Forums

Zener noise / oscillations

Started by Robert Baer July 23, 2012
   Zeners all seem to behave: quiet, no oscillation IF run at or near 
the spec current (usually in the tens of mA).
   But, if one needs to run them at low currents (say 10uA to 500uA) 
then _watch_out_!
   Some brands at certain voltages are extremely noisy and subject to 
oscillation.
   The waveforms seen at low currents (2-50uA) look like randumb 
sawtooth generation, and as the current is increased the amplitude and 
probability increases (do NOT want to say "frequency" as that gives 
wrong impression).
   Then this "converts" to random noise.
   Eventually, there are "bursts" of NO noise. Then at higher current, 
noise bursts decrease in "frequency" and amplitude.

   That is what i see in general.
   However, i have found two zeners that, on a curve tracer, one sees 
little if any noise or spikes mentioned.
   NOW for the question:
   How can one test these particular zeners to ensure they do not or 
will not oscillate?
*
   Yes, there are zeners made for low noise and those have a much lower 
spec current, BUT i cannot afford to have the factory dig the silicon 
mines, etc much less the high $$.

On a sunny day (Mon, 23 Jul 2012 01:16:24 -0700) it happened Robert Baer
<robertbaer@localnet.com> wrote in
<BeCdnSnrv6HGlZDNnZ2dnUVZ_qudnZ2d@posted.localnet>:

> Zeners all seem to behave: quiet, no oscillation IF run at or near >the spec current (usually in the tens of mA). > But, if one needs to run them at low currents (say 10uA to 500uA) >then _watch_out_! > Some brands at certain voltages are extremely noisy and subject to >oscillation. > The waveforms seen at low currents (2-50uA) look like randumb >sawtooth generation, and as the current is increased the amplitude and >probability increases (do NOT want to say "frequency" as that gives >wrong impression). > Then this "converts" to random noise. > Eventually, there are "bursts" of NO noise. Then at higher current, >noise bursts decrease in "frequency" and amplitude. > > That is what i see in general. > However, i have found two zeners that, on a curve tracer, one sees >little if any noise or spikes mentioned. > NOW for the question: > How can one test these particular zeners to ensure they do not or >will not oscillate? >* > Yes, there are zeners made for low noise and those have a much lower >spec current, BUT i cannot afford to have the factory dig the silicon >mines, etc much less the high $$.
I do not normally use zeners for reference, just for over voltage protection. For reference you probably want bandgap based chips. There are some very low power reference chips.
On Monday, July 23, 2012 4:16:24 AM UTC-4, Robert Baer wrote:
> Zeners all seem to behave: quiet, no oscillation IF run at or near > the spec current (usually in the tens of mA).
I'm not so sure about "quiet" but I suppose everything is relative. There's a lot of nice things about a 6.2V zener at the sweet spot current, that are not true for higher voltage zeners, lower voltage zeners, or zeners run away from their sweet spot.
> But, if one needs to run them at low currents (say 10uA to 500uA) > then _watch_out_! > Some brands at certain voltages are extremely noisy and subject to > oscillation. > The waveforms seen at low currents (2-50uA) look like randumb > sawtooth generation, and as the current is increased the amplitude and > probability increases (do NOT want to say &quot;frequency&quot; as that gives > wrong impression).
At the low microamps, YOU ARE ON THE WRONG SIDE OF THE KNEE, you are on the high dynamic impedance side. And remember that gas regulator tubes make excellent sawtooth oscillators blipping from one side of the knee to the other. At the microamp range everyone else is just using bandgap refs. Tim.
"Tim Shoppa" <shoppa@trailing-edge.com> wrote in message 
news:bd4db5e6-a911-4306-b00d-3c4e965286f4@googlegroups.com...
> At the low microamps, YOU ARE ON THE WRONG SIDE OF THE KNEE, you are on > the high dynamic impedance side. > > And remember that gas regulator tubes make excellent sawtooth oscillators > blipping from one side of the knee to the other. >
Like zeners, they also make excellent noise generators, usually with the help of a magnetic field. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
Jan Panteltje <pNaonStpealmtje@yahoo.com> writes:

