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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