October 2005ALMA Cost Review1 A Glimpse of Technology Advances for the ALMA Project. ALMA Correlator...

October 2005 ALMA Cost Review 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, a World Array

*NAOJTokyo

*ESO & Institutes*NRAO

CV & Socorro

*Santiago*ALMA site


ALMA Site

Santiago

Paranal

La Serena


ALMA Site (5000-m, Array Operations Site -AOS-)& Site Transmission


ALMA Array


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.

Operations Support Facility (OSF)


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 )


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


Many Technical Challenges

• Many stability or synchronization problems to be solvedPhase 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 »


System Overview

• Focus on European BackEnd deliverables– Photonic LO

– Digitizers

– TFB cards in Correlator

• Overview of ALMA correlator

Front-EndPhotonic

Local Oscillator

ANTENNA

Data Encoder12*10Gb/s

12 Optical Transmitters12->1 DWD Optical Mux

Digitizer8* 4Gs/s -3bit ADC

8* 250 MHz, 48bit out

IF-Processing(8 * 2-4GHz sub-bands)

Fiber Patch-PanelFrom 270 stations to 64 DTS Inputs

Optical De-Mux

Digital De-Formatter

Correlator

Technical Building

Tunable Filter Block

Central PhotonicLocal Oscillator

30-959 GHz


Photonic LO OscillatorRAL development

Fiber LaserFiber Laser

Optical CombGenerator

Optical CombGenerator

PhaseLock Loop

PhaseLock Loop

ExternalCavity Laser

ExternalCavity Laser

Master Laser

Slave Laser

Round-TripServo

Round-TripServo

Round-Trip PhaseCorrection

CENTRAL CONTROL ROOM

125MHz Ref

PhaseLock Loop

Gunn DiodeOscillator

AOM

0.1-25kmBuried Fibre

High Freq.Optical Ref.

IF Out 4-12GHz

72-84GHz

CryogenicReceiver

SIS Mixer

HEMTAmplifier

ANTENNA RECEIVER CABIN

3

Photomixer Block

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


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


Digitizer Consortium, Assembly & Test Equipment Digitizer custom chips

L3AB, Bordeaux

Concepteur des ICs :

IXL & Obs Bordeaux

Fondeur : STmicroelectronics

Assembleur : Solectron-E

PCB : Atlantec

Banc de test et Clks : IRAM

DG Sub-Assembly

10MHzSynchro

DGS#1

DGD#1

DGS#2

DGD#2

BB#1Input

BB#2Input

4GHzClockInput

250MHzClockInput

FPGA

4 GHz

250 MHzPC and Plug-In Digital

Pattern Acquisition Board

Anti-Aliasing filter

Noise Generator

RF Generators

DTEC Board

250MHzClockInput

Can be replaced by DGCK


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

4 GHz

0 dBm

Clockbuffer

VH

VL

+-

+-

+-

+-

+-

+-

+-

Amplifier

OTA

Bandgap

2-4 GHz

D2

D1

D0Output buffer

Output buffer

Output buffer

D D

DD

DD

DD

DD

DD

DD

Adapter amplifier

D

D

D

D

D

D

Encoder


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

Drain thermique

Vddx

Gnd

Gnd

Gnd

HSStripline

50Ohms 100Ohms diff.

4450

4350

4350

4350

4450Diagramme de l’œil : bit de signe


ALMA demultiplexer

PCB• Circuit multicouches (10 layers)

• Substrat : RO4350 / pre-preg RO4450, collé sur un drain thermique pour écouler les charges thermiques.

Diagramme de l’œil : bit d’une sortie

CMS

Drain thermique

Stripline

100Ohms diff.

4450

4350

4350

4350

4450

100Ohms diff.

100Ohms diff.

4450

4450

4350

4350

50Ohms

50Ohms

Gnd

Gnd

HS

Gnd

Vddx

Gnd

Vddx

Gnd

HS

HS


Digitizer Test Equipment

DG Sub-Assembly

10MHzSynchro

DGS#1

DGD#1

DGS#2

DGD#2

BB#1Input

BB#2Input

4GHzClockInput

250MHzClockInput

FPGA

4 GHz

250 MHzPC and Plug-In Digital

Pattern Acquisition Board

Anti-Aliasing filter

Noise Generator

RF Generators

DTEC Board

250MHzClockInput

Can be replaced by DGCK

DG CorrélateurAUTOCORRELATOR

REQ

ACK

MASTER RESET

CLOCK

DATA[23-0]

PDF BUILDER

CONTROL

LOGIC

CLOCKENABLERST_COR

CLOCKENABLERST_PDF

X00[2-0]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]X11[2-0]X12[2-0]X13[2-0]X14[2-0]X15[2-0]

MUX

PCLK


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


Digital Filtering (TFB)

Digital Filters convolve digitized signals with numerical tap weights∑ Xn-i * piXi = 2- or 3-bit input samplespi = 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


Digital LOand Mixer

x

DDSLO

FIR filter

128 taps(8 bit encoded)

Low Pass

FIR filter


Low Pass

4Gs/sBaseband

32* 3 bits

8 bits

FIR filter


Low Pass

6 bitsReal part

6 bitsImag. part

125 Ms/s

125 Ms/s

8 bits

FIR filter


Low Pass

Complex to RealConversion

62.5 Ms/s

62.5 Ms/s

RequantizationOutputSignal

9 bits

9 bits

InputSignal

• DDS LO + Mixers• Two FIR Filter Stages

• Output Stage : Complex to Real Conversion and Re-quantization

Digital filter core


Digital Filter Card on Test Fixture2 Filters /1 FPGA

FIR Chip

DISTRIBUTION

Filter Core

Filter Core

Configuration

32

input bits

3*32 input bits

3*32 input bits

32

input bits

2 output

bits SB1

2 output

bits SB1

to CPLD2

Monitor


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


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


First Quadrant


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



• 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



• 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


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


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 2005ALMA Cost Review1 A Glimpse of Technology Advances for the ALMA Project. ALMA Correlator...

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Transcript of October 2005ALMA Cost Review1 A Glimpse of Technology Advances for the ALMA Project. ALMA Correlator...