Ultra low frequency VCO
in [Basics]
|
Prev: input impedance of THAT 1512 IC?
Next: EARN $9,000 MONTHLY WITH CJ, GOOGLE, LINKSHARE & CLICKBANK
From: George Herold on 12 Jul 2010 12:15 On Jul 12, 11:09 am, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > j wrote: > > The point is that a lot of this jiber-jaber is pointless. Without the > > OP giving a better definition of the problem its a guess at best > > which measurement technique is required. > > > He never did state the basis for his phase noise number, nor did he > > have an offset frequency. > > > The challenge in making 100 dBc or better measurements is a function > > of the offset frequency and bandwidth. Center frequency isnt the > > issue here. > > You may not be interested, but perhaps other folks are. And how big an > offset frequency can he have on a 60 Hz carrier, anyway? > > 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 Yes! I've enjoyed the discussion. Say could someone explain the the 100 dBc of phase noise spec. I've been thinking of this a one part in 10^5 of jitter in the period. So for instance a 1 Hz signal the jitter is less than 10 micro seconds aand for a 1 MHz signal a jitter of 10 pico seconds. Is that right? George H.
From: John Larkin on 12 Jul 2010 12:22 On Mon, 12 Jul 2010 09:15:37 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jul 12, 11:09�am, Phil Hobbs ><pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> j wrote: >> > The point is that a lot of this jiber-jaber is pointless. �Without the >> > OP giving a better definition of the problem it�s a guess at best >> > which measurement technique is required. >> >> > He never did state the basis for his phase noise number, nor did he >> > have an offset frequency. >> >> > The challenge in making �100 dBc or better measurements is a function >> > of the offset frequency and bandwidth. �Center frequency isn�t the >> > issue here. >> >> You may not be interested, but perhaps other folks are. �And how big an >> offset frequency can he have on a 60 Hz carrier, anyway? >> >> 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 > >Yes! I've enjoyed the discussion. Say could someone explain the the >100 dBc of phase noise spec. I've been thinking of this a one part in >10^5 of jitter in the period. So for instance a 1 Hz signal the >jitter is less than 10 micro seconds aand for a 1 MHz signal a jitter >of 10 pico seconds. > >Is that right? > >George H. The usual oscillator phase noise spec would be " -100 dBc/Hz " at some offset frequency from the carrier. It's often given as a curve. It is possible to convert the curve to an RMS jitter spec... I have a program around somewhere that some s.e.d. guy posted. John
From: Jim Thompson on 12 Jul 2010 12:56 On Mon, 12 Jul 2010 08:52:41 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 12 Jul 2010 11:43:29 -0400, Phil Hobbs ><pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >>Jim Thompson wrote: >>> On Mon, 12 Jul 2010 10:40:00 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>> >>>> Jim Thompson wrote: >>>>> On Fri, 09 Jul 2010 14:08:28 -0400, Phil Hobbs >>>>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>>>> >>>>>> whit3rd wrote: >>>>>>> On Jul 8, 12:29 pm, Phil Hobbs >>>>>>> <pcdhSpamMeSensel...(a)electrooptical.net> 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 >>>>>>> Eh? I'd think it's N**0.5 (the multivibrator has cumulative but >>>>>>> random errors). >>>>>> The time jitter of the edges stays the same, but the resulting phase >>>>>> error goes down by a factor of N due to the division. Phase is like >>>>>> amplitude, so you have to square it to get the noise power--hence N**2. >>>>>> >>>>>> Cheers >>>>>> >>>>>> Phil Hobbs >>>>> Hey Phil! How come no comment on conservation of charge and energy? >>>>> You have a dog in this show ?:-) Weenie! >>>>> >>>>> ...Jim Thompson >>>> I'm mainly here to talk about electronics. One-upmanship also tends to >>>> intimidate the newbies, which I really don't want to do. I try not to >>>> dispense Bad Info myself, and try to help other people's >>>> misunderstandings when I can. Otherwise I just read with interest and >>>> learn stuff. >>> >>> There's no one-up-man-ship involved. Larkin won't (or can't, because >>> he doesn't really understand it) show where the extra charge came >>> from. You (or Win) could put a stop to Larkin's nonsense. Larkin >>> displays me as a fool, and the newbies don't know any better, so >>> they'll never ever learn the correct solution unless someone >>> (politically :) respected steps in. >> >>I don't know about that. It isn't that difficult to calculate a circuit >>with two caps, an inductor, and an elf who opens and closes a switch at >>the right moments. It does help to know elementary differential equations. >> >>I haven't