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A Glimpse of Technology Advances for the ALMA Project. ALMA Correlator

A Glimpse of Technology Advances for the ALMA Project. ALMA Correlator. Hunt for Molecules Paris, September 19-20 2005 Alain Baudry Université de Bordeaux 1, Observatoire Aquitain des Sciences de l’Univers. ALMA, a World Array. * ESO & Institutes. * NRAO CV & Socorro. * NAOJTokyo.

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A Glimpse of Technology Advances for the ALMA Project. ALMA Correlator

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  1. A Glimpse of Technology Advances for the ALMA Project.ALMA Correlator Hunt for Molecules Paris, September 19-20 2005 Alain Baudry Université de Bordeaux 1, Observatoire Aquitain des Sciences de l’Univers ALMA Cost Review

  2. ALMA, a World Array *ESO & Institutes *NRAO CV & Socorro *NAOJTokyo *ALMA site *Santiago ALMA Cost Review

  3. ALMA Site Paranal La Serena Santiago ALMA Cost Review

  4. ALMA Site (5000-m, Array Operations Site -AOS-)& Site Transmission ALMA Cost Review

  5. ALMA Array ALMA Cost Review

  6. Operations Support Facility (OSF) Staff work at the Operations Support Facility (OSF) at an elevation of ~ 2800 m. Astronomers will not normally visit the OSF. A new road connects the high site with the San Pedro/Tocanao highway. The OSF is < ~ 1 hour drive from San Pedro. ALMA Cost Review

  7. ALMA Overview • ALMA is a European & North American bilateral project + Japan to construct and operate an array of - 64 12-m antennas + ACA (12x7-m + 4x12-m) • Reconfigurable array (~ 150 m to 14 km) to image astronomical objects • Wavelength coverage, ~ 3 mm to ~ 300 µm with cooled low noise SIS Rx • Final IF = 4 x 2-4 GHz and 2 polarizations per antenna => 8 digitizers per antenna working at 4 Gsample/s & digitized signal transmitted through optical fibers • Bandwidth selection with Digital Filters: 2 GHz to 62.5 & 31.25MHz • Highly flexible correlator: 8192 spectral points (for each pair of BB or in 1BB ) ALMA Cost Review

  8. Many Technical Challenges • Ambitious Science requirements: extreme sensitivity (a few µJy in 1h in cont., or map spiral galaxies at z=2 in CO and C lines), few kHz resolution, accurate calibration of phase and intensities, etc. Technical requirements difficult to meet Examples- Antennas: surface accuracy ~ 20-25 µm, max pointing error ~ 0.6”/ref source at 2°, fast switching - Rx noise ~ a few quantum limits - Highly stable LO: photonic LO with highly stable lasers beating in photomixers - Digitization early inthe processing chain: at antennas - High speed samplers: working at 4 Gsample/s input up to 4 GHz - Digital filters: new practice in RA - New correl. chip: 4 klags, 1 lag = 2-bit Xer at 125 MHz, ~ 2 million gates ALMA Cost Review

  9. Many Technical Challenges • Many stability or synchronization problems to be solved Phase coherence throughout the array achieved with a stable fiber to carry the LO reference signals to the antennas (e.g. 3 degree phase at 300 GHz => 4 10**-10 stability for transport over 14 km) Fibre length stability achieved by both passive (thermal insulation) and active control (round-trip length control). Frequent atmospheric phase calibrations (overall phase stability) • Production of many (thousands) sub-systems, not traditional in RA => industrial involvement at both developt & production phases • Considerations on cost and reliability (remote site) present troughout the project Design of Subsystems => compromises between fully innovative components (requiring industrial interest for mass production) and « components off the shelf » ALMA Cost Review

  10. Focus on European BackEnd deliverables Photonic LO Digitizers TFB cards in Correlator Overview of ALMA correlator ANTENNA Technical Building 30-959 GHz Photonic Local Oscillator Correlator Front-End Tunable Filter Block IF-Processing (8 * 2-4GHz sub-bands) Digital De-Formatter Digitizer 8* 4Gs/s -3bit ADC 8* 250 MHz, 48bit out Optical De-Mux Data Encoder 12*10Gb/s Fiber Patch-Panel From 270 stations to 64 DTS Inputs Central Photonic Local Oscillator 12 Optical Transmitters 12->1 DWD Optical Mux System Overview ALMA Cost Review

  11. Photonic LO OscillatorRAL development 2 lasers beating in photomixers => signal up to 140GHz and multiplied up to produce the 1st LO frequencies Photomixer Block ALMA Cost Review

  12. Digitizer & Formatter + Mux to Fiber • Numérisation à 4GS.s-1 sur 3 bits / 8 niveaux • 96Gb.s-1 d’information • Transmission par fibre optique à 12 x 10Gb.s-1/antenne ALMA Cost Review

  13. Digitizer Consortium, Assembly & Test Equipment Digitizer custom chips L3AB, Bordeaux Concepteur des ICs : IXL & Obs Bordeaux Assembleur : Solectron-E Banc de test et Clks : IRAM Fondeur : STmicroelectronics PCB : Atlantec ALMA Cost Review

  14. ALMA sampler, 3 bits, 8 levels • CAN : structure de type flash • BiCMOS 0.25µm en SiGe (2.5V) • Entrée : bruit gaussien 2-4GHz • Horloge : 4GHz • Sorties LVDS : 3 (x2) => 4Gsamples/s • Packaging • VFQFPN 44 7x7x1 • Ball-bonding Eléments parasites - Bonding : inductance ~1nH/mm - Pad boîtier : ~0.3pF - Pad puce : ~0.08pF ALMA Cost Review

