[time-nuts] AM vs PM noise of signal sources

Magnus Danielson magnus at rubidium.dyndns.org
Fri Jan 5 18:58:07 EST 2018


Hi Attila,

On 01/05/2018 12:27 PM, Attila Kinali wrote:
> On Tue, 2 Jan 2018 23:34:18 +0100
> Magnus Danielson <magnus at rubidium.dyndns.org> wrote:
> 
> [About AM noise being of equal power as PM noise]
> 
>> Now, for actual sources this is no longer true. The AM noise can be much
>> higher, which is why it can be a real danger to the PM noise if there is
>> a AM to PM noise conversion. One source of such conversion can be the
>> amplification stage, but another could be a mistuned filter, which have
>> different amplitudes of the side-bands, which can create conversion as
>> the balance does not balance the same way anymore.
> 
> Yes, exactly. I am currently trying to understand how noise affects
> circuits an how input and circuit noise get converted to output noise.
> First assumption that needs to be dropped is that the noise processes
> is purely additive and independent of the signal. This means that a
> noise process does not anymore produce equal AM and PM power.

I'd say that first assumption should be that you are not linear.
Still, linear systems can already do conversion of AM to/from PM. The
lack of balance keeps being ignored for so many cases.

Then with nonlinearity things intermodulate and you get all the fun you
want.

> I think I have a 90% solution of the noise processes and conversions
> in a sine-to-square converter (aka zero-crossing detector, aka comparator).
> But there is one process that keeps puzzling me. I think I know where in
> the circuit it must come from, but I have no explanation as to how it happens.

OK, let me see the notes on that...

Cheers,
Magnus


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