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					                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




October 2005                                  ALMA Cost Review                             1
               ALMA, a World Array




                                        *ESO &
               *NRAO                    Institutes   *NAOJ
                                                     Tokyo
               CV & Socorro



                       *ALMA site
                       *Santiago




October 2005                   ALMA Cost Review              2
               ALMA Site



Paranal


La Serena



Santiago




October 2005   ALMA Cost Review   3
               ALMA Site (5000-m, Array Operations Site -AOS-)
                            & Site Transmission




October 2005                   ALMA Cost Review                  4
               ALMA Array




October 2005      ALMA Cost Review   5
                 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.


  October 2005                         ALMA Cost Review   6
                                          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 )
  October 2005                                ALMA Cost Review                          7
                              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
  October 2005                            ALMA Cost Review                            8
                                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 »
   October 2005                                ALMA Cost Review                        9
                                                     System Overview

                      ANTENNA                                       Technical Building
                      30-959 GHz

                                        Photonic                                      Correlator
                   Front-End              Local
                                        Oscillator                               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

                                                             Central Photonic   Fiber Patch-Panel
           12 Optical Transmitters                           Local Oscillator   From 270 stations to
           12->1 DWD Optical Mux                                                64 DTS Inputs




• Focus on European BackEnd                                       • Overview of ALMA correlator
  deliverables
        – Photonic LO
        – Digitizers
        – TFB cards in Correlator
October 2005                                           ALMA Cost Review                                 10
                                 Photonic LO Oscillator
                                   RAL development

               2 lasers beating in photomixers
               => signal up to 140GHz and multiplied up to produce the 1st LO
               frequencies


                                                                               CENTRAL CONTROL ROOM
                                                   Master Laser

                                                   Fiber Laser
                                                     Fiber Laser                                                                         Round-Trip Phase
                                                                                  Optical Comb                                              Correction
                                                                                   Optical Comb
                                                                                                                                                       
                                                                                   Generator
                                                                                      Generator
                                                               Phase
                                                             LockPhase
                                                                  Loop
                                                  Slave Laser Lock Loop
                                                                                                                                                   Round-Trip
                                                   External                                                                                         Round-Trip
                                                                                                                                                     Servo
                                                      External
                                                  Cavity Laser                                                                                         Servo
                                                   Cavity Laser


                                                                                                                                                                  0.1-25km
                                                                                                                                                                 Buried Fi
                                                                                ANTENNA RECEIVER CABIN
                                                                                                                                  z ef
                                                                                                                             125MH R

                                                                                                            Phase
                                                                                                          Lock Loop
                 Photomixer Block                                  Cryogenic
                                                                   Receiver
                                                                                                                        High Freq.
                                                                   SIS Mixer                                            Optical Ref.
                                                                                                          Gunn Diode
                                                                                  3                       Oscillator
                                                                                                                                                 AOM
                                                   HEMT                                72-84GHz
                                                  Amplifier

                                                                                         IF Out 4-12GHz
October 2005                              ALMA Cost Review                                                                                                  11
                       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

October 2005                              ALMA Cost Review                12
               Digitizer Consortium, Assembly & Test Equipment
                          Digitizer custom chips
                                  L3AB,
                                 Bordeaux

Concepteur des ICs :      Assembleur : Solectron-E                                        Banc de test et Clks :
                                                                                                 IRAM
IXL & Obs Bordeaux

    Fondeur :                  PCB : Atlantec
 STmicroelectronics
                                                                                DG Sub-Assembly
                                                                        BB#1                                  DTEC Board
                                                                        Input
                                                                                    DGS    DGD
                                            Noise Generator                          #1     #1


                                                                                                                 FPGA
                                                                        BB#2
                                                                        Input       DGS    DGD
                                                                                                     250MHz
                                                                                     #2     #2
                                                                                                      Clock
                                                                                                      Input

                                              Anti-Aliasing filter


                                                                                  4GHz    250MHz
                                                                                  Clock    Clock
                                              Can be replaced by DGCK
                                                                                  Input    Input




                                                             4 GHz

                                             10MHz
                                            Synchro     RF Generators
                                                                                                     PC and Plug-In Digital
                                                            250 MHz
October 2005                     ALMA Cost Review                                                  Pattern Acquisition Board   13
                                                             ALMA sampler, 3 bits, 8 levels

                                                                               • CAN : structure de type flash
                             +
                                 D   D
               VH            -



  2-4 GHz                    +
                                 D   D
                                                                               • BiCMOS 0.25µm en SiGe (2.5V)
               Amplifier     -

                                                   D       Output
                                                       D            D0
                                                           buffer
                 OTA         +
                             -
                                 D   D
                                                                               • Entrée : bruit gaussien 2-4GHz
               Bandgap
                             +           Encoder           Output
                Adapter      -
                                 D   D             D   D            D1
                                                           buffer

                                                                               • Horloge : 4GHz
                amplifier


                             +
                             -
                                 D   D

                                                   D       Output
                                                       D            D2
                                                           buffer

       4 GHz        Clock
                    buffer
                             +
                             -
                                 D   D
                                                                               • Sorties LVDS : 3 (x2) => 4Gsamples/s
       0 dBm

                             +
                             -
                                 D   D
               VL




                                                        Packaging
                                          • VFQFPN 44 7x7x1
                                          • Ball-bonding

