tutorial on rf (receiver fundamentals)bib-pubdb1.desy.de/record/94568/files/llrf11... · tutorial...

Tutorial on RF (Receiver Fundamentals)Frank Ludwig – DESY

Tutorial on RF (Receiver Fundamentals)

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LLRF2011, 18.10.11Frank Ludwig, DESY

Outline

Introduction to Noise and Systems

Front-Ends ComponentsReceiver StructuresDistortions and Reduction Techniques


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LLRF2011, 18.10.11Frank Ludwig, DESY3

Motivation

- Shortterm amplitude/phase stability <0.01%,<0.01deg (10Hz-1MHz)- Longterm amplitude/phase stability 0.01%, 0.01 deg (forever-10Hz)- Nonlinearity < -55dBc, 1% error- Channel crosstalk < -70dB- Overall latency <100ns

-20 deg off-crest

Actuatorphase noise

Field Detectoramplitude noise

Beam energy jitter(simulated)

Field regulation and noise sources :

Requirements for the receiver, e.g.

ϕΔ,A

Master Reference

Desired cavity field stability


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Introduction to Noise : Phase Noise

Definition of a spectral density : ∫+

−

−

∞→=≡

T

T

ftπTTTu dtetutuFtuF

TfS 22 )()]([ ,)]([1lim)(

22

0

22

0

)]([1lim1)(

,)]([1lim1)(

tFTV

fS

tFTV

fS

TTm

TTm

δϕ

δα

ϕ

α

∞→

∞→

≡

≡

m

f

fmrms dffS

ft ∫=Δ

2

1

)()2(

1

0ϕπ

Microwave signal with noise : )(0

0 )](1[)( titietVtu δϕωδα ++=

Phase noiseAmplitude noise

( ) )](),([ )( )( 02

0 mmn

mu fSfSOfVfS ϕαδ +++=

0)( ,1 |)(| , ,0 =<<−=∀ mφαm fγtδφfffCarrier Amplitude noise Phase noise

)( mα fS )( mφ fS

Offset frequency

Signal spectrum :

...},,,{ jPIUu =Time unlimited signals, e.g. noise

Amplitude noise :Phase noise :Timing jitter :

m

f

fmrms dffSAA ∫=Δ

2

1

)()/( α

dBc = dB relative to carrier10 log [|L(fm)|] dBc/Hz


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Introduction to Noise : Systems

∑=n

nn sφsHsφ )()()(

Only in terms of uncorrelated noise souces!

mfπjs 2=

∑=n

mnφmnmφ fSfHfS )()()( ,2

,

n-th noise sourceTransferfunction

Absolute phase noise:

Relativ phase noise:

Noise appears at the receiveroutput but not on the cavity field!

- Beam diagnostic- Beating 2 LLRF systems

Effective noise bandwidthrelevant for the beam jitter

Algebraic solution of the system in the Laplace-Domain : e.g. LLRF System (simplified)

Measure subsystems phase noise :

Derive subcomponent phase noise spectra from global requierements.


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Measurement techniques : Comparison of background noise :

‘The’ reference: Enrico Rubiola et.al.FEMTO-ST Institute http://rubiola.org

Carrier suppression

Introduction to Noise : 1,2 DUT

<0.5fs resolution


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Front-Ends : Linear Ideal Mixer

Amplitude and phase detection:

f

low pass filter

RFfLOf )ff( LORF +)ff( LORF −

- Mixer preserves phases -> Time jitter conversion from RF to IF:

- If phase is 90 deg between LO and RF-> phase detector (in quadrature)- If phase is 0 deg between LO and RF -> ampl. detector (in phase)

( ) 2RF

2IFRF

2IF tfft Δ=Δ


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Front-Ends : Active / Passive Mixer

Active Gilbert-cell mixer:

GND d GND b

Passive double balanced mixer:

- Active input stage is limited by NF and <4GHz.- Passive mixers for many frequencies available.

