On Jan 3, 7:23=A0am, George Herold <gher...@teachspin.com> wrote:> On Jan 2, 9:51=A0pm, "mook johnson" <m...@mook.net> wrote: > > > > > > > "George Herold" <gher...@teachspin.com> wrote in message > > >news:99290406-72e0-474c-9b20-a0f728df6c6b@r5g2000yqc.googlegroups.com... > > On Jan 2, 7:44 pm, Tim Wescott <t...@seemywebsite.com> wrote: > > > > On Mon, 02 Jan 2012 15:52:58 -0800, George Herold wrote: > > > > Zener noise source (freq < 1MHz.) > > > > > I was revisiting Zener's as noise sources today. I first tried some=12V> > > > (1W*) diodes. (I want to bias them from 15V rails.) > > > > They worked fine, but I found the noise varied by at least 6dB (a f=actor> > > > of 2 in V peak) > > > > for different diodes from the same strip. (After testing 5 I gave u=p.)> > > > > So I fell back to an old circuit. > > > > > +15--+----+ > > > > Z | > > > > ^ 1M > > > > | | > > > > +----|-C+-(buffer)-------( ) > > > > | +--|--C-+--(buffer)-(summer) > > > > 1M Z 100k | > > > > | ^ | 100k > > > > -15--+----| +----+ > > > > GND > > > > > Z are the zeners, 20V (0.5W), > > > > ^ > > > > > You should wrap black tape around glass body ones. (note to self: t=ry> > > > some surface mount) > > > > > For C I used 1uF films but I bet ceramics will work fine too. The > > > > output of each buffer looks like a pulse into an RC filter. (time > > > > constant maybe 1uS depending on bias and buffer resistors) The best > > > > thing is that all 20V/ 1/2 W zeners I've tried give the same noise =to> > > > maybe 10% (in voltage). (Again exact number depend on the R's used)=.> > > > With the R's shown the noise is flat out to about 600 kHz, or so. > > > > > George H. > > > > > *the 1 watters was all I had in the parts box. > > > > IIRC, the noise in an avalanche diode is proportional to current. > > > > Could you have been falling prey to the variability in the Zener volt=age> > > and the low overhead between the diode and the rail? A constant-curre=nt> > > sink would fix that... > > > > -- > > > My liberal friends think I'm a conservative kook. > > > My conservative friends think I'm a liberal kook. > > > Why am I not happy that they have found common ground? > > > > Tim Wescott, Communications, Control, Circuits & > > > Softwarehttp://www.wescottdesign.com-Hidequoted text - > > > > - Show quoted text - > > >Hi Tim, I just had 12V zeners +30k ohm across 15 volts. > > >Zero correlation between zener voltage and noise. > > >(I only tested 5.) > > > >George H. > > > He's talking about the 5% tolerance in Vz causing a large change in the > > actual voltage drop across the 30K resistor. > > > Looks like you were shooting for 100uA but you can get anywhere from 80=to> > 120uA. =A0a 20% swing. =A0 I don't know how strong a function of noise =is to> > bias current but that may explain some of your findings.- Hide quoted t=ext -> > > - Show quoted text - > > Hi Mook, OK here are the numbers from the 5 diodes I tested. =A0Noise is > measured with a SRS spectrum analyzer (which has this weird dBV > units.) > > diode =A0 =A0 voltage =A0 =A0 noise > =A0 =A0 =A0 =A0 =A0 =A0(V) =A0 =A0 =A0 =A0 dbV > 1 =A0 =A0 =A0 =A0 =A011.66 =A0 =A0 =A0-58.3 > 2 =A0 =A0 =A0 =A0 =A011.60 =A0 =A0 =A0-60.5 > 3 =A0 =A0 =A0 =A0 =A011.95 =A0 =A0 =A0-64 > 4 =A0 =A0 =A0 =A0 =A011.95 =A0 =A0 =A0-57.5 > 5 =A0 =A0 =A0 =A0 =A011.78 =A0 =A0 =A0-64.0 > > George H.Doesn't go to DC but can give you a LOT of bang for your buck: Use a soundcard, custom code, and analyze away. You get a dual channel system, plus can use the dual channel source to 'sweep' Ch1 monitor the goes-intos Ch2 monitor the goes-outas Do some math and you get data over the range of 10Hz to 90kHz. Not an SRS, but a cheap competitor.
Zener noise source (freq < 1MHz.)