> On a sunny day (Mon, 23 Jul 2012 01:16:24 -0700) it happened Robert Baer > <robertbaer@localnet.com> wrote in > <BeCdnSnrv6HGlZDNnZ2dnUVZ_qudnZ2d@posted.localnet>: > >> Zeners all seem to behave: quiet, no oscillation IF run at or near >>the spec current (usually in the tens of mA). >> But, if one needs to run them at low currents (say 10uA to 500uA) >>then _watch_out_! >> Some brands at certain voltages are extremely noisy and subject to >>oscillation. >> The waveforms seen at low currents (2-50uA) look like randumb >>sawtooth generation, and as the current is increased the amplitude and >>probability increases (do NOT want to say "frequency" as that gives >>wrong impression). >> Then this "converts" to random noise. >> Eventually, there are "bursts" of NO noise. Then at higher current, >>noise bursts decrease in "frequency" and amplitude. >> >> That is what i see in general. >> However, i have found two zeners that, on a curve tracer, one sees >>little if any noise or spikes mentioned. >> NOW for the question: >> How can one test these particular zeners to ensure they do not or >>will not oscillate? >>* >> Yes, there are zeners made for low noise and those have a much lower >>spec current, BUT i cannot afford to have the factory dig the silicon >>mines, etc much less the high $$. > > I do not normally use zeners for reference, just for over voltage protection. > For reference you probably want bandgap based chips. > There are some very low power reference chips.
Bandgap ones are more convenient. But the very best semiconductor references in terms of noise and stability are those based on zeners. -- John Devereux
On Mon, 23 Jul 2012 14:53:16 +0100, John Devereux
<john@devereux.me.uk> wrote:

> > >Bandgap ones are more convenient. But the very best semiconductor >references in terms of noise and stability are those based on zeners.
Buried zeners, specifically.
On a sunny day (Mon, 23 Jul 2012 14:53:16 +0100) it happened John Devereux
<john@devereux.me.uk> wrote in <87sjci37oz.fsf@devereux.me.uk>:

>Jan Panteltje <pNaonStpealmtje@yahoo.com> writes: > >> On a sunny day (Mon, 23 Jul 2012 01:16:24 -0700) it happened Robert Baer >> <robertbaer@localnet.com> wrote in >> <BeCdnSnrv6HGlZDNnZ2dnUVZ_qudnZ2d@posted.localnet>: >> >>> Zeners all seem to behave: quiet, no oscillation IF run at or near >>>the spec current (usually in the tens of mA). >>> But, if one needs to run them at low currents (say 10uA to 500uA) >>>then _watch_out_! >>> Some brands at certain voltages are extremely noisy and subject to >>>oscillation. >>> The waveforms seen at low currents (2-50uA) look like randumb >>>sawtooth generation, and as the current is increased the amplitude and >>>probability increases (do NOT want to say "frequency" as that gives >>>wrong impression). >>> Then this "converts" to random noise. >>> Eventually, there are "bursts" of NO noise. Then at higher current, >>>noise bursts decrease in "frequency" and amplitude. >>> >>> That is what i see in general. >>> However, i have found two zeners that, on a curve tracer, one sees >>>little if any noise or spikes mentioned. >>> NOW for the question: >>> How can one test these particular zeners to ensure they do not or >>>will not oscillate? >>>* >>> Yes, there are zeners made for low noise and those have a much lower >>>spec current, BUT i cannot afford to have the factory dig the silicon >>>mines, etc much less the high $$. >> >> I do not normally use zeners for reference, just for over voltage protection. >> For reference you probably want bandgap based chips. >> There are some very low power reference chips. > >Bandgap ones are more convenient. But the very best semiconductor >references in terms of noise and stability are those based on zeners.
At 2-50uA?
On Mon, 23 Jul 2012 01:16:24 -0700, Robert Baer
<robertbaer@localnet.com> wrote:

> Zeners all seem to behave: quiet, no oscillation IF run at or near >the spec current (usually in the tens of mA). > But, if one needs to run them at low currents (say 10uA to 500uA) >then _watch_out_! > Some brands at certain voltages are extremely noisy and subject to >oscillation. > The waveforms seen at low currents (2-50uA) look like randumb >sawtooth generation, and as the current is increased the amplitude and >probability increases (do NOT want to say "frequency" as that gives >wrong impression). > Then this "converts" to random noise. > Eventually, there are "bursts" of NO noise. Then at higher current, >noise bursts decrease in "frequency" and amplitude. >
Some of my scribbles on the subject: https://dl.dropbox.com/u/53724080/Circuits/Zener_Noise.pdf -- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
On 7/23/2012 10:16 AM, Robert Baer wrote:
> Zeners all seem to behave: quiet, no oscillation IF run at or near > the spec current (usually in the tens of mA). > But, if one needs to run them at low currents (say 10uA to 500uA) > then _watch_out_! > Some brands at certain voltages are extremely noisy and subject to > oscillation. > The waveforms seen at low currents (2-50uA) look like randumb > sawtooth generation, and as the current is increased the amplitude and > probability increases (do NOT want to say "frequency" as that gives > wrong impression). > Then this "converts" to random noise. > Eventually, there are "bursts" of NO noise. Then at higher current, > noise bursts decrease in "frequency" and amplitude. > > That is what i see in general. > However, i have found two zeners that, on a curve tracer, one sees > little if any noise or spikes mentioned. > NOW for the question: > How can one test these particular zeners to ensure they do not or > will not oscillate? > * > Yes, there are zeners made for low noise and those have a much lower > spec current, BUT i cannot afford to have the factory dig the silicon > mines, etc much less the high $$.
There was a nice - and tolerably long - thread on the subject "Zener Diode Oscillation" - here back in 1997. Winfield Hill and the late Tony Williams posted a lot of interesting measurements and some interesting references from the semiconductor physics literature. -- Bill Sloman, Nijmegen
Jan Panteltje <pNaonStpealmtje@yahoo.com> writes:

> On a sunny day (Mon, 23 Jul 2012 14:53:16 +0100) it happened John Devereux > <john@devereux.me.uk> wrote in <87sjci37oz.fsf@devereux.me.uk>: > >>Jan Panteltje <pNaonStpealmtje@yahoo.com> writes: >> >>> On a sunny day (Mon, 23 Jul 2012 01:16:24 -0700) it happened Robert Baer >>> <robertbaer@localnet.com> wrote in >>> <BeCdnSnrv6HGlZDNnZ2dnUVZ_qudnZ2d@posted.localnet>: >>> >>>> Zeners all seem to behave: quiet, no oscillation IF run at or near >>>>the spec current (usually in the tens of mA). >>>> But, if one needs to run them at low currents (say 10uA to 500uA) >>>>then _watch_out_! >>>> Some brands at certain voltages are extremely noisy and subject to >>>>oscillation. >>>> The waveforms seen at low currents (2-50uA) look like randumb >>>>sawtooth generation, and as the current is increased the amplitude and >>>>probability increases (do NOT want to say "frequency" as that gives >>>>wrong impression). >>>> Then this "converts" to random noise. >>>> Eventually, there are "bursts" of NO noise. Then at higher current, >>>>noise bursts decrease in "frequency" and amplitude. >>>> >>>> That is what i see in general. >>>> However, i have found two zeners that, on a curve tracer, one sees >>>>little if any noise or spikes mentioned. >>>> NOW for the question: >>>> How can one test these particular zeners to ensure they do not or >>>>will not oscillate? >>>>* >>>> Yes, there are zeners made for low noise and those have a much lower >>>>spec current, BUT i cannot afford to have the factory dig the silicon >>>>mines, etc much less the high $$. >>> >>> I do not normally use zeners for reference, just for over voltage protection. >>> For reference you probably want bandgap based chips. >>> There are some very low power reference chips. >> >>Bandgap ones are more convenient. But the very best semiconductor >>references in terms of noise and stability are those based on zeners. > > At 2-50uA?
Not as far as I know - usually about 5mA and ~6-7V. Like I said, not very convenient. -- John Devereux