[time-nuts] Close-in phase noise question...

[wa1zms at att.net]

Bruce-

OK... So, linear operation does therefore seem to be the preferred
way to operate these MMICs rather than operation into compression.
That's what I seem to be observing if only because my final RF
frequency is so high and RX bandwidth so low.

Having said that, if my frequency synthesis scheme involves a mixer
does the same effect of low frequency noise to phase noise conversion still
take place? After all, the mixer element is typically into compression
if it's a FET based mixer. I assume a diode mixer is more immune to
similar effects?

I'm trying to grow my intuitive understanding of the subtle sources of
noise. But I don't recall Maas giving much info on this topic in
his otherwise excellent text.

As always, thanks for your sagely advice.

-Brian


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
Behalf Of Bruce Griffiths
Sent: Monday, December 15, 2008 5:00 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Close-in phase noise question...


wa1zms at att.net wrote:
> Looking for comment here...
>
> The background:
> I'm working on a sub mm-wave LO chain for
> a ham radio application. While chasing issues
> of close-in phase (ie: within 1KHz of RF
> carrier) by peeling the "layers of the onion",
> I'm starting to question the performance of
> the MMICs that are used as buffers and amps
> following my Wenzel reference OCXOs.
>
> Question(s):
> Should any MMIC be allowed to be driven
> close to compression or into compression
> when striving for best close-in noise?
>
> I know and have seen the NF of a MMIC
> degrade while in compression, but my
> target right now is close-in noise rather
> than broadband noise.
>
> My design, in summary, takes 5MHz up to 630GHz
> via several multipliers and PLL stages.
>
> -Brian
>
Brian

The increased nonlinearity when driven into compression will enhance the
conversion of low frequency noise to phase noise.

Bruce

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