Started by ●January 2, 2012
Reply by ●January 4, 20122012-01-04
Reply by ●January 4, 20122012-01-04
On Jan 4, 9:47=A0am, Robert Macy <robert.a.m...@gmail.com> wrote:> On Jan 3, 7:23=A0am, George Herold <gher...@teachspin.com> wrote: > > > > > > > On Jan 2, 9:51=A0pm, "mook johnson" <m...@mook.net> wrote: > > > > "George Herold" <gher...@teachspin.com> wrote in message > > > >news:99290406-72e0-474c-9b20-a0f728df6c6b@r5g2000yqc.googlegroups.com.=..> > > On Jan 2, 7:44 pm, Tim Wescott <t...@seemywebsite.com> wrote: > > > > > On Mon, 02 Jan 2012 15:52:58 -0800, George Herold wrote: > > > > > Zener noise source (freq < 1MHz.) > > > > > > I was revisiting Zener's as noise sources today. I first tried so=me 12V> > > > > (1W*) diodes. (I want to bias them from 15V rails.) > > > > > They worked fine, but I found the noise varied by at least 6dB (a=factor> > > > > of 2 in V peak) > > > > > for different diodes from the same strip. (After testing 5 I gave=up.)> > > > > > So I fell back to an old circuit. > > > > > > +15--+----+ > > > > > Z | > > > > > ^ 1M > > > > > | | > > > > > +----|-C+-(buffer)-------( ) > > > > > | +--|--C-+--(buffer)-(summer) > > > > > 1M Z 100k | > > > > > | ^ | 100k > > > > > -15--+----| +----+ > > > > > GND > > > > > > Z are the zeners, 20V (0.5W), > > > > > ^ > > > > > > You should wrap black tape around glass body ones. (note to self:=try> > > > > some surface mount) > > > > > > For C I used 1uF films but I bet ceramics will work fine too. The > > > > > output of each buffer looks like a pulse into an RC filter. (time > > > > > constant maybe 1uS depending on bias and buffer resistors) The be=st> > > > > thing is that all 20V/ 1/2 W zeners I've tried give the same nois=e to> > > > > maybe 10% (in voltage). (Again exact number depend on the R's use=d).> > > > > With the R's shown the noise is flat out to about 600 kHz, or so. > > > > > > George H. > > > > > > *the 1 watters was all I had in the parts box. > > > > > IIRC, the noise in an avalanche diode is proportional to current. > > > > > Could you have been falling prey to the variability in the Zener vo=ltage> > > > and the low overhead between the diode and the rail? A constant-cur=rent> > > > sink would fix that... > > > > > -- > > > > My liberal friends think I'm a conservative kook. > > > > My conservative friends think I'm a liberal kook. > > > > Why am I not happy that they have found common ground? > > > > > Tim Wescott, Communications, Control, Circuits & > > > > Softwarehttp://www.wescottdesign.com-Hidequotedtext - > > > > > - Show quoted text - > > > >Hi Tim, I just had 12V zeners +30k ohm across 15 volts. > > > >Zero correlation between zener voltage and noise. > > > >(I only tested 5.) > > > > >George H. > > > > He's talking about the 5% tolerance in Vz causing a large change in t=he> > > actual voltage drop across the 30K resistor. > > > > Looks like you were shooting for 100uA but you can get anywhere from =80 to> > > 120uA. =A0a 20% swing. =A0 I don't know how strong a function of nois=e is to> > > bias current but that may explain some of your findings.- Hide quoted=text -> > > > - Show quoted text - > > > Hi Mook, OK here are the numbers from the 5 diodes I tested. =A0Noise i=s> > measured with a SRS spectrum analyzer (which has this weird dBV > > units.) > > > diode =A0 =A0 voltage =A0 =A0 noise > > =A0 =A0 =A0 =A0 =A0 =A0(V) =A0 =A0 =A0 =A0 dbV > > 1 =A0 =A0 =A0 =A0 =A011.66 =A0 =A0 =A0-58.3 > > 2 =A0 =A0 =A0 =A0 =A011.60 =A0 =A0 =A0-60.5 > > 3 =A0 =A0 =A0 =A0 =A011.95 =A0 =A0 =A0-64 > > 4 =A0 =A0 =A0 =A0 =A011.95 =A0 =A0 =A0-57.5 > > 5 =A0 =A0 =A0 =A0 =A011.78 =A0 =A0 =A0-64.0 > > > George H. > > Doesn't go to DC but can give you a LOT of bang for your buck: Use a > soundcard, custom code, and analyze away. > > You get a dual channel system, plus can use the dual channel source to > 'sweep' > > Ch1 monitor the goes-intos > Ch2 monitor the goes-outas > > Do some math and you get data over the range of 10Hz to 90kHz. Not an > SRS, but a cheap competitor.- Hide quoted text - > > - Show quoted text -Hi Robert, You mean a frequency swept source from the sound card? That's very useful too! George H.
