Additional RF system issues: Amplifier linearization Reference Phase distribution Master Clock Anders J Johansson Lund University

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Low Level RF (LLRF) A/D D/A LO LOAD Klystron FPGA Modulator LLRF

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Linearization of power amplifiers Linearization of PA common in mobile communications Makes it possible to use efficient amplifiers and still fulfill transmitt spectrum masks.

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Amplifier compression Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Why linearization in mobile communications Increased demands due to: –Complex modulation schemes –Muliple channels per amplifier –Running at compression/class C for efficiency

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec 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

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Power backoff Pin Pout 1st 3rd

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Predistortion Linearization High Power Amplifiers, Allen Katz, Linearizing Technologies

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Adaptive predistortion Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Feedforward Linearization Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec RF and Microwave Power Amplifier and Transmitter Technologies — Part 3, F. H. Raab et. Al. Envelope elimination and restoration

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec RF and Microwave Power Amplifier and Transmitter Technologies — Part 3, F. H. Raab et. Al. Envelope tracking

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec RF and Microwave Power Amplifier and Transmitter Technologies — Part 3, F. H. Raab et. Al. LINC

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Indirect Feedback Linearization High Power Amplifiers, Allen Katz, Linearizing Technologies

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Power Amplifier Linearization Techniques, an Overview, Joel L. Dawson LINCartesian Feedback

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec LLRF with linearization A/D D/A LO LOAD Klystron FPGA Modulator A/D

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Some details Method I: Power backoff –Classical in accelerators –Expensive in terms of efficinecy, especially with klystrons Method II: Predistortion/adaptive predistortion –Either at baseband or RF –Depends on having a good amplifier model Method IV: Cartesian feedback –Needs good phasematching between mixers –Stability concerns

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Benefits for Accelerators Narrowband signal, i.e. less worries about broadband performance.

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec 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! Development of Linearization for ESS

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Time and Synchronization ESS needs: –A common clock to timestamp events –Stable generation and distribution of pulse events –Stable reference phase for RF

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec 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

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec 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

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Phase noise dBc/Hz vs. Offset frequency in Hz

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Stability Allan stability versus integration time (seconds)

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec 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.

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec PLL: Phase Locked Loop How to use a stable low frequency oscillator to control a high frequnecy source. Phase Detector ref VCO Low Pass filter Divide by M

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Master clock schematic (tentative) GPS 1pps OCXO PLL Frequency Divider/ Distribution 10MHz 1pps Tuning Real time clock Timestamps 10MHz Reference Frequency Generation 704 MHz 352 MHz Control system GPS Time delta logger

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec 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

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Reference phase distribution Master Oscillator LLRF PID

Lund University / Dept. Of Electrical and Information Teechnology / ESS RF Workshop / 14 Dec Conclusions Investigate possibility of running the power amplifiers (klystrons) close(r) to saturation. Design a master clock Design a phase distribution network