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Frank Ludwig / 03.12.04
Content :
1 Introduction to noise
2 Noise characterization of the actual LLRF system
3 Conceptional improvements
4 Different sensors for phase- and amplitude detection
5 Outlook
‚Noise characterization of the LLRF system‘.
Frank Ludwig
Frank Ludwig / 03.12.04
Introduction to noise
Definition of the spectral density :
Replacement circuits of devices:
T
T
ftπTT
TU dtetUtUFtUF
TfS 2
12
1 )()]([ ,)]([1
lim)(
Mean square value of a signal :
dffSUδ U
)(2
(The spectral density of a time limited signal vanishes)
(derived from theParsevalschen theorem)
Bandlimited noise through a filter function :
,else 0 1
)( )()(22
fffHfSdffHfSUδ UU
.)( constfSU
Uδ
t
kHzf 200
kHzf 20
kHzf 2
Noise sources :
Thermic noise white noiseSurface effects, trapping of charges flicker-noise
Real resistor :
= R
(noiseless) Uδ
R
(noisy)
TRkfS BU 4)(
)300,50(/1
kTRHznVSU
Amplifier :
Iδ
=
Uδ
(noiseless) (noisy)
... [Low-noise electronic design, Wiley 1993],[Halbleiter-Elektronik, Rauschen, Springer 1990]
(from datasheet)
Summation of noise sources :
1Uδ
2Uδ
2122
21 2 UδUδCUδUδUδ
Uδ
Frank Ludwig / 03.12.04
Example: 1/f-noise from SIS-junction
IS I S
U
Intrinsically-Shunted-Junction model : Correlation analysis in the time domain :
1)0( C
Localized states within the barrier cause 1/f-noise ?
fluctuation of the critical current,
resistance fluctuationcIδ
nRδ
715.0)0( C
cIδ
nRδ
Aliasing effects ? Better measurement method
cfT=300K, <140pV/Hz1/2, (up to know world record)T<77K, <20pV/Hz1/2, SQUID+FLL-electronics
Superposition of single electron lorentz-type spectra with different occupation time results in a 1/f-noise spectrum.
Frank Ludwig / 03.12.04
Correlation analysis in the frequency domain:
Idea: Redistribution of noise power ?
Conservation of noise power :
)()(2
))()(()(4)(
21
2112
fSfS
fSfSfSfγ
New method :
Amplifier noise can be considered
Finite amplifier bandwidth +++ Frequency dependence of the correlation
coefficient gfcf
702.0)0( C
Microscopic description!
Example: 1/f-noise from SIS-junction
Frank Ludwig / 03.12.04
Noise characterization of the LLRF System (TTF2)
RF digital feedback system (TTF2) :
MHzf 10Bandwidth for transforming 250kHz squared pulses :
Required regulation bandwidth only :
MHzf 1
+I,-I,+Q,-Q detection scheme :
Rotation of the LO-signal in four 90o steps
Re
Im
Phase modulation
(+I,+Q)
(+I,-Q)(-I,-Q)
(-I,+Q)
Frank Ludwig / 03.12.04
Stability requirements on phase and amplitude of the cavity field vector :
Amplitude stability : 410A
Aδ
Phase stability : 01.0δφ
VμUδ XFEL 100(normalized to A=1V)
fSdffSUδ UfU
)(
rms-voltage noise :
XFELTTF UδmVUδ 100.12
Noise measurement at input of an ADC :
ACC5, ProbeDCW, AN-36
time
100ns/div
voltage
2mV/div
Reduce the measuring bandwidth
Low-noise design
Averaging, switched low-pass!
Correlation methods
VμUδUδUδUδ externMOIQDWC 100...2222
Superposition of all noise contributions :
+
-++
and linearity
δφ
Aδ
A
Noise characterization of the LLRF System (TTF2)
Frank Ludwig / 03.12.04
Where comes the noise from ?
Noise characterization of the LLRF System (TTF2)
Frank Ludwig / 03.12.04
XFELDWC UδUδ 0.2
Noise from sensor (down-converter) :
RFf
LOf
DWCUAMPUU SvSS ,2
,, )(
5.8 ,/5.4 , vHznVSU
,US AMPUS ,
v DWCUS ,
HznVS AMPU /7,
HznVS DWCU /70,
linearitydBdBmdBmPRF 70 ],10,40[
Noise characterization of the LLRF System (TTF2)
Frank Ludwig / 03.12.04
Noise from IQ-driver modul :
XFELIQ UδUδ 5.3
LSB jumping from16-Bit DAC, power supply?
- Merge fiberlink+DAC+VM,
- Merge DWC+ADC+fiberlink
- Low-noise design down to 10mHz for long term stability!
Noise characterization of the LLRF System (TTF2)
Frank Ludwig / 03.12.04
)(, fS LO
)(, fS ZFU
Noise from sensor (LO-signal) : Noise conversion at the down-converter :
)()()(2
)()()(
,,
,,,
fSfSfγ
fSfSfS
LORF
LORFZF
Assumption: Mixer acts only as a phase detector :
/30,,
mVK
SS LOZF
, )( 2)( ,2
, fSKfS LOZFU
0)( fγ0, RFS
Noise characterization of the LLRF System (TTF2)
Frank Ludwig / 03.12.04
Noise conversion over the LO-Signal at down-converter from master-oszillator :
XFELMO UδUδ 10
Noise characterization of the LLRF System (TTF2)
Frank Ludwig / 03.12.04
How can we improve the signal-to-noise ratio ?
