[time-nuts] Power supply noise

Max Robinson max at maxsmusicplace.com
Sat Apr 30 04:29:01 UTC 2011


How much are you willing to pay?

Regards.

Max.  K 4 O D S.

Email: max at maxsmusicplace.com

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----- Original Message ----- 
From: "Heathkid" <heathkid at heathkid.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts at febo.com>
Sent: Friday, April 29, 2011 10:35 PM
Subject: Re: [time-nuts] Power supply noise


> ...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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