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SiTime Releases MEMS Oven-Controlled Oscillators as GPS Fail-Safe

December 13, 2023 by Arjun Nijhawan

This ruggedized version of SiTime's Epoch platform acts as a holdover when GPS signals drop because of inclement weather, spoofing, jamming, or other disruptions. 

SiTime recently released the Endura Epoch Platform, a MEMS oven-controlled oscillator (OCXO) designed to increase the security of PNT systems against disruptions such as jamming. SiTime developed this platform to help protect personnel and prevent critical equipment failure. The Endura Epoch Platform provides an “ultra-stable” local clock for mission-critical electronics in the event of a GPS failure, the company says.

 

Endura Epoch Platform

Endura Epoch Platform provides a highly accurate and stable clock. Image used courtesy of SiTime

 

SiTime describes it as a “ruggedized” continuation of the Epoch Platform released in September.

 

“Ruggedization” Through MEMS Technology

The key objective behind the new Endura Epoch Platform is to provide precise and redundant timing to mission-critical positioning, navigation, and timing (PNT) services in the event of a GPS disruption.

Since GPS relies on four satellites to calculate the exact location of the receiver, it is susceptible to attacks such as jamming, an amplified RF signal intercepting incoming GPS signals. If a device’s GPS capability is jammed, it needs a backup clock source of equal precision to continue functioning properly.

The Endura Epoch Platform's MEMS (Micro-ElectroMechanical System) oscillators enable redundancy with a precise clock that offers a programmable frequency from 10 MHz to 220 MHz. Some variants of the Endura Epoch Platform can also operate without a reference clock (holdover condition) with a time error of only three microseconds over 24 hours.

 

Endura Epoch time error

Endura Epoch time error. Image used courtesy of SiTime
 

Because the oscillator uses MEMS—tiny silicon structures—instead of a quartz crystal, it is physically more resilient in a small form factor. SiTime says the Endura Epoch Platform offers 20x better shock sensitivity, 30x better reliability, and 70x better g-sensitivity (a device’s sensitivity to acceleration) than quartz crystal. 

 

The Tiny Form Factor Packs a Punch

According to the datasheet (available from SiTime upon request), the Endura Epoch Platform is the industry’s “smallest ruggedized MEMS oven-controlled oscillator”, with a footprint of only 9 mm x 7 mm. SiTime offers the platform in four different variants: SiT7111, SiT7112, SiT7101, and SiT7102. 

 

Endura Epoch Platform

Endura Epoch Platform has a small form factor to fit in various PNT systems. Image used courtesy of SiTime

 

While all four have the same physical footprint, each variant differs in holdover, frequency range, and over-temperature parts per billion (ppb). In this context, ppb refers to the deviation of the oscillator frequency over the allowed operating temperature (-40°C to 95°C). The SiT7111 has an over-temp ppb of only 1, making it very stable as environmental temperatures change. 

 

MEMS-Based Oscillators Gain Traction

Due to their resilience, MEMS-based technology is gaining traction for applications that require physical durability and stability against environmental stressors. These applications are not just limited to semiconductors and defense. NASA has been conducting extensive research into MEMS oscillators for space use cases, such as satellites, which experience intense environmental stressors from vibration, acceleration, and temperature.

 

MEMS vs. quartz crystal oscillator measurements

MEMS vs. quartz crystal oscillator measurements. Image used courtesy of ECS Inc International
 

While MEMS does have clear advantages, quartz oscillators excel in certain areas. For instance, quartz crystal oscillators generally have better phase noise and jitter performance. According to ECS Inc. International, quartz has a better Q (quality) factor than MEMS, making it useful in applications that are sensitive to jitter and where environmental resilience is less important. 

Endura OCXOs can, however, act as a holdover when PNT systems lose GPS signals because of inclement weather, spoofing, jamming, or other disruptions.