Post on 14-Jan-2016
Frank Ludwig, DESY
Content :
1 Stability requirements for phase and amplitude for the XFEL
2 Next LLRF system for optimized detector operation
3 Limitations from noise and non-linearity
4 Down-converter prototype for CW-modulation scheme
5 LLRF phase noise budget
6 Summary and Outlook
CERN, LLRF05 Workshop 12/10/05
F. Ludwig, M. Hoffmann, G. Möller, S. Simrock / DESY
‚Precision low-noise field detectors‘
T. Filipek, R. Romaniuk / Warsaw University
Frank Ludwig, DESY
Actual LLRF control system using a switched LO-signal :
RFfLOf
time
500us/div
voltage
0.5V/div
time
5us/div
voltage
0.5V/div
voltage
2mV/div
ACC5, ProbeDCW, AN-36
time
100ns/div peak-to-peak comparison
05.0
XFEL2TTF U10U
Amplitude stability : 5105 A
Aδ
Phase stability : 01.0δφ
Stability requirements of the cavity field vector sum :
rmsXFEL V50U (normalized to A=1V)
- 86dB dynamic range of signal-to-noise.
Stability requirements on phase and amplitude for the XFEL
MHzf 10- Bandwidth for transforming the
squared LO-signal :
- Rotation of the LO-signal in four 90o
steps using a squared LO-Signal.
Frank Ludwig, DESY
Where comes the noise from and whatdo we measure after the down-converter ?
Next LLRF system for optimized detector operation
We measure all noise sources of the loop for a finite gain,but not the residual jitter between beam and reference!
How can we improve this ?
Microphonics
. . .
- Conceptional improvements using noise reduction methods, e.g. filtering and averaging.
- Sort the priorities: low noise, low drift, high linearity, absolute accuracy.
- Improve each component.
- Minimize residual jitter by increasing or decreasing the loop gain.
Frank Ludwig, DESY
Jitter transformation :
tf
fT
IF
RF
fst 10
fs160T
MHzf 1Measuring bandwidth :
Precise synchronization system.
Averaging reduces ADC-noise and no aliasing effects.
+
-
Narrowband filtering the IF-signal reduces distortions from mixer non-
linearities. +
No noise from LO-driver.+
Proposed LLRF control system operating with a CW LO-signal :
FPGA
Master-Oscillator
klystron
high-power cavity
down-converter
LO-input
RF-input
ADC-clock
1300-81
LOf
1300
RFf
81=9 x 9IFf
DAC-clock
1300-81
Next LLRF system for optimized detector operation
+ Higher harmonics and disturbancies using bandpass filters can be suppressed.
Frank Ludwig, DESY
Down-converter limitations from noise and non-linearity
Passive Mixer + FET: Active Gilbert-mixers:
+ High linearity
+ Low NF- Large LO drive needed
(additional phase noise)
- High LO/RF crosstalk
+ High conversion gain
+ Low LO drive needed
+ Low LO/RF crosstalk
- Normal NF
- Additional 1/f-noise
Compromise between noise and linearity :
Signal distortions :
- intermodulation effects (IP3)
- higher harmonics (IP2)
IP3
RFP
IFP
dB1,OUTP
Non-lin
earit
y
Noise
floor
Noise
IP2
Spurious FreeDynamic Range (SFDRout)
Dynamic Range (DRout)
Multi-channel detector board :
- Gilbert cell mixer- Linearization during beam pauses- Filtering of distortions
Filtering of distortions :
f
Filter
Signalinformation
Frank Ludwig, DESY
HznV
S AMPU
/7,
HznV
SU
/70
MHzfLO 1300
MHzfRF 13005.8v
HznV
SU
/5.4
,
2,, )( vSSS AMPUUU
Actual down-converter
First mixer stage determines the noise performance.
