A 0.1 ppm Successive Approximation Frequency-Temperature Compensation Method for Temperature Compensated Crystal Oscillators (TCXO)

In this paper, we present a high accurate frequency-temperature compensation method for temperature compensated crystal oscillators (TCXO) which can achieve 0.1 ppm frequency stability over a wide temperature range from -25degC to 85degC by using 1-bit successive approximation differentiated interpolation. By applying a frequency-temperature compensated digital binary word to a digital frequency synthesizer, the generated frequency signal is controlled so as to be temperature compensated. The presented method can be also used for the crystals with abnormal frequency-temperature curve such as with abrupt frequency jump points. Compared to the traditional look-up table method, the presented method can dramatically reduce the storage cost to about 5%. The presented method has been implemented into the Xilinx FPGA and CMOS standard cell ASIC. The test result shows that 0.1 ppm frequency-temperature stability can be achieved with a temperature sensitivity of 0.5degC.