Thank you Bob. I was thinking of the contribution outside the loop, as for most part my PLL loops are around 1Hz and resolving closer than 10Hz isn't easy with a analyzer that stops at 10Hz.
I guess what I'm asking is: should I take any care in the unity gain buffers or would any normal garden variety op-amp work? Wentzel used the 310 in his buffers, and those are a bit special, being a bipolar amp with 2nA input bias current. BR. Thomas 2017-06-28 18:08 GMT+02:00 Bob kb8tq <kb...@n1k.org>: > Hi > > Ok, let’s back up a bit: > > There are two basic regions when measuring a phase locked oscillator. You > can be “inside” the loop bandwidth or “outside”. Yes it’s a bit more > complex > than that, but go with the idea for now. Inside the bandwidth, everything > about > the PLL can / may matter. It can and often does contribute noise to the > result. > That noise might be from the detector, a divider, or even the loop > amplifier. Outside > the loop bandwidth you just see the oscillator phase noise. (There is a > third region > in-between the two where things get even more messy). > > Based on that, you will see some noise from the loop amplifier. Exactly > how much > (is it 0.001 db?) or how far out will always be a “that depends” sort of > thing. Without > measurement (and possibly modeling) there is no single answer to the > question. There > are many noise sources in any phase noise setup so this issue is hardly > unique to the > loop amp. > > Bob > > > On Jun 28, 2017, at 6:29 AM, Thomas S. Knutsen <la3...@gmail.com> wrote: > > > > Hi. > > > > When measuring Phase Noise using PLL, what noise would be contribuded > from > > the PLL into the amplifier? > > Lets say we disconnect the control voltage from the oscillator, shouldn't > > the input stage of the PLL contribute some, altough miniscule part to the > > total noise seen? > > Would this noise be masked by the noise from the phase detector? > > > > > > The reason for asking is that I'm trying to improve my PN measurement > > setup. > > Currently the PLL consist of a unity gain buffer made of TL072 before the > > PLL filter, not unlike what Wentzel did in his amplifier. The PLL filter > is > > a low noise op-amp (OP27). > > > > BR. > > Thomas. > > > > -- > > With Best regards, Thomas S. Knutsen. > > > > Please avoid sending me Word or PowerPoint attachments. > > _______________________________________________ > > 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. > -- With Best regards, Thomas S. Knutsen. Please avoid sending me Word or PowerPoint attachments. _______________________________________________ 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.