[time-nuts] SMD TADD-1 distribution amplifier

Charles Steinmetz csteinmetz at yandex.com
Sat Dec 19 12:23:19 EST 2015


Li Ang wrote:

>Hi Charles,
>I'm making a 1-to-4 distribution amplifier for 10MHz.  Can you give 
>any suggestion
>The opamps I'm considering are LMH6609 LMH6624 LMH6702.
>Does the piezoelectric effect of capacitors need to be considered here?

I'm working on a response to your questions.  In the meantime, since 
I do not know what you plan to do with your distribution amplifier 
(feed a reference oscillator to several instruments and/or radios to 
keep them on frequency?  feed an oscillator as an input signal to a 
phase noise analyzer or DMTD system to characterize its frequency 
stability?), I'm repeating something I posted in November 2014 for 
you to think about:

>This brings up the distinction between *isolation* amplifiers and 
>*distribution* amplifiers.  Most of us need a [number of] feeds for 
>various test equipment, radios, etc.  These feeds should have 50 ohm 
>output impedance, moderate isolation (35dB or more), and should not 
>noticeably degrade the noise, PN, distortion, or xDEV of the 
>source.  That is the job of a distribution amp.
>
>I would generally [use] some version of a two- or three-transistor 
>Class A buffer amplifier [or an IC-based circuit for this].  There 
>are lots of circuits to choose from.  Many are transformer (or 
>autoformer) coupled, some are not (the JPL circuits come to mind) 
>and can also be used to distribute lower frequencies.  You can get 
>[fanout] the NIST way ([high] buffer amp input impedance so you 
>parallel a bunch of them at the input connector), or by using one 
>stage with low output impedance to drive a number of output 
>amplifiers in parallel, or by using an amplifier with very low 
>output impedance (perhaps a high-current monolithic amplifier) to 
>drive a number of 50 ohm build-out resistors, or by fanning out with 
>CMOS logic and following each CMOS final buffer with a Tee network 
>to [re]generate sine waves.
>
>Then there are the times when you are making measurements of 
>oscillators and must absolutely ensure that there is no interaction 
>between them.  That is the job of an isolation amp[, with isolation 
>of 80dB or more].  Rarely will you need more than two or three feeds 
>per oscillator, so what you need are several, one-to-three iso amps 
>(one for each oscillator).  Here, something like the NIST amplifiers 
>makes sense.

I uploaded a basic tutorial on various distribution amplifier 
topologies to Didier's site, but it is still in the "recent uploads" 
section and not yet available for download.  I'll post again when it 
can be searched and downloaded.

Best regards,

Charles




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