PXIe Chassis Bandwidth for FPGA

[RyanTheEngineer]

I am specing out the hardware for an FPGA FlexRIO system. The FPGA and adapter module we will use has already been set, a 7975R and a 5782. For our application, we will be streaming 2 analog inputs to an attached RT controller. From my understanding, these samples will be single precision floating point numbers, each of which is 4 bytes a piece. Assuming the max sampling rate of the 5782 is being used, 250 MS/s, I believe I will need 2GB/s of bandwidth on my PXIe chassis.

Here is my question then, what PXIe chassis should I be considering? The PXIe 1082 has "up to 2 GB/s per slot dedicated bandwidth," but is this an actual or theoretical number? Normally I would just get the next highest thing, just to be sure, but there is a considerable price difference in going to the PXIe 1085, which is also much larger than I need. So I would be saving space and several thousand dollars if I could get away with a 1082. Not sampling quite at the adapter modules max would be acceptable, but I would be interested in knowing where about my maximum sampling speed would be.

Thanks in advance for your help.

[David-A · Accepted solution]

The 1082 has more than enough bandwidth to continuously stream data from both of analog inputs of a 5782.  The 5782 has a 14 bit ADC with two channels that sample at 250MS/s. Those samples are returned as an I16 with the two least significant bits padded with zeroes.

So assuming you are transferring the entire I16 rather than packing the 14 bit data, you would have the following bandwidth requirements.

2 channels x 2 bytes/sample x 250 mega-samples/second = 1GB/s

The 1082 has 2GB/s of dedicated throughput per slot.The 7975 can accomodate up to 1.6GB/s of streaming. I'd recommend calling in to chat with someone if you're looking for a recommendation on what type of chassis to purchase, but based on the streaming requirements you're fine with the 7975 and 1082 combo you were thinking about. Just make sure you get a controller that can accomodate the streaming speeds you're looking for. The 8840 is a good candidate.

[RyanTheEngineer]

David-A, I had forgotten that the ADC read the voltage in as an I16. From previous related applications I always immediately change the data type to a single precision floating point to perform mathematical operations. So yes, I can just send the raw I16 readings from the ADC and transfer them!

Thanks so much for your help!