Frank Ludwig / 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 / 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 :

Frank Ludwig / 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.

Frank Ludwig / 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

Frank Ludwig / 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)

Frank Ludwig / 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)

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

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

Frank Ludwig / 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)

Frank Ludwig / 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)

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

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

Frank Ludwig / 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

Frank Ludwig / 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

Frank Ludwig / 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. + -

Frank Ludwig / Pre-Averaging for the 250kHz concept

Frank Ludwig / Seperate phase and amplitude detectors Seperate phase and amplitude detectors using hybrids:

Frank Ludwig / 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

Frank Ludwig / 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 / 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!