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..
Reply by George Herold●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 Robert Macy●January 4, 20122012-01-04
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.
Reply by Tim Wescott●January 3, 20122012-01-03
On Tue, 03 Jan 2012 17:01:17 +1100, Phil Allison wrote:
> "Tim Wescott"
>
>
>> IIRC, the noise in an avalanche diode is proportional to current.
>>
>>
> ** That would be rule for noise current, not noise voltage.
That makes sense.
--
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 & Software
http://www.wescottdesign.com
Reply by George Herold●January 3, 20122012-01-03
On Jan 3, 1:15=A0am, "Phil Allison" <phi...@tpg.com.au> wrote:
> "George Herold"
>
> Hi Tim, I just had 12V zeners +30k ohm across 15 volts.
> Zero correlation between zener voltage and noise.
> (I only tested 5.)
>
> ** Just tested a 12V / 400mW zener from 1uA to 10mA - =A0using a 10kohms
> series resistor and a high Z ( 680kohms) preamp with a gain of 250 times =
out
> to 50 kHz or so.
>
> White noise snapped on at just under 1uA at 5mV, fell back to 2mV at 30uA
> rising again to 6mV at 100uA - then back to 5mV at 250uA and down to 2mV =
at
> 1mA falling steadily to 0.2mV at 10mA.
>
> Looks like the internal noise generator is a varying current source that =
is
> being shunted by the zener's falling dynamic resistance as average DC bia=
s
> increases.
>
> So there is a tug of war going on.
>
> .... Phil
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 1=
2V
> > > (1W*) diodes. (I want to bias them from 15V rails.)
> > > They worked fine, but I found the noise varied by at least 6dB (a fac=
tor
> > > 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 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 voltag=
e
> > and the low overhead between the diode and the rail? A constant-current
> > 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-Hide quoted 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 t=
o
> 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 tex=
t -
>
> - Show quoted text -
Hi Mook, OK here are the numbers from the 5 diodes I tested. Noise is
measured with a SRS spectrum analyzer (which has this weird dBV
units.)
diode voltage noise
(V) dbV
1 11.66 -58.3
2 11.60 -60.5
3 11.95 -64
4 11.95 -57.5
5 11.78 -64.0
George H.
Reply by Phil Allison●January 3, 20122012-01-03
"George Herold"
Hi Tim, I just had 12V zeners +30k ohm across 15 volts.
Zero correlation between zener voltage and noise.
(I only tested 5.)
** Just tested a 12V / 400mW zener from 1uA to 10mA - using a 10kohms
series resistor and a high Z ( 680kohms) preamp with a gain of 250 times out
to 50 kHz or so.
White noise snapped on at just under 1uA at 5mV, fell back to 2mV at 30uA
rising again to 6mV at 100uA - then back to 5mV at 250uA and down to 2mV at
1mA falling steadily to 0.2mV at 10mA.
Looks like the internal noise generator is a varying current source that is
being shunted by the zener's falling dynamic resistance as average DC bias
increases.
So there is a tug of war going on.
.... Phil
Reply by Phil Allison●January 3, 20122012-01-03
"Tim Wescott"
>
> IIRC, the noise in an avalanche diode is proportional to current.
>
** That would be rule for noise current, not noise voltage.
... Phil
Reply by Bill Sloman●January 2, 20122012-01-02
On Jan 3, 1:44=A0am, 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*) =A0diodes. (I want to bias them from 15V rails.)
> > They worked fine, but I found the noise varied by at least 6dB (a facto=
r
> > 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--+----+
> > =A0 =A0 =A0Z =A0 =A0|
> > =A0 =A0 =A0^ =A0 =A01M
> > =A0 =A0 =A0| =A0 =A0|
> > =A0 =A0 =A0+----|-C+-(buffer)-------( =A0 =A0 =A0)
> > =A0 =A0 =A0| =A0 =A0+--|--C-+--(buffer)-(summer)
> > =A0 =A0 =A01M =A0 Z 100k =A0|
> > =A0 =A0 =A0| =A0 =A0^ =A0| =A0 100k
> > -15--+----| =A0+----+
> > =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 GND
>
> > Z are the zeners, =A020V (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. =A0The
> > output of each buffer looks like a pulse into an RC filter. =A0(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). =A0(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.
>
> > =A0*the 1 watters was all I had in the parts box.
>
> IIRC, the noise in an avalanche diode is proportional to current.
Perhaps you meant inversely proportional to the square root of the
current? It's actually a little bit more complicated than that. At low
currents, the avalanche self-quenches from time to time, and you get
spikes on the output as the diode capacitance charges up until another
charge carrier shows up to start a new avalanche.
At higher currents the avalanche hardly ever quenches, and the noise
is just the statistical noise on a sustained avalanche process
<snip>
--
Bill Sloman, Nijmegen
Reply by mook johnson●January 2, 20122012-01-02
"George Herold" <gherold@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 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 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 voltage
> and the low overhead between the diode and the rail? A constant-current
> 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- Hide quoted 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. a 20% swing. I don't know how strong a function of noise is to
bias current but that may explain some of your findings.