High Quality White Noise Gen
in [Design]
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From: John Larkin on 4 Jun 2010 16:59 On Fri, 04 Jun 2010 16:40:27 -0400, Phil Hobbs <pcdhSpamMeSenseless(a)electrooptical.net> wrote: >On 6/4/2010 12:01 PM, Bill Sloman wrote: >> On Jun 4, 4:41 pm, George Herold<gher...(a)teachspin.com> wrote: >>> On Jun 4, 10:07 am, Phil Hobbs >>> >>> >>> >>> <pcdhSpamMeSensel...(a)electrooptical.net> wrote: >>>> On 6/3/2010 11:12 PM, George Herold wrote: >>> >>>>> langw...(a)fonz.dk wrote: >>>>>> On 3 Jun., 23:11, Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> >>>>>> wrote: >>>>>>> On 6/3/2010 9:49 AM, George Herold wrote: >>> >>>>>>>> On Jun 2, 4:36 pm, John Larkin >>>>>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>>>>>>>> On Wed, 2 Jun 2010 12:30:19 -0700 (PDT), George Herold >>> >>>>>>>>> <gher...(a)teachspin.com> wrote: >>>>>>>>>> On Jun 2, 1:59 pm, whit3rd<whit...(a)gmail.com> wrote: >>>>>>>>>>> On Jun 2, 10:37 am, George Herold<gher...(a)teachspin.com> wrote: >>> >>>>>>>>>>>>>>>> Yup, and if the voltage asymmetry is a problem you can add the signal >>>>>>>>>>>>>>> >from two diodes, one biased from the positve supply and the other from >>>>>>>>>>>>>>>> the negative. >>>>>>>>>>>> Hmmm, you are right.... I still don't think that summing the voltage >>>>>>>>>>>> noise from a bunch of unipolarized zeners is going to get rid of the >>>>>>>>>>>> voltage asymmetry. >>> >>>>>>>>>>> You can use two zeners on a single power supply, in bridge >>>>>>>>>>> configuration; couple the output through a transformer to get >>>>>>>>>>> the difference. Symmetry is guaranteed if you balance the bridge >>>>>>>>>>> correctly. >>> >>>>>>>>>> Ahh, more than one way to skin that cat. >>> >>>>>>>>>> Say speaking of noise sources, a colleague put together a digital >>>>>>>>>> noise source. A counter steps through a look up table that feeds a >>>>>>>>>> DAC. The lookup table holds a whole comb of sine waves equally spaced >>>>>>>>>> in frequency space up to 32kHz. (I don t recall the frequency spacing >>>>>>>>>> but I could find out.. a few Hz or so.) The phases of all the sine >>>>>>>>>> waves were chosen randomly. The DAC was 12 bit (an AD7541 I >>>>>>>>>> think). The whole thing was clocked several times lower than Nyquist >>>>>>>>>> limit (~128 kHz). Now the problem we observed, (and could never >>>>>>>>>> cure), was intermodulation distortion above the 32 kHz cutoff. The >>>>>>>>>> signals above the cutoff frequency were down by only 50 dB, and my >>>>>>>>>> colleague was expecting something closer to 70 dB down. (Is that >>>>>>>>>> right for 12 bit resolution on the DAC? ) I worked on all the layout >>>>>>>>>> and analog portions of the circuit but could never make it any >>>>>>>>>> better. There was talk about clock jitter on SED recently and I >>>>>>>>>> wondered if this could be the source of the problem? Or maybe you >>>>>>>>>> have some other idea. >>> >>>>>>>>> The DAC quantization, and any nonlinearity, will add harmonic >>>>>>>>> distortion. Plus the sines may occasionally peak together and clip the >>>>>>>>> dac. Plus it's not trivial to get -70 dB distortion at these >>>>>>>>> frequencies. >>> >>>>>>>>> We use random number generators and boxcar filters to generate >>>>>>>>> Gaussian noise to feed into dacs. This little box does this, all in a >>>>>>>>> Spartan3 FPGA... >>> >>>>>>>>> http://www.highlandtechnology.com/DSS/T346DS.html >>> >>>>>>>>> Rob cleverly, somehow, allowed the user to program the noise bandwidth >>>>>>>>> from mHz to 2 MHz without affecting the RMS amplitude. >>> >>>>>>>> Very nice, (Are prices listed on your website?) Y'all make stuff >>>>>>>> that's several orders of magnitude above what we're doing. >>> >>>>>>>> You know what I'd really like to make (and could probabbly sell too.) >>>>>>>> is a random pulse generator. Short little pulses maybe 10nS or less >>>>>>>> coming at an average rate of 1us or so. This would be a psuedo shot >>>>>>>> noise generator. With a pot on the output one could change the >>>>>>>> amplitude of the pulses and see how the noise scaled. ... Hmm it >>>>>>>> would be nicer if the average pulse rate could be changed too. So >>>>>>>> that one could keep the average 'current' the same, but made with >>>>>>>> bigger 'electrons'. Sounds like a digital circuit. (Which I find a >>>>>>>> bit boring) an analog 'something' would be more fun. >>> >>>>>>>> George H. >>> >>>>>>>>> John- Hide quoted text - >>> >>>>>>>>> - Show quoted text - >>> >>>>>>> How about avalanching a phototransistor? ;) >>> >>>>>> point it at an Americium source from a smokedetector :) >>>>>> real random noise >>> >>>>> Something optical is nice because you can change light intensity with >>>>> a knob. >>> >>>>> George H. >>> >>>>>> -Lasse >>> >>>> I was just janking your chain--I had no idea that anybody had actually >>>> tried that. Phototransistors are so horrible on so many levels that >>>> it's pretty amusing to see someone trying to make fast pulses out 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 nethttp://electrooptical.net-Hide quoted text - >>> >>>> - Show quoted text - >>> >>> Oh...