The central limit theorem rocks, (summing Zener noise)
in [Design]
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From: Michael A. Terrell on 5 Jun 2010 20:52 Tim Williams wrote: > > >> 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. I'm sure the university has more than a single server. Their network traffic can be divided in a number of different ways to balance the load. Even a typical 'home' grade of broadband router can direct different ports to different computers. -- Anyone wanting to run for any political office in the US should have to have a DD214, and a honorable discharge.
From: Jay Ts on 5 Jun 2010 21:38 George Herold wrote: > 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! Yes, they are very nice. But ... I replaced the opamps with TLE2237's, and it fixed the problem. The higher gain-bandwidth product of the TLE2237 (50 MHz vs. 8) seems to have done the trick. I don't understand exactly why, but it worked, so I'll keep it. ;) The OPA2134 is more optimized for high slew rate, and its low distortion spec is not only published, but hard to beat at the price. I normally use them at much lower gain, so have no problems with frequency response in the audio band. With the TLE2237's still saw a drop of nearly 1 dB at 40 KHz, but at that point I suspected that it was due to the combination of audio cables, sound card and software, so I did a loopback test, using a software white noise generator. And with that, I got almost exactly the same spectrum -- I set Spectrum Lab to the highest level of averaging and smoothing, and the plots of the loopback "wire" and the white noise generator agreed almost pixel-perfect. In the plot, 1 pixel was 0.1 dB, so I am done. I cannot make the circuit work any better with the tools I have at hand. > They should work just fine. Is the power supply well filtered? 100uF > alum. or 10uF ceram. I looked at that, and moving to larger, 100 uF caps did quiet the supplies a little, but I didn't see any difference in the spectrum. > Tim W. (above) had a good description of avalanche zeners. Yes, it was, and thanks for that! It was better than what I read at Wikipedia or anywhere else. Good stuff, and I think I'm starting to understand. Jay Ts
From: George Herold on 6 Jun 2010 16:49
On Jun 5, 9:38 pm, Jay Ts <bitbuc...(a)example.com> wrote: > George Herold wrote: > > 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! > > Yes, they are very nice. But ... I replaced the opamps with > TLE2237's, and it fixed the problem. The higher gain-bandwidth > product of the TLE2237 (50 MHz vs. 8) seems to have > done the trick. I don't understand exactly why, but it worked, > so I'll keep it. ;) > > The OPA2134 is more optimized for high slew rate, and its low > distortion spec is not only published, but hard to beat at the > price. I normally use them at much lower gain, so have no > problems with frequency response in the audio band. Yeah slew rate is nice, I aslo like the 8nV of noise and 1-2pF of input capacitance. > > With the TLE2237's still saw a drop of nearly 1 dB at 40 KHz, but > at that point I suspected that it was due to the combination of > audio cables, sound card and software, so I did a loopback test, > using a software white noise generator. And with that, I got almost > exactly the same spectrum -- I set Spectrum Lab to the highest level > of averaging and smoothing, and the plots of the loopback "wire" and > the white noise generator agreed almost pixel-perfect. In the plot, > 1 pixel was 0.1 dB, so I am done. Excellent. George H. <snip> > Jay Ts- Hide quoted text - > > - Show quoted text - |