Technology

What are GPS Disciplined Oscillators (GPSDO)?

Posted by Rob Rutkowski on Mar 19, 2019 9:26:00 AM

GPS Disciplined Oscillators (GPSDO) are one of today's most trusted and accurate sources of timing.  These powerful devices (sometimes called GPS clocks) consist of a high-quality stable oscillator and a GPS receiver. The GPSDO works by disciplining (or steering) the oscillator output to a GPS device or GNSS satellite signal via a tracking loop.

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Topics: crystal oscillators, RF Technology, GPS & GNSS, Integrated RF, Defense & PNT

Searching for the Perfect Crystal Oscillator? Ask These 4 Key Questions

Posted by Rob Rutkowski on Feb 27, 2019 9:36:00 AM

The harsh truth is, selecting the wrong quartz crystal oscillator can quickly kill any design. With the wide variety of options and specs available in the market today, selecting the perfect crystal oscillator for your design can be a difficult and time consuming task.

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Topics: crystal oscillators