The central limit theorem rocks, (summing Zener noise)
in [Design]
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From: George Herold on 3 Jun 2010 15:41 So the following is the result of a previous thread where John Larkin suggested that one way to get rid of the voltage asymmetry in a Zener noise source was to sum a whole bunch together. I was initially doubtful, but thought I should do the experiment. I had a whole bunch (five) of lockins to test today. They have a build in Zener noise source with terrible asymmetry. So I summed them with an opamp, fed the signal to a digital scope and had it measure the min and max voltage. (There is lots of noise in the measurements so the number are not that accurate.. but the result is clear. The central limit theorem rocks! Number Vmax Vmin. of zeners 1 0.80 -0.33 2 1.20 -0.53 3 1.50 -0.75 4 1.60 -0.95 Thanks John, George H.
From: John Larkin on 3 Jun 2010 16:40 On Thu, 3 Jun 2010 12:41:34 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >So the following is the result of a previous thread where John Larkin >suggested that one way to get rid of the voltage asymmetry in a Zener >noise source was to sum a whole bunch together. I was initially >doubtful, but thought I should do the experiment. I had a whole bunch >(five) of lockins to test today. They have a build in Zener noise >source with terrible asymmetry. So I summed them with an opamp, fed >the signal to a digital �scope and had it measure the min and max >voltage. (There is lots of noise in the measurements so the number >are not that accurate.. but the result is clear. The central limit >theorem rocks! > >Number Vmax Vmin. >of >zeners > >1 0.80 -0.33 >2 1.20 -0.53 >3 1.50 -0.75 >4 1.60 -0.95 > >Thanks John, > >George H. What current are you running the zeners at? More current will improve the distribution at the cost of a bit of amplitude. John
From: langwadt on 3 Jun 2010 17:41 On 3 Jun., 21:41, George Herold <gher...(a)teachspin.com> wrote: > So the following is the result of a previous thread where John Larkin > suggested that one way to get rid of the voltage asymmetry in a Zener > noise source was to sum a whole bunch together. I was initially > doubtful, but thought I should do the experiment. I had a whole bunch > (five) of lockins to test today. They have a build in Zener noise > source with terrible asymmetry. So I summed them with an opamp, fed > the signal to a digital scope and had it measure the min and max > voltage. (There is lots of noise in the measurements so the number > are not that accurate.. but the result is clear. The central limit > theorem rocks! > > Number Vmax Vmin. > of > zeners > > 1 0.80 -0.33 > 2 1.20 -0.53 > 3 1.50 -0.75 > 4 1.60 -0.95 > > Thanks John, > > George H. try subtracting instead ;) gets rid of the non zero mean -Lasse
From: John Larkin on 3 Jun 2010 18:02 On Thu, 3 Jun 2010 14:41:32 -0700 (PDT), "langwadt(a)fonz.dk" <langwadt(a)fonz.dk> wrote: >On 3 Jun., 21:41, George Herold <gher...(a)teachspin.com> wrote: >> So the following is the result of a previous thread where John Larkin >> suggested that one way to get rid of the voltage asymmetry in a Zener >> noise source was to sum a whole bunch together. �I was initially >> doubtful, but thought I should do the experiment. �I had a whole bunch >> (five) of lockins to test today. �They have a build in Zener noise >> source with terrible asymmetry. � So I summed them with an opamp, fed >> the signal to a digital �scope and had it measure the min and max >> voltage. �(There is lots of noise in the measurements so the number >> are not that accurate.. but the result is clear. �The central limit >> theorem rocks! >> >> Number � � � � Vmax � � � Vmin. >> of >> zeners >> >> 1 � � � � � � 0.80 � � � -0.33 >> 2 � � � � � � 1.20 � � � -0.53 >> 3 � � � � � � 1.50 � � � -0.75 >> 4 � � � � � � 1.60 � � � -0.95 >> >> Thanks John, >> >> George H. > >try subtracting instead ;) > >gets rid of the non zero mean > >-Lasse It should make the symmetry converge faster, too. Maybe the mean is zero, but the spikies are just lopsided. If so, the first case, +0.80 and -0.33, is really bent! John
From: George Herold on 3 Jun 2010 19:04
On Jun 3, 4:40 pm, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Thu, 3 Jun 2010 12:41:34 -0700 (PDT), George Herold > > > > > > <gher...(a)teachspin.com> wrote: > >So the following is the result of a previous thread where John Larkin > >suggested that one way to get rid of the voltage asymmetry in a Zener > >noise source was to sum a whole bunch together. I was initially > >doubtful, but thought I should do the experiment. I had a whole bunch > >(five) of lockins to test today. They have a build in Zener noise > >source with terrible asymmetry. So I summed them with an opamp, fed > >the signal to a digital scope and had it measure the min and max > >voltage. (There is lots of noise in the measurements so the number > >are not that accurate.. but the result is clear. The central limit > >theorem rocks! > > >Number Vmax Vmin. > >of > >zeners > > >1 0.80 -0.33 > >2 1.20 -0.53 > >3 1.50 -0.75 > >4 1.60 -0.95 > > >Thanks John, > > >George H. > > What current are you running the zeners at? More current will improve > the distribution at the cost of a bit of amplitude. > > John- Hide quoted text - > > - Show quoted text - This is an old design done years ago. At the time I was looking for maximal noise and didn't really care about the asymmetry. These are made with 20 volt zeners running off the +/- 15 volt rails with I think a meg of resistance... 10uA of current. (I'd have to check the schematic.) George H. |