                                          Eléments parasites
                                              - Bonding : inductance ~1nH/mm
                                              - Pad boîtier : ~0.3pF
                                              - Pad puce : ~0.08pF
October 2005                                                        ALMA Cost Review                              14
                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
                                          4450                Stripline            HS

                                           4350          50Ohms    100Ohms diff.
                                                                                   Gnd
                                           4450
                                                                                   Vddx

                                           4350
                                                                                   Gnd
                                                         Drain thermique



 October 2005                       ALMA Cost Review                                    15
                               ALMA demultiplexer
                                                            PCB
                                             • Circuit multicouches (10 layers)

                                             • Substrat : RO4350 / pre-preg RO4450,
                                             collé sur un drain thermique pour écouler
                                             les charges thermiques.
                                                                                     CMS
                                                                                           Gnd
                                               4350                  100Ohms diff.
                                                                                           HS
                                               4450
                                                                                           Gnd
                                               4350
Diagramme de l’œil : bit d’une sortie                      50Ohms    100Ohms diff.
                                                                                           HS
                                               4450                 Stripline
                                                                                           Gnd
                                               4350        50Ohms    100Ohms diff.
                                                                                           HS
                                               4450
                                                                                           Gnd
                                               4350
                                                                                           Vddx
                                               4450
                                                                                           Vddx
                                               4350
                                                                                           Gnd
    October 2005                        ALMA Cost Review      Drain thermique                   16
                                                                            Digitizer Test Equipment

                                                                                                      X00[2-0]



                                                            DG Corrélateur                            X01[2-0]
                                                                                                      X02[2-0]
                                                                                                      X03[2-0]
                                                                                                      X04[2-0]
                                                                                                      X05[2-0]
                                                                                                      X06[2-0]
                                                                                                      X07[2-0]
                                                                                                      X08[2-0]
                                                                                                      X09[2-0]
                                                                                                      X10[2-0]
                                                                                                                    AUTOCORRELATOR
                                                                                                      X11[2-0]
                                                                                                      X12[2-0]
                                                                                                      X13[2-0]
                                                                                                      X14[2-0]                                       MUX   DATA[23-0]
                                                                                                      X15[2-0]

                                                                                                                         CLOCK
                                                                                                                 RST_COR ENABLE




                                                                                                                                  PDF BUILDER
                                                                                                                                           CLOCK
                                                                                                                                   RST_PDF ENABLE




                                                                                                                           CONTROL
                                                                                                                                              PCLK

                                                                                                                             LOGIC             REQ
                                                                                                                                               ACK
                                                                                                                  CLOCK
                                                                                                                  MASTER RESET




                                    DG Sub-Assembly
                            BB#1                                  DTEC Board
                            Input
                                        DGS    DGD
Noise Generator                          #1     #1


                                                                     FPGA
                            BB#2
                            Input       DGS    DGD
                                                         250MHz
                                         #2     #2
                                                          Clock
                                                          Input

  Anti-Aliasing filter


                                      4GHz    250MHz
                                      Clock    Clock
  Can be replaced by DGCK
                                      Input    Input




                 4 GHz

 10MHz
Synchro     RF Generators
                                                         PC and Plug-In Digital
                250 MHz
                                                       Pattern Acquisition Board


                October 2005                                                       ALMA Cost Review                                                                 17
                               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
 October 2005                          ALMA Cost Review                    18
                            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



 October 2005                       ALMA Cost Review                        19
                                                           Digital filter core

                                           FIR filter                       FIR filter
                                            128 taps        8 bits            64 taps
                              6 bits     (8 bit encoded)    125 Ms/s      (9 bit encoded)   9 bits
                             Real part
                                           Low Pass                          Low Pass        62.5 Ms/s
               Digital LO
    4Gs/s      and Mixer
  Baseband                                                                                                                                  Output
   Input                                                                                                 Complex to Real   Requantization   Signal
   Signal          x                                                                                       Conversion
  32* 3 bits
                  DDS
                   LO
                                           FIR filter                       FIR filter       62.5 Ms/s
                              6 bits
                            Imag. part      128 taps        8 bits            64 taps       9 bits
                                         (8 bit encoded)    125 Ms/s      (9 bit encoded)

                                           Low Pass                          Low Pass




                                      • DDS LO + Mixers
                                    • Two FIR Filter Stages
                • Output Stage : Complex to Real Conversion and Re-quantization

October 2005                                                         ALMA Cost Review                                                         20
                                          Digital Filter Card on Test Fixture
                                                   2 Filters /1 FPGA



                        3*32 input bits

                                          FIR Chip


                                                           Monitor

                                                                             2 output
                                           Filter Core
                    D                                                        bits SB1
                    I
                    S
                    T
                    R
   32                                                                           32
                    I
                    B
input bits                                                                   input bits
                    U
                    T
                    I
                    O
                    N
                                                                             2 output
                                           Filter Core
                                                                             bits SB1

                                                         Configuration
                                                                              to CPLD2




                        3*32 input bits




             October 2005                                                ALMA Cost Review   21
                         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


 October 2005               ALMA Cost Review                22
                           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




October 2005               ALMA Cost Review                    23
               First Quadrant




October 2005    ALMA Cost Review   24
                          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
  October 2005                          ALMA Cost Review   25
                   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
  October 2005                ALMA Cost Review    26
                        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
October 2005                     ALMA Cost Review      27
                                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
   October 2005                                   ALMA Cost Review                                      28
                                  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
   October 2005                       ALMA Cost Review                          29

				
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