The Correlators Spectrometers Mopra Induction May 2005

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The Correlators( Spectrometers ) Mopra
Induction - May 2005
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Frequency Conversion
Mixer
RF
IF
LO
RF
USB
LSB
IF
LO
Frequency
3
Sampling
Sampler
Digitiser
Filter
IF
N
Sampling Clock
SCLK
USB
LSB
BB
Baseband
IF Frequency
Frequency
4
Digitisation
V0
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Coarse digitisers -gt Quantisation noise S/N
compared to ideal 1-bit digitiser - 66 2-bit
3-level - 82 2-bit 4-level - 88
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Digital Spectrometer Types

• Autocorrelation spectrometer (correlator)
• well established
• Polyphase Digital Filter Bank
• new development

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Autocorrelation spectrometer (Correlator)
Power Spectrum -- Autocorrelation Function
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Digital Correlator
INPUT 1
INPUT 2
0
1
3
2
-1
-3
-2
-4
-5
-6
5
4
7
6
8
9
-----
-7
-9
-8
----
Lag (delay) in samples
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Synthesis Array Correlators

• XF
• For each baseline ( N2 )
• Form cross correlation function
• FT to form spectrum
• FX
• For each signal ( N )
• Form spectrum
• For each baseline ( N2 )
• Multiply corresponding frequencies

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• FX correlator has advantages for large N arrays
• Preferred scheme for SKA - very large N
• Key SKA technology
• Demonstrate in upgrade of ATCA - CABB
• - increase max. bandwidth from 128MHz to 2GHz
• - 2048 channels
• Funded under MNRF2001

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• FX
• For each signal ( N )
• Form spectrum
• For each baseline ( N2 )
• Multiply corresponding frequencies

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Fourier Transform Spectrometer
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Polyphase Digital Filterbank
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• Implemented in FPGAs
• Field Programmable Gate Arrays
• Large commercially available chips containing
  many tens of thousands of re-configurable logic
  cells, plus memory and digital multipliers.
• Clock rates of up to 300MHz.

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Conventional Channelisation
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Filterbank Channelisation
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ZOOM

• Standard

• Zoom

• nZoom

• nZoomm

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Autocorrelator 2-bit bandwidths 4MHz to
128MHz At 4MHz BW - up to 16,000 frequency
channels At 128MHz BW - up to 256 frequency
channels 1-bit bandwidth 256MHz - up to 512
channels Digital Filterbank July 2004 - 256MHz
BW - 1024 channels July 2005 - 600MHz BW - 1024
(2048?) channels Sep 2005(??) - 2GHz BW - 2048
channels Next season - 8GHz - 8192 channels
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Mopra 8GHz DFB Spectrometer
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Polyphase Digital Filter Bank Spectrometer-
using commercial hardware
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ATNF 2 x 2GHz DFB PCB - CABB Prototype
PCB 28,600 Pads 136,000 Track segments 18,800
holes 2,300 components 12 signal layers 9
power layers 17 Xilinx FPGAs Each FPGA 21,000
Logic Cells 1.6Mbit RAM 88 18x18 multipliers 564
I/O signals 1152 pin BGA
12U
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