[time-nuts] REF osc distribution.

[Bob Camp]

Hi

There's actually a prior paper on the "figure 1" amp.

Bob

On Sep 5, 2012, at 6:38 PM, David <davidwhess at gmail.com> wrote:

> It is even more difficult when the schematic is wrong like in figure 1
> where the emitter and collector of the PNP are reversed.
> 
> On Wed, 5 Sep 2012 16:26:04 -0600, Tom Knox <actast at hotmail.com>
> wrote:
> 
>> 
>> 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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