Assuming a transformer coupled input (with biasing via a secondary center tap) why not use a fast differential PECL to CMOS level translator? For example, the IDT ICS508 will take 0.3 to 1.0 V p-p input and give 2.5, 3.3, or 5 V swing on the output. The chip works down to DC and keeps the duty cycle in the 40%-60% window up to 250MHz (at 3.3V out). Jitter and noise is not spec'd however.
To increase the noise immunity with a relatively slow 10MHz sine source I'd look at boosting the amplitude with the transformer, then clipping with balanced series resistors and back-to-back diodes so the translator sees a higher dV/dT on its inputs. Might want to look in some old Motorola ECL appnotes for other possible schemes. Bob ________________________________ From: jimlux <[email protected]> To: Discussion of precise time and frequency measurement <[email protected]> Sent: Wed, December 8, 2010 10:31:08 AM Subject: [time-nuts] reference oscillator input circuit 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.
