Hi ...and sometimes they leave the Schottkys out.
The original request was not a really low jitter application. I think Jim can get away with an active circuit. Bob -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com] On Behalf Of John Miles Sent: Thursday, December 09, 2010 4:00 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] reference oscillator input circuit > No, actually to feed a bunch of synthesizer chains (for which the sine > wave will work fine) and to drive sampling clocks on ADC/DAC (for which > one wants a low jitter square wave). > > A digital radio... There are some nice residual plots for AC and CMOS chips at http://www.xs4all.nl/~martein/pa3ake/hmode/dds_ad9910_pmnoise.html . Seems like the AD9515 family in PECL mode is about as good as anything is likely to get at VHF. However, why not use the sine wave directly, converted to differential with a transformer and clipped by back-to-back Schottkys? At VHF clock frequencies any active sine-to-square conversion circuit I'm aware of will contribute more jitter than the ADC's own tJ spec. (Put another way, if I'm a semiconductor house designing a high-end ADC or DAC, I am probably going to put all the secret sauce I have into the on-chip clock conditioning, leaving little or no room for improvement outside the chip.) The eval boards from the various ADC manufacturers bear this out. No one puts anything but a 50-ohm SMA jack, transformer and Schottkys on their clock inputs. -- john, KE5FX _______________________________________________ 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.