Inside Frequency Control

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.

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.

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.

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.

The development of crystal oscillators has literally changed the world. Technically that can (and is) said about many things. But think about it! Without crystal oscillators, we may have never seen precision timing in clocks, wide and clear radio broadcasts, or important communication methods within military and space programs.

Imagine how different our world might be without these now commonplace technologies. 

We can't possibly be the only intelligent life-forms in this infinite universe, can we? I mean, there's still plenty of exploring to do in our own solar system let alone nearby stars, our entire galaxy, and surrounding galaxies. Will our current deep space communication efforts, like Voyager 1, ever stumble across alien life so us humans can say, "Hi! We're here!"? Or will it take so long that our messages would be more like, "Hi! We were here!"? 

Let's explore some current communication efforts to make contact with aliens and how they work.

Bliley Technologies is proud to be partnered with PARC, the Palo Alto Research Center, a leading hub of innovation in a wide range of cutting-edge 21st-century technologies. PARC has deep expertise in the high-tech fields of big data, optoelectronics, semiconductors, large area electronics, model-based reasoning for AI, and is a pioneer in the field of ubiquitous and context-aware computing.

RF engineers are aware that temperature variations are the most significant factor contributing to frequency drift in crystal oscillators. Other variables affecting frequency output, such as humidity and pressure, can be easily alleviated with a hermetically sealed packaging of the crystal in a vacuum, or in an inert gas such as nitrogen. Controlling temperature for precise frequency output in a crystal oscillator circuit, however, requires a higher level of electronic RF design ingenuity. Enter... The Oven Controlled Crystal Oscillator (OCXO).

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...