Ultra low frequency VCO
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From: Phil Hobbs on 13 Jul 2010 22:41 j wrote: >> Genuine phase noise sidebands have flat tops, so they aren't as >> sensitive to modulation frequency as FM noise. Various authors go to >> various lengths in trying to identify regions where the noise goes as >> 1/f, 1/f**2,.... > > What in the world are you saying? Sounds kind of ignorant to me � but > I�ll reserve judgment until you answer. > > I made a living at designing multiloop uw / rf synthesizers and taking > this statement as fact sure wouldn�t have helped. > > regards Which statement? You don't think that pure phase noise is white? Or that different authors say different things? I plead guilty to ignorance of many things. Cheers Phil Hobbs -- Dr Philip C D Hobbs Principal ElectroOptical Innovations 55 Orchard Rd Briarcliff Manor NY 10510 845-480-2058 hobbs at electrooptical dot net http://electrooptical.net
From: j on 13 Jul 2010 23:58 On Jul 13, 7:41 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > j wrote: > >> Genuine phase noise sidebands have flat tops, so they aren't as > >> sensitive to modulation frequency as FM noise. Various authors go to > >> various lengths in trying to identify regions where the noise goes as > >> 1/f, 1/f**2,.... > > > What in the world are you saying? Sounds kind of ignorant to me but > > Ill reserve judgment until you answer. > > > I made a living at designing multiloop uw / rf synthesizers and taking > > this statement as fact sure wouldnt have helped. > > > regards > > Which statement? You don't think that pure phase noise is white? Or > that different authors say different things? > > I plead guilty to ignorance of many things. > > Cheers > > Phil Hobbs > > -- > Dr Philip C D Hobbs > Principal > ElectroOptical Innovations > 55 Orchard Rd > Briarcliff Manor NY 10510 > 845-480-2058 > hobbs at electrooptical dot nethttp://electrooptical.net Yeah, I suspected you were talking about white noise. Unfortunately for folks that design low noise freq synthesizers white noise isnt the tough spot. We typically live in those 1/f places. The whole process is about shaping that noise profile. Without targeted system specs, one can see why its virtually impossible to select loop components such as a VCOs, amps, etc., for this type of job. Btw, I apologize for the ignorant comment didnt mean to sound so nasty. I regret that.
From: Paul Keinanen on 14 Jul 2010 00:16 On Tue, 13 Jul 2010 08:36:35 -0700, Tim Wescott <tim(a)seemywebsite.com> wrote: >On 07/12/2010 11:42 PM, Geoff C wrote: >>> >>> So I guess that all of the suggestions that have been given will work. >>> Or none of them. Or some, if only the OP would tell us the rest of >>> his requirement. >>> >> >> The OP seems to be interested in syncing his PV solar system to the grid, >> at least thats what I infer from reading some other of his posts. Kind of >> makes the 100dBc spec look silly if so. > >No kidding! If he's within 10 degrees one way or another that's >probably plenty good. > >Of far greater concern with PV usage is making sure that putting what is >essentially a negative resistance on the line won't cause instability, >or at least knowing exactly what conditions will lead to instability so >that you may avoid them during installation. > >Particularly if you're going to move from your lab with one or two PV >panels attached to a good solid grid, to some solar farm out in the >boonies where your PV array is the biggest power source for miles. In remote areas, the electricity distribution network is often like a tree (not a ring) and becomes weaker when approaching the leaves of the tree. Connecting one or more 1-3 MW wind turbines at the edges will cause problems. Ideally, it is assumed that the turbine should provide power to the customers at the local branch. However, when operated close to the cut-in wind speed, the power output will vary significantly, causing voltage variations and the lights will flicker at nearby customers in the weak net. With wind turbines at different branches of a weak net, some operated below average, some above average power, power is routed long distances along weak lines through the common distribution point of the original distribution net. The direction of power transfer in the weak lines varies constantly, depending on the local wind variations. In effect, the wind turbines in different branches have a slightly different phase compared to each other and the main power grid. When connecting individual PV or other small scale power sources to a weak net, the control loops must be able to follow much faster phase variations in weak nets with local generation, compared to a strong network.
