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Ultra-Linear Receivers for Digital LLRF Control Systems

John Musson (and Colleagues!) TJNAF. Ultra-Linear Receivers for Digital LLRF Control Systems. Receiver Parameters. Intrinsic Noise Figure Low-end limit Ultimate sensitivity Saturation Large-signal limitations, distortion Linearity Everything in-between!. External Phase Noise

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Ultra-Linear Receivers for Digital LLRF Control Systems

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  1. John Musson (and Colleagues!) TJNAF Ultra-Linear Receiversfor Digital LLRF Control Systems

  2. Receiver Parameters Intrinsic Noise Figure Low-end limit Ultimate sensitivity Saturation Large-signal limitations, distortion Linearity Everything in-between! External Phase Noise ADC Sampler Jitter Interference ”blocking” Reciprocal mixing Additionally, AM demod is inherently linear PM is NOT! Threshold effect

  3. Taxonomy IIP3 = Input 3rd Order Intercept Point P1dB = 1 dB Compression Point K = Boltzmann's Constant To = 290 degrees Kelvin NF = Noise Factor (linear) F = Noise Figure (in dB) SFDR = Spurious-Free Dynamic Range BW = Receiver Bandwidth MDS = Minimum Discernible Signal SNR = Signal to Noise Ratio

  4. All Math Aside....or a Toolbox Smorgasbord To = 290 K (IEEE) KTo = -174 dBm NF = Tsys /290 + 1 F = 10 log NF IIP3 = Pim = 3Ptone – 2PIIP3 NFnet = SFDR3 = 2/3 (IIP3 + 174 – F -10log BW) SFDR2 = ½ (IIP2 + 174 – F -10 log BW) Pphase noise = Punwanted + 10log BW + Prx phase noise

  5. Courtesy “RF and Microwave Designer's Handbook, Watkins-Johnson Company, 1997 “Introduction to Radio Frequency Design,” Wes Hayward, ARRL 1994

  6. 499 MHz Warm Cavity Requirements

  7. Receiver Bandwidth Software Defined Radios (SDRs) can have 2 associated bandwidths: Analog Minimum element in Front End Factors include latency, anti-alias, IF / Digital Generally the narrowest, set by IIR / FIR DR Calculations should use the analog BW SNR should use narrow/digital BW In addition, Closed-Loop control BW for LLRF BW determined largely by sensitivity (KTB) and latency (“Group Delay”) requirements Ex. JLAB LLRF Rx uses a 8 MHz BPF exhibiting 100 ns of latency

  8. Components High IIP3 FET Mixer WJ HMJ5 IIP3 = 35 dBm Try to shield active (vulnerable) amplifier, but not deep enough to destroy noise figure! High IIP2 / IIP3 Amplifier WJ AHJ-2 IIP3 = +26 dBm F = + 4dB HMJ5 AHJ2 Strategy: 3 6 3 BPF BPF Thermopad +17 dBm LO

  9. Don't Forget the ADC!! Effective Dynamic Range = -1.25 + 6.02b + 10log fs b = # of bits, fs = sample frequency 1 Hz BW DR > Analog, and LSB >> MDS Noise Figure can be assigned Function of sample rate and # of bits F = 12 dB (AD 6645 w/ fs = 56 MHz, Rs = 200 Ohms) S/N degradation from sample clock jitter: Sets ultimate PM limit Sets ultimate PM S/N Setsultimate PM limit • Reference: Frerking, M., “Digital Signal Processing in Communication Systems”

  10. Courtesy “Digital Signal Processing in Communication Systems,” Frerking, M., Chapman and Hall,1994 • “Digital Communications,” Proakis, J., McGraw-Hill, 1994

  11. Modeling

  12. Modeling (Dynamic)

  13. Grouping Relevant Terms..... Pmin ~ KToB + Fnet + S/Njitter + Pphase noise + S/Nimposed - ??? (ie Processing Gain from DSP decimation??) JLAB LLRF (Gradient) IF = 70 MHz, fs = 56 MHz, B = 10000 (control BW) -134 + 35 + (<90 dBc for  < 200 ps) + ? + 80 -20 = -39 dBm!! So, our receiver is within spec at Pin > -39 dBm.

  14. What About High-End? FET mixer (IIP3 = +35 dBm) combined with CATV amplifier (IIP3 = +27 dBm), predicts an IIP3 of + 43 dBm (+41 dBm measured) Maintaining an IM supression of 80 dB implies: Pmax = 2* 43 – 80 = + 3 dBm. So, based on the additional requirement of 20 dB of specification compliance, we achieve +3 - (-39) = 42 dB of dynamic range (100 : 1) with 80 dB of supression on either side. Arguably, high-end range can also be extended by noting that IM corruption is correlated….Would most likely lead to a “DC” phase offset” Presumption of some processing gain bails us out!!!

  15. Verification Measurements Noise Figure Y-Factor Effective for F < 25 dB Affordable; easily built into receiver front ends Spectrum Analyzer + LNA Nice paper presented by T. Powers at BIW '98 “Improvement of the Noise Figure of the CEBAF Switched Electrode Electronics BPM System” MDS / Tangential Sensitivity Easy to do; outcome-based! Can also be built-in Dynamic Range 1 dB Compression IIP3 Phase Noise

  16. “Fundamentals of RF and Microwave Noise Figure Measurements,” HP Tech Note 57-1 “Noise Figure Measurement Accuracy- The Y- Factor Method,” HP Tech Note 57-2 “Radio Astronomy,” J. Kraus, Cygnus-Quasar, 1988

  17. Two-Tone IMD Test for IIP3 Courtesy “Improve Two Tone, Third Order Testing,” Mini Circuits Tech Note

  18. Courtesy “Introduction to Radio Frequency Design,” W. Hayward, ARRL, 1994

  19. Phase Noise Or........

  20. Summary • Life for the Analog RF Engineer is STILL interesting! • Back-to-basics design and testing • Made much easier with modern ($$) test equipment • Models are quite reliable for first-cuts • Narrowband techniques can improve most parameters (ala Genesys) • If LLRF becomes more demanding…….(?) • 73, DE WD8MQN

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