(Silly me) Well so how 'bout a photo-transistor with three >>> terminals (one where the base has a lead connected to it.) I'll short >>> the base and collector together and then reverse bias the EB >>> junction. With the bias voltage set just below where the thing wants >>> to zener. Then a photon could set the whole thing off? >>> >>> I thought I had a photo transistor around here someplace, but I >>> couldn't find it. (The original prototype of optical puming used a >>> phototransistor, until I convinced every one that a photodiode was, >>> more sensitive (larger area), less noisy and faster.) >>> >>> Ahh the other silly thought that this generated was using an avalanche >>> zener diode as a photo detector. I know the Zener's I use are >>> sensitive to light, so again if I was to park them just below the knee >>> voltage and then hit them with light could I get some gain out of >>> them? Kinda a poor man's APD. >> >> You might want to search on single photon avalanche photo-detection. >> >> http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-3-2232 >> >> I haven't looked at the full paper but the list of references includes >> some useful stuff. >> >> -- >> Bill Sloman, Nijmegen > >Geiger-mode APDs are mostly a crock unless you need timing accuracy >better than, say, 10 ns. Their dark count rate is a good six orders of >magnitude worse than a PMT of the same area, and their dead time is 10 >times longer. > >On the other hand, they don't die if you put them in a helium >atmosphere, and they last longer than 5 years. > They don't do this, either... http://physicsworld.com/cws/article/news/3446 Hamamatsu makes these tubes. They look like basketballs. John
From: Bill Sloman on 4 Jun 2010 17:56 On Jun 4, 10:40 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > On 6/4/2010 12:01 PM,Bill Slomanwrote: > > > > > On Jun 4, 4:41 pm, George Herold<gher...(a)teachspin.com> wrote: > >> On Jun 4, 10:07 am, Phil Hobbs > > >> <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > >>> On 6/3/2010 11:12 PM, George Herold wrote: > > >>>> langw...(a)fonz.dk wrote: > >>>>> On 3 Jun., 23:11, Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> > >>>>> wrote: > >>>>>> On 6/3/2010 9:49 AM, George Herold wrote: > > >>>>>>> On Jun 2, 4:36 pm, John Larkin > >>>>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>>>>>>> On Wed, 2 Jun 2010 12:30:19 -0700 (PDT), George Herold > > >>>>>>>> <gher...(a)teachspin.com> wrote: > >>>>>>>>> On Jun 2, 1:59 pm, whit3rd<whit...(a)gmail.com> wrote: > >>>>>>>>>> On Jun 2, 10:37 am, George Herold<gher...(a)teachspin.com> wrote: > > >>>>>>>>>>>>>>> Yup, and if the voltage asymmetry is a problem you can add the signal > >>>>>>>>>>>>>> >from two diodes, one biased from the positve supply and the other from > >>>>>>>>>>>>>>> the negative. > >>>>>>>>>>> Hmmm, you are right.... I still don't think that summing the voltage > >>>>>>>>>>> noise from a bunch of unipolarized zeners is going to get rid of the > >>>>>>>>>>> voltage asymmetry. > > >>>>>>>>>> You can use two zeners on a single power supply, in bridge > >>>>>>>>>> configuration; couple the output through a transformer to get > >>>>>>>>>> the difference. Symmetry is guaranteed if you balance the bridge > >>>>>>>>>> correctly. > > >>>>>>>>> Ahh, more than one way to skin that cat. > > >>>>>>>>> Say speaking of noise sources, a colleague put together a digital > >>>>>>>>> noise source. A counter steps through a look up table that feeds a > >>>>>>>>> DAC. The lookup table holds a whole comb of sine waves equally spaced > >>>>>>>>> in frequency space up to 32kHz. (I don t recall the frequency spacing > >>>>>>>>> but I could find out.. a few Hz or so.) The phases of all the sine > >>>>>>>>> waves were chosen randomly. The DAC was 12 bit (an AD7541 I > >>>>>>>>> think). The whole thing was clocked several times lower than Nyquist > >>>>>>>>> limit (~128 kHz). Now the problem we observed, (and could never > >>>>>>>>> cure), was intermodulation distortion above the 32 kHz cutoff. The > >>>>>>>>> signals