1. 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

2. Frank Ludwig / 03.12.04 Introduction to noise Definition of the spectral density : Replacement circuits of devices: Mean square value of a signal : (The spectral density of a time limited signal vanishes) (derived from the Parsevalschen theorem) Bandlimited noise through a filter function : Noise sources : Thermic noise white noise Surface effects, trapping of charges flicker-noise Real resistor : = R (noiseless) R (noisy) Amplifier : = (noiseless) (noisy)... [Low-noise electronic design, Wiley 1993], [Halbleiter-Elektronik, Rauschen, Springer 1990] (from datasheet) Summation of noise sources :

3. Frank Ludwig / 03.12.04 Example: 1/f-noise from SIS-junction S I S Intrinsically-Shunted-Junction model : Correlation analysis in the time domain : Localized states within the barrier cause 1/f-noise ? fluctuation of the critical current, resistance fluctuation Aliasing effects ? Better measurement method T=300K, <140pV/Hz 1/2, (up to know world record) T<77K, <20pV/Hz 1/2, SQUID+FLL-electronics Superposition of single electron lorentz-type spectra with different occupation time results in a 1/f-noise spectrum.

4. Frank Ludwig / 03.12.04 Correlation analysis in the frequency domain: Idea: Redistribution of noise power ? Conservation of noise power : New method : Amplifier noise can be considered Finite amplifier bandwidth + + + Frequency dependence of the correlation coefficient Microscopic description! Example: 1/f-noise from SIS-junction

5. Frank Ludwig / 03.12.04 Noise characterization of the LLRF System (TTF2) RF digital feedback system (TTF2) : Bandwidth for transforming 250kHz squared pulses : Required regulation bandwidth only : +I,-I,+Q,-Q detection scheme : Rotation of the LO-signal in four 90 o steps Phase modulation (+I,+Q) (+I,-Q) (-I,-Q) (-I,+Q)

6. Frank Ludwig / 03.12.04 Stability requirements on phase and amplitude of the cavity field vector : Amplitude stability : Phase stability : (normalized to A=1V) rms-voltage noise : Noise measurement at input of an ADC : ACC5, Probe DCW, AN-36 time 100ns/div voltage 2mV/div Reduce the measuring bandwidth Low-noise design Averaging, switched low-pass! Correlation methods Superposition of all noise contributions : + - + + and linearity Noise characterization of the LLRF System (TTF2)

7. Frank Ludwig / 03.12.04 Where comes the noise from ? Noise characterization of the LLRF System (TTF2)

8. Frank Ludwig / 03.12.04 Noise from sensor (down-converter) : Noise characterization of the LLRF System (TTF2)

9. Frank Ludwig / 03.12.04 Noise from IQ-driver modul : LSB jumping from 16-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)

10. Frank Ludwig / 03.12.04 Noise from sensor (LO-signal) : Noise conversion at the down-converter : Assumption: Mixer acts only as a phase detector : Noise characterization of the LLRF System (TTF2)

11. Frank Ludwig / 03.12.04 Noise conversion over the LO-Signal at down-converter from master-oszillator : Noise characterization of the LLRF System (TTF2)

12. Frank Ludwig / 03.12.04 How can we improve the signal-to-noise ratio ? Noise characterization of the LLRF System (TTF2)

13. 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 : Measuring bandwidth : Conceptional improvements Requirements on synchronization : 250kHz (TTF2) : uncritical 81MHz : normal Direct sampling : critical

14. Frank Ludwig / 03.12.04 Real mixer properties Ideal mixer : Mixing using a non-linear characteristic: Limits on the linearity All combination frequencies : - Intermodulation effects (IP2,3) - 2nd harmonics 1db compression point Noise floor High level mixer Low level mixer Noise problems Crosstalk, isolation, leakage problems

15. 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. + -

16. Frank Ludwig / 03.12.04 Pre-Averaging for the 250kHz concept

17. Frank Ludwig / 03.12.04 Seperate phase and amplitude detectors Seperate phase and amplitude detectors using hybrids:

18. 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. - Clock jitter averages with - Gain a factor of 3-5 from bandwith reduction Amplitude noise reduction by using a limiter. High-level sensors for 250KHz or 81MHz

19. 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:

20. 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!