Tutorial on RF (Receiver Fundamentals) Frank Ludwig DESY

Transcription

1 Frank Ludwig DESY

2 Outline Introduction to Noise and Systems Front-Ends Components Receiver Structures Distortions and Reduction Techniques

3 Motivation Field regulation and noise sources : Beam energy jitter (simulated) -20 deg o-crest A, Δϕ Master Reerence Desired cavity ield stability Requirements or the receiver, e.g. - Shortterm amplitude/phase stability <0.01%,<0.01deg (10Hz-1MHz) - Longterm amplitude/phase stability 0.01%, 0.01 deg (orever-10hz) - Nonlinearity < -55dBc, 1% error - Channel crosstalk < -70dB - Overall latency <100ns Actuator phase noise Field Detector amplitude noise 3

4 Introduction to Noise : Phase Noise 1 2 Deinition o a spectral density : S u ( ) lim FT [ u ( t )], FT [ u ( t)] = T u ( t) e T + T T 2 πt dt u = { U, I, P, j...} Time unlimited signals, e.g. noise Microwave signal with noise : u( t) = V 0 [1 + δα( t)] e iω t+ iδϕ ( t) 0 Amplitude noise Phase noise Signal spectrum : 2 Su( m) = V 0 n ( δ ( ) + + S φ ( m ) + O [ S ( ), S ( )] ) S α ( m ) 0 α m ϕ m m Carrier Amplitude noise Phase noise = 0, δφ( t) << 1, γα, φ( m ) = 0 Oset requency Amplitude noise : Phase noise : Timing jitter : S S α ϕ Δ t ( ( rms m m 1 ) V 1 ) V 1 lim T 2 T 0 1 lim T 2 T 0 1 = (2π ) F [ δα ( t)] T F [ δϕ ( t)] S T ϕ ( m 2 2 ) d, m dbc = db relative to carrier 10 log [ L(m) ] dbc/hz 2 ( Δ A / A) rms = S α 1 ( m ) d m 4

5 Introduction to Noise : Systems Algebraic solution o the system in the Laplace-Domain : e.g. LLRF System (simpliied) Transerunction n-th noise source = n φ ( s) H ( s) φ ( s) n n s = j2π m 2 φ( m) = Hn( m) Sφ, n n Only in terms o uncorrelated noise souces! S ( ), m Measure subsystems phase noise : Absolute phase noise: Noise appears at the receiver output but not on the cavity ield! Relativ phase noise: Derive subcomponent phase noise spectra rom global requierements. Eective noise bandwidth relevant or the beam jitter - Beam diagnostic - Beating 2 LLRF systems 5

6 Introduction to Noise : 1,2 DUT Measurement techniques : Comparison o background noise : <0.5s resolution Carrier suppression The reerence: Enrico Rubiola et.al. FEMTO-ST Institute

7 Front-Ends : Linear Ideal Mixer Amplitude and phase detection: low pass ilter ( ) RF LO ) LO RF ( + RF LO - Mixer preserves phases -> Time jitter conversion rom RF to IF: Δt 2 IF = 2 2 ( ) Δt RF IF RF - I phase is 90 deg between LO and RF-> phase detector (in quadrature) - I phase is 0 deg between LO and RF -> ampl. detector (in phase)

8 Front-Ends : Active / Passive Mixer Active Gilbert-cell mixer: Passive double balanced mixer: Input Transistors: -> NF=14dB GND d GND b - Active input stage is limited by NF and <4GHz. - Passive mixers or many requencies available.

9 Front-Ends: Real Mixer Compromise between noise and linearity : P IF IP3 IP2 Active Mixers Passive Mixers P OUT,1dB + High conversion gain + Low LO drive needed + Low LO/RF crosstalk - Normal NF - Additional 1/-noise + High linearity + Low NF - Large LO drive needed (additional phase noise) - Higher LO/RF crosstalk Noise Spurious Free Dynamic Range (SFDRout) Filtering o distortions : P RF - Intermodulation eects - Higher harmonics

10 Front-Ends : ADCs - SNR Degradation 10 ADC Signal-to-Noise degradation :

11 ADCs : SNR Degradation ADC spectral density landscape: Multi-channel prototype: (2007) e n V = FS,pp 8 10 SNR ( s, ε ) 20 2 s Att. Mixer BPF Trao ADC System NF [db] IIP3 [dbm] / 36 G [db] / -6 ADC domiates the receiver noise +14dBm +8dBm ΔA/A=0.003% ΔP/P=0.003 o Baseband IF Sampling Direct Sampling

12 Receiver Structures : Baseband Sampling Baseband Sampling : Active IQ demodulation : Gain error : 1-2% Phase error: +/- 1º Features : Frequency: GHz IIP 3 : 21.5 dbm IIP 2 : 52 dbm Noise Figure: 12.8 db Conv. Gain: 4.3 db I/Q mismatch: 0.2 db V V RF LO ( t) = A LO cos ( ω + 0 ) ( ωt) ( t) = A cos t ϕ RF ARF ALO ARF ALO I = LPF cos( ωt + ϕ0 ) cos( ωt) = cos ϕ ARF ALO ARF ALO Q = LPF cos( ωt + ϕ0 ) sin( ωt) = sin ϕ Q 2 2 ϕ 0 = tan A = I + Q I Constellation diagram or errors on I,Q : - Splitter imbalance - Phase and amplitude imbalance - Mixer DC-oset

13 Receiver Structures : IQ Sampling IQ Sampling : - Digital I/Q detection - IF and clock signal should be synchronized - Alternating sample give I and Q components o the cavity ield Problems: - Nonlinearities in the analog ront-end or the ADC harmonics aliased to the IF requency. - Mixer DC-osets - Non-linearities have to be corrected!

