1. The Correlators ( Spectrometers ) Mopra Induction - May 2005

2. Frequency Conversion Mixer RF LO IF Frequency USBLSBIFLO RF

3. Sampling Sampler IF Sampling Clock IF Frequency USBLSB Baseband SCLK Digitiser N BB Frequency Filter

4. 00 10 01 11 V=0 Digitisation

5. Coarse digitisers  Quantisation noise S/N compared to ideal: 1-bit digitiser - 66% 2-bit 3-level - 82% 2-bit 4-level - 88%

6. Autocorrelation spectrometer (correlator) - well established Polyphase Digital Filter Bank - new development Digital Spectrometer Types

7. Power Spectrum -- Autocorrelation Function Autocorrelation spectrometer (Correlator)

8. Digital Correlator C C CCCCCCCCCCCCCCCCCCC 0+1+3+2-3-2-4-5-6+5+4+7+6+8+9------7-9-8---- Lag (delay) in samples INPUT 1INPUT 2 C = multiply and accumulate

10. Synthesis Array Correlators XF –For each baseline ( ~N 2 ) : Form cross correlation function FT to form spectrum FX –For each signal ( ~N ) : Form spectrum –For each baseline ( ~N 2 ) : Multiply corresponding frequencies

11. 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

12. FX –For each signal ( ~N ) : Form spectrum –For each baseline ( ~N 2 ) : Multiply corresponding frequencies

13. x 0 (m) x 1 x ρ x M-1 (m) x n M-Point DFT via FFT 0 1 ρ M-1 X 0 (m) X 1 X k X M-1 Fourier Transform Spectrometer

14. Polyphase Digital Filterbank

15. 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.

16. Conventional Channelisation

17. Filterbank Channelisation

18. Standard Zoom n*Zoom n*Zoom^m ZOOM

19. 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

20. Mopra 8GHz DFB Spectrometer DIGITAL FILTER BANK DIGITAL FILTER BANK SAMPLER DIGITAL FILTER BANK DIGITAL FILTER BANK SAMPLER 4-12 GHz IF from mm Receiver Vertex Room Control Room IF UNIT E/O 4 * ( 2GHz BW, 2048 ch. )

21. Polyphase Digital Filter Bank Spectrometer - using commercial hardware

22. 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 ATNF 2 x 2GHz DFB PCB - CABB Prototype 12U