Ultra low frequency VCO
in [Basics]
|
Prev: input impedance of THAT 1512 IC?
Next: EARN $9,000 MONTHLY WITH CJ, GOOGLE, LINKSHARE & CLICKBANK
From: Phil Hobbs on 12 Jul 2010 09:39 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 -- 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: Phil Hobbs on 12 Jul 2010 09:41 whit3rd wrote: > On Jul 9, 11:08 am, Phil Hobbs > <pcdhSpamMeSensel...(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. > > With an LC oscillator (class C transistor drive) the jitter in one > edge > (as determined by the transistor conduction) would be random, and > only a small fraction of the circulating energy would respond to the > edge error. So, the jitter in the LC output is a sequence of > random errors. > > For a multivibrator, however, the internal state resets each cycle; > the jittery time of cycle N becomes the new zero, and the jitter in > cycle N+1 is the sum of those two values. This kind of timing > error is the accumulating kind. The jitter is an arithmetic (sum) > sequence of randoms. > > So, for an LC oscillator you can get the N**2 behavior after > squaring; for a multivibrator oscillator only expect N**1. > I think this is why serious timing eschews the multivibrator. You're moving the goal posts. We aren't talking about the phase correlations, just the instantaneous phase noise. Phase noise sideband power goes down as 1/N**2, period. 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: 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 |