  15. ALMA Sampler: Subassembly, PCB technology, Eye diagram • PCB • Circuit multicouches (6 layers) • Substrat : RO4350 / pre-preg RO4450, collé sur un drain thermique pour écouler les charges thermiques. CMS 4350 Gnd Diagramme de l’œil : bit de signe Stripline 4450 HS 4350 50Ohms 100Ohms diff. Gnd 4450 Vddx 4350 Gnd Drain thermique ALMA Cost Review

  16. CMS 4350 100Ohms diff. 4450 4350 50Ohms 100Ohms diff. 4450 Stripline 4350 50Ohms 100Ohms diff. 4450 4350 4450 4350 Drain thermique ALMA demultiplexer • PCB • Circuit multicouches (10 layers) • Substrat : RO4350 / pre-preg RO4450, collé sur un drain thermique pour écouler les charges thermiques. Gnd HS Gnd Diagramme de l’œil : bit d’une sortie HS Gnd HS Gnd Vddx Vddx Gnd ALMA Cost Review

  17. Digitizer Test Equipment DG Corrélateur ALMA Cost Review

  18. Correlator Overview • Development began with MMA architecture concept at NRAO and with Second Generation Correlator (2GC) concept in Europe • ALMA Correlator evolved to include the Tunable Filter Bank (TFB) from 2GC study => to enhance the performance by 32 in spectral resolution • Frequency demultiplexing and filtering is fully digital (TFB) • Tasks are performed in NA and Europe (TFB); TFB tasks managed at University of Bordeaux • Specifications • 64 antennas, X-correl coefficients for all 2016 antenna pairings • 16 GHz BW, full Stokes polarization analysis, 3.8kHz resolution • High flexibility • Deliverables: total of 32 racks with over 2500 PCBs • Station electronics and filetring cards • Baseline electronics cards • Total power dissipation = 170kW ALMA Cost Review

  19. Digital Filtering (TFB) Digital Filters convolve digitized signals with numerical tap weights ∑ Xn-i * pi Xi = 2- or 3-bit input samples pi = 8-bit (or more) taps loaded from outside Convolution is implemented in FPGAs offering RAMs, DSP blocks (multipliers or adders), PLLs • TFB demuxes each 2 GHz input band into 32 sub-bands • each subband or groups of subbands are frequency centered as required by the astronomer ALMA Cost Review

  20. Digital filter core • DDS LO + Mixers • Two FIR Filter Stages • Output Stage : Complex to Real Conversion and Re-quantization ALMA Cost Review

  21. Digital Filter Card on Test Fixture2 Filters /1 FPGA ALMA Cost Review

  22. Progress to Date • First quadrant hardware is built and verified • Prototype TFB cards tested with dedicated Test Fixture and other tests ongoing in first quadrant of ALMA correlator • Close integration with Computing team; operational software is used in system testing, operating modes are being verified • Project is on schedule and under original budget ALMA Cost Review

  23. Operations • Beginning with first quadrant installation by the construction team • Responsibility for operation and maintenance will be transferred to Chilean staff, with continued support while the remaining quadrants are built and delivered ALMA Cost Review

  24. First Quadrant ALMA Cost Review

  25. TFB Spectral Flexibility (1) • Example of 13 lines arbitrarily distributed in 2 GHz • Actual ‘Line Forest’ sources exhibit even more lines ~ 20 to 25 lines per GHz in Orion • With TFB cards these 13 lines can be analyzed simultaneously with different spectral resolutions ALMA Cost Review

  26. TFB Spectral Flexibility (2) • With 8 sub-channel filters one can have (see Mode Tables) • Correlated BW = 500 MHz • Spectral resolution = 0.976 MHz with all 4 X-products and smooth result to get effective resolution of 1.95 MHz ALMA Cost Review

  27. TFB Spectral Flexibility (3) • Use just another sub-channel filter to obtain high frequency resolution at appropriate IF frequency around 840 MHz • Correlated BW = 62.5 MHz • Spectral resolution ~ 120 kHz with all 4 X-products • One still has several filters and spectral channels available for other scientific purposes ALMA Cost Review

  28. Many Correlator Mode Options • Frequency division mode (max of 8192 spectral points in 1 Baseband per Quadrant) or Time division mode (64 spectral points in 1 Baseband per Quadrant) • Several Modes • Select Number of Sub-channels <=> Correlated Total Bandwdth • Select Efficiency • Sample Factor: Nyquist or Twice Nyquist (with twice less spectral points) • Improve further Efficiency: 4-bit x 4-bit Quantization (less spectral points) • Select Polarization <=> 1 Baseband or 2 Basebands without or with (full Stokes analysis) polarization cross-products • Resources are exchangeable among • Basebands = 1 or 2 max per Correlator Quadrant • FIR filters = 32 max per Baseband • X-products: 1, 2 or 4 ALMA Cost Review

  29. Science Cases • Line and Dust Study in Young Stellar Objects • 1 sub-array of 16 antennas for CO line observation (230 GHz) in 62.5 MHz bandwidth (~ 80 km/s velocity coverage) with high spectral resolution (7.6 kHz or 0.01 km/s) • 2 other sub-arrays of 24 antennas each in 2 other frequencies to provide spectral imaging of other weaker lines in narrow total BW (~ 80 km/s) and accurate spectral index measurement of dust in broad ‘continuum’ bandwidths • High number of channels in broad BWs essential to search for new molecular species … interferometry … glycine • Broad BWs with several spectral channels and different receiver bands useful to measure unknown z in distant CO galaxies • Line Survey & Imaging in Orion-like young/massive sources • Requires both broad & narrow BWs … now possible with many more channels ALMA Cost Review

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