It is even more difficult when the schematic is wrong like in figure 1 where the emitter and collector of the PNP are reversed.
On Wed, 5 Sep 2012 16:26:04 -0600, Tom Knox <[email protected]> wrote: > >Hi Bob; >There are many designs I have seen employed at NIST that have low phase noise >and low noise floor. But it is often not that easy to build a working >prototype that actual achieves those levels of performance. power supply >design, parts layout, shielding, and part selection all play a substantial >role in achieving that level of performance. > >Thomas Knox > >> From: [email protected] >> Date: Wed, 5 Sep 2012 18:05:41 -0400 >> To: [email protected] >> Subject: Re: [time-nuts] REF osc distribution. >> >> Hi >> >> The NIST bipolar designs can indeed do better than a good quality OCXO for >> short term and close in phase noise. If you have a wide band floor at -185 >> dbc/Hz on your OCXO they aren't quite up to that level. >> >> Bob >> >> On Sep 5, 2012, at 5:55 PM, Tom Knox <[email protected]> wrote: >> >> > >> > I have seen that many commercial ref distribution amps are not as good as >> > a quality low phase noise 5 or 10MHz oscillator, considering the time and >> > resources that went into their design >> > I think it would be difficult to design a amp capable of distributing >> > something much cleaner then a LPRO. >> > Thomas Knox >> > >> > >> > >> >> From: [email protected] >> >> Date: Wed, 5 Sep 2012 17:37:34 -0400 >> >> To: [email protected] >> >> Subject: Re: [time-nuts] REF osc distribution. >> >> >> >> Hi >> >> >> >> You *can* get the job done with a CMOS inverter biased up and filtered. >> >> An op amp is likely not as good as the full bipolar approach and may be >> >> better / worse than the gate depending on exactly what you are looking at. >> >> >> >> Bob >> >> >> >> On Sep 5, 2012, at 12:59 PM, Michael Tharp <[email protected]> >> >> wrote: >> >> >> >>> On 09/05/2012 12:46 PM, Bob Camp wrote: >> >>>> Hi >> >>>> >> >>>> There are a number of discrete transistor buffers that have very good >> >>>> isolation and short term stability / phase noise performance. I'd take a >> >>>> look at the one from the NIST papers and Bruce's more modern re-design. >> >>>> All >> >>>> are in the archives. http://tf.boulder.nist.gov/general/pdf/498.pdf is a >> >>>> pretty good place to start. >> >>>> >> >>>> Mostly what they do is to run a common emitter amplifier followed by >> >>>> several >> >>>> common base amplifiers. They may or may not follow that with a buffer. >> >>>> Each >> >>>> channel gets a separate string of amplifiers. All the common emitter >> >>>> amps >> >>>> are driven in parallel by the reference source. >> >>>> >> >>>> The transistors used are normally cheap stuff like the 2N3904. Except >> >>>> for >> >>>> the power supply nothing in the circuit costs much. None of it is hard >> >>>> to >> >>>> find. >> >>> >> >>> For an integrated (op-amp) solution, how does OPA830 stack up? I'm >> >>> trying one out for a GPSDO design to buffer the signal from the OCXO for >> >>> 50 ohm output, but I may also build a distribution amplifier at some >> >>> point. >> >>> >> >>> At $1.91 for single pieces on Digi-Key it's not terribly expensive, but >> >>> something cheaper could probably get the job done. There are also dual >> >>> and quad versions (OPA2830 and OPA4830). >> >>> >> >>> -- m. tharp _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
