Re: spread-spectrum model

On Thu, 18 Apr 2024 12:14:04 -0700, John Larkin
<jjSNIPlarkin@highNONOlandtechnology.com> wrote:

On Thu, 18 Apr 2024 13:16:04 -0400, Joe Gwinn <joegwinn@comcast.net>
wrote:
>

On Thu, 18 Apr 2024 08:26:56 -0700, John Larkin
<jjSNIPlarkin@highNONOlandtechnology.com> wrote:
>

I'm designing a switching power supply module and could reduce EMI by
going spread-spectrum on the switching frequency. The simple one below
reduces things by 20 dB. Probe the SS node and FFT.
>
The ss inside switching reg chips is no doubt more sophisticated. In
an FPGA, we could do some sort of pseudo-random thing.
>
On a multi-channel power supply, there may be some small advantage to
have a separate spread per channel. That would be easy.

>
I'd check for cross-correlation as well, so no ganging up in systems
using multiple channels in some signal path.

>
When my engineers get too fussy about stuff like that, I remind them
"it's just a power supply."

Noise at the local level is best correlated, as it is more
predictable - you avoid low-frequency beat frequencies in the
local regulators - which can and will show up in a detector's
BW and in the regulators' outputs.

A master clock, phase shifted for various local users, can be dithered
for the system (box), which is the actual, final radiator.

Your engineers can get REAL fussy, if the system's non-compliant
way past the development's due date.

RL