Hello,
Well, for the CMOS stuff 100ps should do just fine. Of course, less is better, but there's only so much one can reasonably do for so many channels... Even a PICTIC should be able to do better than 500 ps for a single channel. From what I've read, a few hundred units of HP5370 should solve the problem as well, but then there's only so much space...
Indeed, with such a precision, several dozens of TDCs could easily fit into one FPGA chip. The task is to design clever data processing to handle all the events.
We may be able to deliver such a custom product, but you have mentioned your need to save as much money as possible -- it should have be made more precise by means of technical specification to say more about time/price.
I'd be very much interested. 7ps to me seems to be even more than I'd need for the CMOS stuff. Just out of curiosity: Does this work already from 0ps on or is the minimum count higher than that? And what's the limiting factor to accuracy you experience with your current design? Is it actually the FPGA and its properties or something else?
Of course, the 7ps _RMS_ is the jitter of the TDC. The measurement is continuous w.r.t. reference clock, i.e. "0ps" is of course possible.
There is (almost) no other component than the FPGA. So, the limit is indeed the FPGA itself, you may include its power-supplies and comparators, as well.
However, you have been probably asking, how far from the limits imposed bhy single FPGA cell's inherent jitter are we -- this is what I exactly can not answer with certainty, but according to our indirect measurements, best cells of the given FPGA exhibited estimated jitter about 1..3ps, whereas our last complete design has overall 7ps RMS, under the assumption of asynchronous measured signal. Under deterministic worst case, the precision will drop to 21ps abs max. (Note: this last number may be a too pesimistic value; stay tuned for newer revision after soldering recent pcbs).
Feel free to ask more, if you were interested in testing our device. Best regards, Marek _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