actually followed the original discussion closely enough to >>know who made the first technical error. The larger error IMO is to >>keep getting into these tiresome p***ing contests, which I decline to >>do. If what you want is merely to have the correct solution posted, >>post it and let's move on to some electronics. >> >>Cheers >> >>Phil Hobbs > >I don't think any specific problem has been clearly stated, such that >it can be analyzed. My comment, that seems to have ruffled feathers, >is that one shouldn't assume as a working tool that charge, coulombs >stored in various capacitors in a circuit, is conserved. Sometimes it >is, sometimes it isn't, sometimes the concept is silly. > >The argument did make me go back and review some basics, which is >good. Messing with all this digital and software and opamp stuff can >make the old EE101 math get rusty. > >John Dodge, dodge, dodge. You specifically stated, in... Message-ID: <3b893612tjjndo8o4v1evro050nonjgp41(a)4ax.com> "... charge is not conserved." Where, oh great pretend guru, where does the excess charge come from? ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Obama isn't going to raise your taxes...it's Bush' fault: Not re- newing the Bush tax cuts will increase the bottom tier rate by 50%
From: Tim Wescott on 12 Jul 2010 12:57 On 07/08/2010 12:29 PM, Phil Hobbs wrote: > Paul Keinanen wrote: >> On Tue, 06 Jul 2010 09:52:43 -0700, Tim Wescott <tim(a)seemywebsite.com> >> wrote: >> >>> On 07/06/2010 09:10 AM, Daku wrote: >>>> On Jul 5, 8:59 pm, Tim Wescott<t...(a)seemywebsite.com> wrote: >>>>> I'd hardly call 60Hz "ultra low frequency". But it is pretty darned >>>>> low. >>>>> >>>>> All the suggestions you've gotten so far are good as far as they go >>>>> and >>>>> may well be perfect -- but what are you trying to do? Do you need sine >>>>> wave out or square? If sine wave, how pure? Do you have any >>>>> specifications on jitter, phase noise, or frequency accuracy? >>>> I am trying to design a PLL for very low frequencies, e.g., power line >>>> grid. >>>> I am concerned with the VCO as it is a crucial sub-circuit. I am >>>> aiming for >>>> a phase noise of approximately -100 dBc/Hz but not very sure of the >>>> offset >>>> frequency. Ideally, I would like to have frequency accuracy of 1 - 5% >>>> at most. >>>> Also, I am aware that S-parameter methods are not appropriate at these >>>> low >>>> frequencies. >> >> If you want to track the _actual_ mains frequency, just use a mains >> driven synchronous motor. To get the noise sidebands down, use some >> flywheels :-). >> >>> I think that those specs would be difficult to achieve with an >>> all-analog oscillator running at 60Hz. Not impossible -- I could do >>> it, and Joerg could do it in a fraction of the time I'd take. Using >>> some sort of direct digital synthesis -- even if it's just a >>> microprocessor -- running off of a crystal reference would be almost >>> trivial in comparison and would probably take less board space and >>> would be far more repeatable in manufacturing. >>> >>> If you just had to do this purely in the analog domain your best bet >>> might be a pair of crystal oscillators, frequency steered with >>> varactors, carefully built, and with their outputs mixed down to >>> 60Hz. But that's a solution I would expect to see in a bit of kit >>> from the 50's through the 80's -- anything later and I'd expect to >>> see a DDS. >> >> Just a few minutes ago, the Nordel AC network (Danish isles, Finland, >> Norway, Sweden) was running at 50.11 Hz or +2200 ppm above nominal in >> order to allow the mains synchronized clocks to catch up. >> A simple fundamental frequency VXCO can be pulled about +/-100 ppm >> with the load capacitance. About 1000 ppm is the maximum with >> adjustable serial inductance and adjustable parallel load capacitance >> at the crystal. >> >> At 50/60 Hz, even a trivial processor can generate a variable >> frequency sine wave using the NCO (Numerically Controlled Oscillator) >> principle to generate a sine wave, which can be locked to the incoming >> signal in some loop configuration. >> >> Even a trivial processor might be able to generate both sine and >> cosine waveforms for 49.98, 50.00. 