> > * we want to avoid RTMs and instead put the DAC/ADCs on the AMC card > > and have analog plug-ins using the FMC form factor (see my document). > > **Are you sure you would get noise performance from such setup that > > satisfies you? > > Unless the FMC connector is particularly bad with analog signals, I think it > should not be worse than the current hardware.
I want to repeat what Sebastien has said, that we want the signals to come out the front, and to avoid the use of RTMs as the standard output. There may be some special use cases (e.g. many channels of slow ADC) that *might* work with the RTM architecture, but for the DSP AMC cards we want all the DACs on the AMC card and their outputs routed immediately to the small RF/analog daughter cards. I want to stress again that the levels of channel crosstalk relevant to quantum information/optical clock experiments are vastly more stringent than for typical signals propagating through large "high-speed" connectors. I think it will be necessary to use minimal length unshielded traces and have multi-cavity shielding on the daughtercards to ensure low crosstalk. The use of a connector like an FMC, even with grounding wires between differential pairs, is inevitably going to be worse than using dedicated board-to-board RF connectors like SMP/GPO or their smaller cousins GPPO/G3PO. These connectors are explicitly designed for these types of applications, and allow for board misalignments etc. The cost savings from using FMC, which might amount to $50 per AMC, are not worth if the crosstalk will make the cards not useful for researchers. For reference, Samtec offers an intermediate solution called Isorate, which is designed to have higher isolation than typical high speed connectors while being cheaper than SMP. They spec 80 dB isolation at 1.3 GHz and 70 dB at 7.6 GHz, so probably we are talking between 90 and 75 dB isolation in our frequency range of interest for RF/microwave signals. Best, Daniel _______________________________________________ ARTIQ mailing list https://ssl.serverraum.org/lists/listinfo/artiq
