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

[John Miles]

The painful part is probably the first few stages, if you are starting at 5
MHz.  You probably want to do some HP 8662A-like tricks using crystal
filters to shave off the broadband noise below 1 GHz, and maybe SAW filters
above that.  This will do nothing for noise within 1 kHz, though... do you
really need a clean signal that close to the carrier all the way up to 630
GHz?

The noise characteristics of the MMICs seems to depend a lot on the fab
technology.  I can't seem to find my .PDF copy of it right now, but I have
one paper on microwave regenerative dividers where the authors measured the
residual PN of several contemporary parts driven to saturation.  At 4.5 GHz,
the 10 dB/decade corner frequency wasn't reached until past 100 kHz for the
Stanford Microdevices SGA-4186, which didn't speak well for the PN
performance of SiGe HBT parts.  They showed -143 dBc/Hz at 1 kHz for that
one.

The GaAs HBT part (Mini-Circuits ERA-5SM) they tested was among the best
(-156 dBc/Hz at 1 kHz).  Second-worst was an InGaP/GaAs HBT part (Stanford
NGA-489) at about -153 dBc/Hz at 1 kHz.  Still much better than the SiGe
part.

My understanding is that the newer GALI-series parts from Mini-Circuits are
InGaP HBT devices so they'd presumably perform about like the NGA-489.
You'd want to measure them to make sure, though, if your app is that
critical.

Take a look at NRAO's recent publications, especially those associated with
the ALMA array (many of which are on their site).  They're doing the real
bleeding-edge work at sub-mm these days.

-- john, KE5FX

> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com]On
> Behalf Of wa1zms at att.net
> Sent: Monday, December 15, 2008 8:54 AM
> To: time-nuts at febo.com
> Subject: [time-nuts] Close-in phase noise question...
>
>
> 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
>

>