superstable constant current or constant voltage generation

[Popescu Nicolae]

Hello,
Does anyone know of any equipment out there capable of generating a
controllable constant voltage or constant current with an extreme
time/temperature stability of about 10ppb (parts per bilion) or around? The
power is not necessarily relevant. The temperature range should be between 0
and 40C, time period 12hrs.
If not, any ideas?
Thanks

 

[Vlad]

Hello,
Does anyone know of any equipment out there capable of generating a
controllable constant voltage or constant current with an extreme
time/temperature stability of about 10ppb (parts per bilion) or around? The
power is not necessarily relevant. The temperature range should be between 0
and 40C, time period 12hrs.
If not, any ideas?
Thanks

What about a good reference voltage (IC) inside of a small temperature
controlled oven? The type that is used to control the temperature of
crystal oscillators.

Vlad

 

[Rene Tschaggelar]

Hello,
Does anyone know of any equipment out there capable of generating a
controllable constant voltage or constant current with an extreme
time/temperature stability of about 10ppb (parts per bilion) or around? The
power is not necessarily relevant. The temperature range should be between 0
and 40C, time period 12hrs.
If not, any ideas?
Thanks

One of the amazing parts I recently came across was the
reference from Linear Technology, the LTZ1000, which has
a stability of 50ppb/K.
I didn't work with it though.

Rene

 

[Winfield Hill]

Rene Tschaggelar wrote...

One of the amazing parts I recently came across was the reference
from Linear Technology, the LTZ1000, which has a stability of 50ppb/K.
I didn't work with it though.

What's the application, Popescu?

 

[mike]

Hello,
Does anyone know of any equipment out there capable of generating a
controllable constant voltage or constant current with an extreme
time/temperature stability of about 10ppb (parts per bilion) or around? The
power is not necessarily relevant. The temperature range should be between 0
and 40C, time period 12hrs.
If not, any ideas?
Thanks

What are you going to do with the result???

Long story short, I once tried to build a stable current source for a
yig oscillator. I never could get the noise level low enough to be
useful, much less worry about high stability. The TEK 492 spectrum
analyzer uses a super-beta transistor pair driving a low noise op-amp
driving a transistor with a low-noise resistor in the emitter.
Put all that and your reference in an oven and you might get there.

There's been a lot of technology improvement in the last two decades,
but there are error/noise/thermocouple sources everywhere.
Unless all you care about is the average value of the current, you have
a lot more to worry about than the reference stability.
mike

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[Winfield Hill]

mike wrote...

Long story short, I once tried to build a stable current source for a
yig oscillator. I never could get the noise level low enough to be
useful, much less worry about high stability. The TEK 492 spectrum
analyzer uses a super-beta transistor pair driving a low noise op-amp
driving a transistor with a low-noise resistor in the emitter.

Be careful, a "low-noise" resistor implies low voltage noise, which by
the Johnson-noise equation implies LOW resistance values. For example,
e_n = sqrt (4kT R) = 1.28nV/rt-Hz for a 100-ohm resistor.

But current noise in a resistor is i_n = v/R = e_n/R = sqrt (4kT / R),
which is another beast entirely and tell us that HIGH resistor values
are required for low current noise. For example, i_n = 12.8pA/rt-Hz
for a 100-ohm resistor in a 10mA current source, but i_n = 1.28pA for
a 10k resistor in the same current source! Yes, using the 10k resistor
would require a 100V voltage reference, but it would be 10x more quiet.
This effect continues for higher DC voltage drops across the resistor,
but somewhere above 100V one runs into trouble with base-current noise
and a performance limit is reached. Was that your experience?

 

[mike]

mike wrote...



Be careful, a "low-noise" resistor implies low voltage noise, which by
the Johnson-noise equation implies LOW resistance values. For example,
e_n = sqrt (4kT R) = 1.28nV/rt-Hz for a 100-ohm resistor.

But current noise in a resistor is i_n = v/R = e_n/R = sqrt (4kT / R),
which is another beast entirely and tell us that HIGH resistor values
are required for low current noise. For example, i_n = 12.8pA/rt-Hz
for a 100-ohm resistor in a 10mA current source, but i_n = 1.28pA for
a 10k resistor in the same current source! Yes, using the 10k resistor
would require a 100V voltage reference, but it would be 10x more quiet.
This effect continues for higher DC voltage drops across the resistor,
but somewhere above 100V one runs into trouble with base-current noise
and a performance limit is reached. Was that your experience?

