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Cubic Function Generator Design

Explore the design of a cubic function generator for compensating crystal oscillator temperature variations. Learn about the different types of crystal oscillators and their characteristics. Delve into the specifics of TCXO and cubic function generator design.

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Cubic Function Generator Design

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  1. CSE598A/EE597G Spring 2006 Cubic Function Generator Design Boram Lee, Jaehyun Lim Department of Computer Science and Engineering The Pennsylvania State University

  2. Crystal Oscillator – f vs. T characteristic Z AT-cut 25  35¼o 20 8’ Y -1’ 15 7’ 0’ 6’ Z 10 Y-bar quartz 1’ 5’ 5 (ppm) 4’ 2’ 0 3’ f f 3’ -5 2’ 4’ 1’ -10 Inflection Point 5’ 0’ -15 6’ -1’ -20 7’ 8’ -25 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

  3. Crystal Oscillator – f vs. T characteristic • XO (crystal oscillator) • does not contain means for reducing the crystal’s f vs. T characteristic • OCXO (oven controlled crystal oscillator) • crystal and other temperature sensitive components are in a stable oven • oven temperature adjusted to the temperature where the crystal’s f vs. T has zero slope • over 1000X improvement over the crystal’s f vs. T variation • Large package, high power consumption – not suitable for mobile/battery powered devices • TCXO (temperature compensated crystal oscillator) • temperature sensor generates a correction voltage • the correction voltage applied to a variable reactance in the crystal network (ex. varactor) • the reactance variations compensate for the crystal’s f vs. T characteristic • about 20X improvement over the crystal’s f vs. T variation

  4. Uncompensated crystal frequency Frequency / Voltage T Compensated frequency of TCXO Compensating voltage Cubic Function Generator • Application • frequency compensation in TCXO

  5. TCXO – Temperature Compensation : linear coefficient of temperature depend on cut-angle : cubic coefficient of temperature : inflection point temperature (≈ 25 °C) : actual temperature

  6. Cubic Function Generator • Design I Cubic Functional Voltage Generator cubic term voltage conversion circuit (Low Temperature) cubic term voltage conversion circuit (High Temperature) Cubic Wave Temperature sensor ∑ linear term voltage conversion circuit

  7. Cubic Function Generator • Design I out out Vg T T

  8. Cubic Function Generator • Design I Vg out T out T

  9. Cubic Function Generator • Design I out out out T T T <low temperature> <high temperature> <linear term> out <pseudo cubic wave> T

  10. Cubic Function Generator • Design II linear linear input square cubic wave cube

  11. Cubic Function Generator • Design II • analog voltage multiplier • analog voltage adder • op-amp • bias circuits

  12. Cubic Function Generator • Specification • power consumption : 50 mW • size : 0.3 mm x 0.3 mm • supply : 5 volt single supply • input range : 1.5 V ~ 3.5 V • TSMC 0.35 / AMIS 0.5

  13. Cubic Function Generator • Schedule • week 1 : op-amp design, test Design I • week 2, 3 : multiplier design • week 4, 5 : bias circuits, project progress presentation • week 6 : make improvements of basic blocks • week 7 : finalize of cubic function generator • week 8 ~ : final revision of cubic function generator, layout, project final presentation

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