above the cutoff frequency were down by only 50 dB, and my > >>>>>>>>> colleague was expecting something closer to 70 dB down. (Is that > >>>>>>>>> right for 12 bit resolution on the DAC? ) I worked on all the layout > >>>>>>>>> and analog portions of the circuit but could never make it any > >>>>>>>>> better. There was talk about clock jitter on SED recently and I > >>>>>>>>> wondered if this could be the source of the problem? Or maybe you > >>>>>>>>> have some other idea. > > >>>>>>>> The DAC quantization, and any nonlinearity, will add harmonic > >>>>>>>> distortion. Plus the sines may occasionally peak together and clip the > >>>>>>>> dac. Plus it's not trivial to get -70 dB distortion at these > >>>>>>>> frequencies. > > >>>>>>>> We use random number generators and boxcar filters to generate > >>>>>>>> Gaussian noise to feed into dacs. This little box does this, all in a > >>>>>>>> Spartan3 FPGA... > > >>>>>>>>http://www.highlandtechnology.com/DSS/T346DS.html > > >>>>>>>> Rob cleverly, somehow, allowed the user to program the noise bandwidth > >>>>>>>> from mHz to 2 MHz without affecting the RMS amplitude. > > >>>>>>> Very nice, (Are prices listed on your website?) Y'all make stuff > >>>>>>> that's several orders of magnitude above what we're doing. > > >>>>>>> You know what I'd really like to make (and could probabbly sell too.) > >>>>>>> is a random pulse generator. Short little pulses maybe 10nS or less > >>>>>>> coming at an average rate of 1us or so. This would be a psuedo shot > >>>>>>> noise generator. With a pot on the output one could change the > >>>>>>> amplitude of the pulses and see how the noise scaled. ... Hmm it > >>>>>>> would be nicer if the average pulse rate could be changed too. So > >>>>>>> that one could keep the average 'current' the same, but made with > >>>>>>> bigger 'electrons'. Sounds like a digital circuit. (Which I find a > >>>>>>> bit boring) an analog 'something' would be more fun. > > >>>>>>> George H. > > >>>>>>>> John- Hide quoted text - > > >>>>>>>> - Show quoted text - > > >>>>>> How about avalanching a phototransistor? ;) > > >>>>> point it at an Americium source from a smokedetector :) > >>>>> real random noise > > >>>> Something optical is nice because you can change light intensity with > >>>> a knob. > > >>>> George H. > > >>>>> -Lasse > > >>> I was just janking your chain--I had no idea that anybody had actually > >>> tried that. Phototransistors are so horrible on so many levels that > >>> it's pretty amusing to see someone trying to make fast pulses out 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 nethttp://electrooptical.net-Hidequoted text - > > >>> - Show quoted text - > > >> Oh...(Silly me) Well so how 'bout a photo-transistor with three > >> terminals (one where the base has a lead connected to it.) I'll short > >> the base and collector together and then reverse bias the EB > >> junction. With the bias voltage set just below where the thing wants > >> to zener. Then a photon could set the whole thing off? > > >> I thought I had a photo transistor around here someplace, but I > >> couldn't find it. (The original prototype of optical puming used a > >> phototransistor, until I convinced every one that a photodiode was, > >> more sensitive (larger area), less noisy and faster.) > > >> Ahh the other silly thought that this generated was using an avalanche > >> zener diode as a photo detector. I know the Zener's I use are > >> sensitive to light, so again if I was to park them just below the knee > >> voltage and then hit them with light could I get some gain out of > >> them? Kinda a poor man's APD. > > > You might want to search on single photon avalanche photo-detection. > > >http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-3-2232 > > > I haven't looked at the full paper but the list of references includes > > some useful stuff. > > > -- > >Bill Sloman, Nijmegen > > Geiger-mode APDs are mostly a crock unless you need timing accuracy > better than, say, 10 ns. Their dark count rate is a good six orders of > magnitude worse than a PMT of the same area, and their dead time is 10 > times longer. > > On the other hand, they don't die if you put them in a helium > atmosphere, and they last longer than 5 years. Horses for courses. They can be a lot more compact and robust than PMTs - on which I'm rather more expert. -- Bill Sloman, Nijmegen
