Frank Ludwig / 03.12.04 Content : 1 Introduction to noise 2 Noise characterization of the actual...

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


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


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.


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


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)


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



Where comes the noise from ?



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 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!



)(, 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 conversion over the LO-Signal at down-converter from master-oszillator :

XFELMO UδUδ 10



How can we improve the signal-to-noise ratio ?



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


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


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


Pre-Averaging for the 250kHz concept

RFf

LOf

CLKf


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


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


Unsolved problems

Shielding, cable effects and rf-packaging, gun pulses :

Consistency check +I-I=0, +Q-Q=0 ?:

Disturbancies from high-level gun pulses:


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!

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