hi gopal, how many spectral channels do you need?
for 800 MHz bandwidth, you can use a pair of asiaa dual adc's at 2Gsps, and get four signal inputs per roach2, and clock the fgpa at 250 MHz. . for 400 MHz bandwidth, i suggest you use a pair of adc16 boards in quad input mode (sample at 960 Msps, four inputs per board), so you can get 8 signal inputs per roach2. fpga clock of 240 MHz. we might have a design for this you can use if you'd like. for 200 MHz bandwidth, i suggest you use a pair of adc16 boards in octal input mode (sample at 480 Msps, eight inputs per board), so you can get 16 signal inputs per roach2. fpga clock of 240 MHz. best wishes, dan On Thu, Mar 20, 2014 at 10:08 AM, Gopal Narayanan <[email protected]>wrote: > Hello Casperites > > I'm looking for advice. We are at the point of launching into a wideband > spectrometer project for building ROACH-2 based spectrometers to handle 32 > independent front-end inputs. This is a conventional spectrometer (no > cross-correlations needed). Our maximum bandwidth needed is 800 MHz. We are > also interested in modes of bandwidth 200 and 400 MHz. I should note that > legacy IF processors with band-limiting filters for the above BWs already > exist, and we are building our spectrometer to these bandwidths. > > I am debating between the KatADC board and the wideband ASIAA 5GSPS ADC > based boards. I ran some preliminary Simulink designs with the KatADC > boards, and I run into timing issues when I use ADC sampling rate > 1200 > MHz. For 1.5 GSPS sampling, the FPGA clock gets up to 375 MHz with the > KatADC, so perhaps this is the issue. I would like to squeeze 4 pixels into > one ROACH-2 if possible. Has anyone run the KatADC close to its maximum > sampling rate with the ROACH-2s? Are plan-ahead and other more advanced > techniques needed for this? > > Alternatively, we could use the ASIAA ADC board, which has a divided-by-8 > for the FPGA clock from the ADC sample rate. Keeping FPGA clock rates at > nominal values might be easier with the ASIAA board, especially when we are > only interested in relatively low sample clocks to 1.6 GHz. We are > considering the 8-bit DMUX 1:1 version of the ASIAA board. > > Any pointers/advice/suggestions in choosing an appropriate ADC board is > appreciated! > > Thanks > Gopal > > > -- > Gopal Narayanan Ph #: (413) 545 0925 > Department of Astronomy e-mail: [email protected] > University of Massachusetts Amherst MA 01003 > >
