The central limit theorem rocks, (summing Zener noise)
in [Design]
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From: George Herold on 4 Jun 2010 23:00 On Jun 4, 3:20 pm, Jay Ts <bitbuc...(a)example.com> wrote: > On Fri, 04 Jun 2010 06:33:46 -0700, George Herold wrote: > > On Jun 3, 11:52 pm, Jay Ts <bitbuc...(a)example.com> wrote: > > >> Here is a schematic of a little circuit I created yesterday after > >> following the original thread on this topic: > > >>http://jayts.com/images/WhiteNoiseGen-Med.png > > >> I just put some ideas together from the discussion here, along with > >> other things I found from some quick Internet searches. > > >> I used two opamps to bring the output up to about +4 dBu (commonly used > >> in pro audio). > > >> I put the output of the circuit into a PC 24/96 audio card, and on a > >> spectrum analyzer app, it showed about a 6 dB drop in amplitude from > >> near DC (0 dB) to 40 KHz (-6 dB). I did not think this was really bad, > >> but if anyone knows how to make this flatter, short of an esoteric and > >> expensive "noise diode", please comment. > > > What opamp(s) are you using? > > Both are TI OPA2134. Slew rate is 20 V/us, and the gain-bandwidth > product is 8 MHz. Ahh, I love those opamps! I saw that TI has come out with an 'improved' version. 5nv of voltage noise and 12 MHz GBW, but 7pF of input capacitance. (not good for PD front ends.) They should work just fine. Is the power supply well filtered? 100uF alum. or 10uF ceram. Tim W. (above) had a good description of avalanche zeners. Near the knee the noise is biggest. If you're a bit above or below the knee there is a voltage asymmetry with higher voltages towards the knee (it changes sign depending if you're above or below). George H. > > They should be able to handle a gain of 33 to well over 40 KHz, > but since I never trust datasheets or theories (or myself), I > may try adding more gain stages to make sure. > > The schematic makes it look like the opamps are separate chips because > gschem didn't have a dual opamp symbol for the 2nd (using pins 5-7 > instead of 1-3). > > Jay Ts- Hide quoted text - > > - Show quoted text -
From: Jan Panteltje on 5 Jun 2010 08:22 On a sunny day (Fri, 4 Jun 2010 20:21:47 -0500) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <PEhOn.58537$HG1.13599(a)newsfe21.iad>: >http://myweb.msoe.edu/williamstm/Images/Gaussian_Noise1.jpg I get: You tried to access the address http://myweb.msoe.edu/williamstm/Images/Gaussian_Noise1.jpg, which is currently unavailable. Please make sure that the Web address (URL) is correctly spelled and punctuated, then try reloading the page. Make sure your Internet connection is active and check whether other applications that rely on the same connection are working.
From: Tim Williams on 5 Jun 2010 11:29 >> http://myweb.msoe.edu/williamstm/Images/Gaussian_Noise1.jpg > > I get: > You tried to access the address ... The server was down yesterday. Oddly enough, FTP still worked. It's working now. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: whit3rd on 5 Jun 2010 11:57 On Jun 4, 6:21 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: > Incidentially, I have a Gaussian Noise Generator from the 60s which uses a > pair of 6D4 gas thyratrons (in magnetic field, for some reason). The magnets are there to make ionized-gas filaments break up (otherwise the thyratron would latch ON just like its 'normal' operation instead of just amplifying noise). That, at any rate, is the explanation I heard four decades back...
From: John Larkin on 5 Jun 2010 12:56
On 04 Jun 2010 18:50:30 GMT, Jay Ts <bitbucket(a)example.com> wrote: >But, I now have some questions ... like, why is the noise voltage >waveform more asymmetric at lower currents, why is it asymmetric >at all, and why is it that there is more noise at low currents >than at high currents? Trying understand these things is making >me feel stupid. ;-) Are there any solid state physics geniuses >around who would like to try explaining this? This doesn't explain it, but it does suggest what's happening: ftp://jjlarkin.lmi.net/Zener_Noise.pdf I'd suggest a few mA for using ordinary zeners as reasonably symmetric noise sources. I really don't understand how semiconductors work, but I'm a circuit designer, so I don't have to. John |