New low-phase-noise high-stability MEMS super-TCXOs

To address persistent and novel threats, defence forces must be interconnected. They must share real-time information that will enhance situational awareness and analysis, enabling faster, more effective decisions. Radio frequency (RF) systems used for surveillance, intelligence, reconnaissance and communications play a critical role in the ability to detect threats sooner and respond faster, but the RF spectrum is congested and contested in the battle for dominance.

The effort for real-time collaboration creates high levels of complexity in data exchange. Advanced sensors, surveillance systems and communications equipment generate an unprecedented flow of data, requiring high data rates, low latency and high-security systems. This is driving an exploding demand for bandwidth.

To meet the bandwidth demand, RF systems must make more efficient use of the RF spectrum. Precision timing can help make this efficiency happen: SiTime’s new, low-phase-noise, high-stability MEMS Super-TCXOs are building blocks toward success in conflict, delivering faster, more accurate, reliable and secure data transmission in RF systems.

The clock is at the core of RF system performance

In recent years, the Department of Defence has developed The Joint All-Domain Command and Control (JADC2) strategy to use advanced cyber-hardened technologies for closer collaboration across the forces and strategic partners. The strategy endeavours to improve the speed, efficiency and effectiveness of command and control (C2) decision-making. The effort includes an integrated sensor ecosystem for a comprehensive understanding of the contextual environment. It also addresses the transport infrastructure for networks to specifically enhance speed and bandwidth. The strategy supports better decision-making, as well as activity monitoring across domains, even when the electromagnetic spectrum is degraded and contested.

Frequency accuracy is a cornerstone of effective signal processing, ensuring signal synchronisation, efficient spectrum use, interference mitigation, jamming resistance and reliable system performance. A high-performance clock ensures that RF systems—for example tactical radios, datalinks, advanced sensors and satellite communication user terminals—provide consistent performance over time and across all environmental conditions. This ensures operational capability throughout the mission.

Robustness of the frequency source is a critical selection criterion in modern RF systems. As interconnectivity expands into munitions, small UAVs, small sats and other applications resulting in diverse operational scenarios, a frequency reference must operate across a range of environments. Because of this, solutions must not only have good frequency stability and phase noise, but also stability across temperature, low sensitivity to vibration, resilience to shock and reduced size, weight and power (SWaP).

New, RF-grade low-phase-noise silicon MEMS super-TCXOs replace quartz TCXOs and OCXOs

Quartz TCXOs and OCXOs are the traditional source of timing for RF systems. While they are proven solutions for many scenarios, their limitations are also well known: they can be fragile, are subjected to frequency jumps due to temperature or vibration and can be bulky and power-hungry. This often leads to more complicated system designs to accommodate the limitations of quartz oscillators. Or, alternatively, it leads to custom oscillator solutions that are expensive and have long lead-times for development and procurement. 

SiTime pioneered silicon MEMS timing technology and now delivers game-changing low SWaP-C (Size, Weight, and Power – Cost) for RF systems. SiTime’s new Endura Low Noise Super-TCXOs are ruggedised low-phase-noise MEMS oscillators that deliver:

• Low close-in phase noise: -161 dBc/Hz phase noise at 10 kHz offset for a 10 MHz carrier
• Low broadband phase noise: -175 dBc/Hz broadband phase noise for a 10 MHz carrier
• Exceptional frequency stability: 1E-11 Allan deviation at 10 seconds
• Unparalleled g sensitivity: 1E-11/g
• Highly rugged design: > 20,000 g shock survivability
• Quartz OCXO levels of temperature stability: ±0.1 ppm over the entire temperature range (-40 to 105°C) without temperature induced frequency jumps
• Incredibly compact and efficient: 5.0 x 3.5 x 1.2 mm3, < 150 mW, surface mount package

Endura Low-Noise Super TCXO phase noise is virtually insensitive to random vibrations (50 Hz to 2 kHz per MIL-STD-883, Method 2026) even at higher amplitude than quartz. Three quartz TCXOs from three different manufacturers show the same behaviour under vibrations with an increase in phase noise in the order of 20 dBc/Hz: this is due to the inherent construction of COTS quartz TCXOs.

The key to Endura Super-TCXO performance is the silicon MEMS resonator that it uses as a frequency source. The MEMS resonator is nearly 1,000 times smaller than a typical quartz resonator and is made of high-strength silicon material encapsulated in an ultra-clean cavity, eliminating contaminations that cause frequency jumps, aging and failures. This use of high-purity semiconductor processes results in unmatched quality and reliability with excellent part-to-part repeatability, predictable system performance and a meantime between failure (MTBF) of 1 billion hours. Because the MEMS resonator is light weight and has superior material strength and structural design, Endura Super-TCXOs are highly shock resistant and vibration insensitive.

The Endura Super-TCXO achieves exceptional temperature stability with SiTime’s DualMEMS technology. Due to the small size of MEMS resonators, DualMEMS technology can combine two MEMS resonators closely to one another on the same die. The first MEMS resonator, the TempFlat resonator, is designed to achieve an ultra-low temperature coefficient. The second MEMS resonator, the TempSense resonator, is intentionally designed to have a high-temperature coefficient. The frequency difference between the two MEMS resonators provides an extremely accurate reading of the temperature (~30 micro-Kelvin) which allows for precise and fast temperature compensation.

Low SWaP-C super-TCXO for next-generation robust and reliable RF systems

SiTime’s new Endura low-phase-noise Super-TCXO promises to enable the design of new tactical radios, satellite communication user terminals, datalinks and advanced sensors that were not possible before. The Endura Super-TCXO improves communication sensitivity, quality and reliability and supports the development of systems with high-speed data rate, low latency and spectrum utilisation for real-time, data-informed decisions and swift coordination, critical for operation effectiveness.