From: John Larkin on 4 Jun 2010 19:24 On Fri, 4 Jun 2010 14:56:44 -0700 (PDT), Bill Sloman <bill.sloman(a)ieee.org> wrote: >On Jun 4, 10:40�pm, Phil Hobbs ><pcdhSpamMeSensel...(a)electrooptical.net> wrote: >> On 6/4/2010 12:01 PM,Bill Slomanwrote: >> >> >> >> > On Jun 4, 4:41 pm, George Herold<gher...(a)teachspin.com> �wrote: >> >> On Jun 4, 10:07 am, Phil Hobbs >> >> >> <pcdhSpamMeSensel...(a)electrooptical.net> �wrote: >> >>> On 6/3/2010 11:12 PM, George Herold wrote: >> >> >>>> langw...(a)fonz.dk wrote: >> >>>>> On 3 Jun., 23:11, Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> >> >>>>> wrote: >> >>>>>> On 6/3/2010 9:49 AM, George Herold wrote: >> >> >>>>>>> On Jun 2, 4:36 pm, John Larkin >> >>>>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> � � �wrote: >> >>>>>>>> On Wed, 2 Jun 2010 12:30:19 -0700 (PDT), George Herold >> >> >>>>>>>> <gher...(a)teachspin.com> � � �wrote: >> >>>>>>>>> On Jun 2, 1:59 pm, whit3rd<whit...(a)gmail.com> � � �wrote: >> >>>>>>>>>> On Jun 2, 10:37 am, George Herold<gher...(a)teachspin.com> � � �wrote: >> >> >>>>>>>>>>>>>>> Yup, and if the voltage asymmetry is a problem you can add the signal >> >>>>>>>>>>>>>> >from two diodes, one biased from the positve supply and the other from >> >>>>>>>>>>>>>>> the negative. >> >>>>>>>>>>> Hmmm, you are right.... I still don't think that summing the voltage >> >>>>>>>>>>> noise from a bunch of unipolarized zeners is going to get rid of the >> >>>>>>>>>>> voltage asymmetry. >> >> >>>>>>>>>> You can use two zeners on a single power supply, in bridge >> >>>>>>>>>> configuration; couple the output through a transformer to get >> >>>>>>>>>> the difference. Symmetry is guaranteed if you balance the bridge >> >>>>>>>>>> correctly. >> >> >>>>>>>>> Ahh, more than one way to skin that cat. >> >> >>>>>>>>> Say speaking of noise sources, a colleague put together a digital >> >>>>>>>>> noise source. � A counter steps through a look up table that feeds a >> >>>>>>>>> DAC. �The lookup table holds a whole comb of sine waves equally spaced >> >>>>>>>>> in frequency space up to 32kHz. �(I don t recall the frequency spacing >> >>>>>>>>> but I could find out.. a few Hz or so.) �The phases of all the sine >> >>>>>>>>> waves were chosen randomly. � �The DAC was 12 bit (an AD7541 I >> >>>>>>>>> think). �The whole thing was clocked several times lower than Nyquist >> >>>>>>>>> limit (~128 kHz). �Now the problem we observed, (and could never >> >>>>>>>>> cure), was intermodulation distortion above the 32 kHz cutoff. � The >> >>>>>>>>> signals above the cutoff frequency were down by only 50 dB, and my >> >>>>>>>>> colleague was expecting something closer to 70 dB down. �(Is that >> >>>>>>>>> right for 12 bit resolution on the DAC? ) �I worked on all the layout >> >>>>>>>>> and analog portions of the circuit but could never make it any >> >>>>>>>>> better. � There was talk about clock jitter on SED recently and I >> >>>>>>>>> wondered if this could be the source of the problem? �Or maybe you >> >>>>>>>>> have some other idea. >> >> >>>>>>>> The DAC quantization, and any nonlinearity, will add harmonic >> >>>>>>>> distortion. Plus the sines may occasionally peak together and clip the >> >>>>>>>> dac. Plus it's not trivial to get -70 dB distortion at these >> >>>>>>>> frequencies. >> >> >>>>>>>> We use random number generators and boxcar filters to generate >> >>>>>>>> Gaussian noise to feed into dacs. This little box does this, all in a >> >>>>>>>> Spartan3 FPGA... >> >> >>>>>>>>http://www.highlandtechnology.com/DSS/T346DS.html >> >> >>>>>>>> Rob cleverly, somehow, allowed the user to program the noise bandwidth >> >>>>>>>> from mHz to 2 MHz without affecting the RMS amplitude. >> >> >>>>>>> Very nice, (Are prices listed on your website?) �Y'all make stuff >> >>>>>>> that's several orders of magnitude above what we're doing. >> >> >>>>>>> You know what I'd really like to make (and could probabbly sell too.) >> >>>>>>> is a random pulse generator. �Short little pulses maybe 10nS or less >> >>>>>>> coming at an average rate of 1us or so. �This would be a psuedo shot >> >>>>>>> noise generator. �With a pot on the output one could change the >> >>>>>>> amplitude of the pulses and see how the noise scaled. �... Hmm it >> >>>>>>> would be nicer if the average pulse rate could be changed too. �So >> >>>>>>> that one could keep the average 'current' the same, but made with >> >>>>>>> bigger 'electrons'. �Sounds like a digital circuit. �(Which I find a >> >>>>>>> bit boring) an analog 'something' would be more fun. >> >> >>>>>>> George H. >> >> >>>>>>>> John- Hide quoted text - >> >> >>>>>>>> - Show quoted text - >> >> >>>>>> How about avalanching a phototransistor? ;) >> >> >>>>> point it at an Americium source from a smokedetector :) >> >>>>> real random noise >> >> >>>> Something optical is nice because you can change light intensity with >> >>>> a knob. >> >> >>>> George H. >> >> >>>>> -Lasse >> >> >>> I was just janking your chain--I had no idea that anybody had actually >> >>> tried that. �Phototransistors are so horrible on so many levels that >> >>> it's pretty amusing to see someone trying to make fast pulses out 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 nethttp://electrooptical.net-Hidequoted text - >> >> >>> - Show quoted text - >> >> >> Oh...