Hamm, Erwin C.||Newell, Darrell E.
M.S. (Master of Science)
Department of Industry and Technology
Oscillators; Crystal; Hysteresis; Electric resonators
This paper describes a method of utilizing a low frequency mode of vibration of an AT cut resonator to temperature compensate a second AT cut resonator to an accuracy of ± 2 pp 10⁷ over the temperature range 0°C to +70°C. The hysteresis of the system using this approach was less than ± 3 pp 10⁸ (the resolution of the frequency counter used.) AT cut resonators in the 2.0 to 4.0 MHz range exhibit an abundant amount of low frequency modes of vibration in the 100 kHz to 1.0 MHz range. In a properly designed resonator these modes are suppressed. Certain geometries and contours do exist that do not suppress these modes. In the DMDTCXO (Dual Mode Digitally Temperature Compensated Crystal Oscillator) a two loop oscillating scheme was developed to allow a 3*0 MHz AT cut resonator to vibrate in two modes of oscillation, approximately half the time each. The 810 kHz low frequency mode used was digitized to an eight bit address, and an eight bit correction word was used to compensate the 3-0 MHz mode of the resonator. Seeing both modes occupy nearly the same volume of quartz, hysteresis effects are minimized. The second oscillating loop contains a second AT cut 3.0 MHz resonator that vibrates continuously. For half of the time the second resonator is phase-locked to the first resonator. During the remaining half cycle, the output is held at its previous value to present a continuous output from the system. The system was compensated over the range 0°C to +70°C, and tested at several varying temperature rates. The test results obtained are analyzed in the text. The potential of the DMDTCXO as a very stable resonator system was demonstrated. Further areas of study are suggested to realize the full potential of such a system.
Rubach, Robert W., "Dual mode digitally temperature compensated crystal oscillator" (1981). Graduate Research Theses & Dissertations. 2669.
ix, 104 pages
Northern Illinois University
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