A double-oven OCXO (an oven inside another oven) can reach <☐.5 ppb stability. OCXOs achieve high stability by encasing the crystal along with temperature-sensing and compensation circuits inside a heated metal enclosure to create an oven with a relative constant temperature. These devices have very high stability, typically better than ±50 ppb, and more commonly in the range of ☐.5 to ☒0 ppb. What is an OCXO? OCXO stands for oven-controlled oscillator. These devices are used in applications where precision timing references are required, such as high-performance telecom and networking equipment, including small cells, synchronous Ethernet, optical transports, and GNSS modules. These devices typically have frequency stability of ☐.05 ppm to ±5 ppm over the operating temperature range. What is a TCXO? A TCXO is a temperature-compensated oscillator and is an active device. Typical frequency stability variation over temperature of XOs is between ☑0 and ☑00 parts-per-million (ppm). Basic crystal oscillators, XOs, are also known as OSC and SPXO in various geographies. What is an Oscillator? An oscillator is an active device that uses a resonator and an oscillation circuit to generate a clock signal. The resonator (or crystal) devices are used as external timing references for semiconductor ICs with an integrated oscillator circuit (i.e., on-chip clock generation). What is a Resonator? A resonator (X, XTAL) is a passive device that vibrates at a fixed frequency. These devices are used as external timing references for semiconductor ICs with an integrated oscillator circuit (i.e., on-chip clock generation) What is a Crystal? A crystal (X, XTAL) is a passive resonator that vibrates at a fixed frequency. So, what exactly is an OXCO? Well, since you ask, this is probably the perfect time to introduce some oscillator-related terminology, which was kindly provided as part of a handy-dandy Epoch Platform MEMS-Based OCXOs FAQ by the nice folks at SiTime. ![]() However, if you want to add “affordable” and “realistic” into the equation, then your best choice to achieve a holdover of ☑.5µs over 8 hours is to use an oven-controlled oscillator (OCXO). Wowzers!Īctually, it’s reasonably easy to achieve this level of accuracy all you need is to incorporate an atomic clock in each node (I didn’t say it was “cheap and easy”). What sort of holdover accuracy are we talking about here? Well, for 5G base station infrastructure, network operators usually aim for ☑.5µs over 8 hours or more. It is this value that the node uses in its timestamps, it is this value that is constantly being reevaluated in the context of the prime clock, and it is this value that the node must rely on should it happen to lose access to its upstream reference clock source for any reason, in which case the node is said to be running in a “holdover mode.” What is sometimes overlooked by people like your humble narrator (I pride myself on my humility) is that every node must include its own oscillator that it uses to maintain its local time-of-day (ToD) value. Every node (router, server, switch…) in the network must be synchronized to maintain the fastest possible data throughput, reliability, and uptime.Įvery infrastructure node must be time-synchronized (Source: SiTime) “Grand Master Clock”) and any downstream clocks.Ĭonsider a 5G radio access network (RAN), for example. These timestamps are used to determine and correct any errors between the prime clock (a.k.a. Suffice it to say that this involves the network nodes passing timestamped packets of data back and forth. But I fear I might be in danger of leading us all into the weeds, so let’s come at this from a slightly different direction.ĭo you recall my relatively recent column What Is Time, What Time Is It, and Why Do We Care? That column was sparked by my reading the Intel PTP Servo Solution for Time Synchronization Applications whitepaper in which I was introduced to some of the concepts involved in synchronizing packet-based networks. Furthermore, if I had thought about it, I’d have got it wrong. ![]() For example, I was just made aware about a feature pertaining to oven-controlled oscillators that I’d never really thought about. ![]() The reason I mention this here is that I’m constantly discovering new things I don’t know. ![]() As I said in my blog, I was proud to discover that I already didn’t know pretty much all of Lawrence’s “Known Unknowns.” Krauss: The Known Unknowns: A Brief Account of What We Know and What We Don’t Know About the Cosmos. This was in the context of a recently published book by Lawrence M. I’ve had to read a lot of books to get where I am today. As I wrote in a recent blog, not knowing all the stuff I don’t know didn’t come easy.
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