(Silly me) �Well so how 'bout a photo-transistor with three >> >> terminals (one where the base has a lead connected to it.) �I'll short >> >> the base and collector together and then reverse bias the EB >> >> junction. �With the bias voltage set just below where the thing wants >> >> to zener. �Then a photon could set the whole thing off? >> >> >> I thought I had a photo transistor around here someplace, but I >> >> couldn't find it. � (The original prototype of optical puming used a >> >> phototransistor, until I convinced every one that a photodiode was, >> >> more sensitive (larger area), less noisy and faster.) >> >> >> Ahh the other silly thought that this generated was using an avalanche >> >> zener diode as a photo detector. �I know the Zener's I use are >> >> sensitive to light, so again if I was to park them just below the knee >> >> voltage and then hit them with light could I get some gain out of >> >> them? �Kinda a poor man's APD. >> >> > You might want to search on single photon avalanche photo-detection. >> >> >http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-3-2232 >> >> > I haven't looked at the full paper but the list of references includes >> > some useful stuff. >> >> > -- >> >Bill Sloman, Nijmegen >> >> Geiger-mode APDs are mostly a crock unless you need timing accuracy >> better than, say, 10 ns. �Their dark count rate is a good six orders of >> magnitude worse than a PMT of the same area, and their dead time is 10 >> times longer. >> >> On the other hand, they don't die if you put them in a helium >> atmosphere, and they last longer than 5 years. > >Horses for courses. They can be a lot more compact and robust than >PMTs - on which I'm rather more expert. Vain fathead. John
From: George Herold on 4 Jun 2010 23:12 On Jun 4, 4:40 pm, Phil Hobbs <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > On 6/4/2010 12:01 PM, Bill Sloman wrote: > > > > > > > On Jun 4, 4:41 pm, George Herold<gher...(a)teachspin.com> wrote: > >> On Jun 4, 10:07 am, Phil Hobbs > > >> <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > >>> On 6/3/2010 11:12 PM, George Herold wrote: > > >>>> langw...(a)fonz.dk wrote: > >>>>> On 3 Jun., 23:11, Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> > >>>>> wrote: > >>>>>> On 6/3/2010 9:49 AM, George Herold wrote: > > >>>>>>> On Jun 2, 4:36 pm, John Larkin > >>>>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >>>>>>>> On Wed, 2 Jun 2010 12:30:19 -0700 (PDT), George Herold > > >>>>>>>> <gher...(a)teachspin.com> wrote: > >>>>>>>>> On Jun 2, 1:59 pm, whit3rd<whit...(a)gmail.com> wrote: > >>>>>>>>>> On Jun 2, 10:37 am, George Herold<gher...(a)teachspin.com> wrote: > > >>>>>>>>>>>>>>> Yup, and if the voltage asymmetry is a problem you can add the signal > >>>>>>>>>>>>>> >from two diodes, one biased from the positve supply and the other from > >>>>>>>>>>>>>>> the negative. > >>>>>>>>>>> Hmmm, you are right.... I still don't think that summing the voltage > >>>>>>>>>>> noise from a bunch of unipolarized zeners is going to get rid of the > >>>>>>>>>>> voltage asymmetry. > > >>>>>>>>>> You can use two zeners on a single power supply, in bridge > >>>>>>>>>> configuration; couple the output through a transformer to get > >>>>>>>>>> the difference. Symmetry is guaranteed if you balance the bridge > >>>>>>>>>> correctly. > > >>>>>>>>> Ahh, more than one way to skin that cat. > > >>>>>>>>> Say speaking of noise sources, a colleague put together a digital > >>>>>>>>> noise source. A counter steps through a look up table that feeds a > >>>>>>>>> DAC. The lookup table holds a whole comb of sine waves equally spaced > >>>>>>>>> in frequency space up to 32kHz. (I don t recall the frequency spacing > >>>>>>>>> but I could find out.. a few Hz or so.) The phases of all the sine > >>>>>>>>> waves were chosen randomly. The DAC was 12 bit (an AD7541 I > >>>>>>>>> think). The whole thing was clocked several times lower than Nyquist > >>>>>>>>> limit (~128 kHz). Now the problem we observed, (and could never > >>>>>>>>> cure), was intermodulation distortion