Hi Ross, I am commenting this older thread prompted by your most recent message re DMUX1:2 ADCs, to which Homin responded today.
Your approach, and the advice received from Dan and Glenn, is sound---in principal. With suitable bit codes, you can run DMUX1:2 4-bit versions of the ASIAA ADC at full rate, in dual channel 2.5 GSa/s mode, hosted on a ROACH1. And with two ADC boards installed you can enable four such 2.5 GSa/s input channels on ROACH1. Whether the ROACH1 can process the four channels with Virtex 5 resources of course depends on what you want to do, Dan gave one benchmark. We have a PFB resource utilization memo which may be able to help you. There is a caveat, however: my group is among a few CASPER collaborators who are doing wideband correlator design using ASIAA 5 GSa/s ADCs. We decided some time ago to standardize on using the 8-bit DMUX 1:1 version of the ADC supported by ROACH2. In our case we without question needed the computational resources of Virtex6-SX475, so the higher GPIO interface speed (translates to Z-DOK speed) in some sense came for free. Though we could probably meet our requirements with fewer than 8-bits, there was no penalty for enabling them by using the DMUX1:1 board. A consequence of this is that all our developments and contributions to the CASPER open source infrastructure support this configuration (8-bit and ROACH2). In brief we have contributed yellow block work, ADC characterization, and resource calculations for PFBs. Now, we are not the only ones doing this kind of work, and much of what we do is probably transferable to the ROACH1 and 4-bit case. However, at least from my biased perspective, you may find the ROACH2 8-but case to be better supported, and thus the hardware cost savings through using ROACH1 may prove to be false economy. The 4-bit and 8-bit ADCs are equal in cost. (By the way the 8-bit ADC board can be used on ROACH1 but you would be limited to 1.8 GSa/s per channel or 3.6 GSa/s per ADC board.) All that said, I have a few DMUX1:2 ADCs sitting in the lab fully assembled, working, and unused, and I would be happy to loan these to you. Actually they probably belong to Homin / ASIAA, so I guess subject to his ok. Our wideband developments are documented on a public Wiki: https://www.cfa.harvard.edu/twiki/bin/view/SMAwideband Dig down for ADC characterization and our resource memo. Cheers, stay in touch. Jonathan Weintroub CfA +1-617-495-7319 On Feb 12, 2013, at 4:09 PM, Ross Williamson wrote: > Hi Dan and Glenn, > > All sounds good - I think have the ROACH-1 design will help us out a lot here > to get started. We really don't need a very high spectral response as we are > just trying to measure the amplitude and phase of a PSFs wings referenced to > the central core of the PSF. > > Cheers, > > Ross > > On Tue, Feb 12, 2013 at 1:05 PM, G Jones <glenn.calt...@gmail.com> wrote: > Note that the design Dan is referring to currently has only been > tested to ~1.5 GHz BW. Getting to higher bandwidths will likely > require some work to meet timing. Also the data comes out over 10 > gigabit Ethernet so requires something to catch the data. > > On Tue, Feb 12, 2013 at 4:02 PM, Dan Werthimer <d...@ssl.berkeley.edu> wrote: > > > > hi ross, > > > > how many frequency channels do you need in your two input correlator? > > > > we have a full stokes VEGAS 1K channel spectrometer design > > that uses a pair of ADC08-5000's. > > (a full stokes spectrometer is the same thing as a two input correlator) > > > > our current design is for roach2, but we had tested working designs > > for roach1 last year, and we can probably dig these up. > > > > best wishes, > > > > dan > > > > > > On Tue, Feb 12, 2013 at 12:53 PM, Ross Williamson > > <rwilliam...@astro.caltech.edu> wrote: > >> > >> Hi All, > >> > >> I'm new to CASPER/ROACH boards and so apologies if this is obvious. We > >> are hoping to build a simple 2-channel correlator with a fairly high > >> bandwidth. We are in the process of ordering a ROACH-1 board and I was > >> thinking of also purchasing the ADC1X5000-8 ADC - A few questions: > >> > >> 1) Should I even be looking at an ADC1X5000-8 for use as a correlator? > >> 2) I believe I need the DMUX 1:2 version to work with ROACH-1 board - is > >> that correct? > >> 3) I should be able to run 2 channels at 2.5GHz 4bits with a single board > >> - correct? > >> 4) If I wanted to could I purchase another ADC1X5000-8 and try and run > >> with 5GHz bandwidth on each channel using the ROACH-1? > >> > >> Best regards, > >> > >> Ross > >> > >> -- > >> Ross Williamson > >> Research Scientist - Sub-mm Group > >> California Institute of Technology > >> 626-395-2647 (office) > >> 312-504-3051 (Cell) > > > > > > > > -- > Ross Williamson > Research Scientist - Sub-mm Group > California Institute of Technology > 626-395-2647 (office) > 312-504-3051 (Cell)
