[time-nuts] Replacement High-Speed AOP for Distribution Amplifier

Bruce Griffiths bruce.griffiths at xtra.co.nz
Mon Apr 6 22:29:24 UTC 2009


Samuel

Wideband oapmps should only used in distribution amplifiers when their
inferior flicker phase noise and phase noise floor characteristics are
acceptable.
One can easily achieve a far lower flicker and broadband phase noise
floor using discrete components rather than opamps.
Even the simple discrete component buffers used in some Austron
frequency standards will have better phase noise characteristics than an
opamp based distribution amplifier.

If you decide to use opamps you need to look at:

1) Slew rate
2) Distortion at the anticipated output level and frequency.
3) Opamp input noise both in the flicker region as well as at high
frequency.

Using an input step up transformer can be helpful in reducing the phase
noise of an opamp based distribution amplifier.
It is also advisable to use a very low noise power supply as power
supply noise will modulate the opamp RF phase shift thereby increasing
the flicker phase noise level.

Bruce

Samuel D. [x86/CPC] wrote:
> Hi there,
>
> I'm working on a new GPS-Disciplined Rubidium Frequency Standard and I'm now
> designing the distribution amplifier stage. There is many schematics
> everywhere on the Internet, the most famous is the TADD-1 reviewed by the
> not-less-famous TVB. Almost all of them use high-speed Op Amps originally
> designed for video processing. The most common AOP are the MAX477 (used in
> TADD-1) and the MAX4135. Unfortunately, both of them are now obsolete and
> will be discontinued soon. I checked Digikey and Farnell, but those parts
> are not available anymore, so, I'm looking for an equivalent (or better!)
> replacement. 
>
> Any hints ?
>
> PS : A French member of that list, Daniel, contacted me some weeks ago. Due
> to a corrupted Outlook file, I lost your contact and wasn't able to keep in
> touch with you. Please send me an email if you read this ;)
>
> ---------------------
> Samuel DEMEULEMEESTER
> Presse Non Stop - Canard PC
> http://www.canardpc.com
> Tel : +33.6.13.73.4003
> MSN : sam at x86.fr 
>
>
>
>
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