above the 32 kHz cutoff. The > >>>>>>>>> signals above the cutoff frequency were down by only 50 dB, and my > >>>>>>>>> colleague was expecting something closer to 70 dB down. (Is that > >>>>>>>>> right for 12 bit resolution on the DAC? ) I worked on all the layout > >>>>>>>>> and analog portions of the circuit but could never make it any > >>>>>>>>> better. There was talk about clock jitter on SED recently and I > >>>>>>>>> wondered if this could be the source of the problem? Or maybe you > >>>>>>>>> have some other idea. > > >>>>>>>> The DAC quantization, and any nonlinearity, will add harmonic > >>>>>>>> distortion. Plus the sines may occasionally peak together and clip the > >>>>>>>> dac. Plus it's not trivial to get -70 dB distortion at these > >>>>>>>> frequencies. > > >>>>>>>> We use random number generators and boxcar filters to generate > >>>>>>>> Gaussian noise to feed into dacs. This little box does this, all in a > >>>>>>>> Spartan3 FPGA... > > >>>>>>>>http://www.highlandtechnology.com/DSS/T346DS.html > > >>>>>>>> Rob cleverly, somehow, allowed the user to program the noise bandwidth > >>>>>>>> from mHz to 2 MHz without affecting the RMS amplitude. > > >>>>>>> Very nice, (Are prices listed on your website?) Y'all make stuff > >>>>>>> that's several orders of magnitude above what we're doing. > > >>>>>>> You know what I'd really like to make (and could probabbly sell too.) > >>>>>>> is a random pulse generator. Short little pulses maybe 10nS or less > >>>>>>> coming at an average rate of 1us or so. This would be a psuedo shot > >>>>>>> noise generator. With a pot on the output one could change the > >>>>>>> amplitude of the pulses and see how the noise scaled. ... Hmm it > >>>>>>> would be nicer if the average pulse rate could be changed too. So > >>>>>>> that one could keep the average 'current' the same, but made with > >>>>>>> bigger 'electrons'. Sounds like a digital circuit. (Which I find a > >>>>>>> bit boring) an analog 'something' would be more fun. > > >>>>>>> George H. > > >>>>>>>> John- Hide quoted text - > > >>>>>>>> - Show quoted text - > > >>>>>> How about avalanching a phototransistor? ;) > > >>>>> point it at an Americium source from a smokedetector :) > >>>>> real random noise > > >>>> Something optical is nice because you can change light intensity with > >>>> a knob. > > >>>> George H. > > >>>>> -Lasse > > >>> I was just janking your chain--I had no idea that anybody had actually > >>> tried that. Phototransistors are so horrible on so many levels that > >>> it's pretty amusing to see someone trying to make fast pulses out 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 nethttp://electrooptical.net-Hidequoted text - > > >>> - Show quoted text - > > >> Oh...(Silly me) Well so how 'bout a photo-transistor with three > >> terminals (one where the base has a lead connected to it.) I'll short > >> the base and collector together and then reverse bias the EB > >> junction. With the bias voltage set just below where the thing wants > >> to zener. Then a photon could set the whole thing off? > > >> I thought I had a photo transistor around here someplace, but I > >> couldn't find it. (The original prototype of optical puming used a > >> phototransistor, until I convinced every one that a photodiode was, > >> more sensitive (larger area), less noisy and faster.) > > >> Ahh the other silly thought that this generated was using an avalanche > >> zener diode as a photo detector. I know the Zener's I use are > >> sensitive to light, so again if I was to park them just below the knee > >> voltage and then hit them with light could I get some gain out of > >> them? Kinda a poor man's APD. > > > You might want to search on single photon avalanche photo-detection. > > >http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-3-2232 > > > I haven't looked at the full paper but the list of references includes > > some useful stuff. > > > -- > > Bill Sloman, Nijmegen > > Geiger-mode APDs are mostly a crock unless you need timing accuracy > better than, say, 10 ns. Their dark count rate is a good six orders of > magnitude worse than a PMT of the same area, and their dead time is 10 > times longer. > > On the other hand, they don't die if you put them in a helium > atmosphere, and they last longer than 5 years. > > 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 nethttp://electrooptical.net- Hide quoted text - > > - Show quoted text - PMT's and APD's are too expensive, for a simulation, PD shot noise should be easy, or a zener. (how much does an APD cost, in hundreds?) George H.
