Prototype of Software-Defined Self-Calibrating Temperature Compensated Oscillator

Distributed systems employ network time and frequency synchronization, typically IEEE 1588 PTP or its derivatives, to achieve a common, synchronized time and frequency on all nodes. Time and frequency synchronization is required as the oscillators of nodes produce non-ideal clock signals to drive the operation of the individual nodes, i.e., their frequencies deviate from the nominal one by an oscillator-specific static offset and a continuously changing drift. Network time and frequency synchronization operate when nodes can successfully communicate with the primary (reference) clock. During this process, they measure their actual deviations from the primary clock and compensate for that by applying a node-specific method. However, when communication fails with the primary clock, the node goes into the so-called holdover mode, and it starts to deviate from the primary clock due to drift. The main source of drift is temperature variations for most of the applications. Temperature Compensated Oscillators (TCXO) and Oven Controlled Oscillators (OCXO) are developed to keep oscillator temperature-related frequency deviations low, however, these devices are substantially more expensive than standard oscillators, they are bigger, and they use more power also, so they are not an option in a large number of applications. However, it is possible to augment the oscillator with low-cost temperature sensors (e.g. thermistor), and in normal synchronized operation collect information about the frequency-temperature relationship of the oscillator and build a model of it, then apply this model in holdover mode to reduce temperature related drift. In essence, we construct a low-cost, self-calibrating Software-Defined Temperature Compensated Oscillator (SD-TCXO) with this approach. The paper introduces a hardware and software prototype for the SD-TCXO, and initial performance data about its evaluation.