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The proposed MCXO circuit was fabricated in a 0.18-μm, 1.8-VDC silicon CMOS process; it features power consumption of less than 5 mW. It can achieve frequency stability within ±0.1 ppm over a range of temperatures from -40 to +85°C. Figure 5 shows the frequency deviation for two repeated cold to hot and hot to cold temperature runs for one proposed MCXO, which is better than for a conventional TCXO.5,6 For all temperature runs, the protocol initiated with a 10 minute “soak” time followed by a change of 1°C every minute. The entire testing process was automated including protocol control and data collection.

5. Frequency stability under temperature tests.

By employing ultrasmall AT-cut crystal units, the proposed MCXO has a smaller size of 13 x 13 x 1.75 mm, comparing with a traditional MCXO using SC-cut dual-mode crystal,7 which has a size of 38.1 x 38.1 x 12.7 mm, making the proposed MCXO more suitable for applications in portable productions.

Liang Chen, Engineer

Yangbo Huang, Engineer

Yonghu Zhang, Engineer

Gang Ou, Engineer

College of Electronic Science and Engineering, National University of Defense Technology, Changsha, Hunan, China, People's Republic of China.

References

1. S.S. Schodowski, “Resonator self-temperature-sensing using a dual-harmonic-mode crystal oscillator,” in Proceedings of the 43rd Annual Symposium on Frequency Control, Denver, CO, May 31-June 2, 1989, pp. 2-7.

2. A. Benjaminson and S. C. Stallings, “A Microcomputer-Compensated Crystal Oscillator Using a Dual-Mode Resonator,” in Proceedings of the 43rd Annual Symposium on Frequency Control, Denver, CO, May 31-June 2, 1989, pp. 20-27.

3. T. Schmid, J. Friedman, Z. Charbiwala, Y. H. Cho, M. B. Srivastava, "XCXO: An Ultra-low Cost Ultra-high Accuracy Clock System for Wireless Sensor Networks in Harsh Remote Outdoor Environments," 2007.

4. M. Harada, K. Kubota, and H. Takahashi, “Research on Miniaturization of Low-Frequency Range SMD Crystal Unit," in Proceedings of IEEE International Frequency Control Symposium, 2007, pp. 150-153.

5. H. Rokos, "Precision, Low Power, analogue TCXO using a Single Integrated Circuit," in Proceedings of European Frequency Time Forum, 1996, pp. 515-519.

6. Mi Zhang, Wei-xun Cao, “A 0.1 ppm Successive Approximation Frequency-Temperature Compensation Method for Temperature Compensated Crystal Oscillators (TCXO),” in Proceedings of World Congress on Computer Science and Information Engineering, 2009, pp. 493-498.

7. E. Jackson and B. Rose, “The microprocessor compensated crystal oscillator-new developments,” in Proceedings of IEEE International Ultrasonics, Ferroelectrics, and Frequency Control, 1999, pp. 376-379.

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