Oven Controlled Crystal Oscillators (OCXOs) Essentials
Oven Controlled Crystal Oscillators (OCXOs) Essentials
These High-Performing Quartz Crystal Oscillators Provide Exceptional Accuracy for Many Essential Applications
An oven controlled crystal oscillator (OCXO) is a quartz oscillator whose crystal is specifically cut for exceptional frequency accuracy. When the crystal is heated to a specific internal temperature, it is highly useful for clocking reference accuracy.
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The OCXO is outfitted with its own heating component encapsulated in metal or ceramic packaging to maintain its frequency. It also contains a thermistor which measures the temperature at which the OCXO emits its accurate frequency. When designed effectively, the OCXO only ever sees a temperature variation of .5 degrees. It comes as no surprise that the OCXO&#;s stability is sought after for many applications that require that level of precision.Engineers in the design community take advantage of the performance that this quartz crystal oscillator provides by integrating it into important applications that our world depends on today, including networking and communications.
Where Are Oven Controlled Crystal Oscillators Used?
Imagine a large network whose information travels outward at greater and greater distances. It is important that the information at the furthest point in the network is as accessible as any other part. An accurate frequency generated by an OCXO provides a stable backbone to ensure the fidelity of information sent across the network.
OCXOs are necessary for the hub or center point of any large system that relies on frequency to communicate information. The OCXO also can help effectively control the central electronics within that main hub. Engineers include OCXOs whenever maintaining system accuracy is highly necessary. It would be difficult to imagine satellite communications or any other long-haul transmissions (for example, fiber optic sensors on the highway) without a highly dependable starting point. From central office equipment to radio transmitters and cell towers, the OCXO is a vitally important component, which ensures an unwavering temperature for the most accurate frequency.
Another Key Use for Oven Controlled Crystal Oscillators &#; Testing Equipment
When testing products that are meant to provide accurate readings, such as frequency spectrum analyzers or oscilloscopes, it is important to have another highly accurate tool for measurement or comparison. Enter the OCXO. The high level of accuracy in this quartz crystal oscillator plays an essential role for testing applications that provide accurate measurements. In the case of testing a standard MHz surface mount quartz oscillator for phase noise and jitter, the OCXO serves as a comparative tool. What better way to test a strong, stable frequency than crystal oscillator circuitry that is primarily characterized by its strength and stability.
Where to Find Superior Oven Controlled Crystal Oscillators in Today&#;s Marketplace
In a marketplace where engineers are under pressure to deliver on time and under budget, some manufacturing companies have developed inferior electronic components &#; including quartz crystal oscillators &#; hoping that engineers will buy them in a pinch.
However, inferior products and counterfeits pose a significant risk to engineers. These products may not have been designed as they should and may not have the shelf life and high performance of products designed by a superior manufacturer of crystal oscillators and other circuits. It is important to choose an authorized distributor of high-quality electronic components. In the case of OCXOs, these oscillators should include a rigorous testing process. Forced aging and stress testing the OCXO allows it to perform as accurately as possible. Premier quartz oscillator manufacturers will run these tests for a number of months to ensure that a customer will receive the product after the initial aging performance of the OCXO, so the product is primed for the engineer&#;s use case.
It is also important to remember that an inferior manufacturer is not going to stand behind their work when their ethos is building products cheaply and quickly under potentially deceptive premises. On the other hand, a leading manufacturer will always provide engineering support for its customers to ensure their products are working as desired.
The value that an outstanding crystal oscillator manufacturer offers is not limited to the electronic components themselves. A leader in frequency solutions will want to see its products used successfully in a wide variety of applications, especially those that will innovate in any given industry and benefit those who will use the product. A company like this will work tirelessly to support its customers by offering far more value than any fly-by-night business that is simply looking to capitalize on the growth of the electronics industry.
For an exemplary offering of educational materials and engineering support, visit these resources on frequency solutions and more. Discover state-of-the-art frequency solutions and a wealth of information on how these products contribute to many essential industries.
OCXO Lead Times Explained: How Aging Factors into ...
&#;Good things come to those who wait,&#; as the saying goes, and while aging is a part of all life cycles, crystals shouldn&#;t age prematurely. The careful production stages and the time it takes to complete them are necessary to the efficient operation of OCXOs.
