[time-nuts] REF osc distribution.

Bob Camp lists at rtty.us
Wed Sep 5 21:37:34 UTC 2012


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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