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Additional RF system issues: Amplifier linearization Reference Phase distribution Master Clock

Additional RF system issues: Amplifier linearization Reference Phase distribution Master Clock. Anders J Johansson Lund University. Low Level RF (LLRF). LOAD. Modulator. Klystron. LLRF. D/A. A/D. FPGA. LO. Linearization of power amplifiers.

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Additional RF system issues: Amplifier linearization Reference Phase distribution Master Clock

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  1. Additional RF system issues:Amplifier linearizationReference Phase distributionMaster Clock Anders J Johansson Lund University

  2. Low Level RF (LLRF) LOAD Modulator Klystron LLRF D/A A/D FPGA LO

  3. Linearization of power amplifiers • Linearization of PA common in mobile communications • Makes it possible to use efficient amplifiers and still fulfill transmitt spectrum masks.

  4. Amplifier compression Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson

  5. Why linearization in mobile communications • Increased demands due to: • Complex modulation schemes • Muliple channels per amplifier • Running at compression/class C for efficiency

  6. List of linearization techniques • Power backoff • Predistortion • Adaptive predistortion • Feedforward Linearization • Envelope elimination and restoration (EER) • LINC (LInear amplification with Nonlinear Components) • Cartesian feedback List by Joel L. Dawson

  7. Power backoff Pout 1st 3rd Pin

  8. Predistortion Linearization High Power Amplifiers, Allen Katz, Linearizing Technologies

  9. Adaptive predistortion Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson

  10. Feedforward Linearization Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson

  11. Envelope elimination and restoration RF and Microwave Power Amplifier and Transmitter Technologies — Part 3, F. H. Raab et. Al.

  12. Envelope tracking RF and Microwave Power Amplifier and Transmitter Technologies — Part 3, F. H. Raab et. Al.

  13. LINC RF and Microwave Power Amplifier and Transmitter Technologies — Part 3, F. H. Raab et. Al.

  14. Indirect Feedback Linearization High Power Amplifiers, Allen Katz, Linearizing Technologies

  15. LINCartesian Feedback Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson

  16. LLRF with linearization LOAD Modulator Klystron A/D D/A A/D FPGA LO

  17. Development of Linearization for ESS • Investigate the different options from the viewpoint of ESS • Klystrons / IOTs • Narrow bandwidth • Huge power • Overhead from FPGA/DSP minimal • Needs accurate non-linear models of amplifiers!

  18. Time and Synchronization • ESS needs: • A common clock to timestamp events • Stable generation and distribution of pulse events • Stable reference phase for RF

  19. Phase reference • Crystal oscillators • Very low phase noise • Big drift • Cheap • Atomic clocks (cesium /rubidium ) • Low drift • Large phase noise • Costly • Maser • Very Low drift • Expensive

  20. Stability and phase noise • Two main measures of oscillators and clocks • Allen variance or stability • Slow variations • ” Allan variance is defined as one half of the time average of the squares of the differences between successive readings of the frequency deviation sampled over the sampling period” • Phase noise • Fast variations

  21. Phase noisedBc/Hz vs. Offset frequency in Hz

  22. StabilityAllan stability versus integration time (seconds)

  23. OCXO: Oven Controlled Crystal Oscillators • Stabilize a crystal oscillator by putting it inside a temperature controlled oven (which in turn may be inside an temperature controlled oven etc.) • May still be tuned by voltage and/or temperature • Typically 10 MHz.

  24. PLL: Phase Locked Loop • How to use a stable low frequency oscillator to control a high frequnecy source. ref Phase Detector Low Pass filter VCO Divide by M

  25. Master clock schematic (tentative) Tuning Frequency Divider/ Distribution 10MHz 1pps 1pps PLL GPS OCXO GPS 10MHz 704 MHz Reference Frequency Generation 352 MHz Timestamps Real time clock Time delta logger Control system

  26. Reference phase distribution • The reference phase needs to be distributed to all LLRF stations • Taken from the master clock • Linear or star topology • Example: linear distribution

  27. Reference phase distribution PID PID PID Master Oscillator LLRF LLRF LLRF LLRF LLRF LLRF

  28. Conclusions • Investigate possibility of running the power amplifiers (klystrons) close(r) to saturation. • Design a master clock • Design a phase distribution network

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