Author Topic: LM399 based 10 V reference  (Read 339220 times)

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Offline Andreas

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Re: LM399 based 10 V reference
« Reply #1100 on: February 14, 2020, 10:06:15 pm »

I am using some MAX4051A (with Kelvin sensing) in my LM399 ageing box:

edit: the MAX4051(A) has the advantage that I do not need any level shifters to the 5V logic which would be needed with CD4051/CD4067.

with best regards

« Last Edit: February 14, 2020, 10:22:59 pm by Andreas »

Offline notfaded1

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Re: LM399 based 10 V reference
« Reply #1101 on: February 15, 2020, 02:04:29 am »
Calculating the noise of individual reference from measurements in pairs is rather difficult, as the noise is not constant in time  :-DD. So the individual noise amplitudes will scatter quite a bit. So the cornered hat version is not really practical, as the individual measurement will contain quite scattering.

There are usually 2 practical method to check the noise:
One is to amplify the noise with an AC coupled amplifier. So there will be lower frequency cut off, at maybe some 0.1 Hz.

The other method is using a known lower noise reference to subtract. A first approximation could be using the average of several (e.g. 5) references as the point to compare too. Once really bad units are out, one can assume the average is lower than the individual units.
I seem to remember seeing this somewhere on here where someone had 5 LTZ1000 references that were averaged (must be nice).  Is there a multiple LTZ1000 (or even two) reference design pcb on eevblog?
« Last Edit: February 15, 2020, 02:06:38 am by notfaded1 »

Online Kleinstein

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Re: LM399 based 10 V reference
« Reply #1102 on: February 15, 2020, 10:10:11 am »
TiN has a board with 4 x LTZ1000. The circuit is pretty straight forward: separate references and than average with resistors and have a buffer / amplifier after that.  So there is limited need for a special board - just use 2 identical boards and a single buffer / amplifier  (e.g. have one board partially populated).

For the LM399 references one could use a single source for the driving current, so only one amplifier to 10 V needed, that can supply the current to all refs. 

Even with extra emitter resistors, the current mirror type current source will likely no be very accurate or stable. A resistor from a higher voltage (even if just the 15 V from an 7815) is  more stable.
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