Ultra low frequency VCO
in [Design]
|
Prev: AofE 3rd Edition
Next: Labelling Prototypes
From: Phil Hobbs on 12 Jul 2010 10:40 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 -- 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 12 Jul 2010 10:54 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.
From: Phil Hobbs on 12 Jul 2010 11:09 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 net http://electrooptical.net
From: Jim Thompson on 12 Jul 2010 11:17 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. > >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 Yep. ...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: j on 12 Jul 2010 11:25
Its not that its not interesting but you need to change the topic to phase noise measurements or something of that nature. Or stable low freq Osc for example. It appears that the OP wanted to discipline to line and use that as a long term ref.. Its not clear to me how he came up with the 100 dBc number without an offset Im not sure what you mean by how big an offset offset generally refers to the position of the measurement relative to the carrier. The closer the offset the more difficult the measurement ... generally do to the limitation of the measuring equipment. The interesting part is the solution to those challenges. Im not trying to be a malcontent here just seems like the discussion doesnt have direction. |