[time-nuts] Advice on 10 MHz isolation/distribution /Phase Noise of 74AC gates (John Miles)
GThorp at pascall.co.uk
Fri Feb 26 16:59:41 UTC 2010
Your results look very interesting. The big variation with input level
shows how important it is to get that right. Incidentally, I didn't
blame the CMOS for the 1/f^3 slope, as that was 18dB below the OCXO's
phase noise. The divider output dominated from ~100Hz outwards, and
showed 1/f slope down to the noise floor. (The E5052 doesn't do added
I suspect that the input and output interfaces are the main barriers to
achieving the potential performance. The switching threshold is roughly
proportional to Vcc, so with a finite slew rate, the supply pin acts as
a jitter modulator. The common practice of using a Schmitt input to
square up a sine wave is likely to make things worse if anything.
Increasing the slew rate with a non-saturating limiter is probably the
best approach. (My measurement benefitted from starting at 100MHz where
the slew rate is inherently 10 times as high.) Supply noise will
amplitude modulate the output, which can also cause problems, depending
on the AM-to-phase mod conversion factor of whatever it's driving into.
Pascall Electronics Ltd - Registered in England No: 1316674 VAT Registration No: GB 448705134 Registered Office: Brunswick Road, Cobbs Wood, Ashford, Kent, TN23 1EH
The transfer of any controlled technology contained in or attached to this email is covered by the "Open General Export Licence (Technology for Military Goods)", granted by the United Kingdom Secretary of State.
The information contained in this email is provided as a personal communication of the sender and, as such, is not binding on Pascall Electronics Ltd. unless the intended recipient has been notified by signed postal or fax communication that the sender is authorised to commit Pascall Electronics Ltd. on the subject matter concerned.The contents of this email are confidential to the intended recipient at the email address to which it has been addressed. It may not be disclosed to or used by anyone other than this addressee, nor may it be copied in any way. If received in error, please contact Oli Poole, at opoole at pascall.co.uk, quoting the name of the sender and the addressee and then delete it from your system.
More information about the time-nuts