MEMS timing disrupts quartz in modern automotive
Article By : Etienne Winkelmuller
The MEMS-based precision timing technology is critical in the safe and reliable operation of next-generation automotive systems.
The cars of the future are here today. From advanced driver assistance systems (ADAS) to an array of electric vehicle (EV) options to semi-autonomous cars, next-generation technologies are transforming the automotive market. Keyless entry and start, telematics, smartphone integration, voice recognition, back-up cameras and smart mirrors have become standard features for many modern cars. Some of the latest models offer automated parallel parking, lane-keep assist technology, and other self-driving features as cars steadily advance toward fully autonomous driving.
As a result, automotive designs have redefined the safety, convenience, and infotainment features that we expect in today’s smart, connected cars. Automotive is one of the fastest-growing semiconductor market segments, and key drivers of this growth include electronic components for ADAS and EV applications. According to the U.S. International Trade Commission (USITC), gasoline-powered vehicles contain a semiconductor value of $330 while hybrid electric vehicles have from $1,000 to $3,500 worth of semiconductors. The average car contains around 1,400 semiconductors, controlling everything from safety systems to the drivetrain.
In addition to sensing, communications and processing chips, there’s another technology that’s critical to the safe, reliable operation of automotive systems: precision timing.
Figure 1 Timing is a crucial part of automotive designs spanning from ADAS to telematics to smart mirrors. Source: SiTime
For most car owners, “automotive timing” means timing belts, camshafts, or ignition timing to keep engines running smoothly and efficiently. For automotive system developers, timing means clocking devices ranging from integrated clocks and buffers to oscillators and resonators. Each type of timing device performs a different, essential clocking function to ensure accurate, stable and reliable frequency control for digital components. Precision timing is especially important for complex automotive systems such as ADAS that generate, transmit and process large amounts of data.
Quartz timing limitations
To keep automotive systems operating smoothly, today’s cars use up to 70 timing devices. That number is growing as more cars adopt smarter technologies with each new vehicle model. Clock generators and oscillators provide precise, reliable timing references for a wide array of digital systems in automotive designs. They provide critical clocking functions within electronic control units (ECUs) for ADAS, in-vehicle networks, infotainment, and other subsystems.
Timing devices help synchronize rapid, continuous data transfer from various sensors to ADAS computers. They are also crucial in vehicle-to-everything (V2X) and 5G communications. Next, timing helps build the foundation of global navigation satellite systems (GNSS), including global positioning system (GPS) technology, which is at the heart of telematics.
However, while the pace of automotive innovation continues to accelerate, one critical electronic component remains stuck in the slow lane: quartz-based timing devices. The most commonly used clock source across all industries and applications is the crystal oscillator (XO). And this 70-year-old technology has matured to a point where improvements are only marginal. Furthermore, quartz crystals have fundamental limitations such as fragility and susceptibility to mechanical and environmental stresses.
As the complexity of automotive systems increases, quartz timing devices are becoming a choke point for reliability and safety due to their inherent drawbacks. These limitations drive up cost and complexity and limit system reliability. Additionally, automotive electronics operate in unforgiving environments subject to mechanical shock and vibration, temperature swings and electromagnetic interference. Constant vibration from rough roads and moving parts can take a toll on sensitive electronics such as quartz timing devices.
Next, automotive applications must support extended temperatures, from −40 °C to +125 °C, and there’s growing demand for temperature operation as high as +150 °C. Changing weather conditions in addition to heat generated by the engine or battery packs can drive temperature extremes, degrading the accuracy of quartz-based components. This susceptibility of quartz timing regarding environmental stressors can negatively impact the performance and reliability of automotive systems, from ADAS to battery management.
Figure 2 A crystal or resonator (left) is a moving or resonating passive device that connects to the external oscillating circuit in the chip. An oscillator (right) contains a resonator and an oscillator IC in one active device and the resonator is based on silicon MEMS instead of the traditional quartz crystal. Source: SiTime
How MEMS timing bolsters automotive reliability
Timing devices based on microelectromechanical system (MEMS) technology are disrupting today’s clocking market. They provide a superior alternative to quartz components for applications such as ADAS and EV battery management, which require high reliability while handling environmental stressors.