From: Bill Sloman on 5 Jun 2010 13:47
On Jun 5, 1:24 am, John Larkin <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > On Fri, 4 Jun 2010 14:56:44 -0700 (PDT),Bill Sloman > > > > <bill.slo...(a)ieee.org> wrote: > >On Jun 4, 10:40 pm, Phil Hobbs > ><pcdhSpamMeSensel...(a)electrooptical.net> wrote: > >> On 6/4/2010 12:01 PM,Bill Slomanwrote: > > >> > On Jun 4, 4:41 pm, George Herold<gher...(a)teachspin.com> wrote: > >> >> On Jun 4, 10:07 am, Phil Hobbs > > >> >> <pcdhSpamMeSensel...(a)electrooptical.net> wrote: > >> >>> On 6/3/2010 11:12 PM, George Herold wrote: > > >> >>>> langw...(a)fonz.dk wrote: > >> >>>>> On 3 Jun., 23:11, Phil Hobbs<pcdhSpamMeSensel...(a)electrooptical.net> > >> >>>>> wrote: > >> >>>>>> On 6/3/2010 9:49 AM, George Herold wrote: > > >> >>>>>>> On Jun 2, 4:36 pm, John Larkin > >> >>>>>>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: > >> >>>>>>>> On Wed, 2 Jun 2010 12:30:19 -0700 (PDT), George Herold > > >> >>>>>>>> <gher...(a)teachspin.com> wrote: > >> >>>>>>>>> On Jun 2, 1:59 pm, whit3rd<whit...(a)gmail.com> wrote: > >> >>>>>>>>>> On Jun 2, 10:37 am, George Herold<gher...(a)teachspin.com> wrote: > > >> >>>>>>>>>>>>>>> Yup, and if the voltage asymmetry is a problem you can add the signal > >> >>>>>>>>>>>>>> >from two diodes, one biased from the positve supply and the other from > >> >>>>>>>>>>>>>>> the negative. > >> >>>>>>>>>>> Hmmm, you are right.... I still don't think that summing the voltage > >> >>>>>>>>>>> noise from a bunch of unipolarized zeners is going to get rid of the > >> >>>>>>>>>>> voltage asymmetry. > > >> >>>>>>>>>> You can use two zeners on a single power supply, in bridge > >> >>>>>>>>>> configuration; couple the output through a transformer to get > >> >>>>>>>>>> the difference. Symmetry is guaranteed if you balance the bridge > >> >>>>>>>>>> correctly. > > >> >>>>>>>>> Ahh, more than one way to skin that cat. > > >> >>>>>>>>> Say speaking of noise sources, a colleague put together a digital > >> >>>>>>>>> noise source. A counter steps through a look up table that feeds a > >> >>>>>>>>> DAC. The lookup table holds a whole comb of sine waves equally spaced > >> >>>>>>>>> in frequency space up to 32kHz. (I don t recall the frequency spacing > >> >>>>>>>>> but I could find out.. a few Hz or so.) The phases of all the sine > >> >>>>>>>>> waves were chosen randomly. The DAC was 12 bit (an AD7541 I > >> >>>>>>>>> think). The whole thing was clocked several times lower than Nyquist > >> >>>>>>>>> limit (~128 kHz). Now the problem we observed, (and could never > >> >>>>>>>>> cure), was intermodulation distortion above the 32 kHz cutoff. The > >> >>>>>>>>> signals above the cutoff frequency were down by only 50 dB, and my > >> >>>>>>>>> colleague was expecting something closer to 70 dB down. (Is that > >> >>>>>>>>> right for 12 bit resolution on the DAC? ) I worked on all the layout > >> >>>>>>>>> and analog portions of the circuit but could never make it any > >> >>>>>>>>> better. There was talk about clock jitter on SED recently and I > >> >>>>>>>>> wondered if this could be the source of the problem? Or maybe you > >> >>>>>>>>> have some other idea. > > >> >>>>>>>> The DAC quantization, and any nonlinearity, will add harmonic > >> >>>>>>>> distortion. Plus the sines may occasionally peak together and clip the > >> >>>>>>>> dac. Plus it's not trivial to get -70 dB distortion at these > >> >>>>>>>> frequencies. > > >> >>>>>>>> We use random number generators and boxcar filters to generate > >> >>>>>>>> Gaussian noise to feed into dacs. This little box does this, all in a > >> >>>>>>>> Spartan3 FPGA... > > >> >>>>>>>>http://www.highlandtechnology.com/DSS/T346DS.html > > >> >>>>>>>> Rob cleverly, somehow, allowed the user to program the noise bandwidth > >> >>>>>>>> from mHz to 2 MHz without affecting the RMS amplitude. > > >> >>>>>>> Very nice, (Are prices listed on your website?) Y'all make stuff > >> >>>>>>> that's several orders of magnitude above what we're doing. > > >> >>>>>>> You know what I'd really like to make (and could probabbly sell too.) > >> >>>>>>> is a random pulse generator. Short little pulses maybe 10nS or less > >> >>>>>>> coming at an average rate of 1us or so. This would be a psuedo shot > >> >>>>>>> noise generator. With a pot on the output one could change the > >> >>>>>>> amplitude of the pulses and see how the noise scaled. ... Hmm it > >> >>>>>>> would be nicer if the average pulse rate could be changed too. So > >> >>>>>>> that one could keep the average 'current' the same, but made with > >> >>>>>>> bigger 'electrons'. Sounds like a digital circuit. (Which I find a > >> >>>>>>> bit boring) an analog 'something' would be more fun. > > >> >>>>>>> George H. > > >> >>>>>>>> John- Hide quoted text - > > >> >>>>>>>> - Show quoted text - > > >> >>>>>> How about avalanching a phototransistor? ;) > > >> >>>>> point it at an Americium source from a smokedetector :) > >> >>>>> real random noise > > >> >>>> Something optical is nice because you can change light intensity with > >> >>>> a knob. > > >> >>>> George H. > > >> >>>>> -Lasse > > >> >>> I was just janking your chain--I had no idea that anybody had actually > >> >>> tried that. Phototransistors are so horrible on so many levels that > >> >>> it's pretty amusing to see someone trying to make fast pulses out 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 nethttp://electrooptical.net-Hidequotedtext - > > >> >>> - Show quoted text - > > >> >> Oh...(Silly me) Well so how 'bout a photo-transistor with three > >> >> terminals (one where the base has a lead connected to it.) I'll short > >> >> the base and collector together and then reverse bias the EB > >> >> junction. With the bias voltage set just below where the thing wants > >> >> to zener. Then a photon could set the whole thing off? > > >> >> I thought I had a photo transistor around here someplace, but I > >> >> couldn't find it. (The original prototype of optical puming used a > >> >> phototransistor, until I convinced every one that a photodiode was, > >> >> more sensitive (larger area), less noisy and faster.) > > >> >> Ahh the other silly thought that this generated was using an avalanche > >> >> zener diode as a photo detector. I know the Zener's I use are > >> >> sensitive to light, so again if I was to park them just below the knee > >> >> voltage and then hit them with light could I get some gain out of > >> >> them? Kinda a poor man's APD. > > >> > You might want to search on single photon avalanche photo-detection. > > >> >http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-16-3-2232 > > >> > I haven't looked at the full paper but the list of references includes > >> > some useful stuff. > > >> > -- > >> >Bill Sloman, Nijmegen > > >> Geiger-mode APDs are mostly a crock unless you need timing accuracy > >> better than, say, 10 ns. Their dark count rate is a good six orders of > >> magnitude worse than a PMT of the same area, and their dead time is 10 > >> times longer. > > >> On the other hand, they don't die if you put them in a helium > >> atmosphere, and they last longer than 5 years. > > >Horses for courses. They can be a lot more compact and robust than > >PMTs - on which I'm rather more expert. > > Vain fathead. I've worked with PMT's - which is more than I can claim about SPAD's - and I've persuaded the IEEE that I do know a little about PMTs - see the IEEE Transactions on Electronic Devices volume 38 pages 679-680, published in March 1991. You do need to base your abuse on something more than your right-wing intuition. Going off half-cocked like this does rather expose your enthusiasm for believeing what you want to believe despite the absence of any evidence to support your point of view. -- Bill Sloman, Nijmegen |