Input Transistors:-> NF=14dB


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Front-Ends: Real Mixer

- Intermodulation effects- Higher harmonics

+ High linearity+ Low NF- Large LO drive needed

(additional phase noise)- Higher LO/RF crosstalk

+ High conversion gain+ Low LO drive needed+ Low LO/RF crosstalk- Normal NF- Additional 1/f-noise

Passive MixersActive MixersIP3

RFP

IFP

dB1,OUTP

Noise

IP2

Spurious FreeDynamic Range (SFDRout)

Compromise between noise and linearity :

Filtering of distortions :


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10Front-Ends : ADCs - SNR Degradation

ADC Signal-to-Noise degradation :


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ADC spectral density landscape:

IF Sampling Direct SamplingBaseband

s

20),f(SNR

pp,FSn f

2108

Ve

s ε

=

ADCs : SNR Degradation

+14dBm

+8dBm

Att. Mixer BPF Trafo ADC System NF [dB] 1 11 3 1 35 41 IIP3 [dBm] 48 36 35 35 / 36 G [dB] -1 -11 -3 9 / -6

Multi-channel prototype: (2007)

ΔA/A=0.003%

ΔP/P=0.003o

ADC domiatesthe receiver noise


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Receiver Structures : Baseband Sampling

Gain error : 1-2%Phase error: +/- 1º

Features :Frequency: 0.8 – 1.5 GHzIIP3: 21.5 dBmIIP2: 52 dBmNoise Figure: 12.8 dBConv. Gain: 4.3 dBI/Q mismatch: 0.2 dB

Constellation diagram for errors on I,Q :

- Splitter imbalance- Phase and amplitude imbalance- Mixer DC-offset

Active IQ demodulation :Baseband Sampling :

( )tAtV LOLO ωcos)( =( )0cos)( ϕω += tAtV RFRF

( ) ( ) 00 cos4

cos2

cos2

ϕωϕω LORFLORF AAtAtALPFI =⎭⎬⎫

⎩⎨⎧ ⋅+=

( ) ( ) 00 sin4

sin2

cos2

ϕωϕω LORFLORF AAtAtALPFQ =⎭⎬⎫

⎩⎨⎧ ⋅+−=

⎟⎠⎞

⎜⎝⎛= −

IQ1

0 tanϕ 22 QIA +=


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Receiver Structures : IQ Sampling

- Digital I/Q detection- IF and clock signal should be synchronized- Alternating sample give I and Q componentsof the cavity field

Problems:- Nonlinearities in the analog front-end or theADC harmonics aliased to the IF frequency.

- Mixer DC-offsets- Non-linearities have to be corrected !

IQ Sampling :


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Receiver Structures : Non-IQ Sampling

Most harmonics do not alias into the signal

Non-IQ Sampling : Example: M=4, N=15

(N, M: integers, N samples in M IF periods)

Sample frequency:

Phase advance :

-> Overestimated systemof linear equations

-> least mean square algorithm


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Receiver Structures : 1 DUT Characterization

ΔA/A=0.003%

ΔP/P=0.002o

< 0.0018°, 4fs

-150dBc/Hz

Receiver subsystem noise contributions :Frond-EndLO-GenerationADC

Intermediate frequency [10MHz, 50MHz]:

CLK

BPF - DDC- CIC Filter- Calibration

Front-End <-150dBc/Hz

LNA

LO and CLK Generation

ϕΔ,AAΔ

Reference

ADC

Single Channel Receiver

ADC+ DDC -147dBc/Hz

-150dBc/Hz

AM

)(sREFϕ,REFf )(sLOϕ

,LOf)(sIFϕ

,IFf

PM

Mixer: LOREFIF

LOREFIF

fffsss

−=−= ),()()( ϕϕϕ

ϕΔ LO: )( )( sffs REFREF

LOLO ϕϕ ⎟⎟

⎠

⎞⎜⎜⎝

⎛=

2

,, )()( ⎟⎟⎠

⎞⎜⎜⎝

⎛=

REF

IFREFIF f

ffSfS ϕϕ

- Substract reference part- 2 DUT + eliminate AM part


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Receiver Structures : Vector-Sum Scaling

Multi-Channel Receiver (ILC,XFEL) for VS-LLRF Systems:

- Correlated noise from LO, CLK generation orfrom a limited signal integrity limits the field detection!