Actual down-converter performance:
Noise from actual down-converter :
MHz1f ,U2U XFEL
MHz10f ,U6U XFEL
-
-
,U2U XFEL ,U6U XFEL
,U6.0U XFEL
,MHz10f
,MHz1.0f ,MHz0.1f (CW-LO-Signal)
(Switched LO-Signal)
(Cavity filtered)
LLRF05: G.Möller, [43] Multichannel down-converter board for cavity field detection at the TTF.
Frank Ludwig, DESY
14
IF Output
Matching
Circuit
BPF
9MHz
SMD-Filter
Input
Matching
Circuit
Output
Matching
CircuitLNA
Evaluation
Board
AD6645
14 Bit, 80 MSPS,100fs jitter
BPF
BPF
1300 MHzStripline Filter
1291 MHzStripline Filter
Attenuator
LO-input
RF-input
Low-Noise-AmplifierLO Input
Matching
Circuit
Active Mixer
LT5522
1300 MHz
1300-9 MHz
80 MHzOversampling
80 MHz
ADC clock
-5dBm
MHz2f 19dBGain
Down-converter prototype for CW-modulation scheme
Frank Ludwig, DESY
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-120
-110
-100
-90
-80
-70
-60
-50
-40
-30
-20
-10
0
-1200 2 4 6 8 10 12 14 16 18 20 22 24 28 30 32 34 36 38 40 0 2 4 6 8 10 12 14 16 18 20 22 24 28 30 32 34 36 38 40
dB
FS
dB
FS
Frequency - MHz Frequency - MHz
f = 80MHzf = 9MHz @ -1dBFSs
a
f = 80MHzf = 81MHz @ -1dBFSs
a
0 5 10 15 20 25 30 35 40
0 5 10 15 20 25 30 35 40
Down-converter prototype for CW-modulation scheme
Oversampling : Undersampling :
Oversampling promises betterSNR than undersampling.
SFDR = 86dBSNR = 72dB
SFDR = 62dBSNR = 60.7dB
Signal bandwidth:
Bandlimited noise from Mixer
Noise from ADCf
ADC-noise, oversampling, clock phase noise requirements
LLRF05: T.Filipek, Frequency Conversion in Field Stabilization System for Application in SC cavity of linear accelerator.
Frank Ludwig, DESY
)f(Ssg
1 )f(S
s
s )f(S
s )f(S mKLY,
2
12
12mMO,
2
12m,
2
12
12mR,
)f(S mKLY,
)(, mVMφ fS)(, mRu fS)(, mφ fS )(, mMOφ fS
)(, mRφ fS )(, mMICφ fS
0f
12ω
pωg ,ω
The effective noise bandwidth for the down-converter is given by : 1212 ωgω
1st order HP1st order LP 1st order LP
- MO and klystron contributions decreases with gain. - Down-converter contributions increases with gain.
LLRF phase noise budget – Residual jitter
(simplified)
Beam jitter
Frank Ludwig, DESY
Phase noise budget (Switched LO, single cavity)
Phase noise spectra : Contributions to residual jitter :
Measured down-converter noise is largerthan residual noise and beam jitter.
MHz1300f,kHz500f 0p
Hz/dBc 110)f(S mAMP,
Hz200f ,100g 12
Hz/nV70)f(S m,u
)(, mMOφ fS TTF2 (new supply)
MHz10f
MHzf 10
- Noise is filtered by the cavity.
- The down-converter is not a good indicator for the residual jitter!
Frank Ludwig, DESY
Phase noise budget (Switched LO, single cavity)
Phase noise spectra : Contributions to residual jitter :
MHz1300f,kHz500f 0p
Hz/dBc 110)f(S mAMP,
Hz200f ,100g 12
Hz/nV70)f(S m,u
)(, mMOφ fS TTF2 (new supply)
MHz1f
MHz1f
Measured down-converter noise is largerthan residual noise and beam jitter.
- Noise is filtered by the cavity.
- The down-converter is not a good indicator for the residual jitter!