Noise characterization of the LLRF System (TTF2)
Frank Ludwig / 03.12.04
Properties of the RF digital feedback system (81MHz-CW) :
Precise synchronization of ADC-clocks, averaging over time jitters.
Changing of the bandwidth using averaging of the ADC.+
-
Suppresion of higher harmonics and disturbancies using narrow bandpass filter.
+No noise from IQ-driver and no additional ,uncorrelated effects‘.+
- May be limited by the effective ADC resolution.
Jitter conversion :
Tf
ft
IF
RF
fst 10
fsT 160
MHzf 1Measuring bandwidth :
RFf
LOf
IFf
Conceptional improvements
Requirements on synchronization :
250kHz (TTF2) : uncritical
81MHz : normal
Direct sampling : critical
Frank Ludwig / 03.12.04
Real mixer properties
Ideal mixer : Mixing using a non-linear characteristic:
Limits on the linearitydown up down down down down down down down down downLT5522 LT5521 LT5526 MC1502 CDB-9050 DBM-182 MBA-15L HMJ7 HMJ7-1 IAM-92516 AD8343
P(RF) dBm -7 -15 -10 -5 -10 -10 -10 -10 -12P(LO) dBm -5 -5 -5 7 -5 7 21 21 -3 -10P(IF) dBm -7NF dB 13,2 12,5 12,3 7,5 15 8,5 8,5 10,5 12,5 14,1IP3 dBm 25 24,2 16,5 12 -3 34 34 27 16,51dB dBm 10,8 11 5 0 23 23 9 2,8MS11 dBPS11 degMS22 dBPS22 degMS33 dBPS33 degGain dB -0,4 -0,5 0,5 6 6 -7,5 -6,5 -8,5 -8,5 -5,5 7,1RF to IF degisol IF RF dBiso LO RF dB 50 38 55 30 33 25 24 24 34iso LO IF dB 49 59 55 25 35 20 14 24 30 56 54IF(min) MHz 0,1 10 0,1 0 30 0 0 0 0
RFf
LOf
IFf
RFfRFf
LOfLOf
LORF ff IFfIFfLORF ff )cos(ˆ)( RFRFRFRF φtωUtU )cos(ˆ)( LOLOLOLO φtωUtU
y
x
...33
2210 xaxaxaay
)()()( tUtUtx LORF
All combination frequencies :
...3,2,1,0, , μνfμfνf LORFk
- Intermodulation effects (IP2,3)- 2nd harmonics
RFP
IFP
dBP11db compression point
Noise floor High le
vel m
ixer
Low le
vel m
ixer
Noise problems
Crosstalk,isolation,leakageproblems
Frank Ludwig / 03.12.04
Low-level sensors for 250KHz or 81MHz
‘Parallel‘ connection of Gilbert-cell-mixers and using low-noise amplifiers :
Noise reduktion of about 4-8, high integratino, low crosstalk.
Small signals, active noisy mixer. +-
RFf
LOf
DWCUAMPUU SvSNS ,2
,, )/(
20,5.8 ,/1 /, NvHznVNSU
NSU /, AMPUS ,
v DWCUS ,
HznVS AMPU /8.0 ,
HznVS DWCU /10 , )1( 001.0 MHzfδφ
Frank Ludwig / 03.12.04
Pre-Averaging for the 250kHz concept
RFf
LOf
CLKf
Frank Ludwig / 03.12.04
Drifts of measurement setup and M.O.
-100
-50
0
50
100
150
0 500 1000 1500 2000 2500 3000
time [s]
volt
age
[uV
]
Drift of Amplifier Drift of phasedetector Drift of Master Oscillator
Seperate phase and amplitude detectors
/5.5 mVK
HznVkHzfS
HznVkHzfS
GHzRFU
MHzRFU
/20)10(
/10)10(
3.1,
80,
Seperate phase and amplitude detectors using hybrids:
)81,1,160( MHzfMHzfpsVμ RF
fsT 70
Frank Ludwig / 03.12.04
High noise reduction, low-noise passive mixer, high signal level. RF-packaging, crosstalk, isolation and matching problems.
+- Increase the signal by using high-level GaAs JFET-ring-mixer.
MHzfRF 1300
MHzfLO 1219
MHzfCLK 36
dBm20
dBm0
- Clock jitter averages with N/1
sμ1
- Gain a factor of 3-5 from bandwith reduction
Amplitude noise reductionby using a limiter.
High-level sensors for 250KHz or 81MHz
Frank Ludwig / 03.12.04
Unsolved problems
Shielding, cable effects and rf-packaging, gun pulses :
Consistency check +I-I=0, +Q-Q=0 ?:
Disturbancies from high-level gun pulses:
Frank Ludwig / 03.12.04
Outlook
R&D :
- Decrease phase noise of master-oscillator!
- Phase- and amplitude measurement for the injector
- Test separate phase- und amplitude detectors including hybrids and ultra low-noise amplifiers
- InP-based HEMTS, p-HEMT as mixers, RSFQ-logic, intermodulation effects in SIS devices
- Measurement of phase- and amplitude using optical reference instead MO ?
- Low-cost phase- und amplitude detectors for mass production - 81MHz-CW or 250kHz (TTF2) or a combination
- Coupling of the MO and MLO
- Correlation measurement of the short and long-term stability between different modules
Thanks for your attention!