[time-nuts] REF osc distribution.

Tom Knox actast at hotmail.com
Wed Sep 5 22:26:04 UTC 2012


Hi Bob;
There are many designs I have seen employed at NIST that have low phase noise and low noise floor.  But it is often not that easy to build a working prototype that actual achieves those levels of performance. power supply design, parts layout, shielding, and part selection all play a substantial role in achieving that level of performance. 

Thomas Knox



> From: lists at rtty.us
> Date: Wed, 5 Sep 2012 18:05:41 -0400
> To: time-nuts at febo.com
> Subject: Re: [time-nuts] REF osc distribution.
> 
> Hi
> 
> The NIST bipolar designs can indeed do better than a good quality OCXO for short term and close in phase noise. If you have a wide band floor at -185 dbc/Hz on your OCXO they aren't quite up to that level. 
> 
> Bob
> 
> On Sep 5, 2012, at 5:55 PM, Tom Knox <actast at hotmail.com> wrote:
> 
> > 
> > I have seen that many commercial ref distribution amps are not as good as a quality low phase noise 5 or 10MHz oscillator, considering the time and resources that went into their design 
> > I think it would be difficult to design a amp capable of distributing something much cleaner then a LPRO.  
> > Thomas Knox
> > 
> > 
> > 
> >> From: lists at rtty.us
> >> Date: Wed, 5 Sep 2012 17:37:34 -0400
> >> To: time-nuts at febo.com
> >> Subject: Re: [time-nuts] REF osc distribution.
> >> 
> >> Hi
> >> 
> >> You *can* get the job done with a CMOS inverter biased up and filtered. An op amp is likely not as good as the full bipolar approach and may be better / worse than the gate depending on exactly what you are looking at.
> >> 
> >> Bob
> >> 
> >> On Sep 5, 2012, at 12:59 PM, Michael Tharp <gxti at partiallystapled.com> wrote:
> >> 
> >>> On 09/05/2012 12:46 PM, Bob Camp wrote:
> >>>> Hi
> >>>> 
> >>>> There are a number of discrete transistor buffers that have very good
> >>>> isolation and short term stability / phase noise performance. I'd take a
> >>>> look at the one from the NIST papers and Bruce's more modern re-design.  All
> >>>> are in the archives. http://tf.boulder.nist.gov/general/pdf/498.pdf is a
> >>>> pretty good place to start.
> >>>> 
> >>>> Mostly what they do is to run a common emitter amplifier followed by several
> >>>> common base amplifiers. They may or may not follow that with a buffer. Each
> >>>> channel gets a separate string of amplifiers. All the common emitter amps
> >>>> are driven in parallel by the reference source.
> >>>> 
> >>>> The transistors used are normally cheap stuff like the 2N3904. Except for
> >>>> the power supply nothing in the circuit costs much. None of it is hard to
> >>>> find.
> >>> 
> >>> For an integrated (op-amp) solution, how does OPA830 stack up? I'm trying one out for a GPSDO design to buffer the signal from the OCXO for 50 ohm output, but I may also build a distribution amplifier at some point.
> >>> 
> >>> At $1.91 for single pieces on Digi-Key it's not terribly expensive, but something cheaper could probably get the job done. There are also dual and quad versions (OPA2830 and OPA4830).
> >>> 
> >>> -- m. tharp
> >>> 
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> >> 
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