Crystal Oscillators Still Deliver Superior Performance
By: Roger Burns, Engineering Sales Manager, Fox Electronics
Competition from silicon MEMS, SAW, and other oscillators has made
crystal oscillators better than ever.
In today’s electronics world, everyone is always looking for the newest, fastest,
quietest piece of technology they can find, often leaving tried and true products
in the dust for what’s “hot.” Although trading older technology for newer is usually par for the course, there are times when older technology not only competes
with but is as good as if not better than what’s currently being touted as the
best in the market.
New customizable crystal oscillators like those from Fox Electronics provide a
wider range of options with fewer compensating factors, coupled with lower
pricing.
Take crystal oscillators. Thought to be technology of the past after the onset of
silicon oscillators based on microelectromechanical systems (MEMS) and before that, surface acoustic wave (SAW) oscillators/crystal oscillators have held
their own. With the addition of cost-effective, configurable technology, manufacturers can produce crystal oscillators that provide significant business and
performance advances across a wide frequency range of 750 kHz to 1.35 GHz.
These days, designers require higher frequencies and low jitter in oscillators,
while buyers demand low cost and quick delivery. Key to cost-effective solutions are timely oscillator options that can deliver the highest desired performance while minimally affecting the design steps. Fortunately, in the ongoing
battle to push the limits of technology and lower component costs, oscillator
manufacturers continue to close the gap between high-level performance and
cost-effective purchasing, with conventional crystal technology paired with
configurable oscillator technology.
Improved Cost Efficiencies
Designers and manufacturers now have new options for applications such as
telecommunications and data networks as well as consumer products, thanks
to some recent developments in oscillator technology. These include configurable oscillator technology, making the delivery of oscillators and voltage-controlled crystal oscillators (VCXO) more timely and affordable than ever before.
Thus, this type of oscillator remains extremely competitive with its MEMS and
SAW oscillator counterparts in terms of cost, performance, and delivery times.
What sets configurable crystal oscillator technology apart is its ability to deliver technical and business advantages across a frequency range of 750 kHz
to 1.35 GHz with low jitter (less than 1 ps) and phase noise characteristics
comparable to conventional crystal oscillators and SAW oscillators, as well as
www.FutureElectronics.com
jitter and phase noise characteristics better than MEMS oscillators. Designers
of subscriber applications such as wireless WiMAX or WiBRO data networks
find this combination particularly attractive. This customizable technology also
enables new crystal oscillators to find homes as diverse as the clock source in
10G Ethernet, optical networks, storage-area networks (SANs), FPGAs, ADSL,
and many other applications (see the figure).
Modular Architecture Lowers Noise Characteristics
The modular building-block architecture of these new configurable oscillators,
versus the “one-solution-fits-all” approach of programmable oscillators, provides the desired frequency without compounding the noise in the performance
of the finished product.
A configurable oscillator begins with a conventional oscillator crystal blank
that runs the output through a series of functions, just like a programmable
oscillator. But it uses one of several fractional-N phase-locked loops (PLLs)
chosen based on the desired frequency for the final application, instead of a
conventional integer PLL that just blankets a wide frequency range. Because
the fractional-N PLL does not divide the reference frequency, it helps eliminate
one of the noise problems associated with programmable oscillators.
To compensate for spurs, which show up as noise elements in any fractional-N
PLL, the configurable oscillator design employs third-order delta-sigma modulator (DSM) technology to lower the overall amplitude of the spurs by spreading
them over a larger bandwidth, lowering the total spur level. Combined with
ASICs, this modular design allows for accurate performance, lower noise, decreased costs, shorter lead times, and increased flexibility.
Constructing An Oscillator
Depending on the needs of the application, three types of output buffers are
available on configurable crystal oscillators. The most popular, high-density
CMOS (HCMOS), is used for most lower-frequency applications, with low-voltage positive-emitter coupler logic (LVPECL) and low-voltage differential signaling (LVDS) outputs available for higher-frequency applications.
The available combinations create HCMOS oscillators and VCXOs from 750 kHz
to 250 MHz, LVPECL oscillators and VCXOs from 1.00 MHz to 1.35 GHz, and
LVDS oscillators and VCXOs from 1.00 MHz to 1.35 GHz. Applying a modular
approach to such common components as crystal blanks, fractional-N PLLs,
DSMs, and output buffers enables designers to configure an affordable crystal
oscillator package that satisfies the frequency, noise requirements, and output
type of each application.
Small package sizes down to 3.2 by 2.5 mm combined with the use of commonfrequency crystal blanks make the new crystal oscillators available at price
points lower than those of conventional oscillators, SAW oscillators, and MEMS
oscillators. Designers receive a compact, functional oscillator that operates at
a custom-specified frequency, with the quick delivery time of programmable
oscillators and the low jitter and noise characteristics of conventional oscillators (see the table).
Shorter Lead Times
The new configurable crystal oscillators offer significant promise in terms of
performance, price, and product delivery to satisfy both the technical and business needs of designers and buyers. So, whether oscillators are used at their
specific frequency or tuned to higher frequencies using multipliers or PLLs,
the need for accurate, affordable, low-noise, and stable performance never
changes.
In addition to its desirable performance characteristics, the manufacturing
costs and lead times of this new configurable technology make crystal oscillators an attractive alternative for applications with volumes too low to benefit
from an economy of scale in custom-manufactured conventional oscillators.
This is particularly true for specialized applications, where order volumes might
be as low as 1,000 or 2,000 units, as opposed to consumer electronics applications where order volumes are often in the hundreds of thousands or greater.
Configurable oscillators are available for as low as $0.39 per unit in quantities
of 10,000.
Roger Burns has held various positions in technical support, sales and marketing, and field applications in his more than 15 years at Fox Electronics. Before joining Fox, he was in the U.S. Navy’s Nuclear Engineering program and
attended Edison College, Fort Myers, FL. He can be contacted at rogerb@
foxonline.com.
More importantly, the price efficiencies of using common modular components
make configurable oscillators a quicker and more cost-effective solution than
conventional oscillators across the board. They deliver low jitter and phasenoise characteristics comparable to those of fixed-frequency oscillators at a
lower cost. Since a configurable oscillator can be produced to custom specifications in just a fraction of the time of a conventional oscillator, it cuts delivery
from eight or ten weeks to less than two weeks, with some manufacturers able
to deliver samples overnight.
Customer Confidence Equals Consumer Contentment
Another recently developed distinctive feature in crystal oscillators is the use
of a serial ID program that internally assigns a unique ID to each oscillator and
tracks the entire manufacturing process. To accommodate decreasing component size, which is so prevalent in the electronics industry, the serial ID is
embedded into the part’s nonvolatile memory. Conventional oscillators aren’t
good candidates for this quality control program since they lack this type of
internal memory.
Fox’s patented ID process quickly and accurately traces any component back to
its original production process, including the raw materials and equipment used
to manufacture a specific part, the electrical testing performed, as well as the
exact date of manufacture. This gives designers a higher degree of confidence
that problems can be traced and corrected, decreasing the risk of exposing
faulty products to the end user.
Performance Without Compromise
www.FutureElectronics.com