[time-nuts] Linear voltage regulator hints...

[Bob Camp]

Hi

Most OCXO’s will meet all spec’s with 1 to 10 mV RMS on the supply lead. That’s mV not uV.

If the noise is flat in a  100 Hz to 100 KHz bandwidth, most will meet their ADEV specs with a mV RMS on the EFC line. Again mV not uV. 

The issue is pretty simple:

Things like an EFC or supply FM modulate the OCXO. Phase / time  (= what you care about) drops off as 1/f. It’s actually pretty hard to find a reference or DAC that is noisy enough to bother a typical OCXO.  

Bob

> On Dec 11, 2014, at 6:26 PM, Neil Schroeder <gigneil at gmail.com> wrote:
> 
> So I've done a lot of work in power lately and I can summarize some of this
> quickly:
> 
> The lowest noise LDOs today are the TI TPSa4700/01 up to 36v/1a and about 4
> uVRms noise,  and the ADP7154/55 up to 5.5v and 600ma with only *0.9* uVRms
> above 100hz.
> 
> Both feature great PSRR -and in the case of the ADI part don't even
> recommend filter caps at all.
> 
> The TI however does still recommend some capacitance.
> 
> Now most people's next question  is how to get their ruby or their
> septuple-oven homebrew design powered by one. The quick answer is an error
> amplifier based ldo balancer for the most accurate distribution of current.
> Also helps with heat.
> 
> Will share a sketch when at my desk next.
> 
> 
> On Thursday, December 11, 2014, Hal Murray <hmurray at megapathdsl.net> wrote:
> 
>> 
>> eb at telight.com <javascript:;> said:
>>> If the plan is to use a three-terminal regulator after all, I'd  suggest
>> not
>>> using a low-dropout (LDO) type if the raw input supply is  noisy - the
>> LDOs
>>> usually have PNP output transistors (for positive  regulators), so may
>> tend
>>> to have poorer HF input ripple rejection  than equivalent ones with NPN
>>> passers.
>> 
>> In this context, what is "high"?
>> 
>> Why don't filter caps solve that end of the spectrum?
>> 
>> 
>> --
>> These are my opinions.  I hate spam.
>> 
>> 
>> 
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