High Quality White Noise Gen
in [Design]
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From: John Larkin on 6 Jun 2010 23:51 On Sun, 6 Jun 2010 20:42:29 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jun 6, 11:08�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >Web-Site.com> wrote: >> On Sun, 06 Jun 2010 18:36:27 -0700, John Larkin >> >> >> >> >> >> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >On Sun, 6 Jun 2010 13:54:05 -0700 (PDT), George Herold >> ><gher...(a)teachspin.com> wrote: >> >> >>On Jun 6, 4:46�pm, "k...(a)att.bizzzzzzzzzzzz" <k...(a)att.bizzzzzzzzzzzz> >> >>wrote: >> >>> On Sun, 6 Jun 2010 13:36:09 -0700 (PDT), George Herold <gher...(a)teachspin.com> >> >>> wrote: >> >> >>> >On Jun 5, 6:52 pm, John Larkin >> >>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> >> On Sat, 5 Jun 2010 15:00:09 -0700 (PDT), Bill Sloman >> >> >>> >> <bill.slo...(a)ieee.org> wrote: >> >>> >> >On Jun 5, 8:18 pm, John Larkin >> >>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >>> >> >> On Sat, 5 Jun 2010 10:47:26 -0700 (PDT),Bill Sloman >> >> >>> >> >> <bill.slo...(a)ieee.org> wrote: >> >>> >> >> >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: >> >> >>> >> ><snip> >> >> >>> >> >> >> >> > 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. >> >> >>> >> >> >> >> 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. >> >> >>> >> >> All you do here is claim how "expert" you are, or maybe were, without >> >>> >> >> ever making actual contributions. >> >> >>> >> >Nothing that you'd be willing to acknowledge, particularly since most >> >>> >> >of my contributions are references to the publshed literature, a >> >>> >> >source that you seem ill-equipped to exploit >> >> >>> >> >> You never *do* anything. >> >> >>> >> >Not at the moment, and I find it frustrating. >> >> >>> >> >> And when I don't have convincing evidence, I experiment and collect >> >>> >> >> some. A mouse isn't a soldering iron. >> >> >>> >> >You burble about 140dB of ripple rejection >> >> >>> >> Burble? >> >>> >Maybe he say you coming through the turgey(sp) wood. >> >> >>> >> I questioned whether the Spice models of the c-multiplier were >> >>> >> accurate at mid-frequencies. None came close to 140, or even 80, dB at >> >>> >> frequencies where Early slope matters. So I tried some experiments. >> >> >>> >The Early effect goes away at at high frequencies? >> >> >>> At high frequencies other parasitics become more important? �Early gets >> >>> swamped by Cce?- Hide quoted text - >> >> >>> - Show quoted text - >> >> >>Hmm OK... LTspice didn't seem to show that, (90dB of attenuation at >> >>100kHz), but maybe I have to do some real measurements. �I'm afraid I >> >>don't really understand the Early effect/ voltage. >> >> >Just imagine a resistor from collector to emitter. The question is, >> >what's the value? >> >> >John >> >> Early effect changes the base WIDTH, thus the current gain. > >Current gain is modulated by the collector-base voltage? That seems >to explain it. For the purposes of measurement and modeling, an equivalent c-e resistor value is perfectly appropriate. That's how it behaves here. Without real numbers, all models are worthless. John
From: Jim Thompson on 7 Jun 2010 00:00 On Sun, 06 Jun 2010 20:51:53 -0700, John Larkin <jjlarkin(a)highNOTlandTHIStechnologyPART.com> wrote: >On Sun, 6 Jun 2010 20:42:29 -0700 (PDT), George Herold ><gherold(a)teachspin.com> wrote: > >>On Jun 6, 11:08�pm, Jim Thompson <To-Email-Use-The-Envelope-I...(a)On-My- >>Web-Site.com> wrote: >>> On Sun, 06 Jun 2010 18:36:27 -0700, John Larkin >>> >>> >>> >>> >>> >>> <jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >On Sun, 6 Jun 2010 13:54:05 -0700 (PDT), George Herold >>> ><gher...(a)teachspin.com> wrote: >>> >>> >>On Jun 6, 4:46�pm, "k...(a)att.bizzzzzzzzzzzz" <k...(a)att.bizzzzzzzzzzzz> >>> >>wrote: >>> >>> On Sun, 6 Jun 2010 13:36:09 -0700 (PDT), George Herold <gher...(a)teachspin.com> >>> >>> wrote: >>> >>> >>> >On Jun 5, 6:52 pm, John Larkin >>> >>> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>> >> On Sat, 5 Jun 2010 15:00:09 -0700 (PDT), Bill Sloman >>> >>> >>> >> <bill.slo...(a)ieee.org> wrote: >>> >>> >> >On Jun 5, 8:18 pm, John Larkin >>> >>> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >>> >>> >> >> On Sat, 5 Jun 2010 10:47:26 -0700 (PDT),Bill Sloman >>> >>> >>> >> >> <bill.slo...(a)ieee.org> wrote: >>> >>> >> >> >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: >>> >>> >>> >> ><snip> >>> >>> >>> >> >> >> >> > 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. >>> >>> >>> >> >> >> >> 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. >>> >>> >>> >> >> All you do here is claim how "expert" you are, or maybe were, without >>> >>> >> >> ever making actual contributions. >>> >>> >>> >> >Nothing that you'd be willing to acknowledge, particularly since most >>> >>> >> >of my contributions are references to the publshed literature, a >>> >>> >> >source that you seem ill-equipped to exploit >>> >>> >>> >> >> You never *do* anything. >>> >>> >>> >> >Not at the moment, and I find it frustrating. >>> >>> >>> >> >> And when I don't have convincing evidence, I experiment and collect >>> >>> >> >> some. A mouse isn't a soldering iron. >>> >>> >>> >> >You burble about 140dB of ripple rejection >>> >>> >>> >> Burble? >>> >>> >Maybe he say you coming through the turgey(sp) wood. >>> >>> >>> >> I questioned whether the Spice models of the c-multiplier were >>> >>> >> accurate at mid-frequencies. None came close to 140, or even 80, dB at >>> >>> >> frequencies where Early slope matters. So I tried some experiments. >>> >>> >>> >The Early effect goes away at at high frequencies? >>> >>> >>> At high frequencies other parasitics become more important? �Early gets >>> >>> swamped by Cce?