New Ruggedized Timing Technology Bolsters Resilience in GPS-Synchronized Defense Equipment
By Odile Ronat, Product Marketing Director, Aerospace and Defense, SiTime
GPS is not only critical for positioning, navigation and timing (PNT) in military and defense operations, it is also continually under threat. Extreme weather, urban canyons, tree canopies and other obstacles can weaken or disrupt GPS signals. Bad actors can jam or spoof signals and such instances have been growing at an alarming rate, specifically in conflict zones. All of this can jeopardize national security. GPS is critical in defense operations because it provides the time reference for synchronized timing across a wide range of equipment and personnel, including command and control centers, mobile military communication systems and networks, ships, aircrafts, ground vehicles, soldiers and more.
Because the signals are not fail safe, the US DoD has made it a strategic priority to develop new PNT systems that are hardened against jamming and spoofing or that can provide trustworthy timing using alternative technologies. One such alternative technology is a new silicon MEMS localized clock designed into systems that are dependent on GPS. The new technology mitigates signal disruptions in GPS-synchronized defense equipment, ensuring reliable and precise PNT even when GPS signals are out.
The Case for Silicon MEMS Oven Controlled Oscillators versus Quartz OCXOs in Military and Aerospace Applications
Traditionally, quartz oven-controlled oscillators (OCXOs) have been the device of choice for precision timing in GPS applications and beyond. Although quartz-based technology has been around for roughly a century, it presents drawbacks in many defense applications. Typical construction makes quartz OCXOs vulnerable to stressors, such as vibration, shock, and temperature fluctuations. Not only can these stressors impact device reliability and performance, but they make the device prone to out-right failure. This is a substantial risk, especially in critical applications such as aircraft navigation, threat monitoring and field communications.
Because of the challenges of quartz technology, only a limited selection of commercially available quartz OCXOs are rated for acceleration sensitivity (g-sensitivity), which is important for vehicle mounted, airborne and field systems. When designed for vibration robustness, quartz OCXOs trade off frequency stability for some environmental ruggedness. In addition, quartz OCXOs consume large amounts of power, typically 1 watt or more. Beyond these challenges, quartz OCXOs are bulky and have strict design requirements, which complicate product design. G-sensitivity rated OCXOs are often pricey and have extended production lead times of many months.
Enter silicon MEMS oven-controlled oscillators, a game-changer for precision timing. Ruggedized MEMS OCXOs stand up to demanding aerospace and defense environments, vibration, shock, and temperature fluctuations—especially important for those systems dependent on GPS synchronization. By leveraging ultra-clean semiconductor processes, MEMS OCXOs can achieve unmatched quality and reliability and part-to-part consistency to enable easier integration, faster product design cycles, and higher system-level performance.
In addition to their ability to better take on harsh environments and bolster reliability, ruggedized MEMS OCXOs outstrip quartz counterparts when it comes to size, weight, and power (SWaP). In fact, MEMS OCXOs are now becoming available in a small 9 x 7 x 3.6 mm3 package, with a weight of 0.35 g, consuming as little as 420 mW of steady-state power and rated at 0.01 ppb/g acceleration sensitivity: this is a 20X size reduction, a 2X power reduction and eliminates the need for vibration compensation. This can save you up to 100 g relative to quartz OCXOs. Due to its small size and low power requirement and its low sensitivity to vibrations, temperature transients, and EMI, a MEMS OCXO clock provides flexibility in board layout.
Ultra-Stable Timing During GPS Disruption
As long as trusted GPS signals are available, the local oscillator is synchronized to the GPS time reference, and you can rely on your PNT systems. Upon loss of the trustworthy GPS signals due to jamming, spoofing or other disruptions, the local clock is no longer synchronized to an external reference clock and the performance of the PNT system depends on the performance of the local oscillator which can drift due to intrinsic noise, aging, temperature changes and vibrations: The local clock is truly the heart of the PNT system. Novel solutions are needed for a SWaP oscillator that provides stability over temperature, environmental stressors and time. Ruggedized MEMS OCXOs are now available to offer the stability needed for next generation PNT systems.
The time during which the local clock is not synchronized to the reference clock is referred to as holdover and the performance for the local clock during holdover is measured as a time error. Time error is the integration of the frequency drift during the holdover period. When the time error becomes too large, system performance rapidly degrades or fails.
Advanced MEMS technology has the ability to substantively lower time error relative to quartz timing. This is due to lower Allan deviation and lower aging, along with low frequency shift during temperature changes and vibrations. MEMS technology has proven to offer 4X lower Allan deviation and 10X lower aging compared to g-sensitivity-rated quartz devices because of material purity coupled with low contamination of the MEMS enclosure. Time error can be further improved with aging compensation done through the digital frequency pull of the device. MEMS OCXOs perform particularly well during temperature transients such as experienced when cooling fans turn on, when the board is located close to a motor or power supply or when a high-power ASIC powers up. The MEMS OCXO temperature transient performance results from its high-precision temperature sensing and high-bandwidth temperature control loop.
Ruggedized MEMS OCXO Local Clocks for PNT Resilience
Ruggedized silicon MEMS OCXOs can effectively provide the stable clock reference from minutes to hours, where quartz crystal OCXOs fall short. They can outperform quartz in stability, reliability, and performance under vibration and have low phase noise and jitter, crucial for high-quality signal transmission. They offer a resilient, high-performance alternative in a compact, low-profile, light weight package. Their performance under vibration can exceed most military requirements, eliminating the need for bulky, complex vibration compensation. The Endura Epoch OCXO, is the first ruggedized MEMS OCXO designed specifically for military applications. It delivers these advantages compared with quartz OCXOs:
- 30x greater reliability
- 20x reduced size
- 2x lower power
- 10x lower aging
- 70x better acceleration sensitivity
By leveraging silicon MEMS manufacturing and semiconductor supply chain efficiencies, these devices are readily available, with a 10- to 12-week lead time, once they are released into production late this year. Their unique programmability, including frequency, voltage, and more, eliminates the need for custom designs with custom qualifications.
If your timing is off, it can have a disastrous impact on military operations in the space, air, maritime, ground and cyber domains – causing equipment malfunctions, increased risk to personnel, or even complete mission failure. Designing ruggedized MEMS silicon-based local clocks into systems that depend on GPS help ensure accurate timing and mission success. These new ultra-resilient, low-SWaP devices make the entire design process easier while improving system quality, reliability, and performance. Ruggedized MEMS silicon-based local clocks can help keep defense operations moving forward safely and securely, even when the signal isn’t loud and clear.