Ultra low frequency VCO
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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%
From: Joel Koltner on 12 Jul 2010 13:13 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:dcim36poktoi3gc0keapvnbjlpsri0lqj4(a)4ax.com... [coaxial ceramic resonators] > I've been "using" them... designing them into GPS LO's since before > you were born ;-) What's the advantage -- for you -- over crystals? Just lower cost? ---Joel
From: Phil Hobbs on 12 Jul 2010 13:19
George Herold 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. Small phase jitter is the quadrature partner of small amplitude noise. Say you have a pure carrier and add ordinary white noise, e.g. by putting a resistor in series with the perfect oscillator's output. The resulting RMS phase deviation in some given bandwidth is <delta_phi> = 1/(sqrt(2*CNR)) where CNR is the carrier to noise ratio (i.e. carrier power/noise power in the given bandwidth). The factor of sqrt(2) expresses the fact that the noise and signal are uncorrelated, so that half the noise power winds up in the I phase as amplitude noise, and half winds up in the Q phase as phase noise. You can derive this from the formula for sums and differences of sines and cosines plus an orthogonality argument--it's quite pretty. It's in my section 13.6 (either edition), but that derivation almost certainly isn't original with me. One very pleasant consequence is that the phase noise statistics are the same as those of the additive noise in the high-CNR limit where the formula applies. The universality of this formula is why essentially all FM and PM detectors have equivalent performance at high SNR--where the additive model breaks down is low SNR, where FM/PM detection schemes really differ in performance. 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 |