Reply by ●January 4, 20122012-01-04
On Jan 4, 8:46=A0am, George Herold <gher...@teachspin.com> wrote:> On Jan 4, 9:47=A0am, Robert Macy <robert.a.m...@gmail.com> wrote: > > > > > > > On Jan 3, 7:23=A0am, George Herold <gher...@teachspin.com> wrote: > > > > On Jan 2, 9:51=A0pm, "mook johnson" <m...@mook.net> wrote: > > > > > "George Herold" <gher...@teachspin.com> wrote in message > > > > >news:99290406-72e0-474c-9b20-a0f728df6c6b@r5g2000yqc.googlegroups.co=m...> > > > On Jan 2, 7:44 pm, Tim Wescott <t...@seemywebsite.com> wrote: > > > > > > On Mon, 02 Jan 2012 15:52:58 -0800, George Herold wrote: > > > > > > Zener noise source (freq < 1MHz.) > > > > > > > I was revisiting Zener's as noise sources today. I first tried =some 12V> > > > > > (1W*) diodes. (I want to bias them from 15V rails.) > > > > > > They worked fine, but I found the noise varied by at least 6dB =(a factor> > > > > > of 2 in V peak) > > > > > > for different diodes from the same strip. (After testing 5 I ga=ve up.)> > > > > > > So I fell back to an old circuit. > > > > > > > +15--+----+ > > > > > > Z | > > > > > > ^ 1M > > > > > > | | > > > > > > +----|-C+-(buffer)-------( ) > > > > > > | +--|--C-+--(buffer)-(summer) > > > > > > 1M Z 100k | > > > > > > | ^ | 100k > > > > > > -15--+----| +----+ > > > > > > GND > > > > > > > Z are the zeners, 20V (0.5W), > > > > > > ^ > > > > > > > You should wrap black tape around glass body ones. (note to sel=f: try> > > > > > some surface mount) > > > > > > > For C I used 1uF films but I bet ceramics will work fine too. T=he> > > > > > output of each buffer looks like a pulse into an RC filter. (ti=me> > > > > > constant maybe 1uS depending on bias and buffer resistors) The =best> > > > > > thing is that all 20V/ 1/2 W zeners I've tried give the same no=ise to> > > > > > maybe 10% (in voltage). (Again exact number depend on the R's u=sed).> > > > > > With the R's shown the noise is flat out to about 600 kHz, or s=o.> > > > > > > George H. > > > > > > > *the 1 watters was all I had in the parts box. > > > > > > IIRC, the noise in an avalanche diode is proportional to current. > > > > > > Could you have been falling prey to the variability in the Zener =voltage> > > > > and the low overhead between the diode and the rail? A constant-c=urrent> > > > > sink would fix that... > > > > > > -- > > > > > My liberal friends think I'm a conservative kook. > > > > > My conservative friends think I'm a liberal kook. > > > > > Why am I not happy that they have found common ground? > > > > > > Tim Wescott, Communications, Control, Circuits & > > > > > Softwarehttp://www.wescottdesign.com-Hidequotedtext- > > > > > > - Show quoted text - > > > > >Hi Tim, I just had 12V zeners +30k ohm across 15 volts. > > > > >Zero correlation between zener voltage and noise. > > > > >(I only tested 5.) > > > > > >George H. > > > > > He's talking about the 5% tolerance in Vz causing a large change in=the> > > > actual voltage drop across the 30K resistor. > > > > > Looks like you were shooting for 100uA but you can get anywhere fro=m 80 to> > > > 120uA. =A0a 20% swing. =A0 I don't know how strong a function of no=ise is to> > > > bias current but that may explain some of your findings.- Hide quot=ed text -> > > > > - Show quoted text - > > > > Hi Mook, OK here are the numbers from the 5 diodes I tested. =A0Noise=is> > > measured with a SRS spectrum analyzer (which has this weird dBV > > > units.) > > > > diode =A0 =A0 voltage =A0 =A0 noise > > > =A0 =A0 =A0 =A0 =A0 =A0(V) =A0 =A0 =A0 =A0 dbV > > > 1 =A0 =A0 =A0 =A0 =A011.66 =A0 =A0 =A0-58.3 > > > 2 =A0 =A0 =A0 =A0 =A011.60 =A0 =A0 =A0-60.5 > > > 3 =A0 =A0 =A0 =A0 =A011.95 =A0 =A0 =A0-64 > > > 4 =A0 =A0 =A0 =A0 =A011.95 =A0 =A0 =A0-57.5 > > > 5 =A0 =A0 =A0 =A0 =A011.78 =A0 =A0 =A0-64.0 > > > > George H. > > > Doesn't go to DC but can give you a LOT of bang for your buck: Use a > > soundcard, custom code, and analyze away. > > > You get a dual channel system, plus can use the dual channel source to > > 'sweep' > > > Ch1 monitor the goes-intos > > Ch2 monitor the goes-outas > > > Do some math and you get data over the range of 10Hz to 90kHz. Not an > > SRS, but a cheap competitor.- Hide quoted text - > > > - Show quoted text - > > Hi Robert, =A0You mean a frequency swept source from the sound card? > That's very useful too! > > George H.I mean TOTAL control of the source. as in 'arbitrary' signal source. and two of them! Plus, my soundcard's [Creative Labs EMU1212] channels match to better than 0.4% and can calibrate to better than 0.05% hold all day. and those errors are mainly at the higher end, roll-off. Playing special tricks youi can easily get down into the 5-10 ppm. I have measured data that shows less than 1ppm, that's using ALL the bits. I routinely use it to find a system's transfer function and noise spectral density, and the operating ambient noise sources: AC mains, PC noise, monitor noise, etc. You'd be surprised how loud those are. That card is the closest I've ever been able to get to a Nyquist rate: useful to 95%, but in spec up to 93% For $100 and a little fussing you have better than $10,000 worth of instrumentation. If you avoid writing software like the plague, there are 'free' SW packages out there [I think] with decent UI's and control panels..
