Ultra low frequency VCO
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From: JosephKK on 9 Jul 2010 08:59 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?
From: Phil Hobbs on 9 Jul 2010 11:56 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 -- 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: whit3rd on 9 Jul 2010 13:22 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).
From: j on 9 Jul 2010 13:22 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. Its 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 its 60 Hz or several GHzs 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 doesnt matter. But Id like to know more about the application and derive solutions from there.
From: Phil Hobbs on 9 Jul 2010 14:08
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 -- 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 |