Well, it depends on trace width matching. We can simulate and characterize it even at much higher frequencies. If we place them really close to the DAC and match widths, remove grounds under pads, we can match it not worse than SMA connectors. We can even do even more crazy thing - try to make them mountable. The only signals that would need to be transmitted is DAC output / ADC input. We can use low profile board to board connectors for rest of the signals - I know ones that have 1mm stacking hight. For RF we could use PCB mounted UFL connectors. This is just crazy idea that need to be verified.
On 30 March 2016 at 23:02, Slichter, Daniel H. (Fed) < daniel.slich...@nist.gov> wrote: > This is an interesting potential solution although I am not sure how the > signal integrity is at ~3 GHz, for example. > > > > *From:* Grzegorz Kasprowicz [mailto:kaspr...@gmail.com] > *Sent:* Wednesday, March 30, 2016 2:44 PM > *To:* Slichter, Daniel H. (Fed) <daniel.slich...@nist.gov> > *Cc:* Grzegorz Kasprowicz <gkasp...@elka.pw.edu.pl>; Leibrandt, David R. > (Fed) <david.leibra...@nist.gov>; Sébastien Bourdeauducq <s...@m-labs.hk>; > artiq@lists.m-labs.hk > *Subject:* Re: [ARTIQ] FW: initial specification of the project > > > > Such assembly technique is called: > > castellated PCB module > > https://www.google.pl/search?q=castellated+RF+modules&biw=1920&bih=917&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjRvuqko-nLAhWnnXIKHe_IARsQ_AUIBygB > <https://www.google.pl/search?q=castellated+PCB+down+converter+modules&biw=1920&bih=917&source=lnms&tbm=isch&sa=X&ved=0ahUKEwj19L7younLAhUKvXIKHQVBCg8Q_AUIBigB#tbm=isch&q=castellated+RF+modules> > > > > On 30 March 2016 at 22:40, Grzegorz Kasprowicz <kaspr...@gmail.com> wrote: > > One more thing - we can fit 5 SMA connectors on FMC panel, in case of 6 > ones, we won't be able to screw them. > > But we can install MMCX ones for clocks and fit in total of 7 RF > connectors, > > Look here > http://www.ohwr.org/attachments/3390/fmc_top.jpg > > Greg > > > > On 30 March 2016 at 22:38, Grzegorz Kasprowicz <kaspr...@gmail.com> wrote: > > Well, we can do another crazy thing - solder small module with RF stuff on > the FMC board, under same shield. > > In this way we keep 3 simple FMCs with expensive ADCs/DACs and define the > functionality by soldering (automatic or manual) of just RF modules. WE can > even design such modules to hold the front-end connectors of leave them on > the FMC. > > Such approach has also some attractive feature - we can make them using > small pieces of Rogers material which is hell expensive and it's hard to > make small vias and thin traces needed for JESD signals. > > these modules could look like that > http://www.emcfastpass.com/wp-content/uploads/2014/09/rf_module_holes.gif > > You can mount them by pick and place or manually. > > IT is also possible to manually disassemble them. > > This is a form factor of popular RF modules, i.e. wifi, GPS and LTE modems. > http://www.emcfastpass.com/rf-modules/ > > And is simply works > > Greg > > > > > > On 30 March 2016 at 22:25, Slichter, Daniel H. (Fed) < > daniel.slich...@nist.gov> wrote: > > > Maybe we should come back to the roots:) What if we use standard FMCs > > (LPC) with DAC/ADC channels and RF stuff _on_ them. > > JESD204B and some pins would go to the FPGA while DAC and RF clock would > > be fed externally. > > In this way we leave general purpose AMC board and define its > functionality > > by FMC boards If we make 3 flavours of FMCs: ADC+ADC, > > ADC+DAC,DAC+DAC, we would cover several use cases: > > Quad ADC, quad DAC, 1xADC 3xDAC, 3xADC 1xDAC. > > FMCs with only DAC and RF stuff on it can be simple, 4 layer boards with > > external sield. > > Look at this shield (my project) > > http://www.ohwr.org/projects/fmc-adc-130m-16b-4cha/wiki > > In this way we could use existing AFCK for quick tests > > We have been working with the notion that should be many possible front > ends for each of the DACs or ADCs, depending on what the particular > application is, and so we want to separate the analog daughtercards from > whatever board has the DACs and ADCs on it. This way, you can reconfigure > the hardware for high-frequency or low-frequency applications, for example, > by changing daughtercards and not having to build entire new AMC cards. > The modularity principle lets one have a single design for the AMC card > (aka DSP card) that can be used for many different applications, by > shifting the analog signal processing circuitry onto a separate card. > > Now, as you suggest we could just change the level at which we make this > break from the AMC card, shift the DACs and ADCs onto the daughter card as > well, and use FMC to communicate with the whole thing. This makes it a bit > more expensive/difficult to reconfigure the analog front end, but the DAC > and ADC costs are not so high that it is impossible to do. I had > envisioned the notion of making the daughtercards simple enough that end > users could redesign/respin easily to accommodate their own applications, > or we could ship unstuffed or partially stuffed boards that they could > complete with the particular filters etc they desire. > > However, I agree that there are compelling arguments for using the > architecture you propose. We would need to pick just a few board styles (I > suggest quad DAC, 2 DAC/2 ADC, and quad ADC), and for each of these board > styles we would need to make several different variants with different > analog front ends (3 types for DAC - low frequency, baseband RF, > upconverted RF - and 2 types for ADC - baseband RF and downconverted RF, > both likely including switchable gain). So now we are looking at making 3 > types of quad DAC boards, 2 types of ADC board, and probably 3 types of > DAC/ADC board (upconvert DAC/downconvert ADC, baseband RF DAC/baseband RF > ADC, and low frequency DAC/baseband RF ADC). So now there are 8 different > daughterboard designs. If we restrict ourselves to just quad DAC or quad > ADC on a given daughtercard, then there are 5 designs, same as in the > current proposal for analog-only daughtercards. I would still want to have > boards be partially stuffed (or stuffed in different configurations on > demand) to allow users to choose the frequencies of interest for analog > filters etc. > > If we proceed this way, we will need an external clock SMA for each FMC > module, because we don't want the high-quality external clock going down > one FMC connector, across the AMC, and up the other FMC connector for > signal integrity/crosstalk reasons. > > Are we thinking we would try to implement the actual VITA 57 standard on > these connectors? Or just use them as convenient high-speed-capable > connectors? I agree with the second idea, but I don't like the first one. > > > > > > >
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