Atacama Large Millimeter/submillimeter Array

Expanded Very Large ArrayRobert C. Byrd Green Bank Telescope

Very Long Baseline Array

Spectrometer PDR

John Ford (NRAO)

– The preliminary Design

Why a New Spectrometer?New Spectrometer Old GBT Spectrometer

Polyphase Filter Bank for RFI rejection Autocorrelation Spectrometer

256 level samplers 3 level samplers

16 high-speed samplers 8 high-speed samplers

1350 MHz bandwidth/sampler 800 MHz bandwidth/sampler

800 MB/s max disk I/O rate < 25 MB/s max disk I/O rate

New technology (FPGA based, Virtex-{5,6} Designed and built in early 1990’s

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Summary of Required Observing Modes

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Overall Block Diagram

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Analog System

• Adapts output of Converter Modules to the ADC– Low-pass filter– Amplification– Test tone injection

• Clock distribution– Split and amplify clock signal– Distribute to all ROACH boards

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Roach Assembly

ROACH Block Diagram

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ROACH 2

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3 GS/s ADC Board

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Clock Synthesizer Board

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Fujitsu Switch in its Natural Environment

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Computing Nodes

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Nehalem Node

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Storage Subsystem

• Project will supply ~100 TB of disk subsystems– Connected to 10 GbEthernet– Fast enough to support writing directly into subsystem

for most observing (But not pulsar searching)– Data accessible for astronomers simultaneously with

spectrometer use

• Project will not supply– VAO integration– Archiving software or methodology– Long-term storage media

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Preliminary Design Work

• Developing support hardware– IF system interface

• Anti-alias low-pass filters• Noise/test signal injection• Amplification

– Analog to Digital Converter sampling clock generation/distribution

– 1 Pulse Per Second distribution– Packaging

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Preliminary Design Work• Concentrating on the hard parts

– 3 GS/s sampling and PFB/FFT calculations– Heterogeneous Computing Approach

• Divide processing into front/back ends• Use FPGAs to fully process bandwidths greater than

200 MHz• Use FPGA front-ends to pre-process, split and

packetize data, then GPUs to provide fine channelization on narrower chunks

– Software Design• Adapting concepts and code from the Green Bank

Ultimate Pulsar Processing Instrument (GUPPI)• Adding support for the K-band FPA processing

pipeline• Integrating with the GBT Monitor and Control System

for user ease.16