Secondary Frequency Versus Temperature Compensation of an OCXO Using a Segmented Polynomial Array

Abstract

The temperature performance of Oven Controlled Crystal Oscillators (OCXOs) and Double Oven Controlled Crystal Oscillators (DOCXOs) have been the pinnacle of quartz crystal frequency versus temperature performance for decades. DOCXOs can provide frequency versus temperature stabilities under +/− 1ppb. This superior performance comes at the cost of the power consumption of running two ovens, as well as footprint impact from the extra circuitry. Wide temperature ranges are also a challenge for DOCXOs due to the need to run the ovens at very high temperatures. This paper focuses on a secondary method of compensating OCXOs for frequency versus temperature performance using a segmented polynomial array compensation. This method of compensation can achieve results unobtainable through conventional compensation methods. A group of eight OCXOs in a $20 \text{mm} \times 20 \text{mm}$ package with SC cut crystals were studied for this paper. The inherent mean frequency versus temperature performance of the most improved unit was ±4.29 ppb over the industrial range of −40 to 85 °C. Using 4 segments to compensate the unit the frequency versus temperature performance was reduced to mean performance of ±0.153 ppb over the industrial range. This is a 28 to 1 improvement over the OCXOs inherent performance. This compensated single oven technology provides superior temperature performance over a wider temperature range with lower power consumption than can be achieved with traditional methods. The theory of this compensation method will be discussed, and data showing the results of frequency versus temperature compensation on the qualification group will be presented.