Dan, Thanks for your good points and others who have helped.
You’re indicating I should perhaps go for a new design (instead of using Roach – presumably due to high data + computation rate). So I’ll check out Simulink or HDL to see how many FPGA I’ll need. However, I still need to sort the single bit samplers using the serial input, but could find Paul Horowitz’s write on this on the Casper site. Also if I’m going to have to design a board to fit all these 300 receiver channels on at 3 GHz, with I&Q downshifters, interface to the FPGA, could you recommend any software that I should use to design these boards? Thank you again for help. Neil From: dan.werthi...@gmail.com [mailto:dan.werthi...@gmail.com] On Behalf Of Dan Werthimer Sent: 18 December 2015 17:31 To: Neil Salmon Cc: James Smith; casper@lists.berkeley.edu Subject: Re: [casper] building 300-receiver channel cross-correlator hi neil, as john pointed out, you can use the differential inputs of an FPGA as a 1 bit ADC if you'd like. there's a nice write up on this by paul horowitz and his students who used xilinx fpga's as adc's. if you want to use the fpga as the digiitzers, you will need 600 LVDS inputs at 300 Msps, which means 600 pairs, or 1200 pins. i think some of the larger fpga's will do this - you'll need to check. (eg: a virtex ultrascale). or you could split up the data over several chips (see below): a larger problem is that you need 300^2/2 complex 1 bit multipliers and accumulators. that probably will not fit on a single FPGA. you might need to break this into four FPGA's. i suggest you develop a complex multiplier accumulator in simulink or HDL, and plunk down 300^2/2 of them, and compile them into a large ultrascale FGPA and see if it will fit into 1 fgpa? or 4? or 9? or 16? best wishes, dan On Fri, Dec 18, 2015 at 8:23 AM, Neil Salmon <n.sal...@mmu.ac.uk<mailto:n.sal...@mmu.ac.uk>> wrote: Thank you for your response. The system is part of a generic microwave/mm-wave aperture synthesis imaging system, so there’s an array of front-end heterodyne receivers with an IF earmarked at a centre frequency of 3 GHz (away from Wifi mobile comms), but the bandwidth is 300 MHz. Front-end initially may be receiving at a centre frequency of 20 GHz, but I could change this to 10 GHz or go up to 35 GHz. (I’ll be taking a single polarisation say horizontal or right-hand circular – I’ve not decided yet) Either way, I’ll need to digitise this 300 MHz bandwidth on each channel, and I’m quite happy with the loss in SNR in using a single bit digitisation, so satisfying the Nyquist criterion there will be I & Q channels, each generating a data stream at 300 M samples per second, ie a total of 600 Mbps for both I&Q per receiver channel, giving the total data rate of 180 Gbps. (sampling clock and mixing LO’s will be synched to a master oscillator) (as for the 3 GHz centre frequency the I&Q digitisation could be bandpass sampling/digital down conversion or a second analogue downshift using a matched pair of mixers and then comparators in each section to generate I and Q digits) So there will be this huge rate of I & Q data from 300 channels that needs to be cross-correlated in real-time with 95% duty cycle to avoid loss of SNR. (software correlation would generate just too much data for harddisk and a GPU PCIe bus solution couldn’t cope with the data rate – or at least I’d be uncomfortable about working close to data rate ceilings of PCIe.) That leaves the FPGA solution. So I need some high speed data bus to get the data into the FPGAs for cross-correlation. As I’m working single bits XOR gates will do nicely for the cross-multiplies and I want to store the four components of the cross-multiply in separate registers, just for diagnostic / trouble shooting. This gives the XOR op rate 54 T ops/sec and the requirement for the 180,000 accumulation registers. For me the challenges with be getting the arrays of single bit digitisers and linking them to the cross-correlators and doing the cross-correlation at this huge rate. Build of analogue front end heterodyne array and image formation algorithms I’ve done before. It’s just the digital hardware I need to sort. I’ve got a few researchers and postgrads around me in the engineering department who have general educational interests in FPGA technologies and the Xilinx and Altera University representative support under the university agreement. So I’m just wondering if I can do this with the Casper tools or others if necessary. Hope this extra information help. Many thanks for your help. Neil From: James Smith [mailto:jsm...@ska.ac.za<mailto:jsm...@ska.ac.za>] Sent: 18 December 2015 14:25 To: Neil Salmon Cc: casper@lists.berkeley.edu<mailto:casper@lists.berkeley.edu> Subject: Re: [casper] building 300-receiver channel cross-correlator Hello Neil, CASPER tools could probably do what you're looking for, but I found your description a bit confusing. You're going to need to clarify somewhat. Regards, James On Fri, Dec 18, 2015 at 4:15 PM, Neil Salmon <n.sal...@mmu.ac.uk<mailto:n.sal...@mmu.ac.uk>> wrote: Anyone help? I’m working in academia and need to build a 300-receiver channel single-bit digitiser / cross-correlator with a single frequency channel having a bandwidth of 300 MHz, centre frequency ~3 GHz. The single bit digitisers sample I&Q giving a total data rate of 180 Gbps and using XOR gates to do the cross-correlations, the total computation rate is 54 T XOR operations per second. I need to accumulate cross-correlations typically for times ranging from 10 ms to a few seconds. The system would comprise an array of single bit digitisers linked via a high speed data bus to FPGA boards for the cross-correlation/accumulation. I’ve no skills in board design but could probably learn VHDL. I don’t have funding to commission a design and build but wondered if anyone in this community could advise how I should go about building this system at our university. Thank you for any help you can provide. Neil "Before acting on this email or opening any attachments you should read the Manchester Metropolitan University email disclaimer available on its website http://www.mmu.ac.uk/emaildisclaimer " "Before acting on this email or opening any attachments you should read the Manchester Metropolitan University email disclaimer available on its website http://www.mmu.ac.uk/emaildisclaimer " "Before acting on this email or opening any attachments you should read the Manchester Metropolitan University email disclaimer available on its website http://www.mmu.ac.uk/emaildisclaimer "