14 Receiver Structures : Non-IQ Sampling Non-IQ Sampling : Example: M=4, N=15 -> Overestimated system o linear equations -> least mean square algorithm Sample requency: Phase advance : (N, M: integers, N samples in M IF periods) Most harmonics do not alias into the signal

15 Receiver Structures : 1 DUT Characterization Receiver subsystem noise contributions : Frond-End LO-Generation ADC < , 4s ΔA/A=0.003% -150dBc/Hz ΔP/P=0.002 o A,Δϕ Reerence AM Single Channel Receiver Front-End <-150dBc/Hz LNA BPF LO (s Intermediate ) IF (s) (s) PM requency [10MHz, 50MHz]: REF, ϕ REF ϕ LO, LO and CLK Generation -150dBc/Hz ϕ IF, ADC+ DDC -147dBc/Hz ADC CLK - DDC - CIC Filter - Calibration Mixer: ϕ IF ( s) = ϕ REF ( s) ϕ LO ( s), IF = REF LO ΔA LO Δϕ LO: ϕ LO ( s) ϕ REF ( s) = REF S 2 (, ), ( ) IF = ϕ IF Sϕ REF REF - Substract reerence part - 2 DUT + eliminate AM part

16 Receiver Structures : Vector-Sum Scaling Multi-Channel Receiver (ILC,XFEL) or VS-LLRF Systems: N Number o Channels LO, CLK Generation N uncorrelated noise sources Sα, ϕ, REC( ) ADC ADC... ADC... 1 N Sα, ϕ, VS ( ) Sα, REC( ) Sα, VS( ) = N Sϕ, REC( ) Sϕ, VS ( ) = + Sϕ, LO ( ) N Sϕ, REC( ) N Sϕ, LO ( ) Example: R3-MFC-Board, Fermilab / B.Chase - Moderate Serial 8-Channel ADC -> Good VS Perormance -> Excellent signal integrity ADC Reerence LO, CLK Gen 1 correlated noise sources S ϕ LO, ( ) - Correlated noise rom LO, CLK generation or rom a limited signal integrity limits the ield detection! - Requirements or the Front-End and ADC are more relaxed compared to single cavity LLRF systems.

17 Receiver Structures : Direct Sampling Direct Sampling : Field detection perormance : Z. Geng, et. Al. Evaluation o ast ADCs or direct sampling RF ield detection or the European XFEL and ILC, LINAC08, THP102 ADS5474 : Short-term stability (1MHz BW) : AM: 0.02% (rms), PM: GHz Temperature coeients : AM :0.03 %FS/ºC, PM: 0.14º/ºC - Under-sampling, Non-IQ sampling (m,n) - No down-converter needed - SNR sensitive to CLK jitter due to high IF Long-term stability : LLRF11, Poster, S Habib - Short-term noise is about 4x worse to non-iq receivers using lower IFs - Very good long-term stability <0.01%, 1.3GHz 8x ADC12D800/500R : Long-term stability (>4h) : AM: <0.01% (pp), PM: <0.1 (pp)

18 Distortions and Reduction Techniques Mechanical vibrations Temperature Humidity

19 Distortions : Mechanical vibrations ACC1 pickup-cable vibrations : ACC456 Ext. Hall 3 : During night During day ACC1-LLRF-System Several degree vector sum phase changes SASE: 0.6% change, when ext. hall door open 2 channels

20 Distortions : Drits Reerence tracking : 5 s m -1 K -1 ADC ADC Identical Frond-Ends? Mixer phase drits ~ 0.2 /K Mixer amplitude drits ~ 0.2%/K Mixer drit not equal (one PCB, temp.) + Humidity dependence on PCBs Reerence LO, CLK Gen Humidity dependence - Suppress only correlated noise + Eicient only or identical receivers, e.g. direct sampling complicated in a distributed system...

21 Distortions : Drits Reerence injection calibration (simpliied): Compensation within LLRF rack 5 s m -1 K -1 2 Field Detector, e.g.non-iq-sampling Δϕ = 0 ADC Reerence 1 LO, CLK Gen Δϕ = LLRF11, Poster Session, J. Piekarski Long-term stability improvements by a actor o 100 rom the ps-range to about 20s (pp). Demands on rack temp-conditioning will be relaxed.

22 Distortions and Reduction Techniques Robust long-term stable machine operation : Beam-based Feedback Compensates all residual drits Learning Feedorward Reerence Injection (Relection at the Cavity) Compensates LLRF system drits Reerence Tracking IPAC10 Drit calibration techniques or uture FELs, F.Ludwig et. al. - Short Heliax type pickup cables - Field detectors located at cavities - Low-Noise Electronic Design - Good signal integrity Decoupling o receiver properties: Linearity Drit Noise -> Non-IQ Sampling -> Calibration -> Cavity VS-Scaling helps!, Channel Parallelization, Hybridsystems (bypass and combine LLRF-Systems with analog baseband receivers) Requires a signal integrity ar <-100dB!

23 Thanks or your attention!