I really enjoy reading the mail on this group, but I thought it was the 'front molecule on the cutting edge'.
Joe -----Original Message----- From: time-nuts-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on Behalf Of John Miles Sent: Monday, December 15, 2008 1:15 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Close-in phase noise question... 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-boun...@febo.com [mailto:time-nuts-boun...@febo.com]on > Behalf Of wa1...@att.net > Sent: Monday, December 15, 2008 8:54 AM > To: time-nuts@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 > > _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.