- Requirements for the Front-End and ADC are morerelaxed compared to single cavity LLRF systems.

⎟⎠

⎞⎜⎝

⎛≡

GenerationCLK LO,Channels ofNumber N

N1

∝ADC

ADC

LO, CLK GenReference

ADC

ADC

. . .

. . .

. . .

∑. . .

N uncorrelated noise sources

1 correlated noise sources

)(,, fS VSϕα

)(,, fS RECϕα

)(, fS LOϕ

)( )( ,, fSNfS LOREC ϕϕ ≤

)()(

)( ,,

, fSN

fSfS LO

RECVS ϕ

ϕϕ +=

NfS

fS RECVS

)( )( ,

,α

α =

Example: R3-MFC-Board, Fermilab / B.Chase- Moderate Serial 8-Channel ADC-> Good VS Performance-> Excellent signal integrity


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Receiver Structures : Direct Sampling

Direct Sampling :

- Under-sampling, Non-IQ sampling (m,n)- No down-converter needed- SNR sensitive to CLK jitter due to high IF

- Short-term noise is about 4x worseto non-IQ receivers using lower IFs

- Very good long-term stability<0.01%, <0.1° @ 1.3GHz

LLRF11, Poster, S HabibLong-term stability :

Field detection performance :ADS5474 : Short-term stability (1MHz BW) :

AM: 0.02% (rms),PM: 0.02° (rms) @ 1.3GHzTemperature coefffients :AM :0.03 %FS/ºC, PM: 0.14º/ºC

Z. Geng, et. Al. „Evaluation of fast ADCs for direct sampling RF field detection for the European XFEL and ILC“, LINAC08, THP102

8x ADC12D800/500R : Long-term stability (>4h) :AM: <0.01% (pp), PM: <0.1° (pp)


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Mechanical vibrations

Temperature

Humidity

Distortions and Reduction Techniques


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ACC1 pickup-cable vibrations :

ACC1-LLRF-System

Several degree vectorsum phase changes

2 channels

During dayDuring night

0.6% change, when

ext. hall door open

ACC456 Ext. Hall 3 :

Distortions : Mechanical vibrations

SASE:


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-1-1Km fs5ADC

LO, CLK GenReference

ADC

- Suppress only correlated noise+ Efficient only for ‘identical’ receivers,

e.g. direct sampling

Reference tracking :

Distortions : Drifts

…complicated in a distributed system...

Mixer phase drifts ~ 0.2°/KMixer amplitude drifts ~ 0.2%/K

Mixer drift not equal (one PCB, temp.) +Humidity dependence on PCBs

Identical Frond-Ends ?

Humiditydependence


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1 2

Reference injection calibration (simplified):

Long-term stability improvements by a factorof 100 from the ps-range to about 20fs (pp).

Demands on rack temp-conditioning will be relaxed.

-1-1Km fs5

Field Detector,e.g.non-IQ-Sampling

ADC

LO, CLK Gen

Reference 1

2 0=ϕΔ

0=ϕΔ

Compensation within LLRF rack

Distortions : Drifts

LLRF11, Poster Session, J. Piekarski


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Robust long-term stable machine operation :

IPAC10‚ Drift calibration techniques for future FELs‘, F.Ludwig et. al.

CompensatesLLRF system drifts

- Short Heliax type pickup cables- Field detectors located at cavities- Low-Noise Electronic Design- Good signal integrity

Reference Tracking

Reference Injection(Reflection at the Cavity)

Learning Feedforward

Beam-based Feedback Compensatesall residual drifts

Distortions and Reduction Techniques

Linearity -> Non-IQ SamplingDrift -> CalibrationNoise -> Cavity VS-Scaling helps!,

Channel Parallelization,Hybridsystems(bypass and combine LLRF-Systemswith analog baseband receivers)

Decoupling of receiver properties:

Requires a signal integrity far <-100dB!


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Thanks for your attention!

tutorial on rf (receiver fundamentals)bib-pubdb1.desy.de/record/94568/files/llrf11... · tutorial...

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