[time-nuts] Phase Noise of 74AC gates

Bruce Griffiths bruce.griffiths at xtra.co.nz
Sat Feb 20 01:58:44 UTC 2010

life speed wrote:
>> From: "Martyn Smith"<martyn at ptsyst.com>
>> Subject: [time-nuts] Phase Noise of 74AC gates
>> I'm not about to say how we achieve -170 dBc/Hz phase noise, but we
>> definitely don't use op amps or logic gates!!
>> Regards
>> Martyn
> Is this an advertisement?  I don't think anybody believes a logic gate provides state-of-the-art reference buffering.
He's made similar comments before.
It actually isnt that difficult to achieve an isolation amplifier phase 
noise floor below -170dBc/Hz if one is careful to use appropriate parts, 
design techniques, and the input signal level is high enough.
The real problem is verifying that performance.

The only way to achieve a phase noise of -180dBc/Hz at 10kHz offset from 
a 74AC04 output is to use a narrow bandpass filter with steep skirts.
The associated filter phase shift tempco will be relatively large.


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