This article is part of the TechXchange: Oscillations, Timing and Synchronization.
SiTime is betting the future of timing will be fabricated out of silicon.
The Santa Clara, Calif.-based company aims to upend the timing landscape using MEMS technology. Its timing devices bring together the smaller form factor and higher power efficiency of silicon with unique properties that, it claims, traditional timing devices are lacking. SiTime said the success of its timing chips stems from their high accuracy and frequency stability. The gains have lured in the likes of Tesla, which is using the timing devices in its Dojo supercomputer system.
While traditional quartz-based timing devices have dominated for decades, the technology is hitting its limits in AI data centers and 5G networks, where precise and robust timing has never been more vital.
To help keep everything inside huge data centers and wireless base stations in sync, Epoch—SiTime's latest MEMS-based oven-controlled oscillator (OCXO)—can output highly stable timing signals even in the face of vibrations, wind, shock, temperature, and other environmental perturbations. The chips are said to be a fraction of the footprint of existing offerings and exhibit 2X better performance.
The energy-efficient Epoch family has programmable frequencies ranging from 10 to 220 MHz, with ±1, ±3, or ±5 ppb of stability spanning an extended operating temperature of –40 to 95°C.
They’re also said to be especially robust against vibrations, which is vital in 5G base stations or other edge deployments, where rough environmental conditions need extra ruggedness and higher reliability.
Samples of the Epoch family—the SiT5811, SiT5812, SiT5801, and SiT5802—are due out later in 2023.
The Importance of Timing Devices to AI and 5G
Like traditional timing devices, the MEMS resonators at heart of SiTime’s oscillators output a predictable frequency that acts like a drumbeat, keeping all of the building blocks of a system or a network in lockstep.
SiTime said the success of MEMS as an alternative to existing timing devices stems from moving them out of the world of materials engineering and onto semiconductor wafers fashioned by foundries. That enables the company to operate in a way more akin to a fabless chip firm, focusing the architecture of its timing devices, while TSMC and its other foundry partners focus on fabricating the silicon and packaging it up.
Joining its other families of timing devices for everything from the aerospace, defense, and automotive industries, Epoch is targeted at the worlds of wired and wireless network connectivity—to start.
In any electronic system, oscillators are used to output regular waveforms that act as a timing signal to keep all components in a system, such as switches, routers, and storage in a data center to the base stations and other wireless infrastructure behind the scenes of 5G networks working with each other in concert. Since all of the nodes in a network must be synchronized, keeping track of time accurately is key.
For instance, the high-bandwidth, low-latency networks weaving through data centers to train and run increasingly large AI models require robust and precise timing to maintain performance and reliability.
Timing requirements for 5G networks are 10X tighter than 4G, said SiTime. All nodes on a wireless network can never be more than a fraction of a millisecond apart even when outages ultimately occur.
The OCXO: Stable Frequencies for Unstable Conditions
Epoch is a family of MEMS-based alternatives to the traditional OXCO, which are designed to deliver very stable frequencies in conditions that are the least conducive to them.
The resonator that serves as the timing element in the OCXO is carefully packaged in what’s called the “oven” in the electronics industry. The enclosure keeps the timing reference in the OCXO at a constant, optimal temperature, which reduces the frequency variations that typically occur due to fluctuations in ambient temperature. Thus, OCXOs bring better short- and long-term stability to the table, and they have frequency stabilities measured in the parts-per-billion (ppb) range where Epoch resides.
While traditional OCXOs are top-of-the-line for many electronic systems, they’re lacking in others, said SiTime. They’re prone to frequency drift in the presence of environmental factors such as temperature, humidity, and vibrations. The company explained that the lack of robustness can be a serious liability in large data centers and cellular networks, where slight discrepancies in timing can hurt performance or even cause failures.
There tend to be several redundant timing sources in such systems to ensure continuous operation. Consequently, the OCXO is frequently tasked with taking over when a system’s main reference clock is disrupted.
In most wired and wireless networks, the primary source of timing that keeps everything working on time often is based on the network timing protocols (for instance, PTP) or global positioning system (for instance, GPS). But anything from system failures and malfunctions to disruptions due to inclement weather can disrupt or disable the timing reference. In that case, the system enters "holdover" mode, in which the OCXO or other internal timing device plays the role until the main reference clock is restored.
Therefore, it’s important for the OCXO or other timing device to maintain frequency stability over a long period—often for several hours at a time—until the system’s timing reference returns to work.
Environmental factors not only cause traditional timing devices to deviate, but they can also degrade their performance over time, which may influence how long they can remain accurate during holdover.
MEMS Timing Devices Adapt to Temperature Swings
To overcome these obstacles, the Epoch features innovations in everything from the MEMS at the heart of the timing devices to the analog, algorithms, and packaging technologies that surround it.
Each OCXO contains a silicon die with a pair of resonators packaged with a mixed-signal circuit used to compensate for temperature variations and other environmental factors. The first device on the die uses SiTime’s MEMS to supply stable frequencies over a temperature slope (dT/dF). It’s said to be 10X more resilient to fluctuations in temperature than existing devices, reducing the risk of activity dips (or abrupt changes of frequency due to stress), and it never needs to interact with the mixed-signal circuitry.
The second device on the DualMEMS die underpins what SiTime calls the most accurate temperature sensor in timing. Unlike the first, its frequency varies based on temperature variations, and the slight differences can be used to sense sudden temperature changes up to 40X faster than the thermistors or other parts packaged up in existing OCXOs. Speed is an asset when operating under fluctuating airflow and rapid temperature changes, which are a constant threat when a system is exposed to the elements.
The temperature reading is taken into account by the mixed-signal circuit inside the package, which is able to compensate for thermal disturbances to keep everything on time. The interplay of all these features gives Epoch superior dynamic stability, ultra-low phase noise, and a wide frequency range, said SiTime. Another key is a new “heater control circuit,” which keeps the OCXO at a constant temperature.
According to the company, Epoch’s resilience to vibrations, temperature, airflow, shock, electromagnetic interference (EMI), or other environmental factors gives it 2X the performance in holdover mode—up to eight hours.
The Epoch family is housed in a 9- × 7- × 3.7-mm package, which is approximately 9X smaller than other ±1 quartz-based oscillators in the same class. Digital control is supported via the 12C and SPI interfaces.
Featuring operating supply voltages of 2.5, 2.8, or 3.3 V, the Epoch programmable OCXOs consume 420 mW of power in steady state that SiTime maintains is 3X less than the competition.
The innovations in Epoch also lend themselves to aerospace, defense, industrial control and automation systems, and other markets. SiTime plans to eventually expand the Epoch platform to cover those areas.
Mass production of the new chips is expected for early 2024.
Read more articles in the TechXchange: Oscillations, Timing and Synchronization.