Session P3a: Low-SWaP Clocks and Oscillators

New OCXO Contributes to Lower Consumption in the Communications Field
Kensaku Isohata, Seiko Epson Corporation; Hiroyuki Shimada, Epson America; Madura Fontaine, Epson America
Location: Seaview A/B
Date/Time: Wednesday, Jan. 29, 2:58 p.m.

With the start of 5G services and the spread of AI applications in data centers, the volume of communication data has been expanding significantly. Furthermore, the communication data traffic is expected to continue to expand toward 6G services in the future. It is critical to achieve even faster wired and wireless communications, while lowering power consumption at base stations and data centers is also becoming an important consideration.
In wireless communications, the recent transition in RAN timing in 5G networks from BBU-sourced to network timing improved many time synchronization capabilities. However, short-term stability and phase noise still limit the performance of these networks. Conventional OCXOs are too large and consume too much power. Conventional TCXOs cannot achieve the required performance.
Reducing the power consumption of an OCXO helps reduce operational costs and improve system reliability. Less power consumption means less heat is generated, which in turn reduces the need for large cooling solutions. All of this helps reduce energy costs, extend equipment life, reduce breakdowns, and ease maintenance burdens.
To address these issues, Epson has developed a small 7050-size, low-power OCXO. One of the main challenges is miniaturizing the SC-cut. Conventionally, it was a circular structure with a 6 mm diameter, but because the resonator size was large, the OCXO itself was large, and a large amount of heat was required to maintain a constant temperature. Therefore, we began developing a smaller SC-cut that can maintain a constant temperature with a small amount of heat and achieved a rectangular shape with an area nearly 90% smaller than 6 mm diameter.
Another challenge is realizing a low-power structure. We considered how to use a small SC resonator to miniaturize the heat-generating object. In addition to the resonator, we developed our own small oscillation IC and small heater IC, and by densely mounting them, we were able to miniaturize the heat-generating object. Furthermore, by bonding them to the 7050-size PKG with a low-thermal-conductivity adhesive, we were able to improve internal insulation and achieve a low-power structure.
In addition, by changing the OVEN control method from the conventional analog method to a digital method, we have succeeded in increasing accuracy and ensuring that the internal oscillator temperature hardly changes even when the ambient temperature fluctuates, reducing the frequency temperature characteristic from ±10 ppb to ±3 ppb. These efforts have resulted in a 50% reduction in power consumption (0.25W@25°C) compared to conventional models, as well as a highly accurate OCXO structure. This reduction in power consumption has also contributed to shortening the oscillator startup time by more than five times.
This OCXO not only achieves low power consumption but also offers a variety of functions and characteristics. To meet future needs for high-speed communications, it is equipped with a PLL function that can support up to 170 MHz by adjusting the settings inside the IC. On the other hand, it also has a jitter reduction function to suppress noise deterioration caused by the PLL. This achieves high stability against both nearby noise due to SC cut and floor noise due to the jitter reduction function. Another feature is that it minimizes the trade-off between aging characteristics and G-sensitivity characteristics.
The new OCXO has a unique thermal insulation structure, which contributes to the network system by reducing power consumption, and in terms of characteristics, it has the same specifications as conventional OCXOs, such as highly stable temperature characteristics, aging, and low phase noise.