From: JosephKK on 14 Jul 2010 00:49 On Mon, 12 Jul 2010 23:23:56 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >JosephKK wrote: >> On Mon, 12 Jul 2010 09:37:07 -0400, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> JosephKK wrote: >>>> On Fri, 9 Jul 2010 10:22:34 -0700 (PDT), j <jdc1789(a)gmail.com> wrote: >>>> >>>>> Resolution of noise vs frequency, (as in bw), is the issue in phase >>>>> noise measurements. The OP never stated the offset from the carrier >>>>> nor bandwidth. Or maybe I just missed it. >>>>> >>>>> Itâs not clear to me why JosephKK thinks this would be either a time >>>>> consuming or difficult measurement to make. Assuming the appropriate >>>>> measurement system is in hand 100 dBc numbers are easily achievable. >>>>> Whether itâs 60 Hz or several GHzâs the global issues are the same in >>>>> making a phase noise measurement. >>>>> >>>>> But having said the above, without the OP responding I guess it really >>>>> doesnât matter. But Iâd like to know more about the application and >>>>> derive solutions from there. >>>> >>>> OK. For a carrier of 60 MHz. Pick an instrument or test setup of your >>>> choice, state the model[s]. Clearly explain just what is going on in the >>>> measurement and the time it takes to accumulate sufficient data to make >>>> the measurement. Explain why it takes that much time to reach a reliable >>>> measurement of -100 dBc phase noise at that carrier frequency. >>>> >>>> Now see how well it scales to one million times lower fundamental >>>> frequency without a similar scaling in measurement time. >>> It's the modulation frequency that's relevant, not the carrier >>> frequency. Measurements get slower when you reduce the bandwidth. >>> >>> (You can see why this doesn't work if you imagine running it >>> backwards--mixing or multiplying up to some very high frequency doesn't >>> allow you to make a measurement with 1 Hz bandwidth any faster. >>> >>> >>> Cheers >>> >>> Phil Hobbs >> >> Now what is the equivalent bandwidth of -100 dBc for a 60 Hz carrier? >> Since you said 20 log() basis 60 * 10^-5 is 600 microHz. That would have >> to take some minutes, and if you wanted a proper 10 to 1 measurement >> buffer, it takes ten times longer. Call it 10,000 seconds? A few hours. >> And the reference stability etc., i remarked on is coming into play. > > >You're confused, I'm afraid. -100 dBc phase noise in a given bandwidth >(say 1 Hz, but it doesn't matter) is 7 microradians RMS. Using a 5V >swing and a CMOS analogue gate as a phase detector, that's > >dV = 7e-6 rad RMS * 5V/(pi rad) = 11 microvolts RMS, > >which is trivial to measure in a 1 Hz bandwidth in a few seconds--it's >80 dB above the noise of a good op amp, so you just have to wait for the >filter to settle. > >Cheers > >Phil Hobbs OK. I have your "Making it All Work" and AoE 2nd Ed and more. Where do i go to get less confused? This phase noise measurement is twisted.
From: JosephKK on 14 Jul 2010 01:00
On Mon, 12 Jul 2010 23:29:42 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >JosephKK wrote: >> On Mon, 12 Jul 2010 09:39:54 -0400, Phil Hobbs >> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >> >>> JosephKK wrote: >>>> On Fri, 09 Jul 2010 11:56:28 -0400, Phil Hobbs >>>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>> >>>>> On 7/9/2010 8:59 AM, JosephKK wrote: >>>>>> On Thu, 08 Jul 2010 15:37:28 -0400, Phil Hobbs >>>>>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>>>> >>>>>>> Phil Hobbs wrote: >>>>>>> >>>>>>>> I don't know that -100 dBc/Hz is that hard at 60 Hz. I bet you could do >>>>>>>> that by running a bog standard multivibrator at 1024*1024*60 Hz and >>>>>>>> dividing down. You'd need a sine shaper, but the phase noise goes down >>>>>>>> by N**2, so you'd get 100 dB improvement just from that. Alternatively, >>>>>>>> you could make an LC VCO and divide that down. >>>>>>> 120 dB. Can't count today. >>>>>>> >>>>>>> Cheers >>>>>>> >>>>>>> Phil Hobbs >>>>>> Sure, you can mathematically "predict" it, but how do you measure it? >>>>>> Or do you switch to another metric which can be both predicted and >>>>>> measured? >>>>> Let's keep the math bashing to the other thread, okay? >>>>> >>>>> Although it isn't highly relevant to the OP's problem, it wouldn't be >>>>> very difficult to measure the residual FM--use MOSFET buffers to drive >>>>> two divider strings running from independent power supplies, and >>>>> cross-correlate their outputs, exchanging them periodically to get rid >>>>> of the drift in the correlator. For the correlator design, see Hanbury >>>>> Brown and Twiss, circa 1963--and they did it with discrete bipolars. >>>>> >>>>> There are hard measurements, but this isn't one of them. >>>>> >>>>> Cheers >>>>> >>>>> Phil Hobbs >>>> My issue was not so much the direct difficulty of the measurement, there >>>> are several fairly straight forward setups. But with the _time_ it would >>>> take to make the measurement using many of those setups. The elapsed >>>> time seriously aggravates other measurement issues, notably including >>>> calibration. >>> Modulation frequency isn't affected by heterodyning or frequency >>> multiplication and division. If you take a 60 MHz sine wave and FM it >>> at 1 Hz modulation frequency and 1 MHz peak frequency deviation (M=1E6), >>> then divide it by a million, you get a 60-Hz sine wave modulated at 1 >>> Hz with a 1-Hz peak frequency division (M=1). >>> >>> Cheers >>> >>> Phil Hobbs >> >> I am sorry. I think i am misreading your post, are you saying you can >> get a 1 MHz deviation on a 60 Hz carrier? Naw, you must be trying to say >> something else and i misunderstood. > > >You can put a 1 MHz phase modulation on a 60 Hz carrier, but you sure >don't wind up with anything pretty. For instance, you could put the 60 >Hz on a varactor-loaded transmission line, and drive the varactors with >1.000000000 MHz. As long as the varactors were driven really >differentially, you wouldn't get any 1.000000000 MHz on the line. > >That's way outside the quasistatic limit, of course, which is where >we're all used to working. It would be a nasty splattery mess, but >you'd get _something_. > >But that wasn't the point I was trying to make. ;) > >Cheers > >Phil Hobbs I understand your post NOT. Please explain more thoroughly, or point me to texts. I still do not understand the way you are using units for phase modulation. I have trouble understanding phase modulating a 60 Hz carrier with a 1 MHz signal. What is the p-p angle you are achieving? How do you know? Sorry about sounding like a fool, but i cannot find common frame for us to understand each other. |