If your hardware is capable of capturing up to 10 millions of timestamps per second and calculating LR "on the fly", it is not a so simple hardware, unless you consider simple hardware a 5megagates Spartan3 (maybe more is needed). Moreover: if your clock is, say, at most in an FPGA, 300MHz, your timestamps will have a one-shot resolution of few nanoseconds. Where have you found a detailed description of the CNT91 counting method? The only detailed description I have found is the CNT90 (not 91) service manual and it uses interpolators (page 4-13 of the service manual).
On Thu, Apr 26, 2018 at 2:45 PM, Bob kb8tq <kb...@n1k.org> wrote: > Hi > > Even with a fast counter, there are going to be questions about clock jitter > and just > how well that last digit performs in the logic. It’s never easy to squeeze > the very last > bit of performance out ….. > > Bob > >> On Apr 26, 2018, at 3:06 AM, Azelio Boriani <azelio.bori...@gmail.com> wrote: >> >> Very fast time-stamping like a stable 5GHz counter? The resolution of >> a 200ps (one shot) interpolator can be replaced by a 5GHz >> time-stamping counter. >> >> On Thu, Apr 26, 2018 at 12:28 AM, Bob kb8tq <kb...@n1k.org> wrote: >>> Hi >>> >>> Unfortunately there is no “quick and dirty” way to come up with an accurate >>> “number of digits” for a >>> math intensive counter. There are a *lot* of examples of various counter >>> architectures that have specific >>> weak points in what they do. One sort of signal works one way, another >>> signal works very differently. >>> >>> All that said, the data you show suggests you are in the 10 digits per >>> second range. >>> >>> Bob >>> >>>> On Apr 25, 2018, at 3:01 PM, Oleg Skydan <olegsky...@gmail.com> wrote: >>>> >>>> Dear Ladies and Gentlemen, >>>> >>>> Let me tell a little story so you will be able to better understand what >>>> my question and what I am doing. >>>> >>>> I needed to check frequency in several GHz range from time to time. I do >>>> not need high absolute precision (anyway this is a reference oscillator >>>> problem, not a counter), but I need fast high resolution instrument (at >>>> least 10 digits in one second). I have only a very old slow unit so, I >>>> constructed a frequency counter (yes, yet another frequency counter >>>> project :-). I is a bit unusual - I decided not to use interpolators and >>>> maximally simplify hardware and provide the necessary resolution by very >>>> fast timestamping and heavy math processing. In the current configuration >>>> I should get 11+ digits in one second, for input frequencies more then >>>> 5MHz. >>>> >>>> But this is theoretical number and it does not count for some factors. Now >>>> I have an ugly build prototype with insanely simple hardware running the >>>> counter core. And I need to check how well it performs. >>>> >>>> I have already done some checks and even found and fixed some FW bugs :). >>>> Now it works pretty well and I enjoyed looking how one OCXO drifts against >>>> the other one in the mHz range. I would like to check how many significant >>>> digits I am getting in reality. >>>> >>>> The test setup now comprises of two 5MHz OCXO (those are very old units >>>> and far from the perfect oscillators - the 1sec and 10sec stability is >>>> claimed to be 1e-10, but they are the best I have now). I measure the >>>> frequency of the first OCXO using the second one as counter reference. The >>>> frequency counter processes data in real time and sends the continuous one >>>> second frequency stamps to the PC. Here are experiment results - plots >>>> from the Timelab. The frequency difference (the oscillators are being on >>>> for more than 36hours now, but still drift against each other) and ADEV >>>> plots. There are three measurements and six traces - two for each >>>> measurement. One for the simple reciprocal frequency counting (with R >>>> letter in the title) and one with the math processing (LR in the title). >>>> As far as I understand I am getting 10+ significant digits of frequency in >>>> one second and it is questionable if I see counter noise or oscillators >>>> one. >>>> >>>> I also calculated the usual standard deviation for the measurements >>>> results (and tried to remove the drift before the calculations), I got STD >>>> in the 3e-4..4e-4Hz (or 6e-11..8e-11) range in many experiments. >>>> >>>> Now the questions: >>>> 1. Are there any testing methods that will allow to determine if I see >>>> oscillators noise or counter does not perform in accordance with the >>>> theory (11+ digits)? I know this can be done with better OCXO, but >>>> currently I cannot get better ones. >>>> 2. Is my interpretation of the ADEV value at tau=1sec (that I have 10+ >>>> significant digits) right? >>>> >>>> As far as I understand the situation I need better OCXO's to check if >>>> HW/SW really can do 11+ significant digits frequency measurement in one >>>> second. >>>> >>>> Your comments are greatly appreciated! >>>> >>>> P.S. If I feed the counter reference to its input I got 13 absolutely >>>> stable and correct digits and can get more, but this test method is not >>>> very useful for the used counter architecture. >>>> >>>> Thanks! >>>> Oleg >>>> 73 de UR3IQO >>>> <1124.png><1127.png>_______________________________________________ >>>> time-nuts mailing list -- time-nuts@febo.com >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >>> _______________________________________________ >>> time-nuts mailing list -- time-nuts@febo.com >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> _______________________________________________ >> time-nuts mailing list -- time-nuts@febo.com >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
