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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: Interesting reading about spread-spectrum, also for on-board designs
Date: Sat, 15 Jun 2024 08:43:12 -0700
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On Sat, 15 Jun 2024 05:57:23 GMT, Jan Panteltje <alien@comet.invalid>
wrote:

>On a sunny day (Fri, 14 Jun 2024 07:55:14 -0700) it happened john larkin
><jl@650pot.com> wrote in <45mo6jhcq8kisjmbrom8i1r17ljr6g4qu8@4ax.com>:
>
>>On Fri, 14 Jun 2024 07:43:53 GMT, Jan Panteltje <alien@comet.invalid>
>>wrote:
>>
>>>Interesting reading about spread-spectrum, also for on-board designs:
>>>
>>> https://www.electronicdesign.com/technologies/power/article/55041243/monolithic-power-systems-choosing-the-proper-parameters-in-frequency-spread-spectrum-fss-design
>>
>>That's cool, except for the usual dreadful fake pcb image.
>
>Fake?
>Sure some fun zig-zag loops in some tracks... ?
>Why would anybody bother making artwork like that when you can just take a picture?

I've wondered that. And when they use a picture, it tends to be some
ancient crufty Dip-package board.

I have rarely used wiggle traces to add delay, but the fake board
images are full of them. And glowing traces. And vias without holes.

Hey, the electronic designers here could post pics of our prettiest
real circuit boards.

>
>
>>We have a bunch of switchers that use our own FPGAs as the
>>controllers, and I need to start up a project to make them
>>spread-spectrum.
>
>I find it interesting, not much experience with spread spectrum,
>but a lot with wideband FM modulation like for the old Ampex video recorders... VHS, Umatic, Betamax too.
>So with a bit of luck you can send your commercials on a few hundred kHz :-)
>
>
>>We don't want the ss modulation to show up in the DC outputs as ripple
>>or anything audible.
>
>RF wideband filtering, inductors.. capacitors...
>

The jitter pattern needs to create spectral spreading at high
frequencies but not change averages at low frequencies. There might be
some math involved.