AN10063 TCXO and OCXO Stability Degradation

Many digital applications rely on cooling systems to maintain the operating temperature within design limits, which are typically -40°C to +85°C for industrial applications. But cooling systems can fail, for example if the fan malfunctions, and this can cause the ambient temperature to increase above system design limits, in some cases to extreme values up to or in excess of +125°C.

Ideally, systems should maintain normal operation during these fault conditions. Sustaining continuous operation can be critical for many systems, for example with cellular base stations which should maintain basic service to support emergency calls. Therefore system designers should choose components to achieve maximum reliability. One of the most vitally important components of any digital system is the oscillator. It provides the synchronization signal for the entire system and is therefore sometimes referred to as the “heartbeat of the system.”

Just like the heart in the human body, malfunction of the oscillator will cause the entire system to fail. Automotive-grade crystal oscillators (XO), which can operate up to +125°C and meet the requirements of many applications, are commonly available. But precision oscillators such as temperature controlled crystal oscillators (TCXOs) and oven-controlled crystal oscillators (OCXOs) that operate above +85°C are rare and very difficult to find. For certain applications, such as Synchronous Ethernet (SyncE), IEEE 1588, and telecom boundary/slave clocks that provide backhaul service to cellular base stations, it is important to understand how such devices behave outside their rated temperature range in order to determine to what extent the system can maintain service during fault conditions.


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