Glen English VK1XX writes: > My intention is to use the average of multiple stationary mode GPS > 1PPS signals to drive a single OCXO, the idea to be a better 1pps > estimate. I'll upsample the inputs to get the control sample rate up.
I'd expect a lot of correlation among multiple GPS receivers, especially when they're fed from the same antenna and are otherwise sharing the same environment. Averaging will only deal with the non-correlated errors in the signal. > Eventually I want to explore the use multiple OCXOs, but not until I > think of a good way to take an average of multiple OCXOs, or, even if > that is a useful idea. I think you'll have trouble isolating these well enough to not (at least occasionally) injection lock on each other. > FPGA based, I'll put the OCXO drive and the 1ppS to the FPGA > differentially into maybe 8 FPGA inputs (that is each signal into 8 > different FPGA pin pairs) , and use IDELAY blocks to delay the 8 > different inputs to provide more edge resolution for each signal. There are a few recent papers on that topic and the IDELAY blocks are indeed used in some of these. Getting them to track over voltage and temperature is apparently a problem, so different methods of implementing the TDC seem to be more useful depending on how far down you want to push the resolution. > The IDELAY blocks can be dynamic but I'll probably use then > fixed. output of the FPGA can be sigma-delta converter, which can > provide almost arbritary number of bits. LVDS output of the 1 bit FPGA > converter signal will go to an outboard LVDS buffer with its own power > supply so bumps on FPGA VCCIO dont affect the output. Getting the residual noise down on that signal will still be a challenge, so you might want to (optionally) consider a proper DAC there depending on how good an OCXO you intend to use. Regards, Achim. -- +<[Q+ Matrix-12 WAVE#46+305 Neuron microQkb Andromeda XTk Blofeld]>+ Factory and User Sound Singles for Waldorf Blofeld: http://Synth.Stromeko.net/Downloads.html#WaldorfSounds _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.