Clock Generator Without Quartz MEMS Oscillators for "Intelligent Edge Computing"

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SiTime Corporation

Wuxi InfiMotion Technology Co., Ltd.

Resonators and oscillators based on MEMS technology are the key to a new era of miniaturization—they open up possibilities for developers to create increasingly smarter and more compact IoT devices. This makes quartz obsolete in such applications.

Eric Garlepp is Senior Director of Product Marketing at SiTime in Santa Clara, USA.

Parker Traweek is Senior Product Marketing Engineer at SiTime in Santa Clara, USA.

IoT technologies are a central driver of the automation of everyday life—from cities, buildings, and transportation to retail and healthcare. They integrate intelligent functions that enhance comfort, safety, and efficiency. As modern lifestyles seamlessly and continuously transition between the physical and digital worlds, the "Internet of Things" is becoming increasingly ubiquitous and powerful.

To support the rapid expansion of IoT and the associated demands for intuitive, seamless responses, data processing and artificial intelligence increasingly need to be shifted to the edge of the network—the so-called edge.

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The latency caused by transmitting information via the edge network, the wired core network, to the cloud data center and back is unacceptable for real-time applications such as virtual and augmented reality (VR/AR), vehicle-to-everything (V2X), smart homes, and smart cities.

At the same time, the growing number of wireless devices in the network leads to increased bandwidth demand—requiring significant advancements in mobile technologies like 5G-Advanced and the upcoming 6G.

Edge Data Centers And AI in Wireless Infrastructures

These advancements in network infrastructure will drive two central developments in the near future: the expansion of edge data centers and the integration of data processing and artificial intelligence into wireless infrastructures and local edge networks.

Similar to central cloud data centers, edge data centers also rely on precise timing. In particular, two applications in the data center environment require highly accurate time control: end-to-end synchronization and high-speed data transmission.

The accuracy of time synchronization in a network largely depends on the environmental stability of the local oscillator in each network node—such as servers, switches, or routers. The most widely used method for time synchronization, the Precision Time Protocol (PTP) according to IEEE 1588, requires the local oscillator to maintain a stable frequency while the 1588 software selects the most reliable timestamp packets.

The higher the frequency stability of the local oscillator, the longer the time constant of the control loop can be set—and the more effective the packet filtering becomes.

Data Centers: MEMS TCXOs Versus Quartz TCXOs

MEMS TCXOs offer up to five times higher stability than quartz TCXOs under rapidly changing temperature conditions, which typically occur in data center servers (e.g., under high processor load and active cooling systems).

Beyond mere time synchronization, precise clock generation is crucial for high-speed data transmission over Ethernet and optical connections—especially due to the requirements for low phase jitter at the clock edge. As data rates increase from 200 to 400 Gbit/s, 800 Gbit/s, and beyond, the allowable jitter is halved with each technological step.

Compared to quartz oscillators, MEMS oscillators are up to ten times less sensitive to disturbances such as supply voltage noise, which can negatively impact phase jitter. Additionally, MEMS oscillators are flexibly configurable and support custom oscillation options—for example, for compatibility with non-standard low-voltage ICs—allowing power consumption to be reduced by more than 30 mA.

With the introduction of 5G-Advanced and 6G, a significant portion of data processing and intelligence will be offloaded from data centers and directly integrated into wireless infrastructure. This enables wireless AI functions with very low latency—even for the smallest and energy-efficient devices like smart wearables.

As timing becomes increasingly crucial in wireless infrastructure and more precise synchronization as well as faster data transmission are essential, MEMS oscillators provide the required reliability and precision for next-generation telecommunications.

Pressure on IoT Endpoints through Miniaturization

In the small IoT devices themselves, the focus of timing is on achieving the right performance with optimal energy efficiency and size. Wearables, ingestibles, smart tags and electronic labels, sensors in devices, and almost all other components generally need to be small and lightweight.

In consumer applications, a visible sensor means the magic is lost. In some industrial applications, the sheer number of sensors being deployed is so large that maintenance becomes impossible, meaning the battery must provide sufficient capacity for the entire lifespan.

This leaves little room for bulky or inefficient circuits. Compact circuits also provide more space for a larger capacity battery, which extends battery life. For small radios, there are always restrictions regarding the positioning of the radio module, e.g., to ensure the clearance required for the proper operation of the antenna.

This can pose a problem for timing, as quartz crystals are inherently bulky. In active mode, the clock frequencies used to operate communication circuits are usually in the double-digit MHz range.

Lower Frequencies Reduce Power Consumption

To reduce power consumption, many IoT endpoints in standby mode use a 32.768-kHz oscillator or resonator to maximize battery life. A clock generator with a significantly lower frequency simply consumes less power.

Unfortunately, quartz crystals with lower frequencies require larger resonators due to physical limitations. MEMS resonators do not have this issue. The smallest MEMS resonators are approximately ten times smaller than the smallest quartz crystals with the same frequency.

MEMS XOs, TCXOs, and resonators offer an additional valuable feature for IoT endpoints with their advantages in performance and space requirements: the possibility of significant size reduction. MEMS resonators can be as small as a few tenths of a millimeter, approximately 0.016 inches x 0.016 inches.

MEMS Components: Resistance to Shocks And Vibrations

As they have significantly less mass than a quartz resonator, they are more resistant to shocks and vibrations, as an acceleration applied to the MEMS structure results in much lower force and frequency shift. Finally, today's leading MEMS resonators exhibit more stable frequencies compared to their quartz counterparts over a wide temperature range of –40 °F to 260 °F, enabling higher clock accuracy and thus more efficient performance of an IoT system.

The miniaturization enabled by MEMS technology allows MEMS clock generators made from silicon to be integrated into the same package as the microcontroller (MCU) or a system-on-chip (SoC). Such co-packaging is not feasible with conventional quartz resonators, which are not silicon-based. These are housed in separate ceramic or metal packages to reliably produce a stable reference frequency.

The Housing As A Limiting Factor

In the past, mechanical and thermal challenges, particularly the mismatch of coefficients of thermal expansion (CTE), have proven to be obstacles to reliable and economical co-packaging with quartz components. The increasing innovation pressure from modern and future IoT applications makes these limitations clearly visible.

The package represents another limiting factor for the continuous miniaturization of IoT products. While advanced semiconductor technologies enable ever smaller feature sizes, thereby integrating more functionality into SoCs and ASSPs, the quartz crystal remains in its own hermetically sealed ceramic package—permanently mounted on the circuit board.

In this context, it can indeed be said that quartz resonators or oscillator ICs are increasingly becoming a bottleneck for further miniaturization in an industry where compact designs are of crucial importance. (kr)

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