Frank Ludwig, DESY
Summary and Outlook
Outlook : - Design a multi-channel board and test within accelerator environment.
- Beam jitter caused by LLRF should be measured with fs-resolution.
Decrease mixers noise :
- Passive front end structures.
- Parallel structures of detectors (VLSI prefered).
- pHEMT Gilbert mixers (promise higher gain and lower noise).
- Additional „Zero-Phase“ detectors.
Summary : - The CW-modulation scheme combines many advantages, for example :
- No aliasing effects and ADC-noise reduction.
- Filtering of distortions, which allows a linearization with improved SNR.
- For multi-channel systems Gilbert mixers are recommended.
- Oversampling promises better SNR than undersampling.
- The down-converters noise contribution to the beam jitter
is reduced by the cavity transfer function.
- Linearize the down-converters
characteristic within the beam pause.
Increase mixer output :
Frank Ludwig, DESY
Summary and Outlook
Thanks for your attention!
Frank Ludwig, DESY
Summary and Outlook
Backup Slides
Frank Ludwig, DESY
HznVSU /70]10,40[ dBmdBmPRF
+ High LO/RF isolation
- Mixing into baseband
causes additional noise
dBmPLO 58-channels from cavity probe : 8-channels to ADC-Board : LO-Input :
(Designed by G.Möller/DESY/MHF-p)
Actual down-converter
LLRF05: G.Möller, [43] Multichannel down-converter board for cavity field detection at the TTF.
Frank Ludwig, DESY
Choice of LLRF system for optimized detector operation
Actual LLRF control system using a switched LO-signal :
MHzf 10
Bandwidth for transforming250kHz squared pulses :
but required regulationbandwidth is only :
MHzf 1
Phase and amplitude detection of the cavity field vector :
Rotation of the LO-signal in four 90o steps,using a 250kHz squared LO-Signal.
Re
Im(+I,+Q)
(+I,-Q)(-I,-Q)
(-I,+Q)RFf
LOf
Down-converter output IF-signal :
time
500us/div
voltage
0.5V/div
time
5us/div
voltage
0.5V/div
Frank Ludwig, DESY
SNR gain from ADC oversampling :
Down-converter prototype for CW-modulation scheme
- The signal within the bandbass filter, respectively noise from mixer stage will not be averaged.
Oversampling
Undersampling
f/1 sf/1
Measuring bandwidth
Optimal IF frequency, clock phase noise requirements
LNA ADC
LO-input
ADC clock
x N
LLRF05: T.Filipek, Frequency Conversion in Field Stabilization System for Application in SC cavity of linear accelerator.
SNR gain from averaging within the measuring time :
Quant. noise
f
f )v,,t(SNRSNR s2
jADC Sample frequency
Measuring bandwidth
ClockjitterInternal jitter
Equiv. Inputnoise of ADC
Number of samples :
BPFBPFRF-input
f
: MMaster-
Oscillator
ADCs SNR,fDigital
I,Q-Detection
IFfI samples
Q samples
Averaging
or
Filtering
Frank Ludwig, DESY
Down-converter limitations from noise and non-linearity
Passive Mixer + FET: Active Gilbert-mixers:
+ High linearity
+ Low NF- Large LO drive needed
(additional phase noise)
- High LO/RF crosstalk
+ High conversion gain
+ Low LO drive needed
+ Low LO/RF crosstalk
- Normal NF
- Additional 1/f-noise
Compromise between noise and linearity :
Signal distortions :
- intermodulation effects (IP3)
- higher harmonics (IP2)
IP3
RFP
IFP
dB1,OUTP
Non-lin
earit
y
Noise
floor
Noise
IP2
Spurious FreeDynamic Range (SFDRout)
Dynamic Range (DRout)
Multi-channel detector board :
- Gilbert cell mixer- Linearization during beam pauses- Filtering of distortions
Filtering of distortions :
f
Filter
Signalinformation