Intrinsic 1/f noise in ADCs and DACs
in [Design]
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From: whit3rd on 8 Jul 2010 19:03 On Jul 8, 3:42 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > > Are you doing an interferometry exercise? With a HeNe laser > > and a reflector moving circa 10**-8 m/s your fringes will > > dance around at 0.02 Hz. Wouldn't you be using > > a video digitizer and software, instead of an ADC, though? > > That's 10**-8 m/s**2, not m/s. It's the acceleration accuracy we > need--a tiny fraction of a fringe, at DC. (Hence the plaque.) How about doppler-shifting your laser reference (retroreflector on a moving disk... like a phonograph turntable) to raise the base frequency of the fringes?
From: Michael A. Terrell on 8 Jul 2010 23:30 Jim Thompson wrote: > > On Thu, 08 Jul 2010 12:22:52 -0400, Phil Hobbs > <pcdhSpamMeSenseless(a)electrooptical.net> wrote: > > >Having spent my career trying to keep clear of the low baseband, I now > >find myself needing to do very precise measurements of acceleration at > >very low frequencies--like 1 nano g (1 microgal, 10**-8 m/s**2) per root > >hertz at frequencies from 10**-4 Hz to about 100 Hz. This is an > >interesting ride, and will be generating a few discussions here, I hope. > > > >[I bought myself a brass plaque for the wall that says, > > > >DC: The Final Frontier > > > > My plaque over the office door says, "Some days you eat the bear and > some days the bear eats you" ;-) AKA: 'We all have our bears to cross'. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
From: John Devereux on 9 Jul 2010 05:04 Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> writes: > Joerg wrote: >> Phil Hobbs wrote: >>> Vladimir Vassilevsky wrote: >>>> >>>> Phil Hobbs wrote: >>>> >> >> [...] >> >> >>>>> Does anybody have any wisdom about the intrinsic 1/f noise of ADCs >>>>> and DACs? >>>> Check ADS1282 from TI. This state of the art ADC has the noise floor >>>> of ~5nv/root(Hz) all the way down to DC. Total dynamic range ~ 133dB >>>> (yes, thus is true number). >>>> >>>> >> >> [...] >> >>> I've seen the ADS1282, which is a very nice part, but (a) it's too slow, >>> and (b) we can't afford 8 of them per sensor anyway, either from a cost >>> or board space point of view. We may be better off in the end using >>> more than one board--we have a bit of space to play with in the axial >>> direction. >>> >> >> Can't you mux 8:1, into one ADC? >> > > That's what we're doing now, with the SAR ADC, but it doesn't work as > well with delta-sigmas. We need at least 1 kHz bandwidth on each > channel, which would need a dedicated delta-sigma apiece. Hi Phil, Like ADS1278 ? -- John Devereux
From: Phil Hobbs on 9 Jul 2010 11:35 On 7/9/2010 5:04 AM, John Devereux wrote: > Phil Hobbs<pcdhSpamMeSenseless(a)electrooptical.net> writes: > >> Joerg wrote: >>> Phil Hobbs wrote: >>>> Vladimir Vassilevsky wrote: >>>>> >>>>> Phil Hobbs wrote: >>>>> >>> >>> [...] >>> >>> >>>>>> Does anybody have any wisdom about the intrinsic 1/f noise of ADCs >>>>>> and DACs? >>>>> Check ADS1282 from TI. This state of the art ADC has the noise floor >>>>> of ~5nv/root(Hz) all the way down to DC. Total dynamic range ~ 133dB >>>>> (yes, thus is true number). >>>>> >>>>> >>> >>> [...] >>> >>>> I've seen the ADS1282, which is a very nice part, but (a) it's too slow, >>>> and (b) we can't afford 8 of them per sensor anyway, either from a cost >>>> or board space point of view. We may be better off in the end using >>>> more than one board--we have a bit of space to play with in the axial >>>> direction. >>>> >>> >>> Can't you mux 8:1, into one ADC? >>> >> >> That's what we're doing now, with the SAR ADC, but it doesn't work as >> well with delta-sigmas. We need at least 1 kHz bandwidth on each >> channel, which would need a dedicated delta-sigma apiece. > > Hi Phil, > > Like ADS1278 ? > That might work fine, thanks. It's a bit of a tight squeeze on the 0.8 inch diameter board, but we'd be able to save some parts on the other side by not having to deal with the truly awful mux charge injection. 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 9 Jul 2010 11:38
On 7/8/2010 7:03 PM, whit3rd wrote: > On Jul 8, 3:42 pm, Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> > wrote: > >>> Are you doing an interferometry exercise? With a HeNe laser >>> and a reflector moving circa 10**-8 m/s your fringes will >>> dance around at 0.02 Hz. Wouldn't you be using >>> a video digitizer and software, instead of an ADC, though? >> >> That's 10**-8 m/s**2, not m/s. It's the acceleration accuracy we >> need--a tiny fraction of a fringe, at DC. (Hence the plaque.) > > How about doppler-shifting your laser reference (retroreflector on > a moving disk... like a phonograph turntable) to raise > the base frequency of the fringes? Adding any sort of motion makes the detection problem much, much harder. Bearing noise, lubricant thinning, creep in flexures, temperature coefficient of Young's modulus.... One of the guys I'm working with on this is a mechanical genius, but he does need to be able to sleep at night. ;) 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 |