I would imagine if you wanted to go to crazy bandwidths you could even use optical transceivers on switches as single bit digitisers...
On Mon, 13 Nov 2023, 14:56 Dan Werthimer, <[email protected]> wrote: > > hi neil, > > paul horowitz, at harvard, had a PhD student who characterized and used > FPGA LVDS inputs as ADC's for a seti experiment. > that thesis is available, and i think there is a publication as well - > paul will know. > > best wishes, > > dan > > > > On Mon, Nov 13, 2023 at 12:48 AM salmon.na via [email protected] < > [email protected]> wrote: > >> Hi Dan, >> >> >> >> Just one further question, in terms of building a single bit >> cross-correlator on an FPGA, exploiting differential LVDS pair for single >> bit digitisation, might there be a suitable reference for this that I can >> include in the paper and an IEEE transaction journal? >> >> >> >> Many thanks, >> >> Neil >> >> >> >> *From:* [email protected] <[email protected]> *On Behalf >> Of *Dan Werthimer >> *Sent:* 11 November 2023 21:52 >> *To:* [email protected] >> *Subject:* Re: [casper] state of the art single bit correlators >> >> >> >> >> >> hi neil, >> >> >> >> i don't think waiting 5 years will help: >> >> there will be faster serdes - the current chips handle ~5 Tbit/sec and >> that will probably double every two years, >> >> but that won't help you because you need other fpga's to convert your >> slow 1 gsps data rate to 100, 200, 400, or 800 Gbit/sec serial. >> >> and the fpga's will have more computing capability. >> >> but i don't think there will be more than 512 LVDS (low speed 1 Gsps) >> inputs, as there's no market demand for that anymore. >> >> there are chips with much higher pin counts (CPUs have 4700 pins), and >> would be easy for AMD or Intel to make an FPGA with more LVDS inputs, >> >> but there's no market. >> >> >> >> best wishes, >> >> >> >> dan >> >> >> >> >> >> >> >> Dan Werthimer >> >> Astronomy Dept and Space Sciences Lab >> >> University of California, Berkeley >> >> >> >> >> >> On Sat, Nov 11, 2023 at 1:39 PM salmon.na via [email protected] < >> [email protected]> wrote: >> >> Hi Dan, >> >> >> >> Those are attractive looking numbers. >> >> >> >> Is it possible to say how that might scale over the next 5-years, will >> the number of pins go up, faster than the processing speed, or the number >> of gate on board? Is it likely to remain I/O bound of compute bound? >> >> >> >> Many thanks, >> >> Neil >> >> >> >> *From:* [email protected] <[email protected]> *On Behalf >> Of *Dan Werthimer >> *Sent:* 11 November 2023 21:30 >> *To:* [email protected] >> *Subject:* Re: [casper] state of the art single bit correlators >> >> >> >> >> >> hi neil, >> >> >> >> for a single frequency channel correlator (continuum correlator), an XF >> architecture (lag correlator) is the way to go, >> >> the number of antennas in your correlator will likely be limited by the >> number of signals you can get into the FPGA. >> >> (the correlator will be I/O bound, not compute bound, assuming you have a >> large FPGA). >> >> >> >> i haven't looked at the number of LVDS inputs available on a large FPGA >> recently, >> >> but i think for a ~1800 pin package, there might be up to ~~512 LVDS >> pairs (1024 pins). >> >> if so, you can have 512 digitizers, which is 256 complex digitizers, >> which is 128 antennas dual pol, or 256 antenna single pol. >> >> >> >> as david hawkins suggested, could also use the high speed serdes on the >> FPGA. >> >> the new pricy FPGAs have serdes that can work at >100 Gbps. >> >> and the larger pricy FPGAs have 32 of these serdes, which means you can >> send 3.2 Tbits/sec into those FGPAs. >> >> that data rate is 3200 real 1Gsps bit streams, or 1600 complex streams >> at 1Gcomplexsamples/sec, or 800 antennas dual pol. >> >> but it would take a lot of electronics to convert 100 1Gbit/sec signals >> into a 100Gbit/sec signal - >> >> the easiest way to convert 100 signals into a single 100Gsps signal would >> be to use an FPGA, >> >> and that would defeat your goal of using a single FPGA for your >> correlator. >> >> >> >> >> >> best wishes, >> >> >> >> dan >> >> >> >> >> >> >> >> On Sat, Nov 11, 2023 at 12:43 PM salmon.na via [email protected] >> <[email protected]> wrote: >> >> Thanks Dan, >> >> >> >> Yes, one antenna for one receiver, and there is only one frequency >> channel, and a single polarisation, so quite a simple configuration. >> >> >> >> A good idea to use differential inputs as single bit ADCs. >> >> >> >> So the FX correlator looks the better architecture. >> >> >> >> So are you saying the FPGA FX correlator would manage making the >> cross-correlations of 512 single bit channels at 1 GbpS, on say a single >> FPGA, Xilinx or Altera ? >> >> >> >> Cheers, >> >> Neil >> >> >> >> *From:* [email protected] <[email protected]> *On Behalf >> Of *Dan Werthimer >> *Sent:* 11 November 2023 20:23 >> *To:* [email protected] >> *Subject:* Re: [casper] state of the art single bit correlators >> >> >> >> >> >> hi neil, >> >> >> >> by number of receiver channels, i presume you mean number of antennas? >> >> are these single or dual polarization? >> >> >> >> how many spectral channels do you need in your correlator ? >> >> >> >> for a large number of spectral channels, >> >> you'll likely want to use an FX architecture correlator (not XF). >> >> in an FX correlator the number of ADC bits doesn't change the FPGA >> utilization for the DSP very much. >> >> >> >> one fun thing you can do with a 1 bit correlator, is use the LVDS >> differential inputs on the FPGA as 1 Gsps digitizers. on a large FPGA >> with a lot of pins you can get about 512 ADC's >> >> (256 antennas, dual pol) built into the FPGA, so the FPGA can be your >> digitizer and your correlator... >> >> >> >> if you only need a small number of spectral channels, you could build an >> XF correlator >> >> with ~512 inputs... (~256 antennas, dual pol, or ~512 antennas single >> pol) in a large FPGA. >> >> >> >> with an XF architecture, the FPGA utilization is J x >> number_of_spectral_channels. >> >> for FX, the utilization goes as K x log_base_2(spectral_channels). >> >> >> >> but constant K >> constant J, >> >> so sometimes (rarely) it is better to use XF, depending on the number of >> spectral channels. >> >> >> >> >> >> best wishes, >> >> >> >> dan >> >> >> >> >> >> >> >> On Sat, Nov 11, 2023 at 11:47 AM salmon.na via [email protected] >> <[email protected]> wrote: >> >> For a paper on non-radioastronomy aperture synthesis technology I need to >> know how many receiver channels can run into an almost top of the range >> FPGA optimally designed single-bit cross-correlator running a 2 Gbps. So >> each receiver is digitised (sine and cosine) in single bits 1 Gbps. I’m >> wondering if there are scaling laws for this and I only need to have a ball >> park figure, ie a precision of say a factor of three or thereabouts. Any >> associate papers related to that which might have clues to the capabilities >> would be helpful. >> >> >> >> Many thanks, >> >> Neil Salmon >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/005601da14d7%24ede171b0%24c9a45510%24%40tiscali.co.uk >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/005601da14d7%24ede171b0%24c9a45510%24%40tiscali.co.uk?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vEdvQAJ9Q5-JOAS1QfJ%3DW8AfQMU9D48cnt_gQ56GA%3DqiA%40mail.gmail.com >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vEdvQAJ9Q5-JOAS1QfJ%3DW8AfQMU9D48cnt_gQ56GA%3DqiA%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/007b01da14df%24a643ba90%24f2cb2fb0%24%40tiscali.co.uk >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/007b01da14df%24a643ba90%24f2cb2fb0%24%40tiscali.co.uk?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vFWXdUnAua1mOU4Tu1VdcaZxRo8jSODooXY-GHeoWmusA%40mail.gmail.com >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vFWXdUnAua1mOU4Tu1VdcaZxRo8jSODooXY-GHeoWmusA%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/009b01da14e7%2481a31340%2484e939c0%24%40tiscali.co.uk >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/009b01da14e7%2481a31340%2484e939c0%24%40tiscali.co.uk?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vEMcdROb%3D%2B-Xmr9XfN%3DT7c6uM3RFnhA99%3DYfA9YR-QBiQ%40mail.gmail.com >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vEMcdROb%3D%2B-Xmr9XfN%3DT7c6uM3RFnhA99%3DYfA9YR-QBiQ%40mail.gmail.com?utm_medium=email&utm_source=footer> >> . >> >> -- >> You received this message because you are subscribed to the Google Groups >> "[email protected]" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to [email protected]. >> To view this discussion on the web visit >> https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/000401da1603%249e525600%24daf70200%24%40tiscali.co.uk >> <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/000401da1603%249e525600%24daf70200%24%40tiscali.co.uk?utm_medium=email&utm_source=footer> >> . >> > -- > You received this message because you are subscribed to the Google Groups " > [email protected]" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vH8Z0O--L%3DGZP-zo1-iTSAms4A64GCS3xxg_f2FpMJEZQ%40mail.gmail.com > <https://groups.google.com/a/lists.berkeley.edu/d/msgid/casper/CAGHS_vH8Z0O--L%3DGZP-zo1-iTSAms4A64GCS3xxg_f2FpMJEZQ%40mail.gmail.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "[email protected]" group. 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