Long lead times are a necessary byproduct of this aging process. While the quartz crystals used in Bliley&#;s oven-controlled crystal (Xtal) oscillators (OCXOs) are ready for production relatively quickly (in the grand scheme of things), the full cycle of manufacturing an OCXO is a lengthy process that requires generous lead times for the finished product:
- Crystal Production (40-80 Days)
- Blank Manufacturing (1-2 Weeks)
- Finished Crystal Manufacturing (1 Week)
- Crystal Conditioning (1-2 Weeks)
- OCXO Manufacturing (1 Week)
- OCXO Aging (1-2 Weeks)
- OCXO Final Testing (1 Week)
Let&#;s take a closer look at the stages of OCXO production from &#;seed&#; Xtal to finished oscillator, and how they impact lead time.
A Crystal Is Born (40-80 Days)
Quartz Xtal production requires meticulous, controlled, and pristine conditions. OCXO quartz is synthetic and grown artificially by hydrothermal method in a vessel called an autoclave.
The Xtals develop in high temperatures above 400 °C and pressures that exceed 1,000 atmospheres. Those two variables determine the rate of Xtal growth. Quartz can grow between 0.2 mm to 1 mm per day, but slower growth yields a higher quality Xtal. The &#;alpha&#; Xtal is ready for processing in about 40 to 80 days.
The quartz block is then cut into individual wafers and the remaining &#;seed&#; is reused to produce new quartz in the autoclave.
Blank Manufacturing (1-2 Weeks)
The angle and thickness of a blank&#;s cut is critical for achieving different frequencies and applications. The wafers are planed (lapped), beveled, and chemically etched according to the precise specifications for the desired function, temperature range and frequency stability.
Once the contouring of the Xtal is complete, the quartz blank, now cushion-shaped, is ready for the next phase.
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Finished Crystal Manufacturing (1 Week)
The slightest imperfection can affect the aging (frequency change over time) and precision of a quartz blank. At this point in production, the quartz crystals are slightly above their target frequency to mitigate any drift and to prepare for electrode application, which also reduces frequency.
X-ray technology is used for inspection, frequency checks, and quality control. The approved blanks are then carefully washed to prepare them for conditioning. The cleaning removes residual elements and impurities from the previous processes to allow for optimal adhesion of the electrode to the blank surface. This also keeps the resonance resistance low.
Crystal Conditioning (1-2 Weeks)
The Xtals that go into OCXOs must be conditioned for 5-10 days through the use of electrodes. In a vacuum, a process called &#;sputtering&#; vapor-deposits the electrode through a stencil, creating a thin film on the surface of the blank.
The span of the electrode determines the oscillation area of mechanical resonance within the blank. By increasing the vibrating mass of the electrodes, Xtals are reduced to the required frequency, and then the blank is finally complete.
OCXO Manufacturing (1 Week)
Finished quartz blanks with leads attached to the electrodes are mounted into the OCXO housing. Special care is taken not to push or pull the blank during mounting, as any stress can accelerate negative aging of the Xtal and affect its performance within the finished electronic.
The blank is sealed within the mount and either evacuated with a vacuum or filled with nitrogen. Because nitrogen is inert, it prevents the entry of reactive materials that might cause premature aging.
The oscillator contains temperature-controlled compartments, which function as an oven to maintain a constant temperature for the quartz Xtal inside it. The oven, in addition to a temperature controlling-circuit, prevents changes in frequency from external temperature variation.
OCXO Aging (1-2 Weeks)
While contaminants and stress can have negative aging effects on quartz Xtals, new oscillators are intentionally aged (also known as burning) for a period of time to relax stress, which is at a maximum just after powering on.
The daily aging rates will eventually stabilize and achieve an equilibrium. The amount of time needed for this type of aging depends on the oscillator frequency, the cut of the Xtal, and the aging rate. The US government publishes a mil-spec (MIL-PRF-) for Xtal aging and performance requirements.
OCXOs with standard frequencies age with power for 7&#;10 days, but the manufacturing process for non-standard frequencies can take several weeks or longer.
OCXO Final Testing (1 Week)
Bliley tests every oscillator per MIL-PRF- standards to ensure they meet requirements. Test protocols check frequency accuracy, the safety of the oscillator circuit, its ability to start reliably, and its drive level, which measures the current flowing through the quartz crystal.
The Importance of Aging & Long Lead Times
As you can see, careful aging is a necessary part of manufacturing quartz crystals and OCXOx, which results in long lead times but high-quality, reliable products.
In summary, the crystals that go into OCXOs need to be conditioned for 5-10 days, and then the OCXOs themselves need to age with power for 7-10 days. For non-standard frequencies we hold stock for, the process is longer; please reach out to us to request what frequencies we stock.
With more than 90 years of experience making reliable and stable crystal oscillators, we promise our oscillators are worth the wait. To learn more about our OCXOs, browse our products.
Contact us to discuss your requirements of ocxo manufacturer. Our experienced sales team can help you identify the options that best suit your needs.
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