Some specifics about ADCs and projects specs

Posted this to the discuss-gnuradio mailing list, but it should be here too:

I suspect the best design method would be to look at the most expensive issues first, make those cheaper and then design the rest around that. The FPGA, ADC and PCB seem to be the most expensive parts right now. I can't say anything about the PCB yet, but the dimensioning of the ADC and FPGA would be an issue of what we can get away with and still have an SDR. The dimensioning of the FPGA depends on the ADC, so the ADC should be the first issue to be dealt with.

A high SINAD and SNR value for the ADC seems to be important at any rate, regardless of bit-count, but those values still seem to be proportional to how many bits of accuracy it has. Low jitter is apparently also important.
The LTC1742 seems attractive in that regard and the price isn't that terrible either, but it's a 14bit device. The ADC12C065 and ADC12DS065 are 12 bits, but I don't know National's price on those. They seem to support undersampling up to 1GHz. If we could use that, we'd have a pretty awesome radio.
Analog Devices' AD9235 is really cheap and seems to support undersampling to 500MHz, which is pretty cool too. More than I need at any rate.

There are of course other manufacturers to consider, but I feel this is a good start at the very least. Gives an idea what we're dealing with.


I think the step after deciding on the ADC would be to dimension the FPGA by deciding what code it needs to run. It will have to deal with a bit of Ethernet, and stuffing all the data from the ADC into the frames. Of course that's not all, but right now it seems that will be its most taxing task, so it should be spec-ed to be able to deal with that. I have no idea what those specs are. Guess I'll have to learn Verilog before I can start guesstimating.