[time-nuts] Power supply noise

Heathkid heathkid at heathkid.com
Sat Apr 30 03:35:19 UTC 2011


...and I used to think batteries were a good/clean source of power.  They 
are better than a linear power supply... yet they make very good temperature 
sensors too!

What is the perfect source of power?  Clean, no ripple, no variation based 
on temperature, etc.?

----- Original Message ----- 
From: "Attila Kinali" <attila at kinali.ch>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, April 29, 2011 11:11 AM
Subject: Re: [time-nuts] Power supply noise


> On Thu, 28 Apr 2011 17:04:25 -0600
> Joseph Gray <jgray at zianet.com> wrote:
>
>> Power supply noise and ripple has been mentioned before, in relation
>> to OCXO's and rubidiums. So, what is considered acceptable in these
>> applications?
>
> This highly depends on your system and what you want to achieve.
> Just like anything else in engineering ;-)
>
> For OCXOs you have usually a "frequency variation on power supply
> voltage change" or something similar. I guess Rb's have something
> similar (dont have a data sheet at hand). From this you can guestimate
> how much modulation you get on PSU noise.
>
> If you have this, then you can calculate how much noise you get from
> the other components in the path of your signal, with regard to the
> PSU noise.
>
> After you have that value, you can cross check with the stabilty you
> wanted go achieve.
>
> Although this looks quite simple, there is a slight "problem" with this
> approach: PSU noise often induces non-linear behavior in circuits.
> And often, the behavior varies a lot with the frequency of the noise.
> Ie you'd have to model a PSU noise transfer function for each device,
> but there no data for this (unless you measure it yourself).
>
> So, usually the approach is to build a system that has very little
> PSU noise. Eg use an LDO after a switched power supply to get rid
> of the switching noise. If this isnt enough, use additional filters
> or noise reduction LDOs (special LDOs made to filter out noise).
> If this still isnt enough, add more filters... until you are satisfied.
>
>
> Attila Kinali
>
>
> -- 
> The trouble with you, Shev, is you don't say anything until you've saved
> up a whole truckload of damned heavy brick arguments and then you dump
> them all out and never look at the bleeding body mangled beneath the heap
> -- Tirin, The Dispossessed, U. Le Guin
>
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