[time-nuts] Slightly OT: interest in a four-output, ultra-low jitter, synthesizer block?

Robert LaJeunesse lajeunesse at mail.com
Thu Jan 25 16:31:32 EST 2018


The problem comes if the load current on the 1.8V regulator sees significant ups and downs. Think output regulator in particular. Might also happen with the digital core if major rollovers align and the core spikes. Those current changes get spread (admittedly reduced, too) by the bypass caps, resulting in noticeable load changes on the VDDA regulator. Any non-zero output impedance and the digital load changes enter back in as noise on what should be the quiet VDDA.

> Sent: Thursday, January 25, 2018 at 4:18 PM
> From: "Hal Murray" <hmurray at megapathdsl.net>
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Cc: hmurray at megapathdsl.net
> Subject: Re: [time-nuts] Slightly OT: interest in a four-output, ultra-low  jitter, synthesizer block?
>
> 
> lajeunesse at mail.com said:
> > I'm sure you know the 1.8V supply regulators should not be fed from VDDA
> > (3.3V), but I'll mention it anyway. 
> 
> Why not?
> 
> That sounds like the sort of issue I should understand but I'm coming up 
> blank.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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