I try to do as little math as possible. The noise was so far out of the
useful range, that I opted to test the yigs by plugging them into the
spectrum analyzer.
If the math has more than three digits...including leading zeros, it's
too complex for me.
What's a "sqrt"???? Is that what I use to water the lawn?;-)

My point was that while it's interesting to contemplate generating an
ultra-stable reference, getting any real use out of it is WAY more
complex than one might imagine.

30 years of training engineers to "think outside the simulator" has led
me to the conclusion that answering a question that has EIGHT zeros
rarely leads to a solved problem.
mike

--
Return address is VALID.
500MHz Tek DSOscilloscope TDS540 $2200
Wanted, 12.1" LCD for Gateway Solo 5300. Samsung LT121SU-121
Bunch of stuff For Sale and Wanted at the link below.
http://www.geocities.com/SiliconValley/Monitor/4710/

 

[ChrisGibboGibson]

mike wrote:

[snip]

30 years of training engineers to "think outside the simulator" has led
me to the conclusion that answering a question that has EIGHT zeros
rarely leads to a solved problem.

Hear hear.

If a new way of doing something *instantly* gives a 2 order of magnutide
increase in precision or something then it's probably worth bothering with.
Simply because if it wasn't totally new someone else obviously already tried
it. And if it worked, we would have heard about it.

An increase of a few percent is rarely worth bothering with or means much. But
if a sudden massive increase is apparent then perhaps you are on to something.

Now watch everyone who has never invented anything new prove me wrong.

Gibbo

 

[Popescu Nicolae]

Does anyone know of any equipment out there capable of generating a

controllable constant voltage or constant current with an extreme
time/temperature stability of about 10ppb (parts per bilion) or around? The
power is not necessarily relevant. The temperature range should be between 0
and 40C, time period 12hrs.
If not, any ideas?

My point was that while it's interesting to contemplate generating an
ultra-stable reference, getting any real use out of it is WAY more
complex than one might imagine.

30 years of training engineers to "think outside the simulator" has led
me to the conclusion that answering a question that has EIGHT zeros
rarely leads to a solved problem.
mike

Having a superstable reference is not good enough to be able to generate a
controlled (i.e. adjustable) and superstable voltage or current. A standard
method would be to use a voltage (or current) SENSOR, a voltage REFERENCE, a
high GAIN and low OFFSET operational amplifier, all in a feedback loop. ALL
these elements in capitals would have to be superstable! A number of you
wandered about the application of such equipment. Imagine an Electron
Microscope and the voltage (or current, for the magnetic lens) used to focalize
the beam. The ultramicroscopes nowadays do require that the stability of the
voltage or current be in the ppb range, this having a strong impact on the
detectable detail at the atomic level.

 

[Norm Dresner]

Does anyone know of any equipment out there capable of generating a
Check out what NIST has to say about their voltage standards
http://nvl.nist.gov/pub/nistpubs/sp958-lide/html/315-318.html

 

[Winfield Hill]

Norm Dresner wrote...

Check out what NIST has to say about their voltage standards
http://nvl.nist.gov/pub/nistpubs/sp958-lide/html/315-318.html

Here's an interesting paper, comparing a new standard with a conventional
Josephson voltage standard, with agreement to 0.5 +/- 1.1 ppb. "Stable
1 volt programmable voltage standard" by S. P. Benz, and others.
http://www.boulder.nist.gov/div814/div817b/pubs/downloads/volt/spb-aplSep97.pdf

 

[Kevin Aylward]

Having a superstable reference is not good enough to be able to
generate a controlled (i.e. adjustable) and superstable voltage or
current. A standard method would be to use a voltage (or current)
SENSOR, a voltage REFERENCE, a high GAIN and low OFFSET operational
amplifier, all in a feedback loop. ALL these elements in capitals
would have to be superstable!

Amplifier gain doesn't have to be stable. If it varies from say, 140db
to 160db (a factor of 10), its error will still be at least lower
than -140db.


Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.