OCXOs (oven-controlled oscillators) offer the pinnacle of performance in timing. Few timing suppliers can achieve OCXO-level stability, which is around ±50 ppb (parts per billion) or better. Because OCXOs provide Stratum 3E* level timing stability, they’re used in high-throughput communications networks that demand more stringent timing performance with each new generation. Moving forward, OCXOs will be essential for emerging 5G and IEEE 1588 synchronization applications that will support mission-critical services like self-driving vehicles.
How do OCXOs achieve this stability?
These high-precision oscillators are designed to maintain frequency under temperature variation, one of the main reasons stability is degraded, by enclosing the resonator along with temperature compensation circuitry and a heating element. But even though these “ovenized” devices are engineered to keep the internal temperature constant, traditional OCXOs are still susceptible to variations in the ambient temperature, especially when the temperature changes quickly.
That’s why designers make painstaking decisions on where to place the oscillator on the board. OCXOs are often placed in a corner, away from fans which cause airflow-induced thermal shock and away from the main processing unit which can generate significant heat. But there are tradeoffs to moving the oscillator away from the chip that it’s clocking, such as increased routing complexity and potential signal integrity issues. Some of our customers have to go through 3 to 5 board layout iterations just to figure out where to pace the OCXO.
In many cases, the OCXO is covered with a special mechanical shield for thermal isolation. But these covers are typically not off-the-shelf items. They require finding a specialized vendor to design and make the cover, additional board space, and extra manufacturing steps to adhere the cover. All of which take time and money, and they’re still not fool proof.
And with all of these protective measures, the OCXO is still not safeguarded against other factors that affect stability and performance. Things like vibration, humidity, time (aging), and electrical noise such as supply voltage or load impedance. This makes timing potentially the biggest source of failure in communications systems. There was no easy way to alleviate all the headaches and risks of using OCXOs, at least not before the introduction of the Emerald Platform, the first MEMS-based OCXOs.
A new super-robust solution
The Emerald Platform is a game-changing solution in precision timing, providing much better reliability and performance in dynamic conditions. It’s based on a programmable platform that can support any frequency from 1 MHz to 220 MHz, and either LVCMOS or clipped sine-wave output. Here are some features compared to traditional quartz-based Stratum 3E OCXOs.
- 10 times better performance in the presence of airflow and thermal shock
- ±5 ppb frequency stability over-temperature
- ΔF/ΔT dynamic stability: ±50 ppt/°C typical (ppt = parts per trillion)
- Allan deviation (ADEV): 2e-11 under airflow
- 20 times better vibration resistance
- 0.1 ppb/g
- No activity dips or micro jumps
- Smallest size
- 9 x 7 mm footprint, 75% smaller
- 6.5 mm height, 40% thinner
- Also available in standard OCXO footprints for drop-in replacement of quartz OCXOs
- Semiconductor-level quality and reliability
- Eliminates batch-to-batch inconsistencies of quartz OCXOs
- No need to sample and test incoming lots
- Unmatched ease-of-use
- No restrictions on PCB placement
- No mechanical shielding required for thermal isolation
- On-chip regulators, no need for external LDOs or ferrite beads
- Resistant to humidity
Solving long-standing quartz OCXOs timing problems
Up to now, communication equipment makers had to rely on a delicate, hard-to-use timing device. The Emerald Platform is designed to solve the long-standing problems of quartz OCXOs which are sensitive to environmental conditions and require protective measures. Emerald products simply work, anywhere—regardless of where they are placed on the board, or where they are deployed in the field.
In short, designers can now sleep better at night without worrying about the difficulties of OCXOs. Equipment makers can reduce design complexity, speed development time, accelerate revenue—and, count on stability when it’s really needed for their systems.
Come back next week to read our following blog on key telecom timing parameters and how Emerald performance compares to quartz OCXOs.
*A Stratum 3 clock has a free run stability of ±4.6 ppm over 20 years and a hold-over requirement of ±0.37 ppm (±370 ppb) over 24 hours, both inclusive of frequency errors under all conditions. Stratum 3E is a more accurate version of Stratum 3, with the same ±4.6 ppm free run stability, but with ±0.012 ppm (±12 ppb) over 24 hour hold-over spec, 37 times tighter than Stratum 3. For more information on timing terminology, download our Glossary of Oscillator Terminology.