On a somewhat related note, does any one have any information as to the likely performance impact of using a single logic gate to convert a sine wave to a pseudo square wave ? (I discovered one of my scopes doesn't consistently accept a sine wave time base input, thru trial and error and rummaging thru my junk box I ended up using a 74ALS00 Nand gate to convert a 10 mhz sine wave into a somewhat square wave (: which the scope will reliably use as a reference input.) Extreme accuracy is not really needed in this application but I am curious how much jitter I may have introduced.
I'll likely try one of the circuts in the attached link at some point. Best regards Mark ----- Original Message ---- From: John Ackermann N8UR <[email protected]> To: Discussion of precise time and frequency measurement <[email protected]> Sent: Wed, December 8, 2010 7:46:12 AM Subject: Re: [time-nuts] reference oscillator input circuit Wenzel has some discussion and circuits at: http://www.wenzel.com/documents/waveform.html. The Shera GPSDO made clever use of the input circuit of a 74HCT4046 PLL chip for squaring. John ---- On 12/8/2010 10:31 AM, jimlux wrote: > I'm looking for suggestions on a general circuit that can be used to > receive an external frequency reference (nominally a real clean sine > wave at, say, 10 MHz, although up to 100 MHz is possible) and turn it > into a "real clean" square wave. Galvanic isolation is a plus (a > transformer or capacitor would probably do that). > > I was thinking about rummaging through the schematics for test equipment > reference inputs (since they've already "solved" the problem, eh?), but > any other ideas would be welcome. > > I've scanned the archives of time-nuts, and while we have a fair amount > of discussion on how to square up the 1Hz (or 100Hz) in a phase > noise/ADEV setup, not so much on what to do with the 10 MHz. Rick has > commented that you don't want to use a comparator. I have the papers by > Dick, et al, and Collins, as well as all the others.. they tend to be > looking at the low frequency problem, although the analysis is certainly > applicable. > > I don't know that I'm looking for the whole multiple limiting stages > scheme in any case. > > Oh, as far as performance.. Say the need is to not horribly degrade a > good quality crystal oscillator... here's a typical set of specs: > 76 MHz > 1Hz <-90dBc > 10Hz <-110dBc > 100Hz <-120dBc > 1k-100k <-125dBc > > Adevs of the oscillator run from 5E-12 at 0.1 sec, down to 1E-12 at 10 > sec, and back up to 2 E-12 at 1000sec. > > _______________________________________________ > 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. _______________________________________________ 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. _______________________________________________ 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.