A proven, well-established technology, MEMS is widely used in electronics systems, from automotive to smartphones to industrial and aerospace applications. MEMS devices serve as gyroscopes, accelerometers (used for air bag deployment), microphones, speakers, magnetometers, and a wide variety of sensor types. Automotive safety systems are among the earliest applications to adopt MEMS technology because of its inherent ruggedness and reliability in tough environments. Silicon MEMS devices can also be manufactured at scale in mainstream fabs, providing high-volume, cost-effective solutions for demanding automotive applications.
MEMS timing components, like their quartz equivalents, are engineered to meet rigorous AEC-Q100 automotive qualification requirements. This industry qualification gives automakers the assurance that their timing components provide the robustness, reliability and performance demanded by automotive electronic systems. Unlike MEMS alternatives, quartz devices typically are qualified to the less stringent AEC-Q200 specification for passive components.
Precision timing devices based on silicon MEMS technology have a solid track record in demanding automotive applications. Designed to endure environmental stressors, MEMS-based timing devices ensure reliable operation of ADAS computers, domain/zone controllers, and radars and LiDAR subsystems.
Rigorous testing has demonstrated that silicon MEMS technology is much more reliable than quartz crystals for clocking applications. This reliability is expressed in terms of failure per 109 hours of operation or FIT. Since 109 hours is a long span of time for testing, the industry uses statistical analysis and accelerated models to determine FIT rates. The FIT rate of a MEMS timing device is < 0.5 FIT—MTTF > 2 billion hours. This is calculated with a 90% Confidence Level, which is up to 50x better than quartz-based timing technology.
Advantages of MEMS for precision timing
Component size matters in today’s highly integrated automotive system designs. MEMS resonators are much smaller than quartz crystals, resulting in smaller footprint timing devices, down to 1.0 mm x 1.2 mm. This makes MEMS devices ideal for space-sensitive automotive applications such as camera modules, smart mirrors, and radar/LiDAR sensors. Smaller size and less mass in timing device designs result in more resilience to mechanical shock and vibration.
Compared to quartz, MEMS resonators have 100x better resilience to EMI disturbances. This resiliency is especially beneficial for applications, such as EV battery management systems, subject to high currents and electromagnetic fields.
Figure 3 The output frequency of MEMS oscillators is generated by programming the PLL to different values, which facilitates a very wide frequency range. Source: SiTime
Silicon MEMS technology also has excellent intrinsic material properties that are superior to quartz. For example, SiTime’s MHz oscillators deliver ±20 ppm frequency stability from -55 °C to 125 °C. They also provide 2x better stability, 20x greater reliability, and 30x more resistance to shock and vibration compared to quartz. Integrated temperature compensation, a key feature of MHz oscillators, improves stability to as low as ±0.1 ppm. This is an added benefit in harsh operating conditions with extreme temperature swings and other environmental hazards. Greater frequency stability enhances timing accuracy, which enables better synchronization in V2X and 5G communications over extended temperature ranges.
MEMS timing devices are free from “cold start issues” at the bottom of the temperature range, which often plague systems using quartz-based oscillators. Silicon MEMS resonators also are not subject to so-called “micro-jumps.” These random, non-reproducible jumps in frequency, common with crystal oscillators, can result in a loss of signal for GNSS/GPS or V2X/5G communications.
Back to the future of automotive
The future of the automotive market will be defined by the tremendous technology innovations and rapid advances in electronics that are underway today. And timing components are a critical part of this future.
Today’s and tomorrow’s smart, connected cars and safety-critical systems require timing components designed to deliver the utmost in reliability, performance and stability. By shifting from legacy quartz technology to MEMS-based precision timing solutions, automakers are making a strategic investment in safer, more reliable automotive system designs.
This article was originally published on Planet Analog.
Etienne Winkelmuller is director of segment marketing for automotive at SiTime.