50.92 Hz etc. in parallel and >> performing a phase comparison between all these in parallel to >> determine the best match. >> > > 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. This actually kind of makes my point, which I didn't state clearly: if you _don't_ use a divider it'll be hard. With a divider it gets easy, as long as you ignore clock jitter in the divider (and clock jitter probably isn't a big deal, given the output frequency). > You might even be able to do it with all analog--the OPA378 has 20 > nV/sqrt(Hz) all the way down to DC. With a 5V sine wave at 60 Hz, that's > something like 1800 V/s, so 20 nV gives you something like 10 > picoseconds per root hertz. You probably lose a factor of sqrt(2) in > there, but that ought to be good enough. Your ALC network would > contribute more than that, almost for sure. Depending on how close to the carrier you want to get, you lose a factor of up to infinity (if you get _really_ close to the carrier). The noise gain is something like 1/(s^2 + w0^2) -- it's an oscillator. Worse, because it's an RC, the constant you're multiplying by is greater than one -- I get Hn(s) ~ 15/(s^2 + w0^2). That's not taking the current noise of the part into account (which, I admit, I haven't checked on because I'm lazy). 1Hz away your noise gain is just about 200, for 4uV/sqrt(Hz). That's doing OK, but at 0.1Hz away the noise gain is about 2000 -- all you have to do is measure close enough to the carrier at a wide enough bandwidth and your noise is too high (sure would be nice if the OP specified what he wanted, but I think we lost him). -- Tim Wescott Wescott Design Services http://www.wescottdesign.com Do you need to implement control loops in software? "Applied Control Theory for Embedded Systems" was written for you. See details at http://www.wescottdesign.com/actfes/actfes.html
From: Jim Thompson on 12 Jul 2010 12:58
On Mon, 12 Jul 2010 08:33:56 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Mon, 12 Jul 2010 10:40:00 -0400, Phil Hobbs ><pcdhSpamMeSenseless(a)electrooptical.net> wrote: > >>Jim Thompson wrote: >>> On Fri, 09 Jul 2010 14:08:28 -0400, Phil Hobbs >>> <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >>> >>>> whit3rd wrote: >>>>> On Jul 8, 12:29 pm, Phil Hobbs >>>>> <pcdhSpamMeSensel...(a)electrooptical.net> 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 >>>>> Eh? I'd think it's N**0.5 (the multivibrator has cumulative but >>>>> random errors). >>>> The time jitter of the edges stays the same, but the resulting phase >>>> error goes down by a factor of N due to the division. Phase is like >>>> amplitude, so you have to square it to get the noise power--hence N**2. >>>> >>>> Cheers >>>> >>>> Phil Hobbs >>> >>> Hey Phil! How come no comment on conservation of charge and energy? >>> You have a dog in this show ?:-) Weenie! >>> >>> ...Jim Thompson >> >>I'm mainly here to talk about electronics. One-upmanship also tends to >>intimidate the newbies, which I really don't want to do. I try not to >>dispense Bad Info myself, and try to help other people's >>misunderstandings when I can. Otherwise I just read with interest and >>learn stuff. >> >>Whit3rd seems to be talking about the phase correlations rather than the >>instantaneous phase noise. Both multivibrators and LC resonators obey >>equations with full locality, i.e. neither one has any memory at all. >> >>For instance, if you have a 1 MHz resonator with a Q of a million, it >>takes a second or so to get its phase to change when you put PM on the >>drive waveform. OTOH, if you change the resonant frequency suddenly, >>e.g. by putting 100V on a Y5V tank capacitor, the resonant frequency >>changes immediately--much faster than 1/Q cycles. >> >>Because of the switching action, multivibrators intermodulate the >>switching element's noise at all frequencies, which makes their jitter >>much worse; also the effective Q of a multivibrator is less than 1, >>which means that there isn't any significant filtering action from the >>resonator. (That's frequency-domain way of thinking about what Whit3rd >>is talking about in the time domain--the conservation of energy issue is >>easier to think about if there's a natural bandwidth limit to the >>sqrt(t) behaviour.) The physical origin of the phase modulation doesn't >>change the way it varies with division ratio, though. >> >>Cheers >> >>Phil Hobbs > >One interesting and often overlooked part is the coaxial ceramic >resonator. It's essentially a shorted transmission line formed in a >block or tube of hi-K ceramic, usually by silver or copper plating it. >They are usually treated by the RF boys as resonators or inductors, >but they really act like time-domain transmission lines. TCs are in >the single-digit PPMs and Qs in the hundreds or thousands. Dielectric >constants are in the hundreds or thousands, so they are very short for >their delay/frequency. > >Remarkable parts. I use them to make instant-start/instant-stop >oscillators in the 600 MHz range. As a VCO, they will have very low >phase noise, somewhere between an LC and a quartz crystal. > >John I've been "using" them... designing them into GPS LO's since before you were born ;-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Obama isn't going to raise your taxes...it's Bush' fault: Not re- newing the Bush tax cuts will increase the bottom tier rate by 50% |