[volt-nuts] Zener, IC, references - which one

[Hendrik Dietrich]

Am 13.02.2015 14:31, schrieb Andrea Baldoni:
> Hello All.
>
> I would like to experiment with voltage references by putting them into a
> ovenized chamber (a DOCXO with a broken crystal) with their bias and buffer
> circuitry. The final goal will be to have the way to calibrate the HP 34401 as
> well as other instruments, but now I want more to "learn by doing".
>
> The chamber has his own heater so I'm not planning to use LTZ1000 or LM399
> unless I leave their internal one unconnected.
>
> Between the ones I am able to find new on the market, there are the zener
> diodes 1N829A (6 EUR new, 8 EUR NOS), the LM399H (12 EUR), the LM329BZ (4 EUR),
> while the LTZ1000 and the SZA263 are available used.
>
> I'm more concerned with long term stability than TC because everything will lie
> in a very constant temperature oven; I would like to use more expensive devices
> only if they have some advantage (IE, the LTZ1000 is really better than 1N829A
> or the advantage come by the fact it has his own oven?).
> Also, about external circuitry, what op amp do you suggest? A chopper one is
> probably not needed, always because it lies in a oven, and it may add noise.
> And about resistors? Yes, there are Vishay Z-foil, but there are other with
> worse tempco but same long term stability?
>
> Best regards,
> Andrea Baldoni
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Hi Andrea,

some comments:

A LTZ1000A voltage reference will not need an outer oven at all. 
Elevated outer temperature makes a elevated internal temp necessary and 
you can expect this to make long term drift worse due to aging. The LTZ 
just as everyone else likes to be as cold als reasonable possible. The 
circuit according to datasheet and good temperature setpoint give 
optimum results.

The LM399s are running very hot already, so this negative effect might 
not show up so much.

If I would have the OCXO can, I would stick several LM329 in it.

Also, if you want a 7V->10V stage with a opamp and resistive divider, 
these might benefit from the oven if they are inside.
Dont use the HP10544 oven, as it is using PWM and I think that is bad 
around a voltage reference. =)

Best regards

Hendrik