- Hide quoted text - >>> >>> >>> - Show quoted text - >>> >>> >>Hmm OK... LTspice didn't seem to show that, (90dB of attenuation at >>> >>100kHz), but maybe I have to do some real measurements. �I'm afraid I >>> >>don't really understand the Early effect/ voltage. >>> >>> >Just imagine a resistor from collector to emitter. The question is, >>> >what's the value? >>> >>> >John >>> >>> Early effect changes the base WIDTH, thus the current gain. >> >>Current gain is modulated by the collector-base voltage? That seems >>to explain it. > > >For the purposes of measurement and modeling, an equivalent c-e >resistor value is perfectly appropriate. That's how it behaves here. > >Without real numbers, all models are worthless. > >John > In your dreams, dorkfish :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | The only thing bipartisan in this country is hypocrisy
From: John Larkin on 7 Jun 2010 00:00 On Sun, 6 Jun 2010 20:31:49 -0700 (PDT), George Herold <gherold(a)teachspin.com> wrote: >On Jun 6, 9:35�pm, John Larkin ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> On Sun, 6 Jun 2010 13:36:09 -0700 (PDT), George Herold >> >> >> >> >> >> <gher...(a)teachspin.com> wrote: >> >On Jun 5, 6:52�pm, John Larkin >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> On Sat, 5 Jun 2010 15:00:09 -0700 (PDT), Bill Sloman >> >> >> <bill.slo...(a)ieee.org> wrote: >> >> >On Jun 5, 8:18�pm, John Larkin >> >> ><jjlar...(a)highNOTlandTHIStechnologyPART.com> wrote: >> >> >> On Sat, 5 Jun 2010 10:47:26 -0700 (PDT),Bill Sloman >> >> >> >> <bill.slo...(a)ieee.org> wrote: >> >> >> >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: >> >> >> ><snip> >> >> >> >> >> >> > 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. >> >> >> >> >> >> 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. >> >> >> >> All you do here is claim how "expert" you are, or maybe were, without >> >> >> ever making actual contributions. >> >> >> >Nothing that you'd be willing to acknowledge, particularly since most >> >> >of my contributions are references to the publshed literature, a >> >> >source that you seem ill-equipped to exploit >> >> >> >> You never *do* anything. >> >> >> >Not at the moment, and I find it frustrating. >> >> >> >> And when I don't have convincing evidence, I experiment and collect >> >> >> some. A mouse isn't a soldering iron. >> >> >> >You burble about 140dB of ripple rejection >> >> >> Burble? >> >Maybe he say you coming through the turgey(sp) wood. >> >> >> I questioned whether the Spice models of the c-multiplier were >> >> accurate at mid-frequencies. None came close to 140, or even 80, dB at >> >> frequencies where Early slope matters. So I tried some experiments. >> >> >The Early effect goes away at at high frequencies? >> >> No, but the optput capacitor impedance continues to decline. >> >> There are a few frequency zones: >> >> Dc to where the base lowpass filter kicks in: 0 dB ripple attenuation. >> >> A region where the Early thing works, roughly -50 dB. >> >> A slope downward, beginning at the corner frequency set by Re and the >> output filter capacitance Cf. > >Ahh excellent. It's this one that makes it not work so well when I >load the output too much. (Or do I just need a bigger cap?) At modest currents, emitter dynamic resistance Re is inverse on current, actually about 25 ohms divided by emitter current in mA. So the corner frequency of Re * Cl changes with load. I don't know how the Early feedthrough changes with load current. Capacitor ESR also forms a voltage divider with Re, so yet more ripple blasts through as Re goes down at higher currents. Not a simple circuit! John
From: Phil Hobbs on 7 Jun 2010 00:10 George Herold wrote: > 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 >>>>> - 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 >> >> - 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. The nice thing about PIN photodiodes is that there's a first-principles relationship between the DC and noise currents. That's a great calibration principle for instruments. I have about 100 InGaAs APD/preamp modules that I got for about 75 cents each--probably 0.5 cents on the dollar. 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: Michael A. Terrell on 7 Jun 2010 01:00
George Herold wrote: > > My daughter (age 10) recited it at the last company/ holiday poetry > reading. > She may make a mistake or two, but she�ll kill ya with charm. Oh, that's just great! More